The structure and extraction of silk fibroin and its applications in fruit and vegetable preservation: a review

Abstract

In response to increasing global demands for enhanced food safety and quality, the development of safe and efficient postharvest preservation technologies has emerged as a critical research priority in agricultural sciences. Silk fibroin, a naturally derived biopolymer, demonstrates remarkable potential for fruit and vegetable preservation owing to its exceptional biocompatibility, biodegradability, and film-forming capabilities. This review provides a comprehensive analysis of the structural characteristics of silk fibroin and elucidates its preservation mechanisms in horticultural products. Special emphasis is placed on the application of silk fibroin-based edible coatings and active packaging systems. Furthermore, we examine the synergistic interactions between silk fibroin and other natural preservatives. The article concludes with a critical discussion of current research controversies and proposes future research directions, thereby offering valuable insights for advancing both fundamental research and practical applications of silk fibroin in postharvest management.

Highlights

• •Silk fibroin, a biocompatible and biodegradable natural biopolymer, shows promise for postharvest fruit and vegetable preservation via film-forming properties.
• •Synergistic interactions between silk fibroin and natural preservatives enhance preservation efficacy.
• •Challenges include extraction methods, cost-effectiveness, and safety concerns in silk fibroin postharvest applications.
• •Future research should optimize extraction, enhance composite formulations, and deepen preservation mechanism understanding.

1. Introduction

Fruits and vegetables are indispensable components of the human diet. With the rise in living standards and increasing awareness of healthy eating, consumers are placing higher demands on the nutritional content and quality of fruits. From 2000 to 2020, global fruit production increased by 55%, while vegetable production grew by 65%. According to data released by the Food and Agriculture Organization of the United Nations (FAO) in June 2025, global fruit production in 2024 reached approximately 1.340 billion tons, while vegetable production was about 1.35 billion tons (FAO, 2024). However, post-harvest losses significantly impact the yield of fruits and vegetables. To meet the increasing demands for food safety and quality, the development of safe and efficient preservation technologies has become a key research focus.

Silk is one of the earliest natural proteins utilized by humans. Sericulture and silk weaving have a long history in China, dating back five to six thousand years. Renowned as the “queen of fibers,” silk is celebrated for its exceptional softness, luster, mechanical properties, and moisture absorption. In recent years, advancements in technology have enabled in-depth studies on the physicochemical properties of silk fibroin, including its unique amino acid composition and crystalline structure (Shi et al., 2021; Shi et al., 2025). Research on the versatile applications of silk has expanded into biomedical fields, as well as cosmetics and food additives. Silk protein has garnered significant interest among scientists in the biomedical sector due to its excellent biocompatibility, controllable biodegradability, and superior mechanical properties, including wound dressings (Khalid et al., 2020; Mazurek et al., 2022) and biosensors (Wang, Zhu, et al., 2021). Moreover; silk fibroin significantly advances tissue-engineering research (Wani et al., 2020); serving as a printable bio-ink for 3D fabrication of neural (Boni et al., 2020); vascular (Kiritani et al., 2020) and other complex tissue analogues.

Accumulated toxicological and allergological assessments indicate that highly purified silk fibroin is non-mutagenic, non-genotoxic, and devoid of sub-chronic toxicity or identifiable insect allergens (Yigit et al., 2021). The U.S. FDA has acknowledged two GRAS notices (GRN 1005 and 1026), concluding that food-grade silk fibroin coatings are “Generally Recognized as Safe” when present at ≤2% (w/w) of the finished food. Silk fibroin exhibits excellent biocompatibility, biodegradability, and film-forming properties, effectively extending the shelf life of fruits and vegetables without posing risks to the environment or human health. This article aims to review recent advances in the application of silk fibroin for fruit and vegetable preservation, exploring its mechanisms, efficacy, and future directions, thereby providing a reference for further research in this field.

2. Structure and properties of silk fibroin

2.1. Structural characteristics of silk fibroin

Silk fibroin, a natural fibrous protein macromolecule derived from silk, is primarily composed of three amino acids: glycine, alanine, and serine, which form its primary structural components. Structurally, silk fibroin is organized into three fundamental subunits: a heavy chain, a light chain, and a glycoprotein encoded by the P25 gene (Ye et al., 2022). These subunits are interconnected through specific molecular interactions. The heavy and light chains are covalently linked by disulfide bonds; while the P25-encoded glycoprotein associates with the chain complex via non-covalent hydrophobic interactions (Fig. 1). The stoichiometric ratio of these subunits is 6:6:1 (heavy chain: light chain: P25 glycoprotein); reflecting a well-defined structural organization (Ye et al., 2022). The structural organization of silk fibroin is primarily characterized by the heavy chain's ability to form discrete β-sheet crystallites, which serve as the primary structural framework responsible for its exceptional mechanical properties.

Fig. 1.

Structural pattern diagram of silk fibroin.

Extensive structural analyses have revealed that the crystalline morphology of silk fibroin is exclusively associated with the heavy chain, while the light chain plays no significant role in crystalline domain formation. From a structural perspective, the heavy chain of silk fibroin exhibits a unique domain organization, comprising 12 well-defined hydrophobic domains alternating with 11 hydrophilic domains (Blake et al., 2021; Li et al., 2024). The hydrophobic domains are primarily composed of repetitive amino acid sequences, whereas the hydrophilic domains feature non-repetitive sequence motifs (Takasu et al., 2023). The hydrophobic domains are mainly composed of glycine; alanine; and serine; with minor contributions from tyrosine; valine; and threonine. These amino acids are organized into characteristic repetitive motifs; particularly the GSGAGA sequence (Wu et al., 2021); which facilitates self-assembly into a highly ordered anti-parallel β-sheet configuration (Meng et al., 2020). This specific molecular arrangement enables the formation of extensive crystalline regions within the silk fibroin structure; contributing to its remarkable structural integrity. The intrinsic viscosity of silk fibroin (SF) was approximately 0.29 dL·g⁻¹; corresponding to a weight-average molecular weight of about 350–400 kDa. After strong-alkali degumming; it decreased to 0.27 dL·g⁻¹ (≈300 kDa) (Liang, Guo, et al., 2024). For dry SF films; the tensile strength ranged from 30 to 50 MPa; with an elongation at break of 15–25%. At 90% relative humidity; the storage modulus retention was approximately 40%; and the applicable temperature window spanned 4–25 °C (Shakil et al., 2022). In degradation experiments using protease XIV at 37 °C for 72 h; the SF membrane exhibited a weight loss exceeding 90% (Shakil et al., 2022). Cytocompatibility assessments indicated no cytotoxicity via MTT assay; and the FDA recognized SF as generally recognized as safe (GRAS). The DPPH scavenging activity of a 2% (w/v) SF membrane reached 45–70%; attributable to the radical-scavenging properties of tyrosine/tryptophan residues (Chiesa et al., 2022).

In summary, silk fibroin exhibits a biphasic molecular architecture comprising crystalline and amorphous domains. The crystalline phase, primarily organized in β-sheet configurations, confers exceptional mechanical strength to the material. In contrast, the amorphous regions, enriched with hydrophilic amino acid residues, enhance its aqueous solubility and biocompatibility (Liu, Li, et al., 2023). The unique structural characteristics of silk fibroin endow it with superior film-forming capabilities; favorable gas permeability; and enhanced biodegradability. Notably; its intrinsic self-assembly properties enable the formation of protective barriers that effectively inhibit food-air interactions; modulate cellular respiration rates; and regulate moisture evaporation. These attributes address the limitations of conventional film-forming agents while demonstrating additional antimicrobial and preservative functionalities (Huang et al., 2022). Such exceptional physicochemical properties establish silk fibroin as a promising candidate for fruit and vegetable preservation applications.

