Effects of non-thermal processing techniques on cereal bran: Focus on changes in bran structure and polyphenol release

Abstract

Cereal bran, a nutrient-rich by-product of grain processing, contains high levels of dietary fiber, polyphenols, and bioactive compounds, offering antioxidant and anti-inflammatory benefits. However, its rigid cell wall structure limits the release of bioactive compounds, requiring modification for food applications. Conventional thermal processing degrades heat-sensitive components and reduces polyphenol yields, whereas non-thermal methods (physical, chemical, and biological) better preserve and enhance the release of bioactive compounds. This review examines the impact of non-thermal processing on bran structure and polyphenol release, focusing on the mechanisms, structural changes, and safety implications. It also compares combined non-thermal methods with single treatments and explores structure–function relationships to support bran's use in functional foods.

Graphical abstract

Highlights

• •Single and combined non-thermal technologies applied in cereal bran modification were reviewed.
• •Operating mechanisms and limitations of non-thermal technologies (physical, chemical, and biological methods) were described.
• •Changes in structures and phenolic compound release of cereal bran affected functional food quality (texture & flavor).
• •Problems and challenges to applying combined non-heating techniques are proposed.

1. Introduction

Cereal grains, belonging to the Poaceae family, are composed of three main anatomical parts: the endosperm, germ, and bran. The residual material remaining after the extraction of the germ and endosperm is commonly referred to as bran (Hemery et al., 2010). As a staple in the human diet, cereals are widely cultivated and processed around the world, with major varieties including wheat, barley, oats, rye, millet, rice, sorghum, and maize (Bamigbade et al., 2025). According to global statistics, annual grain production reaches approximately 3.7 billion tons, of which about 90 % comprises cereals, with more than 70 % attributed to maize, rice, and wheat (Wrigley & Taylor, 2023). With the continuous increase in global cereal production, the cereal processing industry has expanded accordingly, resulting in a substantial generation of cereal waste and by-products (Galanakis, 2022). It is estimated that the waste rate in cereal processing is as high as 30 % (approximately 286 million tons), and globally, around 400 million tons of cereal waste are produced annually—accounting for 12.9 % of all food waste—with bran as a primary component (Fărcaș et al., 2022). Traditionally, large quantities of cereal by-products have been discarded or used as low-value animal feed. However, growing interest in resource recovery has led to increased research attention on the valorization and bioutilization of cereal waste and by-products. Recent studies suggest that, compared to refined grains, these by-products often contain higher concentrations of valuable bioactive compounds, including polyphenols, proteins, vitamins, and dietary fiber (DF) (Verni et al., 2019). Among them, phenolic compounds—secondary metabolites found abundantly in cereal bran—have emerged as particularly promising targets for research and application. These compounds have been shown to reduce the risk of chronic diseases such as cardiovascular disorders and type 2 diabetes, and also exhibit strong antioxidant, anti-inflammatory, and antiproliferative activities (Echenique et al., 2024).

Processing methods for cereal bran can generally be categorized into thermal and non-thermal techniques. Conventional thermal processing—typically conducted at temperatures ranging from 60 °C to 200 °C—modifies the structure of cereal bran primarily through isomerization, oxidative polymerization, and degradation reactions, thereby facilitating the release of bioactive compounds (J. Liu et al., 2020). However, variations in thermal processing conditions and the inherently degradative nature of prolonged heating often lead to reduced polyphenol content, the formation of undesirable by-products, and alterations in the structural and chemical properties of polyphenols. These effects severely limit the value-added utilization of cereal bran and reduce the bioavailability of phenolic compounds for human health. For instance, Saroj et al. (2024) reported that wheat bran (WB) subjected to hot-air oven treatment experienced substantial losses of bioactive compounds due to thermal degradation. Moreover, when hot-air oven treatment was used with gradual heating at lower temperatures, enzymes such as polyphenol oxidase could be activated, further reducing the polyphenol content (Saroj et al., 2024). These limitations stem from the convective heat transfer nature of hot-air oven processing, which is prone to uneven heating. In contrast, non-thermal processing technologies do not rely primarily on heat (or only generate minimal, non-dominant thermal effects) but instead utilize internal energy transfer to alter non-covalent molecular interactions. This approach enables the efficient processing of food matrices and the extraction of high yields and concentrations of bioactive compounds. Based on their underlying mechanisms, non-thermal technologies can be classified into three main categories: physical, chemical, and biological methods. Compared to conventional thermal treatments, non-thermal techniques can improve product quality and nutrient retention, while significantly enhancing the bioavailability of phenolic and other bioactive compounds within the cereal bran matrix. When applied to human food systems, these methods may provide superior health benefits. As a result, non-thermal processing is gradually emerging as a promising alternative to traditional thermal techniques. Furthermore, recent studies have demonstrated that the combined application of two or more non-thermal methods can induce more pronounced structural changes in cereal bran than single treatments alone, resulting in significantly higher release levels of bioactive compounds and enhanced antioxidant and nutritional functionality.

Accordingly, the objective of this review is to provide a comprehensive understanding of the structural composition and phenolic compounds of cereal bran, as well as the covalent and non-covalent interactions between DF, as the main component of cereal bran, and phenolic compounds. In addition, the review provides a comprehensive overview of physical, chemical, and biological non-thermal technologies, summarizing recent progress on the effects of non-thermal processing techniques on cereal bran. It compares the effects of single and combined non-thermal treatments, with a particular focus on structural modifications and the mechanisms of polyphenol release. The novelty of non-thermal techniques compared to traditional thermal methods offers unique advantages in preserving heat-sensitive compounds. Finally, based on the enhanced hydrophilicity and biodegradability of bran structures following non-thermal processing, we examine the potential applications and functional value of these materials. The subject is highly relevant to advancing sustainable food systems, valorization of agricultural by-products, and development of functional foods. This review aims to offer a theoretical foundation for future research efforts focused on applying safe and efficient non-thermal technologies to improve the bioavailability of cereal bran, with a particular emphasis on functional targeting and population-specific applications.

2. Structural composition of cereal bran

Cereal bran primarily consists of the pericarp (including the exocarp and mesocarp), seed coat (comprising cross cells and tube cells), the hyaline layer (nucellar epidermis), and the aleurone layer. It generally accounts for approximately 14 %–19 % of the total grain weight (Agil & Hosseinian, 2014). The cell walls of the exocarp and mesocarp are mainly composed of arabinoxylans (AX), cellulose, and lignin (Barron et al., 2007). The seed coat is rich in cellulose and AX, the hyaline layer predominantly contains AX, while the aleurone layer is composed mainly of AX and β-glucans (BG). Bran is also abundant in poorly digestible carbohydrates, which constitute 50 %–80 % of its composition. These carbohydrates include cellulose, hemicellulose, lignin, and pectin—key components of DF that contribute to improved bowel motility, mucosal protection, modulation of intestinal microbiota, and the regulation of intestinal barrier function (Amoroso et al., 2020). In addition to its essential nutrients, cereal bran is particularly rich in phenolic compounds, which represent one of the most significant classes of bioactive secondary metabolites. These include phenolic acids, flavonoids, and anthocyanins, which contribute to the antioxidant, anti-inflammatory, and disease-preventive properties of bran.

2.1. Dietary fiber composition

DF consists of a limited number of monosaccharides capable of forming diverse secondary and tertiary structures, resulting in its high complexity (Opperman et al., 2025). DF is recognized as one of the key components in the development of functional foods due to its demonstrated roles in maintaining intestinal health, treating gastrointestinal disorders, and preventing chronic conditions such as colorectal cancer and obesity (Schmidt, 2022). Approximately 50 % of DF intake in the human diet is derived from cereals, with the fiber content in cereal bran typically exceeding 10 g per 100 g of dry weight. As a major constituent of cereal bran, DF can be classified based on its solubility into soluble dietary fiber (SDF) and insoluble dietary fiber (IDF)(Elleuch et al., 2011). Compared to IDF, SDF possesses superior technological and functional properties, as well as physiological activities. Techno-functionally, SDF acts as a thickener, emulsifier, stabilizer, or fat replacer to improve food texture and mouthfeel. Physiologically, SDF promotes the proliferation of intestinal probiotics and regulates blood glucose levels. However, the low relative abundance of SDF in cereal brans often limits its utilization in food processing. For instance: WB in the SDF content of only 4.4 %, IDF content of 45.6 %; rice bran (RB) contains only 2.3 % SDF and 38.5 % IDF; tartary buckwheat bran (TBB) contains only 4.8 % SDF and 34.3 % IDF; highland barely bran (HBB) contains only 5.0 % SDF and 26.9 % IDF (Q. Wu et al., 2024). Addressing the contradiction between the low abundance and high functionality of SDF in cereal brans necessitates the application of suitable external processing methods. These methods aim to disrupt the composition of the bran cell wall components, such as cellulose, lignin, and hemicellulose.

Cellulose is a linear, semi-crystalline biopolymer primarily composed of unbranched long chains of D-anhydroglucose units linked by β-1,4-glycosidic bonds. In cereal bran, cellulose is a key structural component of the cell wall, forming both highly ordered crystalline regions and less organized amorphous regions. These cellulose microfibrils are embedded within a matrix of hemicellulose and lignin, which provide structural reinforcement and protection against enzymatic or chemical degradation (Wen et al., 2017). Due to the abundance of hydroxyl groups along the cellulose chains, extensive intra- and intermolecular hydrogen bonding occurs, resulting in a highly organized three-dimensional crystalline architecture (Nuruddin et al., 2016).

Lignin is an amorphous, complex aromatic polymer primarily composed of phenylpropanoid monomers (Li, Song, et al., 2024). With a molecular weight (Mw) exceeding 10,000 Da, lignin contributes to the mechanical rigidity of the plant cell wall and imparts significant structural hardness. It exhibits high rigidity, hydrophobicity, and strong resistance to microbial and enzymatic degradation. The primary monomeric units of lignin include p-hydroxyphenyl, guaiacyl, and syringyl groups, which are interconnected through ester and ether linkages—such as β-O-4 and α-O-4 bonds—as well as carbon–carbon linkages like 5–5 and β–β types (Z.-M. Zhao et al., 2024). Lignin forms covalent cross-links with hemicellulose, particularly through ferulic acid bridges, establishing a tightly bound lignocellulosic matrix that links cellulose and hemicellulose. This cross-linked structure yields a robust and recalcitrant cell wall architecture, which presents challenges for the release of encapsulated bioactive compounds.

Hemicellulose is a highly branched heteropolysaccharide characterized by a β-1,4-linked sugar backbone in an equatorial configuration, and is primarily composed of D-xylose, d-glucose, and D-mannose units. In cereal bran, hemicellulose predominantly exists in the form of AX and β-glucans. Owing to its abundance of hydroxyl groups, hemicellulose can form extensive hydrogen-bonding networks both within and between cellulose chains (García et al., 2016).

However, due to its unstable side chains and amorphous nature, hemicellulose is prone to transformation into other products. The content of AX in WB typically ranges from 5.0 to 26.9 g per 100 g of dry weight, with its distribution across different anatomical layers as follows: 35–47 % in the outer pericarp, 36–40 % in the inner pericarp, seed coat, and hyaline layer, and 18–28 % in the aleurone layer (Fardet, 2010). Structurally, AX consists of a β-(1,4)-d-xylopyranosyl backbone with arabinofuranosyl side chains attached via α-(1,2) or α-(1,3) glycosidic linkages. Its molecular weight typically ranges from 276 to 877 kDa (Sánchez-Bastardo et al., 2017). Additionally, ferulic acid (FA) is often esterified at the C(O)-5 position of the arabinose residues in AX. Based on solubility and extractability, AX can be classified into two fractions: water-soluble and water-insoluble. Water-soluble AX is present in lower quantities in wheat bran due to its weaker association with the surface of the cell wall. In contrast, water-insoluble AX is more abundant as it forms strong covalent or non-covalent interactions with cell wall components. Structural variations in AX—particularly in Mw, FA content, and the arabinose-to-xylose ratio—significantly influence the viscosity, hydration, and gel-forming properties of cereal bran. These changes in physicochemical properties directly affect the rheological behavior, pasting characteristics, water distribution, and thermodynamic properties of processed foods, ultimately impacting product quality (Jing Wang et al., 2020).

Pectin is a class of complex and structurally diverse acidic heteropolysaccharides primarily located in the cell walls of the aleurone layer and adjacent outer tissues of cereal bran. Its backbone is predominantly composed of α-(1 → 4)-linked galacturonic acid residues, some of which may be methyl-esterified—affecting both solubility and gelling properties—while others may exist in salt forms complexed with cations such as calcium or magnesium. Unlike the pectin found in fruits, pectin in cereal bran is mainly classified as rhamnogalacturonan I (RG-I). Due to its highly branched structure and feruloylation, RG-I in cereal pectin exhibits superior water-holding capacity, viscosity-modifying potential, and prebiotic activity, making it a promising candidate for the development of functional foods.

2.2. Phenolic compounds

Phenolic compounds are defined as aromatic molecules containing at least one hydroxyl substituent, and they are widely recognized for their antioxidant, anti-inflammatory, antidiabetic, and anti-obesity properties. In cereal grains, these compounds are predominantly concentrated in the outer bran layers, where they play a defensive role against both biotic and abiotic stresses (Fardet, 2010). Phenolics exist in three forms: soluble free, soluble conjugated, and insoluble bound, with insoluble bound phenolics accounting for the highest proportion (Nemes et al., 2022). Their solubility classification is based on the extent of their association with the food matrix. Most soluble phenolics can be esterified with sugars or conjugated with small peptides through covalent bonds. They are synthesized in the endoplasmic reticulum and subsequently transported and stored in the vacuole. In contrast, insoluble bound phenolics are typically associated with macromolecular components of the cell wall—such as pectin, cellulose, and hemicellulose—through covalent bonds, hydrogen bonds, and hydrophobic interactions (B. Zhang et al., 2020). Phenolic compounds in bran are mainly categorized into free and bound forms. Free phenolics are not physically or chemically associated with other molecules and are generally soluble in polar aqueous or organic solvents. Bound phenolics, which constitute a significant portion of total phenolics in bran, are covalently linked to cellulose, proteins, lignin, and other macromolecules within the cell wall. They can also interact ionically or become physically trapped within the plant matrix or embedded in the cellular structure. In plants, phenolic compounds are synthesized as secondary metabolites via the shikimic acid and phenylpropanoid pathways. Based on their chemical structure, they are classified into flavonoids, tannins, lignans, phenolic acids, anthocyanins, and stilbenes. Among these, flavonoids and phenolic acids are the two most predominant classes in cereal bran.

Phenolic acids are the major class of phenolic compounds in cereal bran and are considered biochemical markers of the pericarp and aleurone layers. They predominantly exist in insoluble or bound forms and can be broadly categorized into two subgroups: hydroxybenzoic acid (HBA) derivatives and hydroxycinnamic acid derivatives. Hydroxybenzoic acids typically possess a C6–C1 structure and include compounds such as vanillic acid (VA), syringic acid, p-hydroxybenzoic acid, and gallic acid. Hydroxycinnamic acids, characterized by a C6–C3 structure, include FA, p-coumaric acid, caffeic acid, and sinapic acid (Martín-Diana et al., 2021). Among the phenolic acids in wheat bran, FA is the most abundant, derived from the metabolism of phenylalanine and tyrosine. It accounts for approximately 64 %–84 % of the total phenolic acids in bran, with concentrations in the aleurone and pericarp layers reaching up to 98 %. The FA content varies depending on wheat bran type, typically ranging from 20 mg to 1500 mg per 100 g of bran, the majority of which exists in the bound form (Roasa et al., 2021). FA is commonly cross-linked to lignin and polysaccharides through ester and ether linkages, forming lignin/phenolic–carbohydrate complexes within the cereal bran matrix. In addition to ferulic acid, WB also contains small amounts of sinapic acid and p-coumaric acid. FA and p-coumaric acid are often esterified to AX, while sinapic and p-coumaric acids are typically present in conjugated forms, linked to oligosaccharides. Owing to its aromatic ring structure, FA exhibits strong free radical scavenging activity and, when present in dimeric form, demonstrates enhanced antioxidant capacity。.

