Advanced extraction techniques and functional applications of millet-derived nutrients: a review

Abstract

Millets, also known as Nutri-cereals, are a traditional food source in many countries. They are comprised of essential nutritional elements, including carbohydrates, proteins, dietary fiber, lipids, vitamins, minerals, and various phytochemical compounds required for healthy longevity. Because of their low glycemic index and gluten-free status, millets suit various dietary requirements. This comprehensive review explores different techniques used for isolating health-promoting components from millets. Conventionally, most of the Nutri-components from millets can be isolated by using solvent extraction. However, it is associated with limitations such as low efficiency and potential degradation of bioactive compounds. The application of innovative extraction methods like ultrasonication-assisted, microwave-assisted, enzymatic-assisted, pulse electric field-assisted, and supercritical fluid techniques play crucial roles in enhancing extraction yield and improving functional attributes. The selection of proper extraction methods varies due to several factors, including the targeted components, the properties of the millet matrix, extraction efficacy, extraction speed, and economic considerations. Additionally, the review underscores the potential of millet bioactive component applications in functional foods, nutraceuticals, and other industrial products. The extraction and utilization of millet nutritional components provide a valuable outline for advancing scientific research and industrial innovation, addressing the global demand for sustainable and health-focused solutions.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-025-06366-0.

Introduction

Millets are a type of cereal from the Poaceae family, come under the category of small-seeded grasses, and are among the earliest crops still grown today (Hassan et al. 2021). They are dryland cereals, also identified as nutri-cereals, which supported that, prior to the green revolution, ensured food safety (Singh et al. 2023). Millets, which are traditional food sources in many areas, have the potential to help with problems like malnutrition, climate change, and resource shortages (Suri et al. 2023). Millets are valued because of their capacity to bear pests and drought (Nithiyanantham et al. 2019). In the kingdom of millets, based on extensive cultivation and significant nutritional role, millets may be classified into two groups, i.e., major, and minor millets. Sorghum (Sorghum bicolor) and pearl millet (Pennisetum glaucum) are the major millets. In contrast, the group of minor millets includes seven other millets, viz. finger millet (Eleusine coracana), proso millet (Panicum miliaceum), brown top millet (Urochloa ramosa), kodo millet (Paspalum scrobiculatum), foxtail millet (Setaria italica), little millet (Panicum sumatrense), and barnyard millet (Echinochloa frumentacea) (Sachdev et al. 2023). Minor millet enriched with micronutrients like iron, calcium, phosphorus, and magnesium their abundance and bioactive compounds such as polyphenols and antioxidants, therefore these grains exhibit therapeutic properties, boost immunity and vitality (Kaur et al. 2023a).

Millets are grown and eaten throughout Asia, primarily in India and China and in some regions of Africa. India is the largest producer of millet among the world. As per FAOSTAT (2024), the estimated worldwide production of millet was 30.86 million tonnes under a harvested area of 29.85 million hectares in the year 2022. Sorghum and pearl millet account for nearly 90% of global millet consumption, in which pearl millet and little millets are grown in over 93 countries worldwide (Singh et al. 2023). Millets are enriched with complex carbohydrates, dietary fiber, essential amino acids, vital minerals (iron, zinc, calcium, phosphorus, potassium), folic acid, carotenoids, coumarins, vitamins, and other bioactive components. According to this nutritional profile, millets are equivalent to functional foods that can improve health and ward against non-communicable illnesses. Because of their small glycemic index and gluten-free status, millets suit various dietary requirements, including those of people with diabetes or gluten sensitivity (Bhatt et al. 2022; Hassan et al. 2021). Millets have a diversity of bioactive components, which highlights their potential to meet a variety of industrial and health requirements.

To illustrate the relationship between millets, bioactive component extraction, and their utilization, the bibliometric networking and overlay visualization features of the VOS viewer (Version 1.6.20) program were applied. Using this method, Scopus-indexed papers on millets were identified using three keywords: millet, extraction, and bioactive. A total of 450 keywords were used to create the network visualization graphic. Network visualization is widely acknowledged as a valuable method for examining diverse bibliometric networks (Dadhaneeya et al. 2023). There are four main clusters in the co-occurrence network analysis of all the keywords in Fig. 1, each representing a cohesive set of terms. A circle represents each keyword. The size of the circle denotes the frequency of use of a particular keyword. The network between millets, bioactive substances, and various methods for extracting components is represented by the central blue cluster. The red cluster investigates the different bioactive substances that are found in millets. The pink cluster represents popular techniques for obtaining bioactive compounds from millet. The green cluster represents the incorporation of isolated substances in food products. The innovative extraction methods for isolating bioactive components from millets can be better understood using this knowledge. Figure 1 indicates poor network association between the keywords “innovative extraction techniques” and “compounds from millet.” This perspective helps to explain why researchers are looking into potentially innovative methods for extracting millets’ health-promoting components.

Fig. 1.

Network visualization of indexed keywords

Potential health-promoting components

The world of millet offers several health-promoting components that support their functional and nutritional benefits. The nutritional components of each millet are given in Table 1. Millet is particularly enriched with dietary fiber, phenolic compounds, and starch in terms of glycaemic index, antioxidant capacity, a more balanced amino acid profile, and gut health modulation as compared to other cereals such as wheat and rice.