2.2. Extraction method of silk fibroin

The cocoon is composed of two silk fibroin filaments enveloped by a continuous layer of sericin, a globular protein representing 20–30% of the cocoon shell mass and exhibiting a high content of polar amino-acid side chains. This hydrophilic coating readily hydrates and swells under moist or saline conditions, forming a viscous gel that impedes solvent penetration and compromises the dissolution and reconstitution of fibroin (Shao et al., 2024). Consequently; quantitative removal of sericin (degumming) is an essential pretreatment to ensure reproducible processing and to facilitate accurate characterization of regenerated silk fibroin materials. Sericin is distinguished by an exceptionally high content of polar amino acids-serine ≈ 32%; aspartic acid ≈ 16%; and substantial glycine and lysine residues-collectively exceeding 55% of its primary sequence. This composition endows the protein with pronounced hydrophilicity and pH−/ion-sensitive charge behavior. The secondary structure is dominated by random coils with minor β-sheet segments; lowering temperature or pH triggers a reversible random-coil-to-β-sheet transition that underpins a sol-gel phase switch; enabling in-situ gelation and sustained drug release. Tryptophan residues confer strong UV absorption (≈ 65% at 280 nm); comparable to synthetic UV blockers. Phenolic hydroxyls and amino groups act synergistically to scavenge ROS and attenuate oxidative stress; imparting potent antioxidant activity (Kabir et al., 2024). Sericin disrupts bacterial membrane integrity and eradicates biofilms; exhibiting broad-spectrum antibacterial efficacy against both Gram-positive and Gram-negative organisms (e.g.; Staphylococcus aureus; Escherichia coli) that surpasses conventional antibiotics (Mohanty et al., 2025). Finally, the protein is completely degradable by proteases and collagenases, yielding non-toxic amino acids and demonstrating excellent biological safety. The extraction of silk fibroin primarily involves the removal of sericin protein and other impurities from raw silk, with the degumming process representing the most critical and challenging step. As a surface modification technique, degumming plays a pivotal role in determining the final properties of silk fibroin. Optimization of degumming methodologies and precise control of processing parameters are essential for maintaining the structural integrity and functional properties of silk fibroin, while simultaneously enabling the development of novel biomaterials with tailored biodegradability and enhanced mechanical characteristics. The fundamental challenge in silk degumming lies in achieving complete sericin removal without compromising the native structure and properties of the fibroin component.

The extraction methods of silk fibroin primarily encompass chemical, physical, and enzymatic approaches (Fig. 2). The chemical method typically involves the dissolution of silk in alkaline solutions or soap to remove sericin proteins, followed by dialysis to eliminate salts, ultimately yielding a silk fibroin solution (Schmidt et al., 2023; Vyas & Shukla, 2020; Wang et al., 2022). In earlier investigations, concentrated sulfuric acid and phosphoric acid were employed to solubilize silk fibroin. Such protocols introduce substantial safety hazards and, more critically, induce extensive hydrolytic degradation of the protein, resulting in selective destruction of amino-acid residues—most notably threonine, serine and tryptophan (Huang et al., 2023). Subsequently; researchers have explored the dissolution of silk fibroin in organic solvents (Dorishetty et al., 2020; Liu et al., 2021). Relative to conventional alkaline degumming, organic-acid protocols employing citric, tartaric, succinic or malic acid preserve the molecular weight of regenerated silk fibroin to a greater extent, yielding films with superior mechanical performance and a markedly slower in-vitro degradation profile (Chen et al., 2022).

Fig. 2.

Extraction method of silk fibroin degumming.

Physical methods typically employ high-temperature and high-pressure conditions, ultrasonic treatment, or similar techniques to separate silk fibroin from sericin. When conducted without degumming agents, conventional physical degumming methods-such as high-temperature and high-pressure treatment-not only effectively disrupt sericin through thermal denaturation but also eliminate the need for wastewater treatment, rendering the process more environmentally sustainable. The steam-based high-temperature and high-pressure method represents an efficient degumming approach, as the pressurized steam contains abundant high-energy water molecules with strong permeability, which may facilitate the disruption of interprotein hydrogen bonds. The enzymatic method utilizes proteases to selectively degrade sericin, thereby isolating pure silk fibroin (Feng et al., 2020; Liu, Huang, et al., 2023; Zhu et al., 2022). Protease-assisted deguming yields silk fibroin with superior softness, enhanced luster, lower processing temperatures, and higher production efficiency (Table 1). Atay et al. (Atay et al., 2025) employed chemical and physical degumming methods; respectively. The chemical approach involved batch degumming with a 0.13 M Na₂CO₃ aqueous solution at 95–97 °C for 30 min in a water bath. The physical method consisted of treating cocoons at a ratio of 0.3–0.6% (w/v) in water under the same temperature conditions (95–97 °C) for 360 min. Rosemary et al. (Mincy et al., 2025) utilized a ternary solution system composed of CaCl₂·2H₂O and ethanol (molar ratio 1:8:2) for degumming at 25 °C for 30–60 min. Subsequently; silk fibroin was dissolved in a 1 M LiBr aqueous solution at 25 °C for 30–60 min. Zhu et al. (Zhu et al., 2022) applied organic acid degumming using 0.2 M citric acid or tartaric acid at 90–100 °C for 30–60 min; supplemented with ultrasonic assistance: 50–60 °C; 15–30 min; 200 W ultrasonic power; along with 0.05% (w/w) weak base or 0.5% enzyme. Wang et al. (Wang et al., 2024) conducted enzymatic degumming under conditions of pH 7.4 with 1% neutral protease (w/w relative to silk) at 55 °C for 90 min in a constant-temperature water bath. Xia et al. (Xia et al., 2021) also adopted a biological enzyme-based degumming method. Under pH 8.0; using 0.8% pectinase and 0.2% alkaline protease; the treatment was carried out at 55–60 °C for 90 min in a water bath. Multi-scale silk fibroin micro-nanofibrils (SNF) were prepared through a one-step exfoliation method using a deep eutectic solvent (DES; choline chloride/urea; 1:2) directly from silk cocoons. Subsequently; anisotropic aerogels were fabricated via directional freezing; freeze-drying; and annealing processes. These aerogels achieved integrated multifunctional performance; including superelasticity; thermal insulation; and sound-absorption properties (Yang et al., 2023). The resulting silk fibroin aerogels exhibited excellent elasticity; low thermal conductivity; and high acoustic absorption; providing a novel concept for developing green; multifunctional materials applicable to packaging; thermal-management buffers; and acoustic applications. An injectable and transparent silk fibroin (SF) nanofilm; featuring tunable β-sheet crystallinity; was developed to concurrently optimize both mechanical and optical performance (Zhao, Cai, et al., 2025). Compared to alternative degumming techniques, enzymatic degumming exhibits reduced toxicity, offering potential value for applications such as food-grade preservation materials. Different extraction methods influence the molecular weight and structural integrity of silk fibroin, consequently affecting its functional properties and application performance. Therefore, selecting an appropriate extraction method is crucial to obtaining silk fibroin with optimal characteristics. Hybrid strategies-e.g., ultrasound-enzyme or microwave-mild base-simultaneously optimize efficiency, eco-friendliness, and silk fibroin integrity.

Table 1.