Flavonoids are a diverse class of phenolic compounds that primarily exist in glycosylated forms. Their basic structure consists of a C6–C3–C6 carbon framework, in which the C6 units are phenolic rings. The attached sugar moieties can be linked through hydroxyl groups or carbon–carbon bonds. Based on the saturation level of the central heterocyclic ring, flavonoids can be divided into unsaturated flavonoids—such as anthocyanins, flavones, and flavonols—and saturated flavonoids, including flavanones and flavan-3-ols. From a chemical classification perspective, flavonoids are generally categorized into seven subgroups: anthocyanins, chalcones, flavanols, flavanones, flavones, flavonols, and isoflavones. According to Feng et al. (2024), the most extensively studied flavonoids in whole grains include catechin, cyanidin, peonidin, eriodictyol, kaempferol, quercetin, rutin, and luteolin. Metabolomic analyses have shown that darker-colored cereals tend to exhibit higher flavonoid content than their lighter counterparts (J. Feng et al., 2022). In addition, Yu et al. (2021) reported that the flavonoid content in rice follows a trend consistent with grain pigmentation: white rice < red rice < black rice, reflecting a strong correlation between grain color intensity and flavonoid concentration (Yu et al., 2021).

2.3. Interaction between dietary fiber and phenolic compounds

As illustrated in Fig. 1, the interactions between DF and phenolic compounds can be classified into two main types: non-covalent interactions and covalent interactions. These interactions not only influence the physicochemical properties of food—such as color, flavor, and stability—but also play a critical role in determining the bioavailability and health benefits of phenolic compounds. Moreover, various factors associated with the cereal bran cell wall—such as its composition, degree of polymerization, chemical structure, ionic strength, pH, and temperature—can significantly affect the binding affinity between phenolics and DF.

Fig. 1.

Covalent and non-covalent bonding interactions linking polyphenolic compounds and dietary fibers in cereal bran.

2.4. Non-covalent interaction

Non-covalent interactions between DF and phenolic compounds are reversible physical associations that primarily include hydrogen bonding, hydrophobic interactions, van der Waals forces, and electrostatic interactions. Environmental factors, including ionic strength, temperature, and pH, influence these interactions. They are largely dependent on the molecular characteristics of phenolic compounds, including the presence of hydroxyl groups, polar functional groups, and aromatic rings. Hydrogen bonds are formed between the hydroxyl groups (–OH) of phenolic compounds and the polar functional groups of DF. The formation of hydrogen bonds reduces the distance between polyphenol and fiber molecules, thereby facilitating van der Waals forces (Diez-Sánchez et al., 2021). Van der Waals interactions occur via π-π stacking between the aromatic rings of phenolic compounds and aromatic structures within the fiber matrix. Both hydrogen bonding and van der Waals forces tend to strengthen at lower temperatures due to reduced molecular motion, resulting in more stable complexes. Hydrophobic interactions arise from the association of the aromatic rings of phenolic compounds with non-polar regions of DF. These interactions are enhanced with increasing ionic strength, resulting in a tighter binding between polyphenols and fiber. Electrostatic interactions occur between negatively charged phenolic acids and positively charged regions of DF. Non-covalent interactions can modulate the bioavailability of phenolic compounds by controlling their release and accessibility, especially in the colon, where microbial fermentation may liberate bound phenolics and exert localized antioxidant or prebiotic effects. Conversely, factors such as molecular size, flexibility, and spatial conformation of both phenolics and fibers can further influence the formation and stability of polyphenol–fiber complexes (Cheng et al., 2025).

2.4.1. Covalent interaction

Covalent interactions between DF and phenolic compounds involve the formation of irreversible complexes through chemical bonding, primarily occurring during food processing or digestion. These covalent bonds include ether linkages formed between hydroxyl groups of phenolic compounds and hydroxyl groups present in DF or other cell wall components; ester bonds formed between the carboxyl groups of phenolic compounds and the hydroxyl groups of cell wall polysaccharides; and carbon–carbon (C—C) bonds directly linking phenolic structures to DF matrices (Das et al., 2023; Fernandes et al., 2023). The formation of ether bonds involves the hydroxyl groups of phenolic compounds undergoing oxidation—catalyzed by oxidases such as peroxidase and polyphenol oxidase—or through thermal processing. In this process, phenolics such as ferulic acid and chlorogenic acid are oxidized into quinone intermediates, which subsequently undergo nucleophilic addition to form ether linkages. Ether bond stability is influenced by pH and enzymatic activity. In alkaline environments (e.g., the intestine), ether bonds may be partially hydrolyzed, while microbial fermentation in the colon may promote their degradation via microbial esterases. Phenolics bound via ether linkages are typically resistant to release in the stomach and small intestine but may be liberated in the colon, where they can exert localized antioxidant or microbiota-modulating effects. Studies have shown that ferulic acid can form dimers through ether linkages with hydroxyl groups on the side chains of arabinoxylan, leading to the cross-linking of cell wall polysaccharides. Similarly, lignin monomers such as coniferyl alcohol can undergo radical coupling with phenolic acids via ether bonds, thereby increasing cell wall rigidity. Ester bonds are formed under heating or acidic conditions through a condensation reaction between the carboxyl groups of phenolic acids and the hydroxyl groups of polysaccharides. These ester linkages are stable in the acidic environment of the stomach. Still, they are susceptible to hydrolysis in the alkaline environment of the intestine or through the action of microbial esterases during fermentation. C—C bonds are generated through radical polymerization, wherein phenolic compounds such as catechins and anthocyanins are oxidized to form phenoxyl radicals. These radicals undergo oxidative coupling with carbon centers on DF to form C—C covalent linkages. The formation of C—C bonds is influenced by temperature and metal ions; high temperatures accelerate radical reactions, and transition metals such as Fe³⁺ and Cu²⁺ catalyze oxidative coupling. C—C bonds are extremely resistant to degradation by human digestive enzymes or gut microbiota, which may result in the complete inactivation of the bound phenolic compounds.

3. Effects of non-thermal processing technologies on the structure of cereal bran and the release of polyphenols

Conventional thermal processing causes extensive disintegration of bran cell walls and a loosened structure, accompanied by a charred and hardened layer, thereby compromising the integrity of the fibrous skeleton (Y. Zhang & Liu, 2022). Concurrently, phenolic compounds undergo high-temperature oxidative losses ranging from 30 % to 50 %, while vitamin losses attributable to thermal sensitivity reach 40 % to 60 %. In contrast to conventional thermal processing, non-thermal processing technologies utilize high-energy inputs in non-thermal forms—such as physical methods, ambient-temperature chemical methods, and biological methods—to selectively disrupt the robust cell wall and cell membrane structures of cereal bran while avoiding or minimizing temperature elevation. Fig. 2 illustrates the structural differences in the cell wall architecture of cereal bran before and after treatment with various non-thermal processing methods (physical, chemical, and biological). This disruption mechanism prevents alterations to the molecular structures of bran constituents, including vitamins, polyphenols, enzymes, proteins, unsaturated fatty acids, and volatile flavor compounds, thereby avoiding deactivation, degradation, oxidation, or volatilization. This capacity to reduce losses of thermally sensitive bioactive compounds represents a significant advantage of non-thermal processing, leading to its increasing recognition and advocacy among researchers. Furthermore, non-thermal processing aligns with the Sustainable Development Goals by reducing contamination. Although non-thermal processing elevates bran from a “food filler” to a “functional structural building block,” establishing a technological foundation for developing high-activity, clean-label whole-grain foods, critical attention must be directed to the distinct characteristics of diverse cereal brans and significant mechanistic variations among non-thermal technologies, which result in divergent impacts on disruption sites, modes of action, and release efficiency of polyphenols within bran structures. Consequently, Fig. 3 delineates methodologies for non-thermal bran processing across structural modulation, bioactive compound liberation, and application scenarios, employing systematic experimentation to achieve moderate and selective disruption of bran architecture with the primary objective of retaining and releasing target bioactive compounds, while comprehensively evaluating the safety and functionality of non-thermal approaches and quantitatively assessing post-treatment content and release rates of target bioactives to enable broad industrial adoption in food processing.

Fig. 2.

Represents the structural changes in the cell wall of cereal bran before and after non-thermal processing.

Fig. 3.

Methods for structure-bioactivity-application of non-thermal processing technologies for cereal bran (X. Li, Xu, et al., 2025; A. Liu et al., 2024; Ma et al., 2023; Pasqualone et al., 2017).

3.1. Single non-thermal processing technology

3.1.1. Biological methods

3.1.1.1. Enzymatic Treatment

Enzymatic treatment involves the specific hydrolysis of chemical bonds within DF components of bran, leading to the breakdown of the cell wall structure, alteration of molecular architecture and physical properties, and subsequent modulation of nutritional functionality and processing performance. This approach is considered an effective and targeted strategy for improving texture and flavor while enhancing the release of bioactive compounds. Additionally, enzymatic processing is controllable and can be tailored through the optimization of enzyme type and reaction conditions to achieve selective modification. The enzymes commonly used for cereal bran modification include cellulase, lipase, protease, oxidase, β-xylanase, β-xylosidase, feruloyl esterase, and α-L-arabinofuranosidase (Ye et al., 2021). For example, xylanase hydrolyzes the β-1,4-xylosidic linkages in arabinoxylans, releasing arabinose and xylose, and reducing the degree of polymerization. Cellulase cleaves β-1,4-glucosidic bonds in cellulose, yielding short-chain oligosaccharides or glucose. β-glucanase breaks β-1,3 or β-1,4 linkages in β-glucans, while pectinase degrades α-1,4-glycosidic bonds in pectin.

3.1.1.2. Microbial fermentation

Microbial fermentation modifies the structure and functional properties of DF through the action of organic acids and enzymes produced by microorganisms, which degrade plant cell walls. The selection of appropriate microbial strains is a critical factor in fermentation efficiency and outcome (Jian Wang et al., 2023). Commonly used fermentation microorganisms include filamentous fungi (e.g., Aspergillus, Trichoderma, Mucor, and Rhizopus spp.), yeasts (e.g., Saccharomyces and Candida spp.), and bacteria (e.g., Lactobacillus and Bacillus spp.). During fermentation, the production of hydrolytic enzymes—such as pectinase, cellulase, α-amylase, xylanase, and β-glucosidase—facilitates the breakdown of cell wall polysaccharides, thereby releasing a greater amount of nutrients and bioactive compounds. This process holds significant potential for enhancing the nutritional value of cereal bran-based food ingredients. Research has shown that metabolic products generated by lactic acid bacteria, yeasts, and fungi can alter the structure of DF. Saccharomyces and Lactobacillus strains, in particular, are well-characterized fermentative agents frequently employed to reduce phytic acid content in WB, while simultaneously increasing SDF, TPC, antioxidant capacity, and imparting unique flavors. Bifidobacterium longum has a preferential ability to degrade high molecular weight arabinoxylans, while Aspergillus niger is known for producing high levels of cellulase. Additionally, basidiomycetes exhibit high enzymatic activity in the degradation of lignin and hemicellulose (Tu et al., 2020).

3.1.1.3. Effects of biological methods on the structural modification of dietary fiber in Cereal Bran

Table 1 compares the structural changes in cereal bran before and after treatment with different biological methods. Biological treatments, such as enzymatic hydrolysis and microbial fermentation, induce structural degradation of the cell wall, particularly in the aleurone layer (Zhou et al., 2010). These processes disrupt the IDF network, reduce the degree of polymerization of DF molecules, increase surface complexity, and expose more hydrophilic functional groups. As a result, small-molecule SDF components are released, while the overall content of cellulose, hemicellulose, and lignin tends to decrease, and SDF content increases significantly. These structural modifications enhance the physicochemical properties and biological activity of cereal bran. Moreover, increased porosity and reduced crystallinity of the fiber matrix improve the bran's WHC, SC, OHC, CEC, CAC, and GAC. For instance, enzymatic treatment with endo-xylanase can degrade up to 50 % of AX in bran, thereby increasing protein solubility (W. Liu et al., 2017). Additionally, enzymatic hydrolysis involving amylase, glucosidase, and protease can effectively separate SDF and IDF, supporting the use of enzymatic treatment for the fractionation and purification of DF. Noticeable disruptions of the bran layer structures have been observed before and after fermentation or enzymatic treatment. These differences arise due to the type, concentration, and activity of endogenous or microbial enzymes involved in the bioprocessing steps, which collectively contribute to the modification of bran structure.

Table 1.

Modification of dietary fiber structure in biologically treated cereal bran.

Material	Method	Processing conditions	Key findings on changes in dietary fiber structure				Ref.
			chemical composition	particle size	Monosaccharide composition	Microstructure morphology
Prosomillet bran	NO Fermentation	①α-Amylase. ②papain. ③amyloglucosidase.	SDF: 4.2 %	–	①Glucose: 0.995 mol. ②Arabinose: 1.037 mol. ③Galactose: 0.925 mol. ④Galacturonic acid:0.682 mol. ⑤Xylose: 0.872 mol. ⑥Mannose:0.214 mol.		(Li, Niu, et al., 2022)
	Fermentation	①Lactobacillus bulgaricus. ②Streptococcus thermophilus. ③Fermentation treatment: 37 °C,24 h.	SDF: 7.6 %	–	①Glucose: 0.991 mol. ②Arabinose: 0.683 mol. ③Galactose: 0.893 mol. ④Galacturonic acid:0.404 mol. ⑤Mannose:0.220 mol.
Millet bran	No enzymatic hydrolysis	①α-Amylase. ②alkaline protease. ③amyloglucosidase.	IDF: 870.96 g/kg. SDF: 10.36 g/kg. Cellulose: 195.61 g/kg. Hemicellulose: 559.95 g/kg. Lignin: 101.59 g/kg.	D3,2: 113.μm	–		(Zheng, Xu, et al., 2022)
	Enzymatic hydrolysis	① cellulase and hemicellulase. ②enzymatic digestion: at 50 °C for 150 min.	IDF: 852.42 g/kg. SDF: 24,76 g/kg. Cellulose: 124.39 g/kg. Hemicellulose: 446.52 g/kg. Lignin: 79.43 g/kg.	D3,2: 74.8 μm	–
Millet bran	NO Fermentation	①α-Amylase. ②neutral protease ③glycosylated sugar	SDF: 13.2 % IDF: 66.5 % Cellulose:17.3 % Hemicellulose: 47.3 % Lignin: 8.8 %.	–	–		(Chu et al., 2019)
	Fermentation	①Fermentation strains: Bacillus natto ②Fermentation treatment: 37 °C, 180 rpm, 47 h	SDF: 1.93 g/100 g. IDF: 12.37 g/100 g. Cellulose:14.3 % Hemicellulose: 44.4 % Lignin: 7.9 %.	–	–
rice bran	NO Fermentation	①α-Amylase. ②papain.	SDF: 10.5 %	–	①fucose: 0.49 mol. ②galactose: 1.11 mol. ③glucose: 1.0 mol. ④mannose: 24.54 mol. ⑤fructose: 0.81 mol. ⑥galacturonic acid: 0.21 mol.		(Jia et al., 2019)
	Fermentation	①Fermentation strains: Trichoderma viride. ②Fermentation treatment: pH = 5.8, 41 h, 10 % of inoculum.	SDF: 33.4 %	–	①fucose: 1.07 mol. ②galactose: 2.12 mol. ③glucose: 1.0 mol. ④mannose: 78.36 mol. ⑤fructose: 2.29 mol. ⑥galacturonic acid: 25.41 mol. ⑦glucuronic acid: 0.48 mol.