Table 1.

Nutritive composition of millet (Bhatt et al. 2022; Hassan et al. 2021; Sharma et al. 2021; Sharma and Niranjan 2018)

Carbohydrates (starch and sugars)

Millets contain 60 to 70% carbohydrates by weight, making them a reliable source of energy (Kaushik et al. 2021). The millet’s carbohydrates are composed of 60–75% starch, 15–20% non-starchy polysaccharides, and 2–3% free sugars. Additionally, they include dietary fiber such as hemicellulose, cellulose, arabinoxylans, and β-glucan (Sharma et al. 2021). A significant component of millet is starch, which consists of two primary polysaccharide componenets: amylose and amylopectin (Kumar et al. 2023). Some millet cultivars can regulate blood sugar levels due to the specific structure of millet starch, which can affect its glycemic sensitivity and digestion. In millet, the overall glycemic index ranged between 42.7 and 58.3 (Bora et al. 2019). Since starch makes up the majority of cereal composition, there is a growing focus on isolating the starch from millet (El Halal et al. 2019). Simple sugars, cellulose, and hemicellulose comprise the remaining carbohydrates (Kumar et al. 2023). Finger millet has the highest quality carbohydrate of all the millets, whereas foxtail millet shows the lowest carbohydrate (Bhatt et al. 2022).

Protein

In millet, protein comes in second place regarding availability after starch (approximately 10% of the total weight). Because they are gluten-free and hypoallergenic, millet are regarded as suitable sources of dietary protein. Millet proteins are valuable nutrients for vegetarian and vegan diets because of their amino acid composition. Lysine, threonine, and tryptophan lack millet protein despite having a balanced amino acid composition (Sachdev et al. 2023). Compared to common cereals, pearl millet protein showed better amino acid balance (Nazari et al. 2018). However, it is challenging to use millet protein on a big scale because of difficulties in dissolving in acidic or aqueous systems. Typically, physical, chemical, or enzymatic modifications alter proteins, which modify their structural, physicochemical, and functional characteristics (Kamara et al. 2010). Additionally, innovative techniques such as microwave, ultrasound, and high-pressure processing notably modify the millet proteins in the structural and quality characteristics by their fractionation. Nevertheless, their effectiveness can be verified in products that do not need many soluble proteins, like cereal breakfasts, meat products, baked goods, protein snack bars, and pet feeds (Sachdev et al. 2023). The proso millet has the highest protein content among all millets (Bhatt et al. 2022). Most cereals lack lysine, whereas millets, including finger millet, kodo millet, and pearl millet, have 2.2–5.5 g of lysine per 100 g of protein and up to 6.5 g in pearl millet (Sharma et al. 2021).

Lipids

Millets contain fat from 1 to 6%, and sometimes, they may have higher contents, which occasionally affects their shelf stability (Mitharwal et al. 2021). These lipids are essential for supporting many physiological processes as well as cell membrane structure and energy storage. Three different lipids are typically found in finger millet, viz. free lipids, bound lipids, and structural lipids in 2.2%, 2.4%, and 0.6%, respectively. Lipids comprise 80% triacyl glycerol, 14% phospholipids, and 6% glycolipids (Mitharwal et al. 2021). As compared to corn and rice, foxtail millet has substantially more significant levels of lipids (> 4%), with over 85% of those being polyunsaturated fatty acids (Wang et al. 2022). Slama et al. (2020) stated that pearl millet oil was rich in total unsaturated fatty acids (77.2%) and omega-6 (ω-6) fatty acids. It also contains high amount of total phenolic content of 220 mg/100 g and antioxidant activity (DPPH radicals scavenging activity) of 79.2%, respectively. The total oil percent in pearl millet seeds (5.1%) was equivalent to maize grains.

Dietary fiber

A significant portion of dietary fiber is also part of polysaccharides comprising non-starchy, hemicelluloses, cellulose, and pectinaceous material (Kaur et al. 2023a; Singh et al. 2023). A significant amount of dietary fiber found in the outer layer of millet seed benefits human health and has an impact on a variety of metabolic and digestive functions. The high content of dietary fiber can be associated to reduce the blood cholesterol level as well as preventing constipation and lowering glycemic load (Kumar et al. 2023). Kodo millet has the highest amount of dietary fiber of any millet, making it a perfect diet for diabetic patients (Bhatt et al. 2022; Saini et al. 2021). Minor millets typically have an overall dietary fiber level of 15–20%, with a higher insoluble proportion (Kaur et al. 2023a). The dietary fiber from pearl millet bran has good functional properties like water-holding capacity and oil-holding capacity (Kaur et al. 2023b).

