Abstract
Millets are important crops in the semiarid tropics of Asia and Africa (especially in India, Mali, Nigeria, and Niger). Finger millet (Eleusinecoracana L.) is stands out as a Nutri-cereal, gluten free making it a versatile and nutritious choice due to good source of carbohydrate (81.5%), protein (9.8%), fat (1.59 g), dietary fiber (11.5 g), phytochemicals, and essential amino acids and its unparalleled richness of calcium (220-450 mg/100 g) and iron (3-20%) compared to other cereals (rice and wheat). Among, the different processing technique, germination is a simple and traditional technique that can also be employed at the household level, which is used to soften the kernel structure, increase the nutritional composition and to enhance nutrient absorption of finger millet grains. The profusion of phytochemicals, a health-promoting reservoir compound in germinated finger millet significantly amplifies its nutraceutical capacity. It possesses notable health-enhancing attributes, including anti-diabetic effects against type 2 diabetes mellitus, anti-diarrheal properties, antiulcer activity, anti-inflammatory characteristics, antitumor effects specifically against K562 chronic myeloid leukemia, anti-atherosclerogenic effect, as well as antimicrobial and antioxidant properties. In terms of functional characteristics, the germination process significantly improves the ability of the millet flour to absorb water and/or oil, its emulsion capacity and stability, but reduced the bulk density and swelling power. This review mainly focuses on the germinated finger millet's nutritional, functional, phytochemical, and therapeutic properties.Household food processing strategy such as germination can be used for improving the nutritional quality to promote finger millet utilization.
Keywords
Introduction
Millets are small-sized, edible seeds belonging to the family of grasses. A major portion of the Asian diet is made up of cereals, which are good sources of starch, protein and micronutrients but lacking in dietary fiber which are vital to confer health-promoting properties. 1 Millets possess a higher protein, mineral and dietary fiber content balanced with optimum protein quality that can enhance the nutritional security of a substantial portion of the population. 2 Finger millet (Eleusine coracana L.) has traditionally served as a significant staple crop in various regions of Eastern and Central Africa, along with India. Globally, finger millet holds the fourth position in terms of significance among the different types of millets, following sorghum, pearl millet, and foxtail millet. 3 In 2017–2018, millet cultivation in 11.94 lakh hectares yielded 19.85 lakh metric tonnes of finger millet. In India, 64.8% of finger millet is produced in Karnataka, with Maharashtra and Tamil Nadu as the second and third largest producers with respective contributions of 5.4 and 7.1%. In 2023–2024 fingermillet production is 13.86 lakh tonnes 4 which is shown Figure 1.
Production status of finger millet in India.
Finger millet exhibits diverse morphological characteristics. It is a diminutive grain containing a singular seed, and its kernel is classified as an achene rather than a typical caryopsis. The removal of the minuscule seed coat involves rubbing and subsequent soaking in water. The kernel shape may take on an oval, round, or globular form, with sizes ranging from 1 to 1.8 mm. 5 Finger millet is a drought-tolerant crop that grows in saline soils with a pH of 5.0 to 8.2, making it a suitable crop for drylands. 6 It has a well-balanced amino acid profile and exceptional protein quality, rendering it as one of the most nutritious grains.7,8 Finger millet is more nutritious than other cereal grains, but is not widely used. 9 Significant amounts of micronutrients (vitamins and minerals) are present in finger millet, including riboflavin, nicotinic acid, thiamine, calcium, phosphorus and iron. 10 It is also a gluten-free. The therapeutic properties of finger millet stem from the presence of bioactive compounds in the grain with the added advantage of being gluten-free.11,12 However, the presence of anti nutrients in the millet, such as trypsin inhibitors, tannins, phytic acid, and certain phenolic compounds, chelate minerals and interact with proteins to decrease its absorption and limit its food value. 13
Macro and Micro Minerals of Germinated and Non-Germinated Finger Millet.