Arabinose and xylose are key marker monosaccharides of hemicellulose. In a study by Li, Hu, et al. (2022) on millet bran, it was found that the ratio of arabinose to xylose in DF decreased after fermentation with Lactobacillus bulgaricus and Streptococcus thermophilus. Additionally, the ratio of arabinose to glucuronic acid was also significantly reduced, indicating the degradation of hemicellulose and pectic polysaccharides (Li, Niu, et al., 2022). Similarly, Jia et al. (2019) reported that fermentation of defatted RB with Trichoderma viride—a strain capable of producing cellulase and various bioactive enzymes—resulted in the release of higher molecular weight DF components. The monosaccharide profile also revealed the emergence of glucuronic acid and significant changes in sugar ratios, suggesting microbial degradation of complex polysaccharides and the release of acidic monosaccharides. Morphological analysis further revealed more banded fiber structures and a disruption of the dense microstructure after fermentation. The resulting looser structure enhanced the hydration and adsorption properties of the DF (Jia et al., 2019).

In recent years, increasing attention has been given to the use of solid-state fermentation (SSF) for modifying DF, as SSF closely mimics the natural habitat of microorganisms and promotes the activity of microbes and their metabolites. This process facilitates the conversion of IDF into SDF, thereby increasing the overall SDF content (El-Housseiny et al., 2021). For instance, Chu et al. (2019) reported that fermentation of millet bran using Bacillus subtilis natto significantly increased the SDF content from 2.3 % to 13.2 %. This enhancement was attributed to the enzymatic degradation of cellulose and hemicellulose, resulting in a more porous and loosely packed microstructure. Consequently, the fermented millet bran exhibited markedly improved functional properties, including water-holding capacity, water swelling capacity, oil-holding capacity, and enhanced adsorption abilities for cholesterol, nitrite ions, and glucose. Additionally, the DPPH radical scavenging activity was significantly elevated, indicating an enhanced antioxidant potential (Chu et al., 2019).

3.1.1.4. Effects of biological methods on the release of bound phenolics from Cereal Bran

Table 2 compares the changes in phenolic compound release from cereal bran before and after treatment with various biological methods. Several factors, including enzyme concentration, reaction time, fermentation temperature, duration, and the selection of microbial strains, influence the efficiency of biotechnological treatments in releasing bound phenolics. Compared with physical and chemical treatments, biological methods offer milder reaction conditions. Additionally, due to the inherent high specificity and efficient catalytic capacity of enzymatic reactions, as well as the fact that microbial metabolism can synchronously carry out multiple reactions through the coordinated action of enzyme systems, the decomposition of anti-nutritional factors in grain bran is accompanied by the synthesis of bioactive compounds. This achieves the goal of converting anti-nutritional factors into high-value-added products. This process involves the integration of a metabolic network encompassing decomposition, transformation, and synthesis, representing a complex interplay of metabolic pathways and enzymatic catalysis. For example, the secretion of cellulase and feruloyl esterase breaks down the cell walls of bran, releasing bound phenolic compounds. Simultaneously, phytase is utilized to degrade the anti-nutritional factor phytic acid, while methyltransferases convert phenolics into active compounds such as VA. Research demonstrates that ferulic acid esterase serves as a pivotal enzyme for liberating phenolic compounds, featuring a catalytic triad of serine-histidine-aspartate within its active site that specifically hydrolyzes ester bonds between ferulic acid and arabinoxylans; when employed alone, this enzyme increases ferulic acid content in bran by 3–5-fold, yet exhibits limited efficacy in releasing other phenolic constituents.

Table 2.

Altered release of phenolic compounds from biologically treated cereal bran.

Material	Method	Processing conditions	Key findings on changes in dietary fiber structure		Antioxidant activity	Ref.
			Total phenolic content	Changes in phenolic compounds
Oat Bran	Un Fermented	–	Free: 0.67 mg GAE/g DW. Bound: 0.96 mg GAE/g DW.	Free Chlorogenic acid: 9.5 μg/g. p-hydroxybenzoic acid: 18.5 μg/g. Vanillic acid: 43.0 μg/g Caffeic acid: 16.7 μg/g. Coumarin acid: 8.7 μg/g. Ferulic acid: 8.8 μg/g. Luteolin: 4.6 μg/g. Apigenin: 7.7 μg/g. Bound Chlorogenic acid: 29.4 μg/g. p-hydroxybenzoic acid: 20.0 μg/g. Vanillic acid: 49.6 μg/g. Caffeic acid: 346.5 μg/g. Coumarin acid: 37.3 μg/g. Ferulic acid: 42.8 μg/g. Luteolin: 7.2 μg/g. Apigenin: 8.4 μg/g.	ABTS Free: 68.64 %, Bound: 81.26 %,	(Li, Yadav, et al., 2024)
	Fermented	①Fermented strains: Lactobacillus fermentum NB02; ②Fermentation medium at 37 °C for 4 d.	Free: 1.05 mg GAE/g DW. Bound: 2.33 mg GAE/g DW.	Free Chlorogenic acid: 21.2 μg/g. p-hydroxybenzoic acid: 36.3 μg/g. Vanillic acid: 194.4 μg/g. Caffeic acid: 37.3 μg/g. Coumarin acid: 18.5 μg/g. Ferulic acid: 57.114 μg/g. Luteolin: 17.3 μg/g. Apigenin: 12.8 μg/g. Bound Chlorogenic acid: 46.9 μg/g. p-hydroxybenzoic acid: 108.151 μg/g. Vanillic acid: 339.05 μg/g. Caffeic acid: 1302.7 μg/g. Coumarin acid: 176.79 μg/g. Ferulic acid: 123.85 μg/g. Luteolin: 50.192 μg/g. Apigenin: 14.471 μg/g.	DPPH Free: 41.23 %, increasing by 1.66 times. Bound: 51.02 %, increasing by 1.23 times. ABTS Free: 79.48 %, Bound: 90.01 %,
Rice bran	Enzymatic hydrolysis	①Enzyme selection: Cellulase. ②Dosage: 50 μL/g. ③Temperature: 50 °C. ④pH: 4.5. ⑤Time: 24 h.	164.3 mg GAE/100 g DW.	Chlorogenic Acid: 0.23 μg/g DW. Vanillic acid: 3.73 μg/g DW. Caffeic acid: 7.41 μg/g DW. Syringic acid: 1.77 μg/g DW. Vanillin: 32.48 μg/g DW. p-Coumaric acid: 9.68 μg/g DW. Ferulic acid: 47.06 μg/g DW. Isoquercitrin: 0.7 μg/g DW. Caffeic acid methyl: 2.3 μg/g DW. Quercetin: 0.1 μg/g DW.	DPPH: 86.6 mg TE/100 g DW. FRAP: 149.6 mg TE/100 g DW. ORAC: 21.12 mg TE/100 g DW.	(G. Zhao et al., 2023)
		①Enzyme selection: Feruloyl esterase. ②Dosage: 20 μL/g. ③Temperature: 40 °C. ④pH: 6.5. ⑤Time: 24 h.	40.57 mg GAE/100 g DW.	Vanillic acid: 7.93 μg/g DW. Syringic acid: 0.44 μg/g DW. Vanillin: 2.37 μg/g DW. p-Coumaric acid: 8.33 μg/g DW. Ferulic acid: 13.17 μg/g DW.	DPPH: 33.04 mg TE/100 g DW. FRAP: 38.8 mg TE/100 g DW. ORAC: 4.9 mg TE/100 g DW.
		①Enzyme selection: Cellulase + Feruloyl esterase. ②Dosage: 50 μL/g + 20 μL/g. ③Temperature: 45 °C. ④pH: 5.5. ⑤Time: 24 h.	169.9 mg GAE/100 g DW.	Vanillic acid: 3.83 μg/g DW. Caffeic acid: 16.6 μg/g DW. Syringic acid: 0.16 μg/g DW. Vanillin: 113.14 μg/g DW. p-Coumaric acid: 14.49 μg/g DW. Ferulic acid: 1260.57 μg/g DW. Isoquercitrin: 7.76 μg/g DW. Quercetin: 0.34 μg/g DW.	DPPH: 103.9 mg TE/100 g DW. FRAP: 168.7 mg TE/100 g DW. ORAC: 13.57 mg TE/100 g DW.

Zhao et al. (2023) investigated the effects of cellulase, feruloyl esterase, and a combination of both enzymes on the release of bound phenolic compounds from defatted RB. Their findings indicated that hydrolysates treated with feruloyl esterase alone yielded only seven detectable monomeric phenolic compounds. A significant difference was observed in ferulic acid release between the single-enzyme treatments and the combined enzymatic treatment, with the latter resulting in a slightly higher release of flavonoids from defatted RB. This indicates that cellulase disrupts the fibrous microstructure but fails to hydrolyze the bonds linking ferulic acid to fibers. In contrast, feruloyl esterase specifically cleaves the ester bonds between ferulic acid and fibers. In contrast, feruloyl esterase specifically cleaves these ester linkages. Furthermore, the antioxidant activity of the cellulase hydrolysate, as measured by DPPH radical scavenging, ferric reducing antioxidant power (FRAP), and oxygen radical absorbance capacity (ORAC), was 1.62, 2.86, and 3.31 times greater, respectively, than that of the feruloyl esterase hydrolysate. Compared to cellulase alone, the combined enzyme treatment significantly increased DPPH and FRAP activities, although ORAC activity did not show further improvement (G. Zhao et al., 2023).

Furthermore, in biological approaches, microbial fermentation primarily facilitates the liberation of phenolic compounds through two pathways: multi-enzyme synergy and metabolic transformation. For instance, lactic acid bacteria (LAB), as heterotrophic anaerobes, generate lactic acid during fermentation that reduces substrate pH to 3.0–4.0; this acidic milieu promotes spontaneous hydrolysis of phenolic acid-polysaccharide ester bonds while accelerating acidolytic cleavage of cell wall cellulose, resulting in extensive pore formation and fissures on bran surfaces with increased specific surface area, which concurrently develops distinctive flavors and enhances phenolic liberation (S. Lin et al., 2024). Simultaneously, secondary metabolites (e.g., short-chain fatty acids) produced during microbial metabolism enhance cell wall permeability, inducing the structural dissociation of lignin-carbohydrate complexes in the bran and thereby further releasing bound phenolic compounds.

Li, Xi, et al. (2024) demonstrated that fermentation of oat bran by Lactobacillus fermentum NB02 resulted in a significant increase in the free phenolic content to 1.05 ± 0.04 mg GAE/g DW and the bound phenolic content to 2.33 ± 0.23 mg GAE/g DW, both significantly higher than those in the unfermented control. This indicates that fermentation promotes the release of phenolic compounds. During fermentation, lactic acid production lowers the pH of the matrix, and feruloyl esterase, secreted by LAB, cleaves the ester bonds between phenolic acids and cell wall polysaccharides, thereby facilitating the liberation of phenolic compounds (Li, Song, et al., 2024). Furthermore, the hydrolysis of bound phenolics and the breakdown of the cell wall during microbial metabolism jointly promote the transformation of low-molecular-weight bound phenolic acids and flavonoids into their free forms. In summary, fermentation technology serves as an effective strategy for releasing bioactive compounds, significantly enhancing the value-added potential of cereal processing by-products.

3.1.1.5. Safety risk assessment of biological treatments on Cereal Bran

Biological methods offer site-selective specificity at ambient temperatures, enabling the precise structural unfolding of bran and phenolic-targeted release while avoiding non-target component degradation. Additionally, microbial metabolism generates flavor compounds (esters, ketones) that mask the bitter taste of bran and synthesizes novel bioactive peptides. Nevertheless, this technology faces limitations, including high enzyme preparation costs, prolonged processing duration, and safety concerns such as toxin production by microbial strains, microbial contamination, fungal contamination, and pesticide residues. Microbial and fungal contamination may occur at multiple stages, originating from the raw material itself, fermentation strains, production equipment, or the production environment. As the outer tissue of grains, bran can accumulate pesticide residues at levels 5–10 times higher than the inner endosperm. Although biological treatment partially degrades organophosphorus pesticides, complete elimination remains unattainable, necessitating that raw bran complies with organic standards or undergoes stringent testing for pesticide residues. Furthermore, certain microbial strains pose toxigenic risks, necessitating continuous toxin monitoring during fermentation, particularly when temperature fluctuations or contamination occur, as these conditions increase hazards. Unsanitary environments can also promote the proliferation of pathogens (e.g., Salmonella, E. coli, and Listeria monocytogenes). While organic acids and bacteriocins produced during fermentation partially inhibit these pathogens and their toxic metabolites, significant health risks persist (H. Lin et al., 2025), including gastrointestinal infections, especially among immunocompromised individuals. Moreover, enzymatic hydrolysis may release or alter antinutritional factors (e.g., phytic acid, tannins, oxalates, and saponins) in bran, impairing the absorption and utilization of essential nutrients.

3.1.2. Ambient-temperature chemical methods

3.1.2.1. Acid and alkali treatments

To effectively extract DF and partially convert IDF into SDF with enhanced physicochemical properties, various reagents can be used. Common acids include hydrochloric acid, sulfuric acid, and citric acid, while sodium hydroxide is typically used for alkali treatment (Abolore et al., 2024). Acidic solutions disrupt the glycosidic bonds in the amorphous regions of IDF, which can affect the crystalline structure of cellulose. Although acid treatment has relatively minimal impact on DF overall, it can still enhance certain physicochemical functionalities of SDF. During alkali treatment, water and sodium ions from NaOH solutions penetrate the internal matrix of IDF. The cleavage of hydrogen and covalent bonds, along with the hydrolysis of hemicellulose, contributes to the breakdown of the cell wall matrix. This promotes water absorption and swelling, facilitating the release of polysaccharides and improving the extraction yield. Additionally, alkali treatment increases the pore size and specific surface area of IDF. The concentration and dosage of acid/alkali reagents, temperature, and reaction time all exert varying degrees of influence on the structure and functionality of DF in cereal bran. An appropriate reaction temperature provides the necessary activation energy, weakens intermolecular interactions, accelerates reaction rates, and promotes fiber modification. However, excessive heat or high concentrations of acid or alkali may result in over-degradation of hemicellulose, leading to a reduction in the mechanical strength of the fibers and thereby compromising their functional properties.

3.1.2.2. Crosslinking treatment

Crosslinking (CL) is a chemical modification strategy used to enhance the extractability, functionality, and valorization of nutrients in cereal bran. This process typically involves the incorporation of phosphate groups into DF chains, allowing otherwise loosely arranged polysaccharide chains to be interconnected via covalent CL. These CL react with active functional groups in the fiber matrix, establishing molecular “bridges” between adjacent chains. The formation of CL points significantly increases intermolecular interactions, leading to either denser surfaces or more open porous structures. This promotes the development of a three-dimensional network, thereby improving the physicochemical properties of DF and enhancing the rigidity and structural stability of the fiber matrix (Hazarika & Sit, 2016). The degree of structural modification induced by CL is largely dependent on the type and concentration of CL agents used. Common crosslinkers include citric acid, phosphates, and epichlorohydrin. Citric acid tends to form ester bond–based network structures, while phosphate-based CL generally imparts greater rigidity to the fiber structure.

3.1.2.3. Etherification treatment

Etherification is a chemical modification technique that alters the functional group composition of IDF by introducing a large number of new substituent groups into its molecular chains. This process modulates the intermolecular forces within IDF, which in turn influences the formation of both surface and internal pore structures. During etherification, fibers located in the amorphous regions of IDF are often degraded, accompanied by the breakdown of lignin and hemicellulose (Kanwar et al., 2023b). The incorporation of numerous polar groups into the polysaccharide chains of IDF enhances internal interactions and increases intermolecular repulsion, resulting in increased molecular chain viscosity. Heating can accelerate the etherification reaction; however, excessive temperatures may cause over-degradation of the reactants or promote undesirable side reactions. Therefore, reaction conditions must be carefully optimized to balance efficiency and product stability (Ren et al., 2006). Common etherification treatments include CM and HP, both of which proceed via substitution reactions. In these processes, free hydroxyl groups on the DF backbone are replaced by CM or HP functional groups, resulting in significant alterations in the structural and functional properties of the DF.