Bioactive components and antioxidant activity

Bioactive components contain phenolic acids, flavonoids, stilbenes, tannins, and lignans (Liang and Liang 2019). They are aromatic secondary metabolites that contribute significantly to sensory and nutritional properties and color development (Kaushik et al. 2021). Millet has a high concentration of antioxidants such as tocopherols, carotenoids, and phenolic components (Liang and Liang 2019). Polyphenols can eliminate free radicals, which also activate antioxidant enzymes, chelate metal catalysts, and inhibit oxidases. For these reasons, polyphenols are used in pharmaceuticals and nutraceutical products (Nithiyanantham et al. 2019). Millets contain flavonoids that are frequently found in plants, such as “orientin, apigenin, catechin, quercetin, luteolin, daidzein, sponarin, violanthin, myricetin, isovitexin, tricin and lucenin-1” (Chandrasekara and Shahidi 2011). These phytochemicals, minerals, vitamins, and fibers are primarily located in the outer bran layers. Millets, due to their antioxidant capabilities, demonstrate several health benefits, like preventing chronic diseases (Sharma et al. 2021). The seed coat fraction of finger millet encompasses about 90% of the total polyphenols, and it is a significant source of polyphenols (0.2–3.0%) (Balasubramaniam et al. 2019).

Important biological substances known as phytosterols give structural stability to membrane cell. These substances also serve as precursors to produce several bio-functional components. Ryan et al. (2007) recognized three bioactive components in millets, viz. b-sitosterol, campesterol, and stigmasterol. Phytosterol content of foxtail millet bran oil includes b-sitosterol, campesterol, stigmastanol, stigmasterol, fucosterol, and ergostanol. Pearl millet is distinguished among the several types of millet due to its typical phytosterol concentration, which is 58 mg per 100 g (Bhatt et al. 2022). Five distinct populations of pearl millet exhibited free radical inhibition activity ranging between 66.9% and 84.7% (Bouajila et al. 2020). Suma and Urooj (2012) reported that the millet bran fraction also have higher amount of antioxidant components. The oil extracted from millet contains many natural antioxidants that have potential health benefits. The oil derived from pearl millet exhibits remarkable antioxidant activity, with a higher percentages of 79.2% (Slama et al. 20202020). Squalene, an influential unsaturated long-chain triterpene compound, plays a crucial role as a precursor in the synthesis of phytosterols within millets. The analysis revealed that fox millet oil contains relatively elevated concentrations of tocopherols, sterols, oryzanol, and squalene, exhibiting therapeutic potential (Ji et al. 2019). Hassan et al. (2021) indicate that millet’s phenolic compounds exhibit potent antioxidant properties. Variations in phenolic content have been observed within millet varieties. For example, pearl millet populations showed total phenols ranging from 72.08 to 136.25 mg GAE/g (Bouajila et al. 2020). Ofosu et al. (2020) found phenolic content in finger millet, barnyard millet, and finger Italian millet to be 107.8, 129.5, and 136.3 mg FAE/100 g, respectively. The phenolic compounds in foxtail millet are most effectively absorbed during gastrointestinal digestion, while its protein hydrolysate exhibits the greatest antioxidant activity in its hydrophobic state (Hutabarat and Bowie 2022).

Vitamins

Millets are rich in various B-complex vitamins, apart from B₁₂, and contain tocopherols and tocotrienols in smaller quantities which are components of Vitamin E. Millets contain between 0.25 and 0.57 mg of thiamin and 0.05 to 0.23 mg of riboflavin per 100 g (Sharma et al. 2021). Assorted studies showed that the germination process can induce alterations in the vitamin content of cereals, leading to a reduction in thiamine levels and a rise in Vitamin B₂, niacin, and Vitamin C content (Kaushik et al. 2021). During germination process, millets exhibit an enhancement in their vitamin B, C, and E contents. Millets are abundant in essential vitamins, with notable quantities such as 0.55 mg/100 g of thiamine, 5.11 mg/100 g of niacin in proso millet, and 2 mg/100 g of riboflavin in kodo millet (Bhatt et al. 2022).

Extraction techniques

The application of methods for extracting health-beneficial components from millet depends on several parameters, viz., structure of millet seed, treatment time, targeted extraction component, method of extraction, and economy. Table 2 represents several methods adopted for the extraction of components. Processing techniques such as mechanical grinding, germination or malting, and fermentation can enhance the nutritional quality and bioavailability of food components. However, excessive or improperly applied processing conditions may lead to the degradation of micronutrients, polyphenols, and dietary fiber. Many studies also reported significantly enhanced nutritional profile, protein, dietary fibre, mineral content (iron, calcium, magnesium), vitamins, and bioavailability across different millet cultivars during controlled processing (Ramakrishnan et al. 2023).

Table 2.

Potential components and various methods of extraction

Sr. No.	Component	Conventional Extraction methods	Innovative extraction methods	References
1	Carbohydrate	1. Pressing and impregnated with water 2. Conventional water extraction 3. Solvent extraction a. Organic solvents b. Green solvents (such as ionic liquids and deep eutectic solvents)	1. Ultrasound-assisted extraction 2. Microwave-assisted extraction 3. Pressurized liquid extraction 4. Supercritical fluid extraction 5. Enzyme-assisted extraction	Mena-García et al. 2019; Saïed et al. 2020
2	Protein	1. Wet extraction a. Alkaline extraction b. Acid extraction c. Enzyme-aided extraction d. Salt-in/salt-out extraction 2. Dry fractionation-Air classification 3. Osborne’s protein fractionation	1. Microwave-assisted extraction 2. Ultrasonic energy-assisted extraction 3. Pulse electric field-assisted extraction 4. Hydrodynamic cavitation extraction 5. Tribo-electrostatic separation 6. High hydrostatic pressure	Eze et al. 2022; Sachdev et al. 2023
3	Fat	1. Mechanical oil expeller 2. Hydraulic press 3. Soxhlet/solvent extraction	1. Enzyme assisted extraction 2. Microwave-assisted extraction 3. Ultrasonication 4. Pulse electric field extraction 5. Supercritical fluid extraction	Pawar and Nema 2023
5	Starch	1. Wet milling -Aqueous 2. Acidic steeping 3. Alkali isolation	1. Enzymatic extraction	Kumar et al. 2023
6	Polyphenols and Antioxidants	1. Heat reflux 2. Soxhlet extraction	1. Microwave-assisted extraction 2. Ultrasound-assisted extraction 3. Supercritical fluid extraction 4. Pressurized fluid extraction 5. Pulsed electric field-assisted extraction	Ajila et al. 2011
7	Vitamin	1. Organic solvent extraction	1. Supercritical fluid extraction 2. Solid-phase extraction	Luque-Garcı´a and Luque de Castro 2001