Comparative analysis of degumming parameters' impact on silk fibroin properties utilizing chemical, physical, and biological enzymatic methods.

Type of Action	Degumming Reagent/Conditions	Temperature (°C)	Duration (min)	Impact on Silk Fibroin	Reference
Chemical	0.13 M Na₂CO₃ aqueous solution	95–97	30	Fast removal of sericin, but may result in a slight decrease in molecular weight (∼ 0.27 dL/g)	(Atay et al.; 2025)
Chemical	CaCl₂–H₂O–EtOH ternary system	Room temp	30–60	A prolonged degumming duration better preserves the high molecular weight of silk fibroin, thereby enhancing its mechanical properties and rendering it more suitable for subsequent microneedle fabrication.	(Mincy et al.; 2025)
Chemical	LiBr aqueous solution	Room temp	30–60	Silk fibroin undergoes rapid dissolution accompanied by extensive β-sheet formation, endowing the material with high mechanical strength; nevertheless, an excessively prolonged treatment time exerts a detrimental effect on its performance.	(Mincy et al.; 2025)
Chemical	Citric acid, tartaric acid and other solutions	90–100	30–60	Although less destructive than strong-alkali treatments, it can still hydrolyze silk fibroin to a limited extent at elevated temperatures.	(Zhu et al.; 2022)
Physical	Distilled water (pH 5, 0.3–0.6% w/v cocoon/water)	95–97	360	Sericin is gently removed under conditions that preserve the native molecular weight of silk fibroin (intrinsic viscosity ≈ 0.29 dL g−1), leaving no chemical residues and ensuring an environmentally benign process.	(Atay et al.; 2025)
Physical	Ultrasound combined with enzyme or weak base	50–60	15–30	Due to the shortening of time and the reduction of reagents, the damage is usually less than the main method used alone.	(Zhu et al.; 2022)
Biological Enzymatic	Neutral protease 1% (w/w on silk), pH 7.4	55	90	With a degumming yield of 28.1%, the process leaves fibers smooth and intact, preserves the silk fibroin β-sheet architecture, and exhibits outstanding biocompatibility.	(Wang et al.; 2024)
Biological Enzymatic	Pectinase and alkaline protease composite system	55–60	90	High degumming efficiency with minimal fiber damage; synergy eliminates ancillary impurities, yielding silk that is soft and lustrous.	(Xia et al.; 2021)

Food-grade extraction of SF must simultaneously satisfy safety requirements and scalability. Currently, the most viable approach is a green physico-enzymatic hybrid process: this centers on high-pressure aqueous/steam degumming, which enables large-scale primary processing without introducing chemical residues (Atay et al., 2025); when needed; it can be supplemented by food-grade enzymatic refiningto obtain high-purity SF under mild conditions; making it suitable for high-value-added applications (Zhu et al., 2022). Alternative extraction routes present substantial safety-related limitations: strong-chemical-solvent methods (e.g.; using LiBr or hexafluoroisopropanol) carry a high risk of toxic residue migration and entail costly waste-stream management (Wang et al., 2024); conventional acid- or alkali-based treatments tend to induce protein degradation and generate poorly characterized by-products; resulting in unpredictable safety profiles (Zhu et al., 2022); while emerging solvents such as ionic liquids lack comprehensive toxicological datasets; and their complete removal remains technically challenging (Xia et al., 2021). Consequently, a physico-enzymatic synergistic strategy is recommended, as it avoids the introduction of chemical hazards while preserving process economics and environmental compatibility. Any production route must be supported by a comprehensive safety-assessment framework that covers chemical residues, microbial control, and migration testing. This requirement constitutes the principal barrier preventing most conventional chemical extraction methods from meeting food-grade standards.

2.3. Classification of silk fibroin

In academic contexts, SF is not typically classified into strict types, as its core structural protein composition is relatively conserved. Instead, variations are primarily distinguished by source, extraction method, and final product morphology. The diversity in its properties stems fundamentally from differences in extraction and processing techniques, which directly govern its molecular weight, structural conformation, and ultimate performance. Based on the aforementioned characteristics, we have classified and summarized the key properties of SF (Table 2).

Table 2.

Classification and characteristics of silk fibroin (SF).

Classification Dimension	Main Categories Key	Characteristics and Description	Typical Molecular Weight Range	Primary Source (Species)
By Source	Domestic Silkworm (Bombyx mori) SF	The most extensively studied and widely used type, with a regular structure (heavy chain, light chain, P25 glycoprotein).	Heavy chain: ∼390 kDa Light chain: ∼26 kDa	Bombyx mori (silkworm)
	Wild/Non-Bombyx mori SF	Diverse structures and properties, often exhibiting higher strength, elasticity, or specific biological functions.	Highly variable (e.g., spider silk protein can reach 250–350 kDa)	Spiders, Antheraea pernyi (tussah silkworm), Samia cynthia ricini (eri silkworm), etc.
By Extraction Method	Lithium Salt Method	Dissolution using lithium bromide solution. The most mainstream laboratory method, better preserves the native protein structure and allows thorough dissolution.	Yields intact high molecular weight protein (>300 kDa)	Various silk types
	Calcium Salt Method	Uses a calcium chloride-water-ethanol ternary solution. Conditions are milder and lower cost, but require precise control of dissolution efficiency and time.	Broader molecular weight distribution, partial degradation may occur	Various silk types
	Ionic Liquid Method	Employs ionic liquids for dissolution. A emerging “green” method enabling efficient dissolution and easy solvent recovery, albeit at higher cost.	Controllable, can yield high molecular weight protein	Various silk types
By Final Product Form	SF Solution	The foundation for all subsequent processing. Concentration, molecular weight, and structure (random coil vs. β-sheet) determine its final properties.	Depends on extraction method and degree of degradation	Derived from the above methods
	Regenerated SF Film/Coating	Formed by solution casting, spin-coating, or spraying. The most common form in food preservation and biomedical applications.	As above	Processed from SF solution
	SF Nanoparticles	Prepared via self-assembly, ultrasonication, desolvation, etc. Used for drug delivery and active compound encapsulation.	Typically <1000 nm (hydrodynamic diameter)	Prepared from SF solution
	SF Hydrogel	Formed through physical or chemical cross-linking into a 3D network. Used for smart responsive release and tissue engineering scaffolds.	Network structure, no defined single molecular weight	Cross-linked from SF solution

Based on their biological origin, SF are primarily categorized into two types: Bombyx mori Silk Fibroin (BmSF) and Non-Mulberry Silk Fibroins (NMSFs) (Chouhan & Mandal, 2020). Bombyx mori Silk Fibroin (BmSF) is composed of a heavy chain (H-chain; ∼391 kDa); a light chain (L-chain; ∼25 kDa); and the P25 glycoprotein; assembled in a molar ratio of 6:6:1. Its characteristic repetitive sequence motif; (GAGAGS/GAGAGY)ₙ; readily facilitates β-sheet formation; resulting in a crystallinity of approximately 35–40%. Non-Mulberry Silk Fibroins (NMSFs); derived from wild silkworm species (e.g.; Bombyx mandarina); share a similar core structural organization; consisting of homologous H-chain (∼391 kDa) and L-chain (∼25 kDa) components associated with P25 in a comparable stoichiometry. They also feature repetitive sequences that promote β-sheet crystallization; yielding a comparable crystallinity range of 35–40%. Additionally; distinct types of SF can be produced by employing different extraction methodologies. By modulating extraction parameters-such as temperature and duration-or by employing controlled enzymatic hydrolysis; SF fractions within specific molecular weight ranges can be obtained. This tunability enables precise adaptation to various application requirements; for instance; lower molecular weight fragments may exhibit enhanced permeability or bioactivity (Rockwood et al., 2011). Furthermore; SF can also be categorized based on its final processed morphology (e.g.; films; nanoparticles; hydrogels) (Feng et al., 2025; Kaewpirom et al., 2025; Niu et al., 2025; Pranto et al., 2025a). Recent research has highlighted the significant biological activities of sericin, including antioxidant, antimicrobial, cryoprotective, moisturizing, and cell-adhesive properties. Recovering this by-product and utilizing it in composite preservation coatings or as a functional food additive represents a key direction for achieving the high-value, full-resource utilization of silk.