3.1.2.4. Effects of chemical methods on the structural modification of dietary fiber in cereal bran

Table 3 compares the structural changes in cereal bran before and after treatment with various chemical methods. Chemical modification alters the internal structure of bran DF primarily by disrupting hydrogen and covalent bonds within the fiber matrix. This disruption reduces the molecular weight and increases the solubility of DF (Anderson & Simsek, 2019). It has been reported that chemical treatment can cause irreversible changes to the insoluble fiber fraction in rice bran, potentially affecting the original fiber structure to varying degrees and inducing distinct changes in its physicochemical properties.

Table 3.

Modification of dietary fiber structure in chemically treated cereal bran.

Material	Method	Processing conditions	Key findings on changes in dietary fiber structure			Ref.
			chemical composition	particle size	Microstructure morphology
Oat	No chemical treatment	①α-Amylase. ②papain. ③amyloglucosidase.	SDF:22.05 %； IDF:44.09 %. Cellulose:14.69 %. Hemicellulose: 22.04 %. Lignin: 7.36 %	D10:30.93 μm； D50:141.33 μm； D90:287 μm. SSA:112.66m2/kg		(Kanwar et al., 2023b)
	Cross-linking	Treatment condition: ①Sodium trimetaphosphate ②Sodium sulfate ③45 °C, 3 h, pH 11.0	SDF:23.7 %； IDF:42.32 %. Cellulose:13.61 %. Hemicellulose: 21.59 %. Lignin: 7.12 %	D10:36.70 μm； D50:146 μm； D90:311 μm. SSA:103.06m2/kg
	Carboxymethylation	Treatment condition: ①Isopropyl alcohol with stirring for 30 min. ②NaOH with stirring for 90 min. ③Chloroacetic acid, 50 °C for 3 h.	SDF:29.79 %； IDF:34.32 %. Cellulose:9.33 %. Hemicellulose: 18.85 %. Lignin: 6.14 %	D10:36,43 μm； D50:165 μm； D90:357 μm. SSA:87.09m2/kg
	Hydroxypropylation	Treatment condition: ①Sodium sulfate ②Propylene oxide 40 °C, 24 h, pH 11	SDF:27.01 %； IDF:39.26 %. Cellulose:12.44 %. Hemicellulose: 19.85 %. Lignin: 6.97 %	D10:54,26 μm； D50:171 μm； D90:320 μm. SSA:78.10m2/kg
Sorghum	No chemical treatment	①α-Amylase. ②amyloglucosidase.	SDF:2.45 %； IDF:52.77 %. Cellulose:19.15 %. Hemicellulose: 23.17 %. Lignin: 10.45 %	D10:13.66 μm； D50:90.4 μm； D90:216.66 μm. SSA:217.66m2/kg		(Kanwar et al., 2023a)
	Cross-linking	Treatment condition: ①Sodium trimetaphosphate	SDF:3.85 %； IDF:51.21 %. Cellulose:18.84 %. Hemicellulose: 23.1 %. Lignin: 9.27 %	D10:35.43 μm； D50:141 μm； D90:260.66 μm. SSA:100.63m2/kg
	Carboxymethylation	Treatment condition: ①2-propanol ②chloro-acetic acid	SDF:10.85 %； IDF:44.35 %. Cellulose:17.2 %. Hemicellulose: 17.3 %. Lignin: 9.85 %	D10:30.2 μm； D50:158 μm； D90:332 μm. SSA:96.77m2/kg
	Hydroxypropylation	Treatment condition: ①propylene glycol	SDF:7.7 %； IDF:47.7 %. Cellulose:16.63 %. Hemicellulose: 21.62 %. Lignin: 9.45 %	D10:32.30 m； D50:153.66 μm； D90:290.33 μm. SSA:98.53m2/kg

During acid treatment, strong inorganic acid solutions are commonly used. As the acid concentration increases, hydrophilic components such as hemicellulose and lignin in IDF are preferentially hydrolyzed, resulting in increased surface openings, internal porosity, and exposure of inner structures (Li, Wu, et al., 2025). In a study on WB by Wang et al. (2022), it was found that increasing sulfuric acid concentration to 1.0 % and 2.0 % further removed starch, protein, and hemicellulose, disrupted hydrophilic groups, and degraded the surface architecture. This significantly increased the SDF content and enhanced the disintegration of cell wall structures. Acid treatment below 2 % concentration not only improved the water-holding capacity (WHC), Swelling capacity (SC), oil-binding capacity (OBC), and cation-exchange capacity (CEC) of wheat bran IDF, but also enhanced its adsorption capacity for Cholesterol binding capacity (CAC), Sodium cholate adsorption capacity (SCAC), and glucose-adsorption capacity (GAC), along with increased α-amylase inhibitory activity.

However, continued exposure to high acid concentrations resulted in excessive hemicellulose degradation and a decrease in the mechanical strength of the fibers, thereby diminishing their functional properties (L. Wang et al., 2022). Under alkaline treatment, high-pH conditions facilitate the breakdown of non-covalent interactions between cellulose and hemicellulose, thereby increasing the bioaccessibility and solubility of hemicellulose. Alkaline reagents are generally preferred over acids due to their superior efficiency in disrupting lignin and other complex cell wall barriers in bran, which promotes the release of valuable components such as arabinoxylans and β-glucans (Y. Zhang et al., 2021). Additionally, alkaline solutions can break ester and ether bonds within hemicellulose, thereby further facilitating the release of fibers. Given the variability in the affinity and binding strength of different IDF fractions to alkaline solutions, as well as their differing proportions of cellulose, hemicellulose, and lignin, treatment can result in the formation of irregular surface morphologies, such as loosely folded or honeycomb-like structures. These morphological changes effectively increase the specific surface area of DF and expose more internal functional groups, which enhance physicochemical properties such as water-holding and oil-binding capacities, as well as the fiber's ability to bind heavy metal ions.

Zhang et al. (2019) compared structural alterations in WB dietary fiber following three modification methods—carboxymethylation, complex enzymatic hydrolysis, and ultrafine milling—demonstrating that carboxymethylation employs a cascade reaction wherein “molecular-level group modification triggers microstructure reorganization, structural reorganization enables charge modulation, and establishes macroscopic functional expression.” This process initially introduces hydrophilic carboxymethyl groups into WB dietary fiber. These groups substitute hydroxyl groups in cellulose/hemicellulose, disassembling the original hydrogen bond network and enhancing hydrophilicity by 37.5 %. Consequently, carboxymethylation significantly outperformed complex enzymatic hydrolysis and ultrafine milling in all functional properties, establishing it as the optimal WB treatment. It simultaneously delivers high water-holding capacity (for hydrophilic foods), high oil-binding capacity (for emulsified systems), and high thermal stability (for baking applications) (M. Y. Zhang et al., 2019). Furthermore, Kanwar et al. (2023a) investigated the physicochemical properties, microstructure, and thermal performance of sorghum dietary fiber (SODF) using three chemical modification methods—cross-linking (CL), carboxymethylation (CM), and hydroxypropylation (HP). Their results likewise demonstrated that CM and HP enhance hydrophilicity through the introduction of carboxymethyl/hydroxypropyl groups, whereas cross-linking elevates adsorption capacity by forming a cross-linked network. All three modification methods effectively optimized the functional properties of SODF, thereby enhancing its suitability for the development of high-fiber foods. Nevertheless, carboxymethylation emerged as the optimal choice, as it increased the SDF content from 2.45 % to 10.85 %—representing an approximately fivefold enhancement (Kanwar et al., 2023a).

3.1.2.5. Effects of chemical methods on the release of bound Phenolics from cereal bran

Table 4 compares the changes in phenolic compound release from cereal bran before and after treatment with various chemical methods. Mild alkaline or weak acid hydrolysis decomposes esterified or bound polyphenols associated with soluble carbohydrates, proteins, and other grain components, thereby liberating free polyphenols. Alkaline solvents, such as sodium hydroxide, offer relative ease of handling. Not only do they release free polyphenols, but they also prevent the degradation of hydroxycinnamic acids, making them an attractive option for large-scale industrial applications. These solvents are typically combined with other chemicals or processing methods to optimize pretreatment efficiency (Melikoğlu et al., 2019). However, substantial portions of polyphenols remain insoluble in alkali-treated bran due to encapsulation within core structures or binding with cell wall components, thereby limiting the effective release of phenolic acids. In contrast, acid hydrolysis more efficiently liberates cell-wall-bound insoluble polyphenols, yielding higher TPC in treated bran. For instance, Nemes, Teleky, et al. (2024) demonstrated that acid treatment of WB markedly enhanced isoferulic acid (Iso FA) release—producing nearly 30-fold higher levels than controls—attributed to the acid sensitivity of ester bonds linking isoferulic acid to arabinoxylan (hemicellulose) in insoluble complexes. Furthermore, acid-pretreated WB exhibited significantly elevated TPC and antioxidant activity. Conversely, alkaline pretreatment with NaOH not only hydrolyzes ester bonds but also enables nucleophilic OH⁻ attacks on phenolic rings: dihydroxybenzoic acid (DHA) undergoes deactivation, while HBA undergoes deprotonation to form phenolate ions that oxidatively cleave, resulting in significantly reduced levels of DHA, HBA, VA, and Iso FA (Nemes, Teleky, et al., 2024).

Table 4.

Altered release of phenolic compounds from chemically treated cereal bran.

Material	Method	Processing conditions	Key findings on changes in dietary fiber structure		Antioxidant activity	Ref.
			Total phenolic content	Changes in phenolic compounds
wheat bran	Acid and alkaline treatments	Control: untreated	27.70 mg GAE/100 g DW.	Dihydroxybenzoic acid: 139.9 μg/g. Hydroxybenzoic acid: 49.6 μg/g. Gentisic acid: 103.3 μg/g. Vanillic acid: 68.3 μg/g. Apigenin-glucoside: 72.7 μg/g. Apigenin-xylosyl-glucoside: 113.2 μg/g. Luteolin-diglucoside: 86.6 μg/g. Ferulic acid: 20.5 μg/g. Iso Ferulic acid: 4.32 μg/g.	DPPH: 95.08 μM TE/g DW.	(Nemes, Teleky, et al., 2024)
		Acids: 50 mL of aqueous solvent of 3 % H2SO4. Reaction conditions: Incubate at room temperature for 2 h.	39.32 mg GAE/100 g DW.	Dihydroxybenzoic acid: 174.2 μg/g. Hydroxybenzoic acid: 107 μg/g. Gentisic acid: 174.2 μg/g. Vanillic acid: 76.2 μg/g. Apigenin-glucoside: 78.5 μg/g. Apigenin-xylosyl-glucoside: 140.8 μg/g. Vanillin derivative: 188.8 μg/g. Luteolin-diglucoside: 103.7 μg/g. Ferulic acid: 62.2 μg/g. Iso Ferulic acid: 128.5 μg/g.	DPPH: 575.83 μM TE/g DW.
		Alkaline: 50 mL of aqueous solvent of 3 % NaOH. Reaction conditions: Incubate at room temperature for 2 h.	6.84 mg GAE/100 g DW.	Dihydroxybenzoic acid: 74.5 μg/g. Hydroxybenzoic acid: 14.9 μg/g. Gentisic acid: 69.0 μg/g. Vanillic acid: 31.7 μg/g. Apigenin-glucoside: 6.84 μg/g. Apigenin-xylosyl-glucoside: 11.7 μg/g. Luteolin-diglucoside: 16.1 μg/g. Ferulic acid: 28.4 μg/g. Iso Ferulic acid: 0.87 μg/g.	DPPH: 80.64 μM TE/g DW.
wheat bran	Alkaline-then-acid method	Step 1: alkali hydrolysis: ①40 mL 2 M NaOH; ② stirring at room temperature for 4 h. Second acid hydrolysis: ①6 M HCl; ②95 °C water bath for 1 h.	–	p-Hydroxybenzoic acid: 20.0 μg/g. Vanillic acid: 73.8 μg/g. Syringic acid: 137 μg/g. trans-Cinnamic acid: 0.88 μg/g. Caffeic acid: 2.28 μg/g. p-Coumaric acid: 44.3 μg/g. Ferulic acid: 1932 μg/g. Salicylic acid: 1.88 μg/g.	–	(K.-H. Kim et al., 2006)
	Acid-then-alkaline method	Step 1: alkali hydrolysis: ①6 M HCl; ②95 °C water bath for 1 h. Second acid hydrolysis: ①40 ml 2 M NaOH; ② stirring at room temperature for 4 h.	–	p-Hydroxybenzoic acid: 22.8 μg/g. Vanillic acid: 44.4 μg/g. Syringic acid: 117 μg/g. p-Coumaric acid: 1.66 μg/g. Ferulic acid: 44.7 μg/g. Salicylic acid: 158 μg/g.	–

The differential phenolic release stems fundamentally from chemical bond sensitivity: acid treatment selectively hydrolyzes ester bonds, whereas alkaline treatment indiscriminately cleaves ester bonds while simultaneously destroying phenolic ring structures. Kim et al. (2006) systematically evaluated the effects of acidic versus alkaline hydrolysis conditions on wheat bran phenolic acid release, revealing that sequential alkali-acid treatment outperformed acid-alkali sequences in terms of total phenolic and ferulic acid content. FA—the predominant monomeric phenolic acid—was primarily liberated during alkaline hydrolysis, followed by vanillic and syringic acids. Acidic conditions or acid-prioritized treatments may degrade certain phenolic acids (K.-H. Kim et al., 2006). These findings indicate that the profile and quantity of released polyphenols are intricately governed by interconnected factors including reagent type and concentration, treatment sequence, reaction time/temperature, and raw material properties, necessitating systematic optimization for specific bran sources and target polyphenols.

3.1.2.6. Safety risk assessment of chemical treatment of cereal bran

Chemical treatment of cereal bran is widely employed due to its low cost and high efficiency. However, chemical modification of DF can lead to substantial degradation of polysaccharides, potentially resulting in incomplete extraction of the polysaccharides. Some studies suggest that chemical methods are among the most effective modification techniques, as the reagents used often cause minimal structural damage to DF molecules while promoting an increase in SDF content (Kanwar et al., 2023b). Nevertheless, certain chemical reagents may alter the molecular structure of DF in ways that reduce transformation efficiency or physiological functionality (Kumari et al., 2025). Moreover, toxicity residues and nutrient loss represent the most significant drawbacks of current chemical methods. The disposal of acidic or alkaline waste liquids used in these processes may cause environmental harm, limiting the application of DF in food products and potentially posing health risks to humans. Consequently, while suitable for experimental research, their application in the food industry remains restricted. Furthermore, treatments such as crosslinking, CM, and HP have their limitations, including complex and time-consuming operational procedures, noticeable product browning, and, in some cases, adverse effects on the rheological properties of the final product (H. Zhang et al., 2018).

3.1.3. Physical methods

3.1.3.1. Ultrasonic treatment

Ultrasound (US) is an environmentally friendly, non-thermal processing technology that typically operates under mild conditions at ambient temperature. It utilizes sound wave energy with frequencies above 20 kHz. The functional effects of ultrasound are primarily attributed to the intense microjets and shock waves generated during sonication. These forces cause vigorous oscillation of polar molecules within the brain, resulting in cavitation phenomena that produce a sponge-like effect and enhance tissue extensibility. The intense mechanical forces from cavitation break chemical bonds between polysaccharide chains, exposing reactive functional groups, disrupting intermolecular hydrogen bonds among cellulose chains, and partially dissociating lignin into phenolic compounds (Huang et al., 2024). This leads to the formation of microporous channels on the surface of the bran, disrupting the compact internal structure. Consequently, the composition, content, and particle size distribution of bran DF are altered, surface hydrophilicity is modified, and bioactive compound release is enhanced—collectively improving the functional properties of the DF.