Conventional methods

The efficiency of the extraction method determines the efficacy of the phytochemicals or bioactive substances that may be isolated. Adopting extraction technique depends on various parameters viz. nature/structure of the cell, processing operational time, extraction temperature, solvent selection, component to be extracted, and economy (Pawar and Nema 2023). Solvent extraction is the most followed conventional method for most potential extraction components. In the laboratory-scale extraction process, Soxhlet extraction encompasses a cyclic procedure where a solvent is repetitively evaporated and condensed, enabling components extraction. This technique effectively extracts lipids and specific non-polar components (Bora et al. 2019).

In the solvent leaching method, sample biomass is suspended in an organic solvent and allowed to leach out bioactive components by allowing treatment time. Then, the residue is separated by centrifugation/filtration. Recovery of the extract is carried out by evaporation of the solvent (Chethan and Malleshi 2007). However, conventional extraction techniques have low extraction efficiency due to higher treatment time and temperature which also cause environmental threats. These problems may be overcome with alternate innovative extraction techniques that improve extraction efficiency and cater to extraction in an environment-friendly way (Ajila et al. 2011).

Innovative extraction techniques

Nowadays, to extract bioactive components from various plant samples, several innovative techniques have been developed, including microwave-assisted extraction (MAE), enzyme-assisted extraction (EAE), ultrasound-assisted extraction (UAE), supercritical fluid extraction (SCFE), and pulsed electric field-assisted extraction (PEFAE). These methods require minimal extraction periods and are environment-friendly (Ajila et al. 2011). Innovative techniques that improve extraction efficiency, selectivity, and sustainability have replaced and assisted conventional methods in extracting health-promoting components from millets. The potential for innovative extraction methods to support the nutraceutical, pharmaceutical, and functional food industries become increasingly promising as researchers continue to investigate and improve these procedures, revealing new opportunities for utilizing millets’ inherent value (Pawar and Nema 2023). Advantages over conventional extraction are rapid extraction, uniform heating, enhanced mass transfer, and good energy efficiency. However, the innovative techniques require special equipment, which adds a barrier to effective implementation for extraction (Saini et al. 2021). Each of these complex extraction techniques has unique benefits and challenges. Many researchers worked on the extraction of nutri components from millets, which is represented in Table 3. To choose the best technique for the effective and sustainable extraction of bioactive components from millets, researchers and industries must carefully consider these variables.

Table 3.