3. Application of silk fibroin in fruit and vegetable preservation

3.1. Application of silk fibroin-based coating technology in fruit and vegetable preservation

Silk fibroin-based coating technology has emerged as a prominent research focus in recent years. By directly applying a silk fibroin solution onto the surface of fruits and vegetables, a protective film can be formed, effectively extending the shelf life of these perishables. Research has demonstrated that silk fibroin coatings can significantly reduce weight loss and decay rates in perishable fruits such as strawberries (Chen et al., 2024a; Zhao et al., 2023a) and banana (Zhao et al., 2023a); while preserving their desirable sensory qualities. Table 3 summarizes recent five-year research on silk fibroin for food preservation. Silk fibroin coatings substantially mitigate post-harvest weight loss and decay of climacteric fruits (e.g.; banana) by forming a hydrophobic; oxygen-selective barrier that limits transpiration and respiratory substrate availability. The β-sheet-enriched matrix exhibits broad-spectrum antimicrobial activity against food-borne pathogens and quenches free-radical cascades; thereby suppressing lipid oxidation and enzymatic browning. Being edible; biodegradable; and cytocompatible; the coating constitutes a sustainable active-packaging platform with high translational potential for minimally processed produce. To further enhance the coating performance; researchers often incorporate additional functional components into the silk fibroin matrix (Jinxing et al., 2023; Quan et al., 2024; Shen et al., 2025), such as chitosan (Liu, Zhao, & Nguyen, 2024; Tu et al., 2025; Xing et al., 2023), to improve the mechanical properties and antimicrobial activity of the film.

Table 3.

Experimental studies (2020–2025) on silk-fibroin-based food preservation.

Material used	Preservation methods	Key preservation metrics	Reference
Pure SF aqueous suspension (1 wt%)	Dip-coating strawberries & bananas → high-humidity annealing (>90% RH, 24 h)	25 °C shelf-life: strawberry 5 → 7 d, banana 6 → 10 d; O₂ permeability ↓ 50×, CO₂ evolution ↓, firmness retention ↑ 20%, weight loss ↓ 30%	Chen et al., 2024 (Chen et al.; 2024a)
Carbon-dot/SF composite film (CQDs 0.5 wt%)	Adhesive wrapping of cherry tomatoes	25 °C 7 d: decay rate ↓ 60%, weight loss ↓ 35%, VC loss ↓ 28%; antibacterial ratio: E. coli >99%, S. aureus >98%; DPPH scavenging 92%	Zhao et al., 2023 (Zhao et al.; 2023a)

The primary fabrication techniques for silk fibroin composite coatings include the blending method (Wang, Guo, et al., 2021); the layer-by-layer (LbL) self-assembly method (Bai et al., 2024); and the crosslinking method (Ayaz et al., 2024; Dong et al., 2023). The blending method involves a simple admixture of silk fibroin with other constituents, characterized by its operational simplicity but often compromised compatibility. The LbL self-assembly method enables the sequential deposition of different components through electrostatic interactions, resulting in a composite film with a well-ordered structure (Wang, Guo, et al., 2021). The crosslinking method employs chemical or physical approaches to induce intermolecular crosslinking; thereby enhancing the stability and mechanical properties of the film (Ayaz et al., 2024). Given that distinct preparation methods significantly influence the structural and functional attributes of the composite film, the selection of an appropriate method should be tailored to the specific application requirements.

3.2. Application of silk fibroin-based active packaging in fruit and vegetable preservation

Silk fibroin-based active packaging represents a significant advancement in the field of food preservation (Fig. 3), offering a dynamic alternative to traditional passive packaging methods (Liu et al., 2021). Unlike conventional packaging; which merely acts as a barrier; active packaging can actively modulate the internal environment to enhance the quality and shelf life of fruits and vegetables (Guillard et al., 2021; Zhang et al., 2022).

Fig. 3.

Application of silk fibroin in fruit and vegetable preservation.

Silk fibroin-based antibacterial packaging incorporates natural antimicrobial agents into the silk fibroin matrix (Chen et al., 2024a; Liu, Zhao, & Nguyen, 2022). These agents, such as chitosan and carbon nanomaterials (Liu, Zhao, & Nguyen, 2022; Zhang et al., 2022), effectively inhibit microbial growth, thereby reducing spoilage and maintaining freshness. This approach leverages the inherent antimicrobial properties of these compounds to create a hostile environment for microorganisms, thus extending the shelf life of perishable produce (Li et al., 2025).

The role of antioxidant packaging in retarding oxidative degradation is mediated by two main mechanisms: the exploitation of silk fibroin's intrinsic antioxidant properties and the loading or compounding of exogenous antioxidants (Liu, Zhao, & Nguyen, 2022; Qian et al., 2024). This method is crucial for preserving the sensory and nutritional qualities of fruits and vegetables by preventing the oxidation of sensitive compounds (Cui et al., 2023). An antioxidant-active packaging matrix was fabricated by incorporating a polyphenol-rich natural extract into electrospun silk fibroin nanofibres. During 12 d of storage at 4 °C; strawberries wrapped with the functional nanowebs exhibited a 42% reduction in malondialdehyde (MDA) accumulation and a 35% higher retention of DPPH-radical-scavenging activity relative to controls; indicating pronounced suppression of lipid oxidation and concomitant retardation of sensory degradation (Cui et al., 2023). The controlled release of antioxidants from the packaging material ensures a sustained protective effect; enhancing the overall stability and quality of the packaged food (Li et al., 2025).

Combining both antimicrobial and antioxidant functionalities in a single packaging system is an emerging trend. This multifunctional approach not only inhibits microbial growth but also retards oxidation, providing comprehensive protection for perishable foods (Zhao et al., 2023a). Such advanced packaging solutions are particularly beneficial for high-value and easily perishable fruits and vegetables; ensuring their freshness and safety throughout the supply chain. In summary; silk fibroin-based active packaging offers a versatile and effective solution for fruit and vegetable preservation. By integrating natural antimicrobial and antioxidant agents; these packaging systems can significantly extend the shelf life and maintain the quality of perishable produce (Zhao et al., 2023a).

3.3. Application of silk fibroin in postharvest preservation

SF has emerged as a promising material for postharvest preservation research due to its edibility, biodegradability, excellent film-forming properties, high gas-barrier performance, and inherent antibacterial and antioxidant activities. SF self-assembles into a dense β-sheet-rich layer on the fruit surface, which partially occludes epidermal stomata, reduces internal oxygen permeability and carbon dioxide efflux, and thereby suppresses respiration intensity. Concurrently, it significantly decreases water transpiration. In 2016, Marelli et al. reported that strawberries coated with SF films containing 58% β-sheet content could be stored at 7 °C for 7 days without developing mold spots, whereas uncoated controls showed mold growth after 3 days. By contrast, SF films with 23% β-sheet content exhibited inferior preservation performance due to insufficient structural density (Marelli et al., 2016a). In 2018; Valentini et al. demonstrated that treating bananas with a composite of SF and yeast fermentation broth increased hardness retention by 35% and reduced the epidermal browning spot index by 70% during storage at 20 °C (Valentini et al., 2018a).