3.1.3.2. High-pressure microfluidization

High-pressure microfluidization (HPMT) and dynamic high-pressure microfluidization (DHPM) are mechanical processing techniques based on intense shear forces generated by high-speed impact, high-frequency vibration, instantaneous pressure drops, and strong shear stress. These forces act through microchannels to shear and collide with the microstructure of cereal bran, resulting in modifications to its structural composition and reduction in DF particle size. Among them, HPMT forces the physical breakage of bran cell walls (cellulose-hemicellulose-lignin network), reduces crystallinity and increases porosity, thereby exposing the encapsulated phenolic compounds; meanwhile, the hydrogen bond breakage and intermolecular force weakening induced by high pressure make the bound phenolic compounds dissociate from polysaccharide or protein complexes, and the pulsed pressure of DHPM enhances the cell wall breaking efficiency through cavitation explosion and micro - jet impact. It may activate endogenous enzymes to promote the hydrolysis of glycosidic bonds. These changes significantly enhance the functional properties of cereal bran, broadening its applicability in various food systems. Moreover, high-pressure microfluidization enhances the physicochemical properties of SDF, including solubility, viscosity, and rheological behavior, thereby increasing its value in the development of high-added-value food products (Q. Zhao et al., 2021).

3.1.3.3. Plasma treatment

The core mechanism of plasma treatment involves bombardment and etching of the bran surface by high-energy reactive species within the plasma—such as electrons, ions, free radicals, excited molecules, and UV photons—which physically and chemically modify the surface. These reactive species induce chemical bond breakage, oxidation reactions, and structural rearrangements, effectively altering the surface morphology, chemical composition, and microstructure of cereal bran without the need for high temperatures or large amounts of chemical reagents. Studies have confirmed that reactive nitrogen species (RNS) and reactive oxygen species (ROS) generated during plasma treatment are the main factors responsible for polysaccharide chain cleavage (Duan & Kasper, 2011). This technique can selectively weaken or disrupt key structural barriers in bran—such as dense networks, hydrophobic layers, and crosslinking points—that limit hydration and bioaccessibility, thereby significantly improving its functional properties.

3.1.3.4. Effects of physical methods on the structural modification of dietary Fiber in cereal bran

Table 5 compares the structural changes in cereal bran before and after treatment with different physical methods. Research by Jiang et al. (2024) found that ultrasonic treatment of corn bran disrupted the IDF cell walls and cellulose and hemicellulose chains, resulting in the highest degree of structural porosity at the microscopic level. The DF exhibited the smallest particle size and the largest specific surface area, with increased SDF content and decreased IDF content. These results indicate structural alterations in the bran dietary fiber; the reduced particle size led to a better adsorption index, while the increased specific surface area facilitated the formation of additional hydrogen bonds or dipole spaces to accommodate water molecules (Jiang et al., 2024). Moreover, ultrasonic treatment significantly increased the average molecular weight of SDF in corn bran, which is closely related to the cavitation effect of ultrasound. Ultrasonic cavitation refers to oxidative reactions generating free radicals, including hydroxyl radicals, hydrogen radicals, and perhydroxyl radicals. The extremely high temperature and pressure formed during the collapse of cavitation bubbles cause the decomposition of water vapor trapped within them, producing reactive hydroxyl and hydrogen radicals. These radicals recombine or react with other gaseous substances in the bubbles, forming active species such as HO₂⁻, O⁻, and H₂O₂. Higher frequencies generate more hydroxyl radicals than lower frequencies, and the number of radicals increases with prolonged ultrasonic treatment time. However, extended duration or high-power treatment may cause IDF agglomeration, which can adversely affect the modification outcome. Notably, extensive research indicates that the key factors influencing structural changes in cereal bran dietary fiber induced by physical methods include treatment intensity, number of treatment cycles, raw material characteristics, and moisture content. When Kang et al. (2024) treated oat dietary fiber (ODF) with DHPM at different pressures, they observed that increasing the pressure to 420 MPa reduced the average particle size of ODF by 51.07 %. This treated ODF possessed a lower cellulose and hemicellulose content, a greater specific surface area and porosity, and an enhanced capacity to adsorb glucose, cholesterol, and bile salts, thereby improving its interaction with nutrients. Beyond 420 MPa, no significant changes occurred in the structural and functional properties of ODF (Kang et al., 2024). Similarly, research by Li, Yadav, et al. (2024) on highland barley bran treated with HPMT at different pressures and cycles revealed that two consecutive 120 MPa treatments caused greater disruption to the crystalline structure of IDF compared to a single 120 MPa treatment. This is because repeated high-pressure treatments likely break intermolecular hydrogen bonds in IDF, loosening its structure and transforming some crystalline regions into amorphous areas, thereby reducing the crystallinity of IDF. These fundamental changes similarly led to significant increases in the IDF samples' WHC, OHC, SC, CAC, and NIAC (Li, Zhang, et al., 2024).

Table 5.

Modification of dietary fiber structure in physically treated cereal bran.

Material	Method	Processing conditions	Key findings on changes in dietary fiber structure			Ref.
			chemical composition	particle size	Microstructure morphology
Oat bran	Dynamic high-pressure microfluidization treatment	①Control: DHPM-0 MPa. ②In the distilled water at a ratio of 1:4 (m/v).	Compared to the control group, the content of hemicellulose in ODF treated at 60 MPa was not significantly different.	①Particle size decreases with increasing pressure. ②D50 is lowest at a treatment of 420 MPa.		(Kang et al., 2024)
		①DHPM-60 MPa. ②In the distilled water at a ratio of 1:4 (m/v).
		①DHPM-120 MPa. ②In the distilled water at a ratio of 1:4 (m/v).	①The cellulose and hemicellulose content tended to decrease significantly with increasing treatment pressure. ②The lowest level was found in the 420 MPa treatment.
		①DHPM-240 MPa. ②In the distilled water at a ratio of 1:4 (m/v).
		①DHPM-420 MPa. ②In the distilled water at a ratio of 1:4 (m/v).
Corn bran	No Ultrasonic	①0.5 % α-amylase, 60 °C for 2 h. ②1 % alkaline protease, 55 °C for 3 h. ③0.5 % saccharase, 50 °C for 2 h.	IDF:84.67 %. SDF:1.98 %.	D10:16.98 μm； D50:137.2 μm； D90:366.6 μm. SSA:60.52m2/g		(Jiang et al., 2024)
	Ultrasonic	①UA power:500 W. ②UA time: 30 min.	IDF:80.33 %. SDF:6.32 %.	D10:12.09 μm； D50:84.01 μm； D90:219.9 μm. SSA:84.83m2/g
Highland barley bran	No High-pressure microfluidization	①α-Amylase. ②papain.	SDF:2.85 g/100 g. IDF:80.98 g/100 g. Cellulose:35.59 g/100 g. Hemicellulose:15.28 g/100 g. Lignin:7.56 g/100 g.	D50:61.42 μm； D90:173.81 μm. SSA:246.3m2/kg		(Li, Zhang, et al., 2024)
	High-pressure microfluidization	①IDF-60: 60 MPa pressurized 1 time.	SDF:3.23 g/100 g. IDF:81.13 g/100 g. Cellulose:36.33 g/100 g. Hemicellulose:16.13 g/100 g. Lignin:7.33 g/100 g.	D50:44.37 μm； D90:123.16 μm. SSA:267.7m2/kg
		①IDF-120: 120 MPa pressurized 1 time.	SDF:3.83 g/100 g. IDF:79.54 g/100 g. Cellulose:36.09 g/100 g. Hemicellulose:13.14 g/100 g. Lignin:6.92 g/100 g.	D50:34.10 μm； D90:90.80 μm. SSA:329.6m2/kg
		①IDF-120-2: 120 MPa pressurized 2 times.	SDF:4.28 g/100 g. IDF:78.24 g/100 g. Cellulose:33.98 g/100 g. Hemicellulose:12.4 g/100 g. Lignin:6.46 g/100 g.	D50:29.74 μm； D90:73.74 μm. SSA:338.8m2/kg

3.1.3.5. Effects of physical methods on the release of bound phenolics from cereal bran

Table 6 compares the changes in phenolic compound release from cereal bran before and after treatment with different physical methods. Various processing parameters, including temperature, pressure, solvent-to-solid ratio, solvent concentration and type, and treatment duration, significantly influence the recovery of phenolic compounds from cereal bran using physical techniques. These factors are considered critical determinants of extraction efficiency. Chen et al. (2018) conducted a comparative study on the effects of ultrasound-assisted extraction (UAE) versus conventional extraction (CE) on the release of phenolic compounds from defatted oat bran across varying temperatures (20–90 °C) and extraction durations (1–25 min). The results demonstrated that esterified and bound phenolics predominated, with ultrasonic temperature having a significant influence on extraction efficiency. As the temperature increased from 20 °C to 70 °C, the TPC yield markedly increased, accompanied by elevated levels of individual phenolics, such as p-hydroxybenzoic acid and protocatechuic acid. Gallic acid and ferulic acid exhibited the most pronounced enhancements. Between 70 °C and 90 °C, no significant difference in extraction rates was observed between CE and UAE. Optimal ultrasonic temperatures enhance diffusivity and volatility in oat bran, disrupting conjugated structures in cereal bran while promoting cytoplasmic delivery of phenolic compounds, thereby liberating bound phenolics. However, excessively high temperatures reduced bound phenolic acid content due to thermochemical degradation (e.g., phenolic acid decomposition and polymerization) and attenuated cavitation efficiency from high-temperature physical effects. Individual phenolic acids, notably p-coumaric acid and ferulic acid, showed significant declines, indicating localized constraints on phenolic release (Chen et al., 2018). In addition, Liang et al. (2024) reported that ultrafine grinding significantly improved the release and bioaccessibility of phenolic compounds in millet bran by disrupting the cell wall structure, thereby enhancing antioxidant activity. The extent of cell wall disruption was influenced by particle size, with a 2-h ball milling process achieving a rupture rate of up to 96.52 %. Under this condition, compared with coarsely ground samples, the TPC increased by 80 %, and the concentrations of sinapic acid, FA, caffeic acid, and isoferulic acid were significantly elevated. Given that phenolic compounds—particularly FA and sinapic acid—are major contributors to antioxidant capacity, their increased release directly enhanced the antioxidant properties of millet bran. Moreover, particle size reduction increased specific surface area, which further facilitated the dissolution of antioxidant components (Liang et al., 2024). Nevertheless, it is worth noting that certain phenolic compounds, such as gentisic acid and sinapic acid analogues, are thermolabile or structurally unstable and may undergo degradation during milling. Therefore, precise temperature control is essential when applying ultrafine grinding to cereal bran. Additionally, high hydrostatic pressure (HHP) treatment has been demonstrated to more effectively preserve phenolics and other bioactive compounds in cereal bran matrices (Scepankova et al., 2018).

Table 6.

Altered release of phenolic compounds from physically treated cereal bran.

Material	Method	Processing conditions	Key findings on changes in dietary fiber structure		Antioxidant activity	Ref.
			Total phenolic content	Changes in phenolic compounds
Oat bran	Ultrasound-assisted extraction	①4 g oat bran +40 mL 80 % ethanol； ②Ultrasonic power: 600 W. ③Ultrasonic frequency: 40 kHz. ④Processing temperature: 20 °C. ⑤Processing time: 15 min.	–	Gallic acid: 27.94 μg/g. p-Hydroxybenzoic acid: 31.56 μg/g. Vanillic acid: 32.14 μg/g. Caffeic acid: 8.08 μg/g. Protocatechuic acid: 1.65 μg/g. Ferulic acid: 4.20 μg/g. Av 2c: 76.58 μg/g. Av 2p: 121.55 μg/g. Av 2f: 86.83 μg/g. Sum phenolic acids: 105.59 μg/g. Sum AVs: 284.96 μg/g.	ORAC: 23.91 μmol/g dm.	(Chen et al., 2018)
		①4 g oat bran +40 mL 80 % ethanol； ②Ultrasonic power: 600 W. ③Ultrasonic frequency: 40 kHz. ④Processing temperature: 70 °C. ⑤Processing time: 15 min.	–	Gallic acid: 67.42 μg/g. p-Hydroxybenzoic acid: 40.81 μg/g. Vanillic acid: 39.43 μg/g. Caffeic acid: 10.24 μg/g. Protocatechuic acid: 3.25 μg/g. Ferulic acid: 14.32 μg/g. Av 2c: 143.43 μg/g. Av 2p: 161.57 μg/g. Av 2f: 142.70 μg/g. Sum phenolic acids: 175.47 μg/g. Sum AVs: 448.84 μg/g.	ORAC: 38.27 μmol/g dm.
	conventional extraction	①4 g oat bran +40 mL 80 % ethanol； ②Processing temperature: 20 °C. ③Processing time: 15 min.	–	Gallic acid: 21.89 μg/g. p-Hydroxybenzoic acid: 21.96 μg/g. Vanillic acid: 27.03 μg/g. Caffeic acid: 6.27 μg/g. Protocatechuic acid: 1.09 μg/g. Ferulic acid: 1.77 μg/g. Av 2c: 65.30 μg/g. Av 2p: 73.07 μg/g. Av 2f: 61.84 μg/g. Sum phenolic acids: 80.03 μg/g. Sum AVs: 200.21 μg/g.	ORAC: 22.39 μmol/g dm.
		①4 g oat bran +40 mL 80 % ethanol； ②Processing temperature: 70 °C. ③Processing time: 15 min.	–	Gallic acid: 65.34 μg/g. p-Hydroxybenzoic acid: 40.65 μg/g. Vanillic acid: 40.72 μg/g. Caffeic acid: 10.79 μg/g. Protocatechuic acid: 2.95 μg/g. Ferulic acid: 10.10 μg/g. Av 2c: 132.43 μg/g. Av 2p: 150.57 μg/g. Av 2f: 131.70 μg/g. Sum phenolic acids: 170.54 μg/g. Sum AVs: 414.73 μg/g.	ORAC: 36.30 μmol/g dm.
Defatted millet bran	Superfine grinding	Coarse powder: Through a 40-mesh sieve (pore size 425 μm).	2684.53 μg/g	Vanillic acid: 110.49 μg/g. Protocatechuic acid: 1.02 μg/g. Gentianic acid: 1.79 μg/g. Sinapic acid: 7.11 μg/g. Syringic acid: 13.54 μg/g. Ferulic acid: 84.02 μg/g. Caffeic acid: 5.18 μg/g. Gallic acid: 1.18 μg/g. Isoferulic acid: 83.10 μg/g. p-Hydroxybenzoic acid: 0.65 μg/g. 2,3-Dihydroxybenzoic acid: 0.39 μg/g. 2,3,4-Trihydroxybenzoic acid: 0.48 μg/g.	DPPH:24.55 %. ABTS:60.43 %.	(Liang et al., 2024)
		Fine powder: 120 mesh sieve (pore size 125 μm)	4170.45 μg/g	Vanillic acid: 88.87 μg/g. Protocatechuic acid: 0.93 μg/g. Gentianic acid: 1.49 μg/g. Sinapic acid: 5.19 μg/g. Syringic acid: 23.97 μg/g. Ferulic acid: 113.77 μg/g. Caffeic acid: 8.25 μg/g. Gallic acid: 0.76 μg/g. Isoferulic acid: 93.77 μg/g. p-Hydroxybenzoic acid: 0.52 μg/g. 2,3-Dihydroxybenzoic acid: 0.35 μg/g. 2,3,4-Trihydroxybenzoic acid: 0.31 μg/g.	DPPH:29.88 %. ABTS:61.38 %.
		Superfine powder: ①fine powder to ZrO2 spheres 1:5. ②ball mill for 2 h , ③pauses of 20 min each, 10 min of grinding.	4843.63 μg/g	Vanillic acid: 115.06 μg/g. Protocatechuic acid: 1.42 μg/g. Gentianic acid: 1.78 μg/g. Sinapic acid: 5.11 μg/g. Syringic acid: 29.25 μg/g. Ferulic acid: 123.55 μg/g. Caffeic acid: 9.76 μg/g. Gallic acid: 1.01 μg/g. Isoferulic acid: 107.37 μg/g. p-Hydroxybenzoic acid: 0.64 μg/g. 2,3-Dihydroxybenzoic acid: 0.57 μg/g. 2,3,4-Trihydroxybenzoic acid: 0.44 μg/g.	DPPH:36.8 %. ABTS:73.77 %.