In food research, diverse approaches are explored to increase the nutritional quality, encompassing methodologies such as processing techniques, biotechnology applications, and nutrient fortification. 14 Conventional techniques such as steeping, germination, and fermentation is employed to enhance the nutritional composition. The process of grain germination is crucial for both practicality and the augmentation of nutritional value. The nutritional significance of germinated millets lies in the enhancement of their nutrient profile through the germination process. During germination, various biochemical changes occur, leading to increased levels of essential nutrients and bioactive compounds. This includes the activation of enzymes, which hydrolyze complex compounds such as starch, proteins, and fats into simpler forms like sugars, amino acids, and fatty acids.15,16
Germination is the most promising technique to decrease anti- nutrients and improve the digestibility of the germinated grains. 17 Germination serves as a cost-effective and efficient methods for modifying the nutritional and functional attributes of millet flours. Additionally, the levels of certain bioactive constituents, including phenolics, flavonoids, and antioxidants, are enhanced through germination, as highlighted in the study by. 18 Finger millet was steeped and allowed to germinate at different temperatures and humidity. For effective germination, optimum moisture, oxygen, suitable temperature and germination time are essential to improve nutritional composition and functional properties of the germinated seeds.19,20 The Image 1 shows germination of finger millet at different time.The present review endeavours a novel and comprehensive analysis of current knowledge on the effect of germination on finger millet. It solely integrates data and information across different dimensions, including a brief analyses of nutritional changes, alterations in functional properties, modification or activation of enzymes and enhancements in therapeutic properties.
Germination of finger millet (eleusinecoracana L.) at different germinated period.
Impact of Germination on Nutritional Composition of Fingermillets
Carbohydrates
Finger millet is notable by its elevated carbohydrate concentration, as indicated by research findings reporting levels of 81.5% in the grain. 21 In a study comprehensively, 10 Gujarat varieties, the carbohydrate content ranges from 71.90–76.38%, 22 place it in line with conventional cereal crops such as rice and wheat. 23 During germination, significant changes occur in its carbohydrate composition. Initially, within 36 h, there is a minor decline in starch levels. Subsequently, between 36 and 48 h, there is a notable surge in sugar levels alongside a decrease in starch levels. Throughout a 96-h germination window, the overall starch content dropped from 71.3% to 35.1%, while maltose escalates from 3.1% to 17.5% and sucrose from 1.8% to 12.8%. The germination process results in a reduction of total carbohydrate content from 76.01% to 74.14% in comparison to non-germinated millets. 24
The variations in carbohydrate composition during germination are further underscored by the increase in reducing sugars from 0.86% to 10.54% and total sugars from 1.70% to 16.10% for a 96-h germination period. Starch content shows an inverse relationship with germination duration, decreasing from an initial 62.83% to 41.19% after 96 h. 25 During early stage of germination carbohydrates used for energy production. 26 These alterations are linked to the function of hydrolytic enzymes, specifically amylases, which disintegrate starch into sugars for the sprouting seed. 27 Several other studies have documented similar patterns, with reducing sugars increasing from 1.44% to 8.36% and total sugars from 1.5% to 16% after four days of germination. 28 The proportion of total reducing sugar to glucose in malted and native millet is decreased as 3:2 and 2:1 respectively, indicating heightened glucose utilization during germination. 29 These modifications in carbohydrate content and composition can significantly influence the nutritional and functional attributes of germinated finger millet. According to researcher the maximum change in sugars and starch content of FM was found after 48 h of germination, because of high amylase activity in 48 and 72 h of germination. 30
Protein and Amino Acids
The Protein in finger millet (FM) is reported to be 7.7 g per 100 g according to USDA data. Grains, when subjected to germination, have enhanced protein levels,31,32 and finger millet exhibits varying outcomes in different research findings. Different studies indicate conflicting results regarding protein content changes during germination. Notably, one research study documented a 29.5% increase in protein content, from 6.1% to 7.9%, after a 96-h sprouting period. 25 Another study noted protein content enhancements ranging between 14% and 40% mibithi 2000. Conversely, contrasting outcomes demonstrated a decline in protein content from 6.04% to 3.41% following 96 h of germination. 33 Nevertheless, inspite of these conflicting results, germination consistently enhances protein digestibility, as evidenced by a 17% rise in in vitro protein digestibility after 48 h of germination at 30 °C. 34 According to Nkhata 35 The changes in protein content during germination accompanied with changes in the amino acid composition. Over a 48-h germination period, aspartic acid exhibited a 7.8% increase, while asparagine saw a reduction of 6.8%, with other amino acids maintaining relative stability. Some amino acids, such as phenylalanine, alanine, and arginine, displayed decreased levels post-germination. These modifications are associated with multiple factors, encompassing the development of new enzymes, generation of fresh amino acids, breakdown of anti-nutritional components,25,36,37 and the equilibrium between protein synthesis and proteolysis. 25 The rise in cysteine, a prevalent enzyme constituent, is especially noteworthy. The purported decline in specific amino acids is believed to stem from the transference of seed nitrogenous substances to the burgeoning embryo. 38 And the consumption of fats and carbohydrates during respiration, potentially leading to anapparent protein content increase due to a decline in dry weight. 37 Table 1 shows amino acid content of germinated finger millet.