Millet: health beneficial components & applied extraction techniques

Sr. No.	Potential extraction components	Millet	Extraction techniques	Major key findings	References
1.	Carbohydrate concentrates	Millet biomass (sweet sorghum, sweet pearl)	Pressing and impregnated with water	Coarse chopping and a second pressing of the following impregnation with water: bagasse ratio of 1 at 25 °C was advised to enhance residual carbohydrate extraction.	Saïed et al. 2020
2.	Polysaccharides	Foxtail millet	Alkali extraction	Polysaccharides yield 46.21 mg/g: alkali concentration of 0.83 mol per L, liquid-solid ratio of 20.9 to 1, and extraction period of 1.1 h at 72.7 ºC.	Zhu et al. 2015
3.	Starch	Proso millet	Alkaline steeping method	Starch yield: 54.1%, with low residual levels of ash (0.62 g/100 g), fat (0.27 g/100 g), and protein (1.21 g/100 g).	Singh and Adedeji 2017
4.	Starch	Finger millet	Ultrasound-assisted hydration	An ultrasound amplitude of 66% and the grain-to-water ratio of 1:3 at 26 min gave the optimum solubility and water binding capacity starch.	Yadav et al. 2021
5.	Dietary Fiber	Pearl millet bran	Green extraction methods (UAE, MAE, EAE, microwave-assisted enzyme extraction, and ultrasound-assisted enzyme extraction)	Dietary Fiber yield 78.8%, w/w: obtained by combining ultrasonic treatment with enzymatic extraction at an amplitude of 35%, at 50 °C temperature, and liquid-to-solid ratio of 40:1 after 10 min of treatment time	Kaur et al. 2023b
6.	Crude oil	Foxtail millet bran	Soxhlet extraction with diethyl ether	Oil-rich in linoleic acid and tocopherols and a good source of natural oil.	Liang et al. 2010
7.	Crude oil	Foxtail millet bran	Subcritical propane (SPE) and supercritical carbon dioxide extraction (SCE)	Oil yield by solvent extraction, SCE, and SPE were 17.14%, 19.65%, and 21.79%, respectively.	Shi et al. 2015
8.	Crude oil	Foxtail millet	Soxhlet apparatus with n-hexane	Oil with high unsaturated fatty acid with linoleic acid of 65%~69% and oleic acid of 12 ~ 17%.	Ji et al. 2019
9.	Crude oil	Pearl millet	Soxhlet extraction	The oil contains high total phenolic content, i.e., 220 mg/100 g, and antioxidant activity of 79.2%	Slama et al. 2020
10.	Protein	Proso millet seeds	High-power ultrasound (US) probe	US treatment for enhancing the functional qualities of protein concentrate was 73.95 W/cm2 for 12.5 min, which led to a decrease in molecular weight and an increase in the negative surface charge.	Nazari et al. 2018
11.	Protein	Foxtail millet	Enzymatic hydrolysis	Enzymatically hydrolysed by proteases (Alcalase 2.4 L) gave maximum protein recovery of 81.8%	Kamara et al. 2010
12.	Antioxidant compound	Foxtail millet	Aqueous, solvent (methanol and ethanol) extraction	Methanol extraction had the maximum level of antioxidant activity, followed by aqueous and ethanolic extracts.	Suma and Urooj 2012
13.	Polyphenols	Finger millet	Solvent extraction	The millet polyphenols were successfully extracted using 1% HCl-methanol.	Chethan and Malleshi 2007
14.	Phenolic Extracts (Total flavonoid content and total phenolic content)	Foxtail Millet Husk	Deep eutectic solvent extraction combined with ultrasonic-assisted extraction (DES-UAE)	Compared to conventional solvent extraction, the optimized UAE-DES yielded significantly increased antioxidant activity, TPC, TFC, α-glucosidase, and acetylcholinesterase inhibitory activities.	Wang et al. 2023
15.	Polyphenols (Phenolic content, Total flavonoids, Tannins)	Finger millet	Ultrasonication	Total flavonoid content increased 1.4-fold in ultrasonication, the phenolic yield was equal to the conventional technique, and tannins showed a substantial increase of 1.1-fold in ultrasonication.	Balasubramaniam et al. 2019
16.	Polyphenols (Phenolic content, Total flavonoids, Tannins)	Finger millet	Enzyme pretreatment before ultrasonication	As compared to the conventional heat reflux method, phenolic yield increased 2.3-fold and, total flavonoids increased 1.3-fold, tannins increased 1.2-fold in Enzyme pretreatment before ultrasonication.	Balasubramaniam et al. 2019
17.	Polyphenols	Seven millets, namely foxtail, prose, two finger millet varieties (Ravi and local), kodo, little millet, and pearl millet	Ultrasound-assisted solvent extraction	Antioxidant activity of phenolic extracts increased in order hull > whole grain > dehulled grain > cooked dehulled grain. Other millet grains have high total polyphenolic content, proving their higher antioxidant activity.	Chandrasekara et al. 2012
18.	Polyphenols components	Sorghum flour	Pulsed electric field	Total phenolic content (24.8%), antioxidant activity (33.9%) higher than the control sorghum flour at optimized conditions: flour to water ratios 45% (w/v), electric field intensity 2 kV/cm and treatment time: 875 µs	Lohani and Muthukumarappan 2016
19.	Polyphenols	Foxtail millet bran	Deep eutectic solvent extraction	Fraction 5 contained the highest abundance of flavonoids, predominantly apigenin-C-dihexoside, ie.185.41 ± 1.73 µg/g	Zheng et al. 2022
20.	Inulin (Prebiotic biomolecule)	Jowar, bajra, and ragi	Aqueous solvent -acidification	The prebiotic effectiveness of inulin was found: bajra > jowar > ragi > commercial inulin. Maximum inulin yield in bajra 0.4727 g/g bajra	Banerjee et al. 2017

Ultrasound-assisted extraction (UAE)

Ultrasound, defined as sound waves with frequencies exceeding ∼20 kHz, offers straightforward, non-thermal, cost-effective, energy-saving, and environmentally friendly advantages for extraction processes. UAE has emerged as one of the most effective methods for preserving phenolic compounds. UAE utilizes acoustic cavitation to enhance solvent penetration and disrupt plant cell walls, facilitating efficient release of phenolics without requiring high temperatures or prolonged extraction times. This helps minimize thermal degradation and oxidation of phenolic compounds, which are often heat- and light-sensitive. The treatment of high-power ultrasound can be accomplished through the use of sonication baths or portable ultrasonic immersion probes, serving a variety of purposes in the field of food manufacturing (Nazari et al. 2018). By generating cavitation bubbles that damage cell walls and improve contact between solvents and bioactive, ultrasonic waves are utilized to improve the extraction process (Sawale et al. 2024). The UAE leads to faster extraction times and higher extraction yields. The sample is sonicated for a particular period during the extraction process, and the extracted components are subsequently recovered by centrifuging the extracts (Balasubramaniam et al. 2019). Nazari et al. (2018) worked on proso millet extract protein with the help of ultrasonication and reported that it improved the functional and structural properties.