3.1.3.6. Safety risk assessment of physical processing methods for cereal bran

Non-thermal physical modification technologies have demonstrated considerable potential not only in effectively altering the structure of cereal bran and enhancing its SDF content but also in promoting the release of phenolic compounds. Compared with biological and chemical methods in non-thermal processing, Non-thermal physical modification methods operate under near-room-temperature conditions or slightly elevated temperatures, and are characterized by low energy consumption, high efficiency, and strong environmental sustainability. It has shown great promise in food processing applications. However, most non-thermal processing physical methods are significantly constrained in practical production applications due to the relatively high cost of equipment and complex operating procedures. For example, due to the inherent high-energy and high-activity mechanisms of action, the potential safety risks associated with the physical processing of grain bran cannot be overlooked. These risks primarily manifest as free radical-mediated oxidative damage, the adsorption or release of contaminants induced by structural alterations, the loss of nutrients caused by mechanical damage, and poor sensory evaluations during the development of functional foods, leading to low consumer acceptance. While these risks are not inevitable, their occurrence is highly dependent on the selection of processing parameters, control of raw material quality, rational design of equipment, and subsequent storage and transportation conditions. Future efforts must focus on further research and development to address the practical application challenges of physical grain bran processing methods. The aim is to optimize conditions that maintain grain quality and ensure that no products hazardous to human health are generated during the reaction processes.

3.2. Combined non-thermal processing technology

3.2.1. Physical–biological combined methods

3.2.1.1. Effects of combined physical and biological methods on the structural modification of Cereal Bran dietary fiber

Table 7 compares the structural changes in cereal bran DF induced by physical or biological methods alone and by their combined application. The mechanism of physico-biological combined methods typically involves first utilizing physical techniques to disrupt the dense bran structure, creating porous channels and reducing crystallinity, followed by the synergistic effects of enzymatic hydrolysis or microbial transformation to achieve SDF conversion and efficient release of phenolic acids. Common current physico-biological combinations include high-pressure homogenization-assisted enzymatic treatment and ultrasound-assisted enzymatic treatment. These approaches strike a balance between efficiency and environmental sustainability, offering broader applicability compared to single-method applications. For instance, Xie et al. (2019) found that cellulase treatment alone reduced rice bran crystallinity from 22.22 % to 11.76 %, whereas the combination of high-pressure homogenization and cellulase treatment increased crystallinity from 11.76 % to 15.78 %. This indicates the disruption of cellulose linkages between crystals, preferential degradation of amorphous regions, and the promotion of glycosidic bond dissociation in RB fiber structures. The combined processing exposed hydroxyl groups in cellulose, altered crystallinity, and effectively enhanced water-binding capacity, demonstrating the efficacy of integrated methods (Xie et al., 2019). Additionally, Li, Niu, et al. (2022) demonstrated in corn bran studies that ultrasound-enzyme combined treatment yielded higher SDF production and significantly elevated xylose and arabinose ratios compared to ultrasound treatment alone. This was attributed to ultrasound disrupting the cross-linking between dietary fiber molecules, creating surface cavities. Meanwhile, cellulase and xylanase treatments further increased glucose content, facilitated cellulose hydrolysis, and resulted in a loose, porous microstructure with enhanced structural openness. These modifications increased the exposure of hydrophilic groups and improved water-holding capacity (S. Li, Hu, et al., 2022).

Table 7.

Effect of combined use of physical and biological methods on structural changes in cereal bran.

Material	Method	Processing conditions	Key findings on changes in dietary fiber structure				Ref.
			chemical composition	Mw	Monosaccharide composition	Microstructure morphology
Wheat bran	Cold plasma	①condition: 0.75 A, 20s.	SDF:7.07 %.	9264 Da.	①Glucose: 54.47 % ②Arabinose: 13.85 % ③Xylose: 31.49 % ④Galactose: 0.18 %		(Li, Xu, et al., 2025)
	enzymatic hydrolysis	①0.004 % acidic xylanase. ②0.001 % α-L-arabinofuranosidase. ③condition: 50 °C, 2.5 h.	SDF:15.08 %.	5528 Da.	①Glucose: 39.68 % ②Arabinose: 21.17 % ③Xylose: 37.24 % ④Galactose: 1.7 % ⑤Rhamnose: 0.2 %
	Cold plasma -enzymatic hydrolysis	①Cold plasma condition: 0.75 A, 20s. ②Enzymatic condition::50 °C, 2.5 h. ③0.004 % acidic xylanase. ④0.001 % α-L-arabinofuranosidase.	SDF:14.65 %.	5168 Da.	①Glucose: 41.51 % ②Arabinose: 18,93 % ③Xylose: 39.56 %
Corn bran	Ultrasonic	①UA power: 500 W. ②UA time: 30 min.	SDF:4.58 %.	30,700 Da	①Mannose:2.57 % ②Galacturonic acid:7.79 % ③Glucose:3.33 % ④Xylose:37.98 % ⑤Arabinose:48.32 %		(Li, Niu, et al., 2022)
	Ultrasonic -assisted enzymatic	①UA power: 500 W. ②UA time: 30 min. ③Enzymatic condition: pH 4.8, 55 °C, 2.5 h, xylanase 120 U/g, cellulase 240 U/g.	SDF:6.98 %.	6410 Da.	①Galacturonic acid:3.36 % ②Glucose:57.53 % ③Xylose:19.08 % ④Arabinose:20.01 %
rice bran	enzymes treatment	①Cellulase, xylanase. ②Enzymatic condition: pH 4.8, 50 °C, 2 h.	SDF: 15.1 g/100 g IDF: 60.2 g/100 g Cellulose:6.5 g/100 g Hemicellulose:12.1 g/100 g Lignin: 29 g/100 g	–	-		(Wen et al., 2017)
	enzyme-micronization treatment	①Cellulase, xylanase. ②Enzymatic condition: pH 4.8, 50 °C, 2 h. ③Ball milling (3000 r/min, 2 h) at 45–55 °C.	SDF: 18.7 g/100 g IDF: 56.4 g/100 g Cellulose:8.7 g/100 g Hemicellulose:14.4 g/100 g Lignin: 24.2 g/100 g	–	-

Moreover, recent years have seen growing interest in combining plasma with enzymatic methods. According to Li, Xu, et al. (2025), enzymatic treatment partially compensates for the losses of arabinose and xylose induced by cold plasma, with the combined modification exhibiting the most pronounced structural changes. Notably, plasma-enzyme treatment of WB dietary fiber reduced SDF yield, which the authors attributed to high-energy ion bombardment during cold plasma processing, causing fiber chain depolymerization and creating favorable conditions for enzymatic degradation. This increased the formation of soluble oligosaccharides that do not precipitate upon ethanol addition (Li, Xu, et al., 2025). However, the efficacy of physico-biological combined methods is often influenced by processing parameters and raw material characteristics, and current applications face certain limitations. For example, multi-stage processing escalates equipment costs, while increased process control points introduce operational complexity and uncertainty. Additionally, the lack of standardization poses a significant bottleneck, as variability in cereal bran sources limits the generalizability of parameters, necessitating customized protocols that hinder large-scale industrial adoption. Future efforts should focus on enhancing process monitoring systems, integrating green technologies, and further reducing costs to improve efficiency.

3.2.1.2. Effects of combined physical and biological methods on the release of bound polyphenols from Cereal Bran

Table 8 compares the effects of physical and biological methods—used independently or in combination—on the release of polyphenolic compounds from cereal bran. Approximately 70 %–85 % of phenolic substances in bran exist in esterified or etherified forms, covalently bound to cell wall polysaccharides, rendering them difficult to absorb directly. The combined physical-biological treatment induces significant and multidimensional modifications in the release of phenolic compounds, facilitating the conversion of bound phenolics to free forms. These alterations are manifested not only quantitatively but also in terms of composition, morphology, and bioactivity. The combined approach achieves complementary energy conversion: physical treatments primarily input mechanical, electrical, or acoustic energy, which rapidly disrupt structural barriers in the initial stage, while biological treatments utilize biochemical energy for precise molecular modifications, forming a synergistic interplay in energy form and temporal sequence. Compared to individual treatments, this combined strategy typically enhances phenolic release efficiency by over twofold, demonstrating notable synergistic advantages. The study by Ren et al. (2006) demonstrated that ultrasonication-assisted cellulase treatment of germinated brown rice increased TPC by 4.22–16.00 mg/100 g DW compared to cellulase treatment alone (R. Li, Song, et al., 2024). In terms of phenolic acid and flavonoid composition, the ultrasonicated group showed substantially higher levels of protocatechuic acid, FA, p-coumaric acid, myricetin, daidzin, and rutin than the non-ultrasonicated cellulase-treated group. This enhancement was attributed to the combined effects of ultrasonic cavitation disrupting surface structures and cellulase hydrolyzing cellulose, resulting in visibly roughened and etched rice particles. These findings indicate that the ultrasonication-assisted cellulase approach synergistically combines enzymatic catalytic efficiency with ultrasound-enhanced mass transfer, significantly improving substrate-enzyme interaction and catalytic performance. Similarly, Nemes et al. (2025) reported that solid-state fermentation of wheat bran by Aspergillus niger increased TPC by 18.44 %, primarily due to structural modification by the fungus and the high activity of cellulase, xylanase, arabinofuranosidase, and β-xylosidase, which collectively promoted phenolic release from cell wall matrices. When ultrasonication was combined with A. niger fermentation, TPC increased by 21.3 % on the first day of fermentation, reaching 1.5 times that of non-ultrasonicated fermented bran (Nemes et al., 2025). These results collectively demonstrate that the integration of ultrasonication with solid-state fermentation generates synergistic effects, significantly enhancing the liberation of bioactive compounds from cereal bran. The significant increase in ABTS antioxidant capacity to 1411 μM TE/100 g by the fifth day under combined treatment can be attributed to the elevated levels of highly antioxidative phenolic compounds such as vanillic acid and protocatechuic acid, coupled with microbial fermentation-induced liberation of free phenolic hydroxyl groups, which enhance electron-donating capacity and modify phenolic structures. This demonstrates that the combined approach leverages physico-biological synergy to directionally convert low-activity phenolics into high-activity metabolites, offering an eco-friendly strategy for valorizing cereal processing byproducts. Crucially, these findings confirm that the molecular architecture of phenolics fundamentally governs their antioxidant efficacy. However, it must be noted that optimizing physical parameters in combined treatments is critical—excessive physical processing may cause excessive degradation of bran fiber, impairing subsequent enzymatic action, while insufficient treatment fails to adequately disrupt structural barriers, thereby limiting bioconversion efficiency. The ideal physical pretreatment should achieve a “critical disruption threshold”—sufficient to fully open bran structures without substantial nutrient loss—a precise balance requiring systematic experimental calibration for different raw materials. Collectively, the combined physico-biological approach modulates bran phenolic states through multi-target mechanisms, not only markedly improving release efficiency but also optimizing compositional profiles and bioactivity, thereby establishing a foundation for developing high-nutrition functional food ingredients.

Table 8.

Effect of combined use of physical and biological methods on changes in phenolic compounds in Cereal Bran.

Material	Method	Processing conditions	Key findings on changes in dietary fiber structure		Antioxidant activity	Ref.
			Total phenolic content	Changes in phenolic compounds
Sprouted brown rice	enzymatic treatment	Enzyme: Cellulase. Cellulase concentration: 0.36 g/100 mL	62.62–76.59 GAE/100 g DW.	↑: Phenolic acid PCA content: 10.28–21.46 mg GAE/100 g DW, p-CA content: 33.57–46.88 mg GAE/100 g DW, FA content: 113.18–139.54 GAE/100 g DW. ↑:Flavonoids Myricetin content: 8.86–13.45 mg RE/100 g DW, Daidzin content: 45.24–57.83 mg RE/100 g DW Rutin content: 491.85–576.82 RE/100 g DW.	DPPH: 192.03–207.53 μmol Trolox/100 g DW.	(Li, Yadav, et al., 2024)
	Ultrasound-assisted cellulase	Cellulase concentration: 0.36 g/100 mL UA power: 800 W, UA time: 25 min.	TPC increased to 69.89–97.29 GAE/100 g DW.	↑: Phenolic acid PCA content: 12.71–25.63 mg GAE/100 g DW, p-CA content: 43.58–58.68 mg GAE/100 g DW. FA content: 138.49–177.83 GAE/100 g DW. ↑: Flavonoids Myricetin content: 9.16–20.21 mg RE/100 g DW. Daidzin content: 50.52–88.44 mg RE/100 g DW. Rutin content: 543.73–798.19 RE/100 g DW.	DPPH: 203.89–218.43 μmol Trolox/100 g DW.
wheat bran	solid-state fermentation	SSF Strains: A. niger; SSF time:6 days； SSF Temperature:30 °C.	TPC increased by 18.44 % on day 6 after SSF;	↑: HBA, VA, VD, FA, Iso FA. ↓: DHBA, PCA, AG, SA, A-X-G, L-X-G, p-CA.	Antioxidant activities: UA < UA + SSF.	(Nemes et al., 2025)
	Ultrasound-assisted and solid-state fermentation	UA power:152-750 W； UA time: 5 min； Strains: A. niger. SSF time:6 days； SSF Temperature:30 °C.	TPC increased by 21.3 % on day 1 after UA and SSF;	↑: VA, PCA, Iso FA,. ↓: DHBA, HBA, AG, VD, A-X-G, L-X-G, p-CA, FA, SA.

↑: ncrease；↓: decrease； SSF: solid-state fermentation；UA: Ultrasound-assisted；HBA: Hydroxybenzoic acid；p-HBA: p-hydroxybenzoic acid； VA: Vanillic acid；VD: Vanillin Derivatives；FA: Ferulic acid；Iso FA: Isoferulic acid；CE: Conventional extraction；PCA: Protocatechuic acid；p-CA: p-coumaric acid; DHA: Dihydroxybenzoic acid；AGL: Apigenin-xylosyl-glucoside; DHBA: Dihydroxybenzoic acid; AG: Apigenin-glucoside; SA: Sinapic acid; A-X-G: Apigenin-xylosyl-glucoside; L-X-G: Luteolin-xylosyl-glucoside.

3.2.2. Physical–chemical combined methods

3.2.2.1. Effects of physical–chemical combined methods on the structural modification of Cereal Bran dietary fiber

The impact of physico-chemical synergistic treatment on cereal bran structure is primarily manifested as multi-level alterations, with significant changes occurring from macroscopic morphology to molecular conformation. The treatment mechanism involves the mechanical disruption of cell wall integrity, which markedly reduces bran particle size, increases the specific surface area, and damages crystalline regions, thereby creating pathways for chemical reagent penetration. This facilitates further hydrolysis of polysaccharide chains, combined with chemical reactions that directionally modify fiber structures, thereby achieving the reconstruction of dietary fiber composition and functionality. Specifically, alkaline solution (NaOH) dissolves hemicellulose-lignin complexes, acid solution controllably degrades β-1,4 glycosidic bonds to release monosaccharides such as arabinose and xylose, while oxidants enhance hydrophilicity through carboxylation. Key influencing factors in the physicochemical synergistic treatment of cereal bran include treatment intensity, duration, and temperature conditions, as well as material properties and processing sequence. Treatment intensity primarily determines the degree of bran structural disruption and chemical bond cleavage, while duration and temperature mainly affect the thoroughness of treatment effects, component stability, and reaction rates. The inherent properties of the material govern the specific surface area and penetration depth. Common physico-chemical combined methods include ultra-high pressure-alkali treatment, ultrafine grinding-chemical crosslinking, and ultrafine grinding combined with acid-base treatment. For instance, Jiang et al. (2024) employed homogenization combined with sulfuric acid and potassium hydroxide as a modification method to treat rice bran IDF. The results demonstrated that the modified RB exhibited higher porosity, GAC, specific surface area (SSA), and α-amylase inhibitory activity (Qi et al., 2016).