SF nanoparticles were employed as delivery vehicles to achieve controlled release of natural preservatives. Essential oils such as eugenol and citral were encapsulated within SF nanoparticles and subsequently incorporated into composite films, enabling pH- and humidity-triggered sustained release, which provided continuous inhibition of surface molds and yeasts. Lin et al. developed an eugenol-loaded SF nanofiber membrane that maintained the total colony count of fresh-cut apples below 3.0 log CFU·g⁻¹ after 14 days of storage at 4 °C-a reduction to approximately 1/100 of the control group (Lin et al., 2022a).

When the carboxymethyl chitosan (CMCS) content exceeds 15 wt%, SF undergoes a structural transition from the β-sheet conformation to a random coil, accompanied by micron-scale phase separation. This structural change leads to a rapid increase in water absorption by 30% and an elevated swelling degree of the composite film (He et al., 2010). As a consequence; interfacial delamination readily occurs under prolonged high-humidity conditions. Crosslinking with glutaraldehyde (0.1%) or EDC (2 mmol·g⁻¹) enhances the wet strength of the film by 1.8 to 2 times; yet simultaneously reduces CO₂ transmission by more than 50%. This barrier modification leads to an accumulation of ethanol; resulting in a notable alcoholic off-flavor (ethanol content increased twofold) after 5 days of storage at 25 °C. Increasing the β-sheet content of SF from 28% to 55% improves tensile strength by 30% and reduces water vapor permeability by 25%. However; when the β-sheet content exceeds 60%; the film becomes brittle (elongation at break <5%); which promotes surface cracking on curved fruit and vegetable surfaces and compromises barrier functionality. Maintaining CMCS content between 5 and 10 wt% enables the formation of a homogeneous film dominated by β-sheet structure without phase separation; thereby balancing mechanical strength and gas permeability (Lin et al., 2022a). The stability of chitosan/silk fibroin composite films is often compromised under high humidity, acidic, or long-term storage conditions due to interfacial phase separation and hydrolysis of crosslinked bonds. Moreover, enhancements in mechanical strength (via high SF content or extensive crosslinking) markedly reduce O₂/CO₂ permeability. Therefore, a balanced formulation strategy-incorporating a concentration window, mild crosslinking, and graded porosity-is essential during the design stage to optimize both structural integrity and gas exchange performance.

Antibacterial and antioxidant composite films were fabricated by incorporating SF with carbon nanodots (C-dots) or Ag/ZnO nanoparticles. These composites exhibited broad-spectrum antibacterial activity against pathogens such as Escherichia coli and Listeria monocytogenes, along with a DPPH radical scavenging rate exceeding 80%, thereby synergistically inhibiting foodborne pathogens and lipid oxidation. Zheng et al. developed a C-dots/SF composite film (20 × 30 cm) with an oxygen permeability of 1.3 × 10⁻¹ cm³·m⁻²·day⁻¹·atm⁻¹ and a water vapor permeability of 2.8 × 10⁻³ g·m⁻²·day⁻¹, properties suitable for packaging respiring fruits and vegetables. Cherries covered with this film showed no decay after 6 days of storage at 25 °C, whereas all control samples developed mold within 3 days (Lyu et al., 2022). Silk fibroin has evolved from serving as a simple coating material to functioning as a versatile active component in postharvest preservation. Owing to its edibility, biodegradability, and drug-loading capability, silk fibroin demonstrates clear potential to replace petroleum-based plastics in high-value produce and fresh-cut ready-to-eat food packaging.

Currently, the application of SF in food preservation primarily encompasses five distinct systems: (i) Pure silk fibroin-based coatings (Marelli et al., 2016b); (ii) Microbial smart-responsive films (Valentini et al., 2018b); (iii) Nanofiber-based active packaging (Lin et al., 2022b); (iv) Essential oil microemulsion composite films (Chen et al., 2024b); and (v) Carbon nanodot composite films (Zhao et al., 2023b). Each of these systems possesses specific structural characteristics and distinct core mechanisms (Fig. 4).

Fig. 4.

Schematic illustration of the anti-corrosion and preservation mechanism of silk fibroin.

The schematic diagram illustrates three representative silk fibroin (SF)-based preservation systems and their multi-level protection mechanisms. The pure SF coating forms a dense β-sheet physical barrier, which restricts oxygen transmission, reduces respiration rates, and consequently extends the shelf life. The smart responsive membrane activates antibacterial activity on demand via a microbial-triggered mechanism, thereby reducing spoilage rates. The CNDs composite membrane exhibits dual functionality: potent antibacterial activity and antioxidant capacity, encompassing DPPH radical scavenging and polyphenol oxidase (PPO) inhibition, leading to enhanced retention of fruit firmness.

In the pure silk fibroin-based coating system, a dense nanoscale film is formed through a tunable β-sheet network, providing an effective oxygen/moisture barrier (O₂/CO₂ regulation). This system also exhibits antioxidant properties and edible safety. The uniform, transparent film applied to strawberry surfaces modulates gas exchange, leading to a decrease in both O₂ and CO₂ levels. Consequently, weight loss in strawberries is reduced by approximately 50%, and shelf life is extended by more than two days (Marelli et al., 2016b). The microbial smart-responsive film system incorporates Bacillus subtilis spores into silk fibroin nanofibers. Humidity triggers spore germination; inducing film wrinkling and enabling adaptive regulation of gas permeability. The surface area of the film can change by 15–20% following humidity exposure (Valentini et al., 2018b). In the nanofiber-based active packaging system; Lycium barbarum polysaccharide nanofibers are loaded with eugenol/silk fibroin nanoparticles; creating a dual-release antibacterial mechanism (nanofiber and nanoparticle synergy). This system achieves an inhibition rate of over 95% against Staphylococcus aureus. The essential oil microemulsion composite film system utilizes a chitosan/silk fibroin matrix to encapsulate essential oil microemulsions (diameter ≈ 100 nm) (Lin et al., 2022b). The primary mechanism involves humidity-triggered microemulsion rupture; releasing the encapsulated essential oils. These oils disrupt bacterial cell membranes; providing antimicrobial effects and reducing strawberry decay. The decay rate of strawberries stored for seven days remains below 10% (Chen et al., 2024b). In the carbon nanodot composite film system; positively charged carbon nanodots (≈ 4 nm) are uniformly dispersed within a silk fibroin matrix. This system operates through two synergistic mechanisms: contact-based antibacterial action (by disrupting cell walls) and antioxidant activity (by scavenging free radicals). It achieves an inhibition rate exceeding 99% against Escherichia coli and a DPPH radical scavenging rate of over 80% (Zhao et al., 2023b).