Amino Acid Profile of Raw Finger Millet (RFM) and Germinated Finger Millet (GFM).
Source: 11, 39-40.
Fats
Finger millet (FM) exhibits a relatively low fat content, as indicated by the USDA at 1.5 g/100 g. The lipid composition in FM consists of free lipids (2.2%), bound lipids (2.4%), and structural lipids (0.6%). Predominant fatty acids found in FM include oleic acid (51.13 g/100 g), linoleic acid (24.42 g/100 g), palmitic acid (20.25 g/100 g), and linolenicacid (4.07 g/100 g), 41 with unsaturated fatty acids constituting 74.4% and saturated fatty acids 25.6% of the overall fatty acid profile. 42 The process of germination exerts an impact on the fat content of finger millet, yielding varying outcomes as reported in different studies. An African variety showed that a decrease from 3.84 g/100 g to 2.73% post-germination, 32 a decrease in crude fat content of finger millet after 36 h germination was reported by Banusha and Vasantharuba 33 whereas another study noted a decline from 0.57% to 0.41% after 48 h, followed by a rise to 0.85% after 96 h of germination. 25 Another researchers documented a 36.09% reduction in fat content due to increased lipase activity during germination. 15 Ektha 43 documented the fat content in germinated finger millet flour (GFMF) as 2.0–0.2 g/100 g. The variations in fat content during germination are ascribed to diverse factors, including fat oxidation to fatty acids, utilization of fat as an energy reservoir, 44 and metabolic processes prompted by the shift from a dormant to an active seed state. 45 The initial decrease in fat content can prolong the shelf life of germinated millet flour by diminishing rancidity, while the subsequent escalation during prolonged germination may be linked to the consumption of carbohydrates and the substitution of sugars as an energy source. 25
Ash
Raw finger millet has an average ash content of 2.28%. 46 Studies on the effect of germination on ash content demonstrate conflicting findings. Some researchers indicate no significant changes between non-germinated and germinated finger millet. 33 For example, Ekhta 45 identified overall ash contents of 2.8 ± 0.17, 2.7 ± 0.10, for whole raw finger millet flour (WRFMF), germinated finger millet, with no significant variances following 48 h of germination. Conversely, alternative investigations noted a notable decline in ash content throughout germinating, with one documenting a decrease from 2.27% to 1.24% after 96 h. 25 This reduction is ascribed to the consumption of minerals during seed germinating metabolic processes and potential depletion of the bran layer due to friction when eliminating roots and shoots from sprouted grains. These diverse outcomes suggest that the influence of on mineral content might be contingent on factors such as germination duration, processing techniques, and distinct finger millet cultivars. 47
Minerals
Finger millet (FM) is a rich source of minerals, particularly calcium, iron, zinc, and phosphorus. It contains nearly eight times the amount of calcium compared to wheat, 6 with calcium concentrations ranging from 220–450 mg/100 g and iron from 3–20%. 27 While mineral content can vary among different genotype, 48 However, Ambuko 49 reported in his study reflects conflict with other studies, the mineral content of calcium, iron, and zinc were not significantly different among the kenya genotypes. But many of the study reported that, germination has been shown to enhance the mineral content and bioavailability in finger millet.35,45,50
Figure 2 illustrates the changes in the mineral content of both germinated and non-germinated finger millet. During germination, calcium content increases significantly, rising from 225.15 to 280 mg/100 g in study of sharma. 15 This increase is attributed to a decrease in oxalic acid, which acts as a calcium chelating agent, making GFMF a good source of bioavailable calcium. 51 Germination has been reported to increase calcium bioavailability by 23.3%. 52 Phosphorus content in malted finger millet is also high, ranging from 3657.83 to 3930.10 mg/kg in brown finger millet (BFM) and 3871.40 mg/kg in dark brown finger millet (DBFM), with peak levels observed at different malting durations for each variety. 53 Sodium and potassium levels show opposite trends during germination. Sodium content initially increases at 48 h of malting but then decreases (from 510.0-150.0 ppm) significantly, while potassium levels increase from 470.0 to 2295.0 ppm. 26 The quantity of manganese found in the unmalted and malted finger millets varied from 180.50–190.63 mg/kg in the dark brown variety, and 146.73–169.43 mg/kg in the brown variety. In the case of the dark brown variety of food grains, a greater quantity of manganese was observed at 96 h, with no significant difference when compared to the 48 h malt. Conversely, for the brown variety, a higher amount of manganese was observed after 48 h of malting compared to the other malting periods. 