3.2.2.2. Effects of physical–chemical combined methods on the release of bound polyphenols in Cereal Bran

Table 9 compares the effects of physical and chemical methods, used either individually or in combination, on the release of polyphenolic compounds from cereal bran. The integration of deep eutectic solvents (DESs) with ultrasound-assisted extraction (UAE) is gaining increasing attention in the optimized extraction of bioactive compounds from plant matrices. This combined approach not only significantly reduces solvent usage and labor costs but also enhances extraction efficiency through the acoustic cavitation effect, which disrupts the plant cell wall structures and facilitates the release of bioactive compounds. In the study by Zheng, Yuan, et al. (2022), the UAE-DES treatment of rice bran was compared with conventional extraction using an 80 % aqueous methanol solution. The synergistic physical–chemical effect of UAE-DES significantly increased the free phenolic content. Among the bound phenolics, p-coumaric acid and ferulic acid were dominant, though slightly lower in concentration than those extracted by traditional solvents. Both extraction methods identified 15 phenolic compounds, with p-coumaric acid, apigenin-C-diglucoside, and N′, N″-di-p-coumaroyl spermidine being the most abundant. Notably, 1-O-p-coumaroyl glycerol was detected for the first time in millet bran. Moreover, the DPPH, ABTS, and FRAP antioxidant activities of the UAE-DES-treated rice bran were significantly higher than those of the conventionally extracted samples, and they were positively correlated with TPC (Zheng, Xu, et al., 2022). Furthermore, Ratanasongtham et al. (2024) investigated the UAE-DES treatment of pigmented Thai rice bran and found that a choline chloride: ethylene glycol molar ratio of 1:2 was the optimal DES. The polarity of DES closely resembles that of water and highly polar organic solvents, and ultrasound cavitation enhances solvent penetration. When DESs were combined with UAE, a notable improvement in the extraction efficiency of antioxidants was observed (Ratanasongtham et al., 2024). Nevertheless, the physicochemical combined approach using UAE-DES treatment for the release of phenolic compounds from cereal bran still presents certain limitations. The synthesis of DESs requires substantial equipment investment, and some DES formulations pose potential safety risks, which restricts the widespread adoption of this combined technology. Due to these constraints in subsequent industrial-scale production, its application remains largely confined to laboratory research at present.

Table 9.

Effect of combined use of physical and chemical methods on phenolic compounds changes in cereal bran.

Material	Method	Processing conditions	Key findings on changes in dietary fiber structure		Antioxidant activity	Ref.
			Total phenolic content	Changes in phenolic compounds
Foxtail millet bran	Conventional Solvent Extraction	① 20 mL of 80 % methanol solution	Soluble phenolics: 3.47 mg FAE/g DW. Insoluble phenolics: 4.93 mg FAE/g DW.	Soluble phenolics Protocatechualdehyde: 1.15 μg/g. p-hydroxybenzoic acid: 28.8 μg/g. Chlorogenic acid: 2.5 μg/g. Vanillic acid: 19.65 μg/g. Syringic acid: 22.93 μg/g. p-coumaric acid: 26.85 μg/g. Ferulic acid: 3.44 μg/g. Sinapic acid: 23.64 μg/g. 1-O-p-coumaroylglycerol: 33.17 μg/g. Apigenin-C-dihexoside: 63.63 μg/g. N′-p-coumaroyl-N″-caffeoylspermidine: 41.46 μg/g. Kaempferol-C, O-dihexoside: 12.45 μg/g. N′, N″-di-p-coumaroylspermidine:64.84 μg/g. N′-p-coumaroyl-N″-feruloylspermidine: 25.51 μg/g. Vitexin: 6.35 μg/g. Insoluble phenolics Protocatechualdehyde: 2.21 μg/g. p-hydroxybenzoic acid: 0.77 μg/g. Chlorogenic acid: 0.9 μg/g. Vanillic acid: 22.54 μg/g. Syringic acid: 26.83 μg/g. p-coumaric acid: 204.62 μg/g. Ferulic acid: 288.29 μg/g. Sinapic acid: 24.85 μg/g.	Soluble phenolics ①DPPH: 7.06 μmol TE/g DW. ②ABTS: 10.45 μmol TE/g DW. ③FRAP: 4.31 μmol TE/g DW. Insoluble phenolics ①DPPH: 9.46 μmol TE/g DW. ②ABTS: 8.38 μmol TE/g DW. ③FRAP: 6.47 μmol TE/g DW.	(Zheng, Xu, et al., 2022)
	ultrasonic-assisted deep eutectic solvent extraction	① DES:Betaine/glycerol in a 1:2 M ②29 mL/100 mL water content in DESs, 61 °C extraction temperature, ③247 W ultrasonic power, and extraction time of 31 min.	Soluble phenolics: 7.80 mg FAE/g DW. Insoluble phenolics: 4.12 mg FAE/g DW.	Soluble phenolics Protocatechualdehyde: 3.78 μg/g. p-hydroxybenzoic acid: 89.32 μg/g. Chlorogenic acid: 5.71 μg/g. Vanillic acid: 61.15 μg/g. Syringic acid: 70.95 μg/g. p-coumaric acid: 96.86 μg/g. Ferulic acid: 5.99 μg/g. Sinapic acid: 76.91 μg/g. 1-O-p-coumaroylglycerol: 73.05 μg/g. Apigenin-C-dihexoside: 95.35 μg/g. N′-p-coumaroyl-N″-caffeoylspermidine: 53.99 μg/g. Kaempferol-C, O-dihexoside: 28.83 μg/g. N′, N″-di-p-coumaroylspermidine:94.3 μg/g. N′-p-coumaroyl-N″-feruloylspermidine: 67.7 μg/g. Vitexin: 14.3 μg/g. Insoluble phenolics Protocatechualdehyde: 2.21 μg/g. p-hydroxybenzoic acid: 0.77 μg/g. Chlorogenic acid: 0.9 μg/g. Vanillic acid: 22.54 μg/g. Syringic acid: 26.83 μg/g. p-coumaric acid: 204.62 μg/g. Ferulic acid: 288.29 μg/g. Sinapic acid: 24.85 μg/g.	Soluble phenolics ①DPPH: 13.29 μmol TE/g DW. ②ABTS: 28.91 μmol TE/g DW. ③FRAP: 12.56 μmol TE/g DW. Insoluble phenolics ①DPPH: 8.29 μmol TE/g DW. ②ABTS: 7.53 μmol TE/g DW. ③FRAP: 5.06 μmol TE/g DW.
Thai pigmented rice bran	Conventional Solvent Extraction	① 80 % methanol solution. ② 0.1 % urea. ③Ultrasonic frequency: 37 kHz. ④Ultrasonic temperature: 50 °C. ⑤40 min of extraction time.	Hom Nin: 3.86 mg GAE/g DW. Mali Dang: 9.94 mg GAE/g DW. Leum Pua: 20.52 mg GAE/g DW.	–	DPPH Hom Nin: 11.29 %. Mali Dang: 26.58 %. Leum Pua: 69.88 %.	(Ratanasongtham et al., 2024)
	ultrasonic-assisted deep eutectic solvent extraction	① choline chloride: ethylene glycol at a 1:2 ratio. ②Ultrasonic frequency: 37 kHz. ③Ultrasonic temperature: 50 °C. ③40 min of extraction time.	Hom Nin: 10.88 mg GAE/g DW. Mali Dang: 18.95 mg GAE/g DW. Leum Pua: 26.49 mg GAE/g DW.	–	DPPH Hom Nin 31.61 %. Mali Dang: 65.04 %. Leum Pua: 77.83 %.

3.2.3. Chemical–biological combined methods

3.2.3.1. Effects of chemical–biological combined methods on the structural modification of Cereal Bran dietary fiber

The combined biological and chemical treatment primarily employs enzymatic methods coupled with hydroxypropylation, carboxymethylation, or phosphate cross-linking as the main binding approaches, which have been widely cited. Its core mechanism lies in leveraging synergistic effects to alter the molecular conformation of fibers, expose functional groups, and introduce new functional groups, thereby achieving structural optimization and improved functional properties. The advantage of this approach is that enzymatic treatment enhances the accessibility for chemical modification, while chemical modification further amplifies the effects of enzymatic treatment. In a study by Zheng et al. (2023), cellulase was used in combination with chemical methods (hydroxypropylation, carboxymethylation, and phosphate cross-linking) to modify DF in millet bran. Cellulase was selected as the biological treatment due to its ability to hydrolyze β-glycosidic bonds and expose hydroxyl groups. For chemical treatments, hydroxypropylation introduced hydroxypropyl groups, carboxymethylation introduced carboxymethyl groups, and phosphate cross-linking promoted the formation of a network structure in the bran. Compared to cellulase hydrolysis alone, the combined biochemical technology more effectively increased the SDF content, WSC, emulsifying ability, and CEC of millet bran. Additionally, it is noteworthy that when hydroxypropylation or carboxymethylation was used as the chemical method, the WHC and emulsifying properties of cereal bran were enhanced. However, when phosphate cross-linking was employed, the adsorption capacity of cereal bran improved, but the porosity of the bran structure decreased (Zheng et al., 2023).

Furthermore, the alkali-enzyme combined technology, as a novel chemical-biological treatment, has gained attention in recent years for processing cereal bran. Its core mechanism involves the initial use of NaOH to disrupt lignin-carbohydrate complexes, releasing cellulose and hemicellulose, followed by cellulase hydrolysis to convert cellulose into soluble oligosaccharides, thereby increasing SDF content. For example, Shaikh et al. (2024) found that the alkali-enzyme combined technology significantly improved the yield of DF extracted from defatted RB. The extracted SDF and IDF demonstrated favorable thermal properties and crystallinity, as confirmed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD), which are beneficial for developing value-added products such as rice porridge (Shaikh et al., 2024). However, this method may lack comprehensive safety risk assessments, and the inability to monitor each reaction step in real-time raises concerns about potential adverse effects on human health, warranting further investigation. The combined use of multiple methods indeed creates complementary effects, overcoming the limitations of single modification techniques, simplifying structural modification processes, and maximizing functional advantages. Nevertheless, given the variety of available biochemical combination methods, it remains essential to make appropriate choices based on target functional properties, application scope, and other factors. Undeniably, different combination approaches can lead to significant differences in the resulting functional properties, developed products, and target consumer groups.

3.2.3.2. Effects of chemical–biological combined methods on the release of bound polyphenols in Cereal Bran

The combined chemical and biological treatment for releasing phenolic compounds from cereal bran typically exhibits a staged characteristic, with the general sequence involving chemical treatment followed by biological treatment. This approach is adopted because chemical methods are typically used to rapidly create a loose and porous bran cell wall structure, thereby significantly increasing the contact area between enzymes and substrates. This facilitates the subsequent biological treatment, where added enzymes or those secreted by microbial fermentation can more readily access and act on the substrates, providing more active sites for enzymatic or microbial fermentation. The two methods complement each other temporally. Overall, the combined chemical and biological approach achieves efficient deconstruction of bran cell walls and targeted release of phenolic compounds through multi-level, multi-mechanism synergistic effects. This synergy is not merely an additive effect but rather forms a series of cascade reactions and positive feedback loops at different scales, resulting in a total effect far greater than the sum of its parts. A commonly employed combination of chemical and biological methods is the acid/alkali treatment coupled with microbial fermentation. In the study by Nemes, Teleky, et al. (2024), Avena sativa oat bran treated with acid hydrolysis followed by Aspergillus niger fermentation showed a significant increase in TPC. The TPC after acid hydrolysis alone was 31.4 mg GAE/g DW, while the combined method yielded 40.7 mg GAE/g DW on day 1 of fermentation and 58.1 mg GAE/g DW on day 6. The combined method consistently outperformed acid hydrolysis alone. This enhanced release is attributed to acid pretreatment disrupting the cell wall structure, and A. niger enzymes facilitating the further release of phenolics, such as vanillic acid, ferulic acid derivatives, and avenanthramides. However, compounds like dihydroxybenzoic acid and protocatechuic acid decreased, likely due to microbial metabolism or conversion into other compounds during the fermentation process. The study confirmed that acid pretreatment increased the content of reducing sugars, providing an enriched substrate for fermentation. The synergy between solid-state fermentation and acid pretreatment effectively enhanced the release of bound phenolics, demonstrating the efficacy of chemo-biological strategies for enriching functional components from plant-based matrices (Nemes, Fărcas, et al., 2024).

Additionally, natural deep eutectic solvents (NADESs)—composed of hydrogen bond donors (HBDs) and acceptors (HBAs)—can effectively disrupt hydrogen bonding networks within bran cell walls and break ester linkages between phenolic acids and polysaccharides. Compared to traditional organic solvents, NADESs offer several advantages, including biocompatibility and biodegradability. For example, in a study by Akbari et al. (2024), corn bran treated using LAB fermentation combined with NADES extraction revealed that polar NADESs such as betaine (Bet): DL-malic acid (MA) and choline chloride (ChCl): D-xylose (Xyl) effectively extracted phenolic acids through hydrogen bonding, increasing extraction yields by 10–24 % compared to ethanol. In contrast, nonpolar NADESs were less effective. The Bet: MA NADES, due to betaine's intrinsic antioxidant properties, achieved the highest ORAC value, while others performed similarly to ethanol. This study established a sustainable dual-technology platform — “biological release via microbial enzymes + chemical extraction via NADESs”—which leverages enzymatic hydrolysis followed by hydrogen bond disruption to damage the cell wall and facilitate polyphenol recovery. Through this method, the total polyphenol yield increased to 3.86 mg GAE/g DW, highlighting the synergistic potential of green solvents and biocatalysis in the valorization of agricultural by-products (Akbari et al., 2024).

To successfully apply the biological-combined NADES method, it is essential to synergistically optimize three key factors: microbial strain characteristics, solvent molecular design, and process parameters. Enzyme activity is crucial for releasing bound phenolic compounds, and studies have shown that the sequence of fermentation before extraction avoids solvent inhibition of enzymes. Additionally, moisture content plays a critical role in enzymatic processes; insufficient moisture limits enzyme diffusion, while excessive moisture reduces oxygen transfer efficiency. When selecting NADESs, it is necessary to match the hydrogen bond network strength with the polarity of the target phenolic acids to optimize dissolution efficiency, as high-viscosity solvents have lower diffusion coefficients, which hinder mass transfer. Furthermore, sugar-based hydrogen bond donors compete with phenolic acids for binding sites, further inhibiting the release of phenolic compounds. Moreover, improper temperature control during chemical modification steps in biochemical hybrid methods often leads to thermal degradation of phenolic compounds in cereal bran, resulting in reduced polyphenol content and impaired antioxidant activity. Current research indicates that combining room-temperature chemical methods with biological methods can mitigate these adverse effects to some extent. Future studies should integrate eco-sustainability principles to establish an optimal balance between functionality enhancement and bioactivity retention in cereal bran processing.