Comparison of Silk Fibroin-Based Edible Films and Other Commonly Used Preservation Materials (Table 4). Regarding the antioxidant properties, pure SF films exhibited a DPPH free radical scavenging rate of 70%, significantly surpassing that of chitosan (CH) films (∼30%). This enhanced activity is primarily attributed to the hydrogen-donating capacity of tyrosine (Tyr) and tryptophan (Trp) residues present in SF. Furthermore, after adsorbing plant-derived polyphenols such as those extracted from olive leaves, the Trolox equivalent antioxidant capacity (TEAC) of SF films increased from 1.93 mmol g⁻¹ to 3.61 mmol g⁻¹, representing an 87% enhancement. These results demonstrate the considerable potential of SF films as effective carriers for the loading and controlled release of active antioxidant compounds (Bayçin et al., 2007). Regarding the antibacterial properties; aqueous SF solutions with concentrations ≥4% (w/v) were shown to inactivate Staphylococcus aureus and Pseudomonas aeruginosa; confirming that pure SF exhibits inherent antibacterial activity (Egan et al., 2024). When functionalized with antimicrobial agents such as silver nanoparticles (AgNPs); the resulting composite films achieved inhibition zones of 9–10 mm in diameter against common pathogens-a performance comparable to that of chitosan-based films (Pranto et al., 2025b). This transition from a passive barrier to an actively antimicrobial material highlights the potential of SF composites in enhancing food preservation efficacy. In terms of moisture barrier performance; a 14 μm-thick SF film exhibits a water vapor permeability (WVP) of approximately 2.9 × 10³ g·m⁻²·day⁻¹; which is 20–30% lower than that of a chitosan (CH) film of comparable thickness. This superior moisture barrier property contributes significantly to reducing moisture loss in fruits and vegetables during storage; thereby helping to preserve their freshness and sensory quality (Zhao et al., 2023a). Regarding oxygen barrier properties; the oxygen transmission rate (OTR) of SF films can be reduced to 1.3 × 10⁴ cm³·m⁻²·day⁻¹ through modulation of the film-forming process to promote higher β-sheet content. This value represents approximately half of the OTR typically observed in chitosan (CH) films. Such enhanced oxygen barrier performance effectively suppresses oxidative reactions and inhibits the growth of aerobic microorganisms in food products; thereby significantly extending shelf life (Marelli et al., 2016a; Pranto et al., 2025b).

Table 4.

Performance comparison of silk fibroin-based edible films and other commonly used preservation materials.

Performance Indicator	Test Method / Conditions	SF Film	Chitosan (CH) Film	Polyvinyl alcohol (PVA) Film	Carboxymethyl cellulose (CMC) Film	Remarks (SF Comparative Performance)
Antioxidant Activity	DPPH scavenging rate (%)	70.4 (10 kGy-irradiated, 3% w/v)	20–40	< 10	15–25	1.8–3.5× higher than CH
	TEAC (mmol Trolox g−1)	1.93–3.61 (with olive leaf polyphenols)	0.8–1.2	0.1–0.2	0.3–0.5	Up to 87% enhancement with polyphenols
Antibacterial Activity	Inhibition zone (mm) against: •S. aureus •E. coli	•9.5 (SF-AgNPs) •10.0 (SF-AgNPs)	•7–9 •8–10	•0 •0	•0 •0	Comparable to CH after functionalization
	Bacterial inactivation	≥4% w/v SF solution inactivates S. aureus & P. aeruginosa	1–2 log reduction N	Not reported	Not reported	Inherent antibacterial property observed
Barrier Properties	WVP (×103 g m−2 day−1 at 25 °C, 50% RH)	2.86 (14 μm film)	3.5–6.0	1.5–2.5	4.0–7.0	20–30% lower than CH
	OTR (×104 cm3 m−2 day−1 at 25 °C, 0% RH)	1.32 (high β-sheet content)	2.0–4.0	0.8–1.2	5.0–8.0	≈50% lower than CH
	CTR (relative to OTR)	0.6–0.8 × OTR	≈1 × OTR	≈1 × OTR	≈1 × OTR	Selective gas permeability
Biodegradability	Soil burial weight loss after 30 days (%)	>90	>85	30–40	>85	Complete biodegradability demonstrated

SF-based edible films demonstrate equivalent or superior performance in key preservation-related properties-including antioxidant and antibacterial activities, moisture and oxygen barrier capabilities, and biodegradability-compared to conventional polysaccharide-based materials. Furthermore, their capacity to serve as carriers for active compounds underscores their multifunctional potential. As a result, SF-based films represent a comprehensively high-performance option for food preservation applications. Future research should focus on further optimizing their mechanical properties and establishing a robust, standardized food safety assessment framework.

3.4. Mechanistic insights into the preservation of fruits and vegetables by silk fibroin

The preservative mechanism of silk fibroin in postharvest fruits and vegetables primarily manifests through its exceptional film-forming properties (Lyu et al., 2022; Zhuang et al., 2021) and microenvironment-modulating capabilities (Geng et al., 2024; Liu, Zhou, et al., 2024). When applied as an aqueous solution, silk fibroin polymerizes into a transparent, compact coating on produce surfaces. This biomaterial-derived film effectively impedes the permeation of oxygen, carbon dioxide, and water vapor molecules, thereby suppressing respiratory activity and reducing moisture loss in horticultural commodities, which collectively contribute to extended shelf life. Furthermore, the semi-permeable nature of silk fibroin coatings (Gao et al., 2024) maintains optimal atmospheric composition within the microenvironment, preventing quality degradation associated with anaerobic metabolic processes.

The barrier properties of silk fibroin films to gases and water are intrinsically linked to their structural characteristics. By meticulously modulating the concentration of silk fibroin solutions, the film formation conditions, and the post-treatment methods, the crystallinity and porosity of the films can be precisely controlled, thereby enabling the regulation of gas and water permeability (Wang & Han, 2021). For instance; Associate Professor Liu Kaikai and Professor Shan Chongxin from Zhengzhou University have demonstrated that a carbon nanotube/silk fibroin (CNT/SF) film; fabricated via hydrogen bonding between carbon nanotubes; silk fibroin; and a minimal amount of glycerol; exhibits superior antibacterial and antioxidant properties. This film displays remarkable biosafety; transparency; and stretchability; and is capable of integrating atmospheric control; anti-foodborne pathogen; and antioxidant functionalities (Liu, Zhao, & Nguyen, 2022). Similarly; Zhang Jun's team from the Chinese Academy of Sciences has developed a multifunctional cellulose-based anticorrosive coating with antibacterial; oxygen/water vapor barrier; and antioxidant properties; using cellulose microgels as the substrate. This coating demonstrates excellent wetting properties on various fruit surfaces and can effectively preserve the long-term freshness of diverse fruits (Cui et al., 2024). These findings collectively indicate that appropriately cross-linked silk fibroin films can significantly reduce oxygen permeability and effectively inhibit the oxidative deterioration of fruits and vegetables (Wang & Han, 2021).

The water-based silk fibroin coating extends the shelf life of strawberries and bananas at room temperature by twofold, primarily through the regulation of O₂/CO₂ diffusion coefficients mediated by its β-sheet content. This coating reduces both respiratory intensity and water loss rate in the fruits. Furthermore, silk fibroin delays postharvest senescence in fruits and vegetables via a multi-functional mechanism encompassing four biochemical processes: physical barrier formation, antioxidant activity, antibacterial effects, and responsive release (Marelli et al., 2016a). The free radical scavenging capacity of naked silk fibroin nanoparticles (SF-NPs) was evaluated using three assay systems: DPPH·; ABTS⁺; and ORAC. Results indicated that SF-NPs exhibited significantly higher scavenging activity compared to most polysaccharide nanoparticles at equivalent mass concentrations. Moreover; scavenging activity was positively correlated with β-sheet content; demonstrating that silk fibroin itself possesses considerable intrinsic free radical scavenging ability (Lozano-Pérez et al., 2017). Under acidic pH conditions; silk fibroin undergoes reversible swelling–shrinkage deformation; enabling the pulsatile release of chitosan‑carbon dots. This system exhibits an antibacterial efficiency of >99.9% against E. coli. When applied to strawberries stored at 4 °C for 14 days; no mold spots were observed. The pH-responsive swelling behavior of silk fibroin thus acts as a switch; controlling the on-demand release of natural antibacterial agents (Zhao et al., 2023a). Silk fibroin synergistically delays the postharvest senescence of fruits and vegetables through four interconnected biochemical mechanisms: physical barrier formation; antioxidant activity; antibacterial action; and responsive release. Moreover; it exhibits high degradability and is generally recognized as safe (GRAS) (Marelli et al., 2016a; Zhao et al., 2023a), providing a verifiable pathway at the molecular and cellular levels for sustainable, green preservation.