53 Zinc bioaccessibility has been reported to decrease in malted finger millet. 54 Iron, zinc, and copper content were adversely affected during germination, with reductions of 63.7%, 16.7%, and 25% respectively after 96hrs of germination. 25 During germination there is no expected biosynthesis and degradation of minerals, these decreases may be due to leaching during soaking and germination stages or utilization by the growing embryo. 53 The changes in mineral content during germination are complex and can be attributed to various factors, including enzymatic hydrolysis of phytate, which can lead to the release of bound minerals like iron, magnesium, phosphorus, sulphur, and zinc. The highly water-soluble nature and single oxidation state of sodium may explain its early release compared to other minerals. 24
Vitamins
Singh 30 reported that finger millets are rich in B vitamins, especially thiamine, but poor in β-carotene (0.01 mg/100 g) compared to other types of millets. According to George 46 the β-carotene and B vitamin content in different varieties of finger millet were increased after germination and also the bioaccesibility were high which ranged from 10% to 16% and 5% to 15% respectively. The variety of finger millet with a brown color had the highest content of total tocopherols (4 mg / 100 g), followed by the variety with a white color. The γ andα-tocopherol isomers are found in finger millet prominently. 55 The ascorbic acid content of finger millet was increased during germination from 9.76 to 17.40 mg/100 g after 96 h of germination. 25 An increase in vitamin C content was observed after malting, as a result of breakdown of starch into glucose by amylases and diastases, wherein the glucose serves as the precursor for vitamin C. 56 And also another study of Saleh 23 reported that thiamine and riboflavin increase during germination. Even though plenty of research studies are available for finger millet, there is a notable lack of studies on the impact of germination on finger millet's vitamin content.
Impact of Germination on Phytochemical Properties of Finger Millets
Total Phenol Content (TPC) and Phytic Acid (PA)
Finger millet comprises diverse phenolic compounds, with soluble extractions ranging from 29.6 FAE/gm (dm) and bound extractions from 2.2 to 11.8 FAE/gm (dm). 57 The phenols in finger millets included ferulic acid and p-coumaric acid, which constitute 64–96 and 50–99% respectively. 11 Proanthocyanins, also known as condensed tannins, are found in various types of finger millets. 58 Processing techniques significantly impact the overall phenolic content (TPC). Germination demonstrates conflicting results, one study reported a decline to 0.023 mg GAE/g, 59 while Pressure boiling or sprouting decreased TPC by 50%, although sprouting enhanced bioavailable phenolics to 67%. 60 Malting for 96 h lessened bound phenolic acids (caffeic by 45%, coumaric by 41%, and ferulic by 48%) while elevating free phenolic acids (gallic, vanillic, coumaric, and ferulic). The decline in bound phenolics during germination is ascribed to esterase activity, whereas the increase in TPC is associated with enzyme activation producing phenolic compounds. 60 These diverse outcomes underscore the necessity for additional investigation to comprehensively grasp how processing impacts the phenolic content of finger millet.
Azeez 61 reported that the raw BFM has a lower phytic acid content than the value reported by Nakarani 22 for selected finger millet genotypes from India. The average amount of phytic acid in raw finger millet was 676.77 mg/100gm, which was decreased to 587.20 mg/100 g after soaking for 12 h, and noted to decrease even further to 238.46 mg / 100 g after 36 h of germination at 37 °C. After germination, concentration of phytic acid in raw millet decreased by 45% after 48 h of germination. 34 Owheruo observed a 23.54% decrease in cream variety of finger millet after 72 h of germination. 32
The impact of germination boosted the activity of innate or native phytase, which can hydrolyse insoluble organic complexes with minerals and may be responsible for the decrease in phytic acid. Phytasehydrolyzesphytate to produce phosphate and myoinositol phosphates, and thereby phytate is reduced by germination.45,48
Trypsin Inhibitors and Tannins
The raw finger millet has a trypsin inhibitor activity of 6.59 TUI/mg. During soaking, should be, trypsin units decrease from 6.37 to 5.70 TUI/mg, and then to 1.91 TUI/mg after 36 h of germination at 37 °C. The decrease in trypsin inhibitor activity in finger millet may be due to modifications rendered to the endosperm and axis of the plant during soaking and germination. 62 Kumar 63 reported a decrease in trypsin inhibitors during germination which was attributed to their conversion into energy sources.