4. Valorization of Cereal Bran via non-thermal processing technologies

Unprocessed cereal bran has long been limited in food applications due to its coarse texture, distinct granularity, lack of elasticity, bitter taste, and difficulty in swallowing. However, when treated with various non-thermal processing methods, cereal bran not only retains its high dietary fiber content but also develops flavor-enhancing components, providing natural sources of dietary fiber, vitamins, minerals, and bioactive compounds while simultaneously improving the texture and mouthfeel of bran-containing foods, extending shelf life, and fundamentally enhancing consumer acceptance. The processed cereal bran has emerged as a key ingredient for boosting functional nutritional components and attributes, significantly contributing to the improvement of food health properties. Particularly, non-thermally processed cereal bran, through the generation of diverse textures and flavor profiles, has found value-added applications primarily in baked goods, dairy products, beverages, and traditional staple foods, such as steamed buns.

4.1. Baked goods

Bread and biscuits are among the oldest forms of baked foods. The modified cereal bran has emerged as a widely used functional ingredient in baking due to its capacity to enhance both nutritional value and sensory qualities. From traditional bread and cookies to soft muffins and convenient cereal bars, the modified cereal bran plays a crucial role in improving the nutritional and functional profile of baked products. Studies have shown that replacing wheat flour with rice bran significantly increases the content of B vitamins and essential minerals in baked products, particularly due to its rich dietary fiber composition (Skendi et al., 2020).

4.1.1. Textural modification

A critical stage in the production of baked goods is dough formation, which strongly determines the final product's quality. Incorporating bran into dough formulations increases the dietary fiber content but also modifies the fiber particle size distribution. However, the direct addition of wheat bran into bakery products may negatively affect dough rheology, reduce loaf or biscuit volume, and introduce undesirable color and off-flavors, resulting in a deterioration of both technological and sensory characteristics. Physical and biological pretreatments of cereal bran have proven effective in mitigating these drawbacks. These methods enhance the compatibility of whole grain flours with baking processes, improving dough rheology and overall sensory acceptability. For instance, Kim et al. (2013) demonstrated that ultrafine grinding significantly reduced bran particle size, increased the digestibility of cellulose and hemicellulose, and improved solubility, thereby enhancing the overall functionality of bran (B. K. Kim et al., 2013). Similarly, Pasqualone et al. (2017) demonstrated that the addition of micronized bran (126–300 μm) to durum wheat bread resulted in a less negative impact on loaf volume, crumb hardness, elasticity, and chewiness compared to coarse bran (Pasqualone et al., 2017).

4.1.2. Flavor modification

Fermented wheat bran—either by yeast or lactic acid bacteria—has been shown to increase phenolic content, thereby enhancing the antioxidant activity of bread. Wu et al. (2022) reported that after 36 h of fermentation with Rhizopus oryzae, the relative concentrations of undesirable aldehydes, such as hexanal, heptanal, and benzaldehyde, in WB were significantly reduced, while the levels of desirable aromatic compounds, including alcohols and esters, increased. When this fermented bran was incorporated into cakes, it imparted improved aroma and flavor characteristics. Furthermore, the high dietary fiber content of fermented bran slowed starch hydrolysis and helped modulate the postprandial glycemic response, aligning better with modern nutritional and health needs (J. Wu et al., 2022). According to current literature, to maintain acceptable physical and sensory properties, the recommended upper limit for wheat bran inclusion in bread and biscuit formulations should not exceed 10 %(Q. Feng et al., 2024).

4.2. Dairy products and beverages

The modified cereal bran is increasingly incorporated into dairy-based products, such as yogurt, smoothies, and milk-based beverages, as a strategic approach to enhance nutritional value and consumer appeal. In recent years, the development of fiber-enriched yogurt has attracted considerable attention. The inclusion of modified cereal bran in dairy products has been shown to improve both textural and flavor properties, contributing to increased creaminess and viscosity. These textural modifications enrich mouthfeel and sensory perception, thereby enhancing overall product palatability. In addition to dairy matrices, cereal bran has also been introduced into beverage formulations, especially as a functional base for plant-based cereal drinks. For example, Faccin et al. (2009) investigated a flavored beverage based on organic RB, with strawberry and chocolate variants. Their findings highlighted that the drink possessed high nutritional value and was rich in essential fatty acids and amino acids. Furthermore, rice bran exerted immunostimulatory effects, attributed to the presence of antioxidant phytochemicals such as phytosterols, sterol derivatives, and γ-oryzanol, offering a novel application of cereal bran in functional beverage development (Faccin et al., 2009).

4.2.1. Textural modification

It is well known that the direct incorporation of unmodified cereal bran into dairy products or beverages often results in undesirable characteristics such as dull coloration and a gritty texture, making it generally less acceptable to consumers. Research indicates that while cereal bran inherently functions as a prebiotic to promote the growth and survival of probiotic species, the viability and population of probiotics remain relatively limited. Modification technologies, however, enhance prebiotic efficacy or improve matrix compatibility by disrupting the fibrous structure of bran, thereby releasing more short-chain carbohydrates accessible to probiotics and boosting their viability. For instance, physical modification increases the surface area of bran, creating additional adhesion sites to facilitate probiotic colonization. In contrast, biological modification employs enzymatic hydrolysis to enhance prebiotic activity and improve sensory properties. Beyond nutritional enhancement, dietary fibers can also serve as stabilizers or fillers to enhance the structure of yogurt. Wu et al. (2022) found that rice bran added before fermentation contributed to a more compact and porous yogurt microstructure with fewer whey pockets, thereby limiting gel rearrangement and enhancing product stability. In contrast, post-fermentation addition of rice bran tended to disrupt yogurt stability. Moreover, the incorporation of rice bran during fermentation facilitated the conversion of bound phenolic acids into their free forms, which was further associated with improved yogurt stability (T. Wu et al., 2023). The soluble and insoluble fractions of cereal bran fiber contribute to yogurt stability via different mechanisms. The porous architecture of insoluble fiber may immobilize free water within the yogurt gel matrix, thereby enhancing structural integrity, whereas soluble fiber increases viscosity, which reduces whey separation (Kieserling et al., 2019).

4.2.2. Flavor modification

The application of modified cereal bran in dairy products and beverages can often alleviate undesirable flavors, such as inherent bitterness, astringency, grassy notes, or raw off-flavors. Modification processes may lead to the degradation or transformation of flavor precursors, resulting in the generation of pleasant flavor compounds such as sweet notes, roasted, nutty, caramel-like, and milky aromas. These processes can also enhance flavor stability and promote flavor integration within the product matrix. Physical modification, particularly under high-pressure or high-shear conditions, can facilitate intense Maillard reactions between reducing sugars and amino acids/proteins, leading to the formation of desirable volatile compounds including pyrazines, furans, pyrroles, and aldehydes. On the other hand, enzymatic modification can hydrolyze components such as cellulose, hemicellulose, and proteins into oligosaccharides, monosaccharides, and free amino acids. These free amino acids, serving as key precursors in the Maillard reaction, may contribute to flavor development but can also lead to pH reduction, intensifying sourness, and potentially altering overall flavor perception. However, excessive acid hydrolysis may result in the formation of off-flavors. It is important to note that the flavor profiles of bran-modified dairy products and beverages are highly dependent on the composition of the final product matrix. Therefore, comprehensive sensory evaluation within the specific application context is essential to ensure consumer acceptability.

4.3. Mantou

When incorporating cereal byproducts into food formulations, functional quality is a primary consideration. The inclusion of cereal bran in steamed buns helps compensate for the dietary fiber, B vitamins, and minerals lost during the refining of wheat flour. This approach offers multiple health benefits, including improved gut health, enhanced satiety, and better control of blood glucose and cholesterol levels. Such applications align with the growing consumer demand for the health benefits of whole grains. Moreover, the process is technically simple and cost-effective, providing an effective strategy to upgrade traditional steamed buns into healthier staple foods that embody the concept of “balanced refinement and coarseness.” This also meets the market demand for high-fiber, functional foods. Research has shown that modified cereal bran can enhance the specific volume of steamed buns, produce a softer texture, more pleasant aroma, higher sensory scores, and stronger antioxidant activity, indicating its considerable application potential in steamed bun production (Tang et al., 2024a).

4.3.1. Textural modification

During microbial fermentation, cereal bran components release gases during steaming, resulting in increased volume and alterations in nutritional composition. Liu et al. (2024) noted that chemical modification, due to potential safety concerns, is less suitable for food applications, making physical or biological methods more desirable. In this context, steamed buns made with biologically modified rye bran achieved a higher specific volume (2.22 mL/g) than those with physically modified bran (2.03 mL/g), making them more appropriate for food use (A. Liu et al., 2024). Zhang et al. (2022) reported that wheat bran modified via combined physical and biological methods produced steamed buns with significantly lower hardness, chewiness, and adhesiveness than those made with unmodified bran. This improvement is attributed to increased levels of soluble arabinoxylans, which enhance gluten network formation, resulting in a softer, more elastic bun with better sensory properties. Additionally, the combined treatment reduced the rough texture and off-flavors commonly associated with bran, while the acidic environment during enzymatic hydrolysis contributed positively to aroma development, improving consumer acceptance (S. Zhang et al., 2022).

4.3.2. Flavor modification

Tang et al. (2024a) found that co-fermentation using yeast and lactic acid bacteria (LAB) for 36 h significantly enhanced the acidification of wheat bran, leading to a phytic acid degradation rate of 51.70 % and a relative volatile ester content of 58.47 %, which jointly contributed to improved bioactivity and flavor (Tang et al., 2024b). Liu et al. (2024) demonstrated that physical modification of rye bran through ultrafine grinding increased anthocyanin and total phenol content by reducing particle size; however, high temperatures during processing resulted in β-carotene loss and decreased water-holding and freeze–thaw stability. The primary aroma compound in physically modified rye bran buns was 2-methylbutanal, which imparts almond, cocoa, and malt notes, and an increase in aldehydes and alcohols was observed. In contrast, microbial fermentation facilitated the enzymatic release of bound polyphenols and the synthesis of more β-carotene, while the porous structure improved oil-holding capacity and freeze–thaw stability. The resulting buns exhibited significantly altered flavor profiles, with elevated levels of phenylacetaldehyde, benzaldehyde, ethyl acetate, borneol, 2,3-pentanedione, furfural, dodecene, hexanoic acid, and octanal. Biological modification significantly increased the content of terpenes and other characteristic flavor compounds, such as hexanoic acid and cyclohexanone (A. Liu et al., 2024). Therefore, for steamed bun applications, biological modification is superior to physical treatment.

5. Conclusion

The structural changes of cereal bran significantly affect the release characteristics of its internal bioactive substances and are directly related to the texture and flavor quality of bran food. Given the sensitivity of these key influencing factors, selecting the appropriate processing technology is particularly crucial. Among them, non-thermal processing technology shows significant application value in modifying cereal bran due to its unique thermal-sensitive protection advantages. However, it should be noted that different non-thermal processing technologies will lead to specific structural modifications of bran and differentiated release characteristics of phenolic substances due to the differences in their mechanisms of action.

When a single non – thermal processing technology (including biological method, room - temperature chemical method or physical method) is used to treat cereal bran, although changes in structural characteristics such as cell wall structure destruction, reduction in cellulose and hemicellulose content, decrease in molecular weight and particle size, and increase in specific surface area can be observed, the degree of these structural modifications is relatively limited. The release level of phenolic compounds supports this conclusion: the amount of phenolic substances released after treatment with a single non-thermal processing technology is significantly lower than that released after treatment with a combined non-thermal processing technology. Moreover, this also indicates that a single non-thermal processing technology has a limited effect on improving the bioavailability of bioactive components in cereal bran. Based on this, we suggest prioritizing the use of combined non-thermal processing technology to treat cereal bran, thereby enhancing the bioavailability of its bioactive components more effectively.

When using combined non-thermal processing technology to treat cereal bran, its synergistic effect primarily affects the structure of the cereal bran and phenolic compounds through the relay action of “physical wall-breaking + precise biological/chemical modification.” Physical means destroy the dense cell wall structure, increase the specific surface area, expose bound polyphenol sites, and create channels for bio-enzymatic hydrolysis or chemical solvent penetration. The biological method precisely hydrolyzes glycosidic bonds to degrade fibers, while the chemical method participates in the competitive cleavage of phenolic acid-polysaccharide ester bonds. The synergistic effect of combined non-thermal processing technology overcomes the barriers that are difficult to break through with a single technology, reflecting the innovative potential of “structure-function” collaborative design.

Although combined non-thermal processing technology offers significant advantages in cereal bran modification, it still faces numerous challenges in practical applications, primarily due to the diversity of combined schemes within this technology and the unique advantages and limitations of each method. For this reason, it is necessary to establish a systematic multi – dimensional evaluation system, focusing on the following influencing factors: On the horizontal spatial scale, the structural changes of cereal bran are comprehensively affected by the initial structural characteristics of raw materials (including varietal differences and microstructure), the ultra - microstructure of cell walls (involving spatial scale and component content distribution), the combination of processing methods and their process sequence, and the basic moisture content of raw materials. Vertically, the structural changes of cereal bran mainly depend on the dynamic control of physical processing parameters (such as equipment set values, processing time, cycle times, and temperature conditions) and biochemical processing conditions (including the type selection, concentration ratio, and dosage control of chemical reagents or enzymes). This multidimensional factor analysis provides a crucial foundation for optimizing the combined processing technology.

In addition, certain safety issues persist in the use of combined non-thermal processing technology, particularly when it comes to the combined application of biological and chemical methods, where safety concerns are particularly prominent. Specifically, the biological method may pose microbial safety risks, including contamination with toxigenic strains and fungal infections. At the same time, the enzymatic hydrolysis process may release or transform anti-nutritional factors (such as phytic acid, tannins, oxalates, and saponins) in bran, thereby interfering with the bioavailability of essential nutrients. The chemical method faces environmental pressure due to the toxicity of chemical reagent residues, nutrient loss, and the treatment of waste liquids. Additionally, chemical treatment can easily lead to irreversible browning reactions in bran, which seriously affect the sensory quality of the products. In contrast, the physical method shows better safety advantages in combined processing. Therefore, considering safety and sustainability, the physical method is a more suitable core component of combined non-thermal processing technology. In the future, the balanced development and safety assessment of combined non-thermal processing technology still need to be further developed to promote the high-value, green utilization of agricultural by-products.

6. Future perspectives

Future research should focus on multi – dimensional innovation in the high - value utilization of non - thermally processed cereal bran, with breakthroughs potentially achieved in the following directions: Firstly, efforts should be made to optimize the synergistic effects of combined non - thermal processing technologies and build a “zero - waste” complete utilization processing chain for cereal bran. By precisely controlling processing parameters, efficient conversion and value-added transformation of bran by-products can be achieved. While ensuring stable structural changes, this will not only promote the directional release of internal bioactive substances but also meet the needs of functional food development. During this process, it is necessary to focus on monitoring the potential safety risks and ecological environmental impacts of key links, such as biological and chemical methods. This includes establishing standardized industrial production technical specifications and safety evaluation systems, as well as promoting the transformation of combined non-thermal processing technologies from the laboratory to industrialization. Secondly, the application of combined non-thermal processing technologies in cereal bran should not be limited to improving the texture, flavor, and sensory quality of bran products. Still, it should also focus on developing innovative technologies and formulas. It is recommended to combine the concept of precision nutrition with the design of precise functional foods tailored to the health needs of specific populations, providing systematic solutions for the entire grain health industry and green food manufacturing. In addition, consideration can be given to expanding the application dimensions of combined non-thermal processing technologies in cereal bran. For example, developing a targeted delivery system based on modified bran and achieving sustained release of active ingredients in the gastrointestinal tract, as well as precise release in the colon, can be accomplished by constructing an intelligent embedding system, thereby maximizing overall improvement in bioavailability and nutritional efficacy.

CRediT authorship contribution statement

Xiaoyan Qin: Writing – original draft. Wenyan Wang: Software. Yuqian Zheng: Software. Xi Wang: Software. Zhilong Chen: Data curation. Jun Zhao: Supervision. Sheng Li: Supervision, Funding acquisition, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

No data was used for the research described in the article.