Microwave-assisted extraction (MAE)

Millets are heated using microwave energy in a solvent to speed up the leaching of the bioactive components. Microwaves with a frequency of 300 MHz to 300 GHz are used to help MAE in open systems at ambient pressure or closed systems (controlled pressure and temperature) (Sachdev et al. 2023). Microwave heating is based on the direct interaction of electromagnetic waves, typically at 2.45 GHz, with polar solvent molecules, involving phenomena like dipole rotation and ionic conduction. This heating mechanism enables tissue and cell breakdown, releasing bioactive substances from plasma membranes or cell walls (Mena-García et al. 2019). Kaur et al. (2023b) worked on the extraction of fiber concentration from pearl millet bran by using green technologies, including microwave-assisted extraction. There is limited research on extracting health-beneficial components from millet using microwave-assisted extraction. Hence, more investigation is needed to explore microwave applications for extracting nutritional components from millet.

Enzymatic-assisted extraction (EAE)

Enzymes disintegrate cell walls and liberate bioactive components from millet matrices during enzymatic extraction. This method uses excellent selectivity, specificity, and enzyme activity to break down cell membranes (Nadar et al. 2018). Since aqueous media are typically used in enzyme technology, it is considered a green process (Mena-García et al. 2019). Many researchers reported particularly well for extracting carbohydrates, proteins, and phenolic components from millets. Various commercial enzymes like cellulase, amylase, papain, pectinase, and hemicellulose are available for enzymatic treatment. To broaden the scope of activities and increase the extraction’s effectiveness, a mixture of enzymes is typically used. Combining enzymatic pretreatment with other green extraction methods, such as MAE, UAE, and PEFAE, is a innovative tactic to improve the performance of enzyme technology (Nadar et al. 2018). The enzymatic hydrolysis of proteins offers a favourable method to enhance protein functionality (Kamara et al. 2010). According to Mena-García et al. (2019), these methods typically result in high efficiency and shorter extraction time at low temperatures. For example, the maximum extraction yield of total dietary fiber from pearl millet bran (78.8%, w/w) was obtained by combining ultrasonic treatment with enzymatic extraction at an amplitude of 35%, temperature of 50 °C, and liquid-to-solid ratio of 40:1 following 10 min of treatment. Moreover, the strong impact of the enzyme assisted by ultrasound on the extracted dietary fiber was visible in SEM images (Kaur et al. 2023b).

Pulse electric field assisted extraction (PEFAE)

Pulsed electric fields have recently been employed for plant extraction. The pulsed electric field, a non-thermal processing method, utilizes short-duration, powerful electric field pulses to treat materials between two electrodes (Lohani and Muthukumarappan 2016). PEF aims to increase extraction by destroying the structure of the cell membrane. Applying an electric field to a plant cell leads to the separation of molecules within the cell membrane, sorting them based on their charge, owing to the dipolar characteristics of these membrane molecules. When molecules bearing electrical charges repel each other, it results in the formation of pores within exposed regions of the membrane once the transmembrane potential exceeds a critical threshold of approximately 1 V. This incidence significantly enhances the membrane’s permeability (Martín-García et al. 2020). The magnitude of the electric field, pulse duration, quantity of pulses, frequency, matrix product, and treatment duration are all variables that directly influence electroporation (Lohani and Muthukumarappan 2016; Martín-García et al. 2020). The extraction of protein from millet material can also be accomplished using several innovative and environmentally friendly approaches, including pulse electric field, microwave, high pressure, etc. (Sachdev et al. 2023). PFE can enhance mass transfer due to the drilling of the membrane structure and reduce extraction time. Although the literature is scarce on utilizing PEF for bioactive component extraction from millet, there is a substantial amount of information available regarding the extraction of starch from different commodities (Castro et al. 2023). The pulsed electric field as a pre-treatment is employed to improve the extraction of flavonoids, phenolic acid derivatives, and total free phenolic components from brewers’ spent grains (Martín-García et al. 2020). Consequently, it can be argued that this technology has the potential to be successful in extracting other bioactive components, too. The PEF may also be used on millet as a pre-treatment procedure before traditional extraction to speed up extraction (Martín-García et al. 2020).

Supercritical fluid extraction (SFE)

Supercritical fluid extraction involves the use of fluids characterized by low viscosities, high densities, and diffusivities that lie between the properties of gases and liquids. These operations occur at temperatures and pressures exceeding critical points (Shi et al. 2015; Devittori et al. 2000). The most common supercritical solvents include carbon dioxide, ethanol, propane, ethane, butane, and water. Due to its environmentally benign characteristics, such as its non-flammability and lack of pollution, carbon dioxide (critical temperature:31ºC, critical pressure:73.8 bar) has often been chosen (Pawar and Nema 2023). The extraction of bioactive components can be controlled by working conditions such as pressure and temperature. Supercritical carbon dioxide (SC-CO₂) extraction method was applied to extract crude oil from proso millet bran (Devittori et al. 2000). Additionally, products extracted using SC-CO₂ are entirely free from solvent residues, unlike those obtained through conventional methods. Shi et al. (2015) worked on subcritical propane and supercritical carbon dioxide extraction for foxtail millet bran oil extraction. They reported that the application of supercritical propane extraction led to an increased extraction yield of tocopherols compared to solvent extraction and supercritical carbon dioxide extraction.