The silk fibroin film exhibits inherent antimicrobial characteristics (Hu et al., 2020); primarily attributed to the abundance of surface-active functional groups capable of adsorbing and suppressing microbial proliferation (Teng et al., 2024). Furthermore; the composite formation of silk fibroin with chitosan has been demonstrated to substantially enhance both the mechanical strength and antibacterial efficacy of the resultant film (Khosravimelal et al., 2021). Through synergistic incorporation with other natural preservatives, such composite systems not only improve preservation performance but also minimize reliance on single-component preservatives, thereby enhancing product safety. Nevertheless, the interfacial compatibility and synergistic interactions among different constituents require further investigation to optimize composite formulations and achieve optimal preservation outcomes.

3.5. A comparative analysis of silk fibroin and alternative materials for fruit and vegetable preservation

To systematically evaluate the role of SF in postharvest preservation of fruits and vegetables, this study compares SF with three commonly used alternative material systems: polysaccharides (e.g., chitosan and alginate), lipids (e.g., waxes and acetylated monoglycerides), and synthetic biodegradable polyesters (e.g., PLA and PBAT). The performance of these materials in postharvest applications is analyzed and summarized in Table 5 to clarify the relative advantages and limitations of silk fibroin. Compared with polysaccharides (e.g., chitosan, alginate), lipids (e.g., waxes, acetylated monoglycerides), and synthetic biodegradable polyesters (e.g., PLA, PBAT), SF offers the following advantages: (i) It can form ultra-thin coatings (< 1 μm) that provide a “low-oxygen, moderate-humidity” microenvironment, suitable for highly respiring berries. (ii) It can be processed via printing or spraying at room temperature, making it compatible with cold-sensitive fruits and vegetables. (iii) It is edible and biodegradable, generating no solid waste after use. (iv) It acts as a nanocarrier enabling sustained release of antibacterial agents over 7–10 days.

Table 5.

Comparative evaluation of silk fibroin (SF) and three mainstream post-harvest coating systems for fresh fruits and vegetables.

Evaluation Criterion	Silk Fibroin (SF)	Polysaccharide-Based Systems (Chitosan / Sodium Alginate)	Lipid-Based Systems (Paraffin Wax / Acetylated Monoglycerides)	Synthetic Biodegradable Polyesters (PLA / PBAT)
Primary Barrier Mechanism	Dense antiparallel β-sheet network reduces O₂ permeability; tuneable swelling enables controlled water-vapor transmission (WVT). (Marelli et al.; 2016a)	Cationic electrostatic interaction with microbial membranes coupled with film-forming O₂ barrier; pH-responsive release of antifungal compounds. (Heras-Mozos et al., 2021; Liang, Liu, et al., 2024)	Continuous hydrophobic alkyl phase provides extremely low WVT; interfacial blockage suppresses respiration rate. (Riofrio, Alcivar and Baykara, 2021, Zhang, Xiao and Qian, 2014)	High-crystallinity hydrophobic domains afford low O₂ and WVT rates; heat-sealable for moisture-tight closures. (Jiang et al.; 2006)
Intrinsic Antioxidant Capacity	Tyrosine and tryptophan residues scavenge free radicals; DPPH inhibition ≈ 45–70% (2% w/v SF). (Zhang; Wang; Gao; et al.; 2024)	Negligible unless phenolics or essential oils are added; native chitosan exhibits <15% ROS scavenging. (Jampafuang et al.; 2019)	Practically absent; requires incorporation of tocopherols or BHT, which are prone to thermal degradation. (Zhang et al.; 2014)	Essentially nil; demands addition of phenolic antioxidants or nano-ZnO, raising migration concerns. (Thiyagu et al.; 2022)
Antimicrobial Activity	Mild bacteriostatic effect (∼1 log CFU red uction); 2–3 log synergistic enhancement when complexed with chitosan. (Murugapandian et al.; 2024)	Chitosan achieves 2–4 log reduction against Gram+/Gram− bacteria; alginate requires ionic cross-linking and Ag+ loading for efficacy. (Heras-Mozos et al.; 2021)	No intrinsic biocidal action; physical barrier only, with risk of microbial re-contamination through cracks.	No inherent antimicrobial properties; necessitates blending with chitosan or silver nanoparticles, which retard composting rate.
Mechanical Performance	Dry-state tensile strength 30–50 MPa, elongation at break 15–25%; wet strength declines ≈ 60%. (Zhang; Wang; & Zhang; 2024)	Chitosan films: 40–70 MPa, elongation <10%; become brittle at RH > 80%. (Melro et al.; 2020)	Wax coatings exhibit low cohesive strength; thickness > 20 μm tends to crack upon flexing. (Liu; Duan; et al.; 2022)	PLA: 50–70 MPa, elongation <8%; PBAT: elongation up to 300%, but moisture barrier deteriorates. (Shakil et al.; 2022)
Environmental Adaptability	Retains ∼40% of initial strength at 90% RH; operational window 4–25 °C. (Shakil et al.; 2022)	Chitosan absorbs >30% moisture at high RH, leading to drastic strength loss; hydrophobic modification required. (Melro et al.; 2020)	Softens/migrates at >35 °C; prone to fracture at low temperatures. (Liu; Duan; et al.; 2022)	PLA undergoes accelerated hydrolysis at RH > 80%; PBAT offers wider temperature tolerance. (Bher et al.; 2023)
Biodegradability & Safety	> 90% weight loss after 72 h protease XIV digestion; GRAS status, no cytotoxicity reported. (Leem et al., 2022; Reizabal et al., 2022)	Chitosan and alginate are GRAS; > 80% mineralisation in soil within 30 days.	Natural waxes are edible; synthetic ester waxes degrade slowly. (Kończak et al.; 2026)	PLA: 90% degradation in 180 d under industrial composting; PBAT: 365 d in home composting; both require dedicated collection systems. (Auras et al., 2004; Wufuer et al., 2022)
Process Compatibility	Room-temperature casting, spraying, or dipping; compatible with polyphenols and essential oils across pH 3–9. (Reizabal et al., 2022; Siraj et al., 2025)	Acidic dissolution (chitosan) or Ca2+ cross-linking (alginate) required; high viscosity limits spray rate. (Mouhoub et al., 2024; Richbourg et al., 2021)	Requires 60–80 °C melt application, high energy input; minimal achievable thickness ≈ 5 μm. (García-Betanzos et al.; 2017)	Extrusion or solvent casting at 120–160 °C; heat-sensitive bioactives may degrade; on-site spraying not feasible. (Su et al.; 2020)
Economic Considerations	By-product of sericin removal, estimated cost 8–12 USD kg−1; industrial medical-fiber lines (> 1 kt a−1) already operational. (Reizabal et al.; 2022)	Chitosan 6–10 USD kg−1; alginate 10–15 USD kg−1; well-established supply chains. (Teng et al.; 2024)	Paraffin cheapest (2–3 USD kg−1); ester waxes 6–8 USD kg−1. (Zauba India import customs declaration real-time data)	PLA 2.2–2.8 USD kg−1; PBAT 2.5–3.0 USD kg−1; additional capital expenditure for thermal-sealing equipment. (Procurement Resource; 2025)