Applications of the extracted components

Millet’s nutritional components have found numerous applications in a wide range of industries, as follows.

Functional foods

Functional foods are those that provide health benefits or reduce the risk of chronic diseases beyond basic nutrition. Developing functional food products that contain extracts derived from millet can elevate the levels of various essential nutrients in the food. Cereal products and their components offer a valuable means to add probiotics, prebiotics, and fibers to the human diet (Das et al. 2012). Pearl millet bran enriched with a significant amount of dietary fiber, that could be potentially used for manufacturing functional food products (Kaur et al. 2023b). Isolated β-glucans from millet can be used in foods as thickeners, stabilizers, and fat substitutes, as they have been associated to be beneficial for health by lowering cholesterol and controlling glycemic response, as endorsed by the FDA and EFSA. The recommended daily intake for health benefits is 3 g per day according to the FDA or 4 g per 30 g of available carbohydrates as per EFSA (Mejía et al. 2020). In general, millets are commonly used to create traditional dishes like chapati, dosa, pasta, bread, and cookies. Foods made from millet are potential sources of probiotics and prebiotics with potential health advantages (Nithiyanantham et al. 2019). According to Zhou et al. (2023), the protein component of the raw millet material had a substantial impact on the final Huangjiu brewing product characteristics, including its total soluble solids, reducing sugar content, alcohol content, and amino acid. The protein isolates from millet are palatable and nutritionally sound. To meet the needs of humans for protein, insufficient amino acids, and complementary proteins can be added to the diet to improve its nutritional quality (Sachdev et al. 2023). According to a study, millet has the capacity to promote the growth of gut flora, as evidenced by pre-biotic activity score (Arya and Shakya 2021). Sharma and Niranjan (2018) reported many foxtails millet-based products, viz. ready-to-eat extruded snacks, Sikhye beverages, Yakju beverages, biscuits, burfi, probiotic dahi, millet gel, etc. Moreover, foxtail millet extract demonstrates inhibitory effects on the growth of HepG2 liver cancer and MDA breast cancer cells. In tests on HT-29 colorectal adenocarcinoma cells, foxtail millet phenolic compounds displayed significant antiproliferative activity, hindering DNA stratification and thus aiding in the prevention of both early and advanced stages of carcinogenesis. Most of phenolic components in plants are in bound form which reduces the ability to perform as good antioxidants (Acosta-Estrada et al. 2014). Therefore, the extracted bioactive components -such as phenolic acids and flavonoids can be efficiently fused into various food matrices, including bakery products, snack bars, dairy alternatives, and nutritional supplements. Other practices such as microencapsulation, nanoemulsion, and inclusion complexes are increasingly being employed to protect these compounds during processing and improve their bioavailability and stability (Lohani and Muthukumarappan 2016).

The dietary fiber from foxtail millet is anticipated to lower glucose absorption levels. The protein hydrolysates of foxtail millet can inhibit angiotensin-converting enzyme (ACE), thereby reducing angiotensin II and effectively lowering blood pressure in hypertensive rats (Hutabarat and Bowie 2022). Modified protein from millet improves the functional properties. It allows them to fortify them in foods such as soups, sauces, non-dairy whiteners, salad dressings, toppings, and many other functional foods (Sachdev et al. 2023). Noodles, bread, pasta, extrudate, injera, sourdough bread, non-sour dough, different cookies, fat replacer, and other foods have all been produced by food scientists that are gluten-free functional foods that are used by people who cannot consume gluten. Also, millet extract is utilized for the preparation of many varieties of wholesome products, including millet-fortified biscuits, multi-millet cookies, noodles made from millet-blend composite flour with exceptionally low glycemic indices, and the innovative addition of pearl millet flour pasta (Saini et al. 2021). Millet proteins have limited solubility in acidic and aqueous system however it can be modified through enzymatic hydrolysis or ultrasound to enhance their functional properties, enabling their use in foods like soups, sauces, dressings, toppings, non-dairy whiteners, and nutritional products (Nazari et al. 2018).

Pharmaceutical and nutraceuticals

Millets provide vital bioactive substances that can be used in the production of nutraceuticals, which may give health benefits beyond essential nutrition. Polyphenols are added to supplement formulas to reduce risk and enhance health and wellness (Chandrasekara et al. 2012). Millet polyphenols, including flavonoids, phenolic acids, and tannins, have demonstrated significant antioxidant, anti-inflammatory, and anti-cancer activities in various studies. A green approach for utilizing polyphenols in nutraceutical foods was developed using finger millet polyphenols (Balasubramaniam et al. 2019). Foods contain phytochemicals such as polyphenolic substances having antioxidant properties that lower the risk of cardiovascular disease and cancer. Antioxidant activities of soluble and bound phenolic extracts from six commonly consumed types of millets (kodo, finger, foxtail, proso, little and pearl) were evaluated against free radicals and reactive oxygen species (Chandrasekara and Shahidi 2011). The radical and reactive oxygen species scavenging activities of the phenolic extracts from analysed millet varieties were efficient, which exhibited the ferulic and p-coumaric acids were the major polyphenols within the extracts (Chandrasekara and Shahidi 2011). Phytochemicals also serve as inhibitors of enzymes that hydrolyze carbohydrates. Short-chain fatty acids are produced during soluble dietary fiber fermentation. Propionate could prevent the production of new cholesterol. High blood pressure, asthma, cardiovascular illnesses, migraines, diabetes, and the immune system can all be controlled and treated with millet’s natural nutrients (Nithiyanantham et al. 2019). According to Sachdev et al. (2023), millet proteins are significant biomaterials used in micro and nanofabrication. An isolated protein may also be used in various pharmaceutical formulations, oral drug delivery systems targeted at molecular targets, and biopolymers that can replace plastic. Millet’s extract can be utilized to tackle the protein-energy malnutrition that is particularly common in children and breastfeeding mothers in underdeveloped countries due to a shortage of protein-rich meals and supplements. Millets, which are full of necessary minerals like calcium, chromium, zinc, and magnesium, may help fight malnutrition while also preventing diabetes and reducing the aging process (Mitharwal et al. 2021). Dietary supplements made with millet bioactives help meet specific nutrient needs or health objectives.

Other industrial applications

The pharmacological uses of millet’s bioactive components, which include antioxidant and anti-inflammatory properties, show promise for the creation of innovative pharmaceuticals and cosmetics products. Beyond its nutritional content, millet is acknowledged for its many possible health advantages, such as promoting wound healing, averting cardiovascular disease, and reducing blood glucose and cholesterol levels (Liang and Liang 2019). Modified starch from pearl millet has excellent potential for utilization in edible coatings/films, composite films, nanoparticle development, fat replacers, enzyme production, thickeners, stabilizers, and many other pharmaceutical and medical applications (Saini et al. 2021). Millet’s bioactive components offer the potential to bridge the fields of industry, preventive healthcare, and nutrition. Their capacity to deliver sustainable solutions for numerous industries while simultaneously improving human well-being.

Limitations

The limitation of the study include innovative extraction methods often requires expensive equipment and materials which can increase production and maintenance costs and are also needed skilled technicians (Castro et al. 2023). In-addition, excessive solvent use, high functional cost and suboptimal extraction yields possess significant challenges in scaling up these innovative techniques. The innovative techniques are facing regulatory challenges, as they might not yet be widely recognized or approved by food safety and regulatory authorities. There might be concerns about residual solvents or other processing agents that could remain in the final product, affecting its safety and regulatory (Sawale et al. 2024).

In theory, for the application of these isolated functional components from millet for functional foods and nutraceutical foods, health-related claims in all forms of food advertising, such as labeling, should be governed by clear and comprehensive regulations. However, a unified regulatory framework for such claims is lacking. The disparities in international food regulations complicate the marketing of functional food products, as noted by Díaz et al. (2020). In American regulations, there are three approved categories for health-related claims: “nutrient content claims,” “structure/function claims,” and “health claims.” Unlike U.S. regulations, Japan approves only four categories for nutrition claims: “rich in,” “source,” “low,” and “does not contain,” each with specified minimum and maximum nutrient limits (Malla et al. 2013). In Europe, functional foods and nutraceuticals lack a specific regulatory framework or statutory definition. However, they must comply with legal requirements based on their content, particularly when making nutrition and health claims, as outlined in Regulation (EC) 1924/2006 ((Díaz et al. 2020). In India, many laws regulate food, but none specifically cover functional foods. The FSSAI Act 2006 needs to be expanded to better regulate India’s functional food and nutraceutical industry (Shyam and Thakur 2023).

Conclusions and future perspectives

Millets are Nutri-cereals and enriched with vital functional nutrients and bioactive composition. The isolation of these components from millets by different extraction techniques promotes efficient utilization of millets. The conventional extraction techniques are time-consuming, non-efficient, and deteriorate quality. However, the application of innovative techniques aids in the efficient isolation of functional components. These isolated components have enormous potential applications in the formulation of different functional foods, nutraceuticals, supplements, and pharmaceuticals, which give particular importance in cereals processing.

The isolation of many other functional components from different millets using different innovative techniques and its utilization are yet to be demonstrated. Innovative approaches seem optimistic and more focused on improving the quality of extracted components. Therefore, in the future, the application of innovative extraction techniques for the isolation of functional components from millets have broad scope due to its advancement over conventional methods. More clinical studies on millet-based functional food are to be performed to confirm their health benefits. Additionally, sustainable millet cultivation, post-harvest processing, and promotion initiatives are essential to address global nutrition concerns and promote a health-conscious culture. For a healthier and more sustainable future, scientific research and industry innovation in this field must have to come together.

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Author contributions

Krantidip R. Pawar: Conceptualization; Visualization; Writing-original draft. Prabhat K. Nema: Conceptualization; Validation; Writing-review & editing; Supervision. Dhiraj Kumar Yadav: Writing-review & editing; Resources; Methodology; Visualization. Sanket Balasaheb Kokane: Writing-review & editing; Software analysis. Vinod T. Atkari: Writing-review & editing; Supervision.

Funding

Not applicable.

Data availability

The authors express their consent to the publication of the data of this article.

Code Availability

All content presented in this article is approved by the authors.

Declarations

Ethics approval

This article does not contain any studies with human or animal subjects.

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All participants provided informed consent before participating in the study.

Consent for publication

All authors agree to publish.

Conflict of interest

The authors declare that they have no conflict of interest.