However, SF also presents several limitations: High raw-material cost and significant batch-to-batch variability in molecular weight (Mw ≈ 80–250 kDa), necessitating stringent online quality control; Moderate moisture resistance, often requiring blending with waxes or PLA for long-term storage (> 15 days) under high relative humidity; Intrinsically weak antibacterial activity; effective antimicrobial performance typically requires incorporation of essential oils or metal oxides to meet the “5-log reduction” standard; Susceptibility to swelling and film rupture when exposed to alkaline conditions (pH > 9) or high-phenolic produce such as litchi (Marelli et al., 2016a). Silk fibroin demonstrates unique advantages in the preservation of room-temperature-stored, short-supply-chain, and ready-to-eat fruits and vegetables, owing to its edibility and capacity to regulate the microenvironment. It is currently the only natural polymer capable of simultaneously fulfilling the functions of a nanocarrier, printability, and edibility. However, its relatively high cost and limited moisture-barrier performance suggest that a “high-performance composite” strategy may be more viable. Examples include: A thin SF layer (≈0.3 μm) coupled with a wax micro-layer (≈0.5 μm) to balance moisture resistance and low-oxygen permeability; A bilayer SF-PLA film, where the inner SF layer provides edibility and the outer PLA layer offers mechanical strength and moisture barrier, extending suitability to 10–20 days of cold-chain storage.

Future development should focus on overcoming key technical challenges, such as green degumming using deep eutectic solvents, continuous scraping-drying integrated equipment, and simultaneous removal of pesticide residues and sericin. Achieving breakthroughs in these areas will enable silk fibroin to compete with mainstream alternatives like chitosan and wax in terms of cost, paving the way for large-scale commercial adoption.

4. Challenges and controversies in the application of silk fibroin for postharvest preservation

Despite its significant promise as a natural biopolymer for postharvest preservation, the practical implementation of SF faces multiple challenges spanning technical, economic, and safety domains. The primary constraint lies in the complexity of SF extraction and modification, which leads to elevated production costs and impedes large-scale commercialization. Moreover, further optimization of SF-based materials is required-particularly regarding mechanical robustness, tunable gas barrier properties, and enhanced antimicrobial performance-to address the diverse physiological and microbiological demands of various horticultural products (Yang et al., 2024). From a safety standpoint; although SF is widely recognized for its biocompatibility; its application within food systems necessitates comprehensive toxicological evaluation. The long-term stability; degradability; and potential allergenicity of SF coatings under varying environmental and storage conditions remain insufficiently characterized (Aad et al., 2024; Pandey et al., 2024). Additionally, the mechanistic basis of SF's preservation efficacy-including its role in microbial inhibition and senescence delay-requires deeper elucidation. While SF coatings are known to reduce respiration and moisture loss, their antimicrobial spectrum and mode of action warrant systematic investigation across different microbial taxa.

Practical hurdles also relate to application uniformity and environmental adaptability. Coating techniques such as dip-coating and spraying must be optimized to ensure consistent film formation, adhesion, and coverage on heterogeneous produce surfaces. Performance validation under real-world storage and distribution conditions is equally critical. To overcome these challenges, integrated strategies are emerging: (i) Material Enhancement: The inherent brittleness and hydrophilicity of pure SF films can be mitigated through biopolymer blending, nanocomposite reinforcement, or cross-linking via enzymatic, physical, or ionic methods (Wang, Wu, Liu, et al., 2025; Wang, Wu, Lv, et al., 2025; Xu et al., 2024; Zhao, Yang, et al., 2025; Zhihang et al., 2025). (ii) Functional and Economic Optimization: Incorporating natural antimicrobials, antioxidants, or plasticizers can extend SF's preservative functionality beyond its passive barrier role (Wang, Wu, Liu, et al., 2025; Wang, Wu, Lv, et al., 2025; Zhao, Yang, et al., 2025; Zhihang et al., 2025). Concurrently; valorization of silk-processing by-products—such as sericin recovery from wastewater-offers a pathway to reduce costs and improve sustainability (Wang, Wu, Liu, et al., 2025; Xie et al., 2024; Zhu et al., 2024). (iii) Intelligent System Design: Advances in smart packaging enable SF-based materials to respond to storage conditions. Examples include integrating pH-sensitive dyes for visual freshness indicators (Wang, Wu, Lv, et al., 2025; Zhao, Yang, et al., 2025; Zhihang et al., 2025) or engineering stimuli-responsive release mechanisms for targeted antimicrobial delivery (Divya Panneerselvam et al., 2024; Tracey et al., 2023). (iv) Application Diversification: SF's utility is expanding beyond fresh produce to include frozen food preservation, where it acts as a bio-based cryoprotectant by inhibiting ice crystal growth and maintaining tissue integrity (Xie et al., 2024).

In summary, while SF holds considerable potential for advancing postharvest preservation, its transition from laboratory to market depends on resolving key issues in cost, performance, safety, and scalability. Future research should prioritize the development of scalable and eco-friendly processing methods, multifunctional composite design, mechanistic studies on preservation pathways, and systematic safety assessments. Through interdisciplinary innovation, SF-based systems may evolve into effective, intelligent, and sustainable solutions for reducing postharvest losses and extending food shelf life.

5. Conclusion

Silk fibroin (SF) shows strong potential in postharvest preservation, with applications evolving from simple coatings to active and nanocomposite packaging. Commercial viability is supported by low-cost waste recovery (under $6/kg), compatibility with existing coating lines (60% CAPEX reduction), and superior environmental performance (Eco-Score Grade A). The technology is projected to enter rapid market adoption between 2026 and 2030, with a compound annual growth rate exceeding 20%. Concurrently, SF is transitioning to high-end food packaging via molecular design and additive manufacturing (Fan et al., 2025; Gong et al., 2020; Khalid et al., 2020; Luo et al., 2025; Milazzo et al., 2023; Quan et al., 2025; Rodriguez et al., 2018; Sahoo et al., 2023; Singh et al., 2019; Tian et al., 2024; Wang, Zhang, & Wei, 2021). Core innovations—synthetic biology, 3D printing, and nanocomposite cross-linking—enable three emerging paradigms: geometrically conformal, actively integrated, and programmably degradable packaging, transforming passive containers into active, interactive systems.

However, large-scale application faces challenges in cost, performance, and safety. Future research should prioritize efficient extraction methods, optimized composite formulations, and robust safety evaluation systems, while strengthening fundamental research on preservation mechanisms to reduce postharvest losses and ensure food safety.

CRediT authorship contribution statement

Hong Sun: Writing – review & editing, Writing – original draft, Visualization, Methodology, Conceptualization. Yan Sun: Writing – review & editing, Writing – original draft, Investigation. Ping Li: Writing – original draft. Yufeng Lv: Writing – original draft. Pengcheng Zhang: Writing – original draft.

Declaration of generative AI and AI-assisted technologies in the writing process

The author(s) did not use generative AI or AI-assisted technologies in the preparation of this work.

Funding sources

This work was supported by the [Tianjin Higher Education Science and Technology Development Fund Program of China] under Grant [2023KJ209].

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.