The tannin content has been reported to decrease during different durations of germination. In the non-germinated millets, tannin content ranges from 1350–1700 mg/100gm, and after 24 of hrs germination, there is 50% decrease, and after 36 h, there is 80% decrease in tannin content. 64 Researchers have reported that reduction in tannin content on germination enhances the nutritional composition of millet.17,65 Increased enzymatic activity and polyphenol leaching in soaking water can be the cause of a decrease in tannin during germination. 25
Oxalic Acid
The oxalic acid content in finger millet is decrease after soaking and germination. After soaking for 12 h, the amount of oxalic acid in the millet decreased from 118.43 mg/100 g to 96.15 mg/100 g. At 25 °C, it further reduced to 53.85 mg/100 g following 16 h of germination. The decrease may be due to activity of oxalate oxidase and oxalate decarboxylase. 62 Similar result has reported by Brudzyński and Salamon. 66 Soluble oxalate leaches during germination as result of enzymatic activity, resulting in a decrease in oxalic acid. Since oxalate affects calcium bioavailability, it is important to reduce oxalate levels in finger millet for enhanced mineral bioavailability. 67
Dietary Fiber (DF)
Finger millet contains approximately 22.0% dietary fiber, including non-starch polysaccharides, cellulose, pectin, and lignin. 68 Dietary analysis of ragi revealed high levels of arabinose, xylose, and glucose, with minor amounts of galactose, mannose, and rhamnose. Dharmaraj 41 reported that germinated finger millet had lower fiber content compared to native finger millet, with TDF, IDF, and SDF values of 3.34 ± 0.11, 2.62 ± 0.04, and 0.72 ± 0.05 g/100 g, respectively. During germination, the arabinose to xylose ratio decreased from 1:1 to 1:0.38 at 96 h, indicating arabinoxylan breakdown, which was supported by high xylanase activity at this time point. 69 Roopa and Premavalli 70 reported that dietary fiber has numerous health benefits, including hypoglycemic and hypolipidemic effects, lowering serum cholesterol, preventing cardiovascular diseases like atherosclerosis, and possessing antitoxic and anticancer properties.
Flavonoids
Compared to other millets, finger millet is a good source of flavonoid compounds. which are mostly soluble.71,72 Finger millets specifically contain esterified forms of flavonoids that are different from other millets. 73 The major flavonoids in millets are quercetin, catechin, gallocatechin, epicatechin, and epigallocatechin. Additionally, proanthocyanidins or condensed tannins are found in significant amounts in the grain, with procyanidin B1 and B2 being the major dimmers. 72 Total Flavonoids Content (TFC) in native FM was reported by Hithamani 61 to be 5.54 ± 0.40 mg CE/g, but it dropped to 3.33 ± 0.32 mg CE/g upon sprouting. Conversely, Owheruo observed a significant reduction in TFC in FM germinated for 96 h, from 1.4 to 1.09 mg CE/g in the African variety of finger millet. 32 The native grain's bioaccessible flavonoid content was 1.09 mg/g, or about 20% of the grain's total flavonoid content. When compared to the native sample, sprouted, pressure-cooked, and microwave-heated samples revealed a significantly lower bioaccessible flavonoid content. 61
Impact of Germination on Enzyme Activity of Finger Millet
Carbohydrate Degrading Enzymes
The study on malting of finger millet reported high enzyme activity, especially concerning amylase, in the Indaf-15 variety. The activities of amylase and pullulanase, enzymes involved in starch degradation, were maximum at 72 h of germination. The increase in sucrose content was expected due to the conversion of glucose to sucrose by sucrose synthase, but sucrose content slightly decreased at 96 h due to the rise in sucrase activity. Maltose and maltotriose were observed during germination, originating from the degradation of starch by amylase and pullulanase. Cereals contain low amounts of raffinose series oligosaccharides compared to pulses, as substantiated by the negligible activity of α- galactosidase 69 α-amylase is produced during germination in finger millet, and its production is influenced by the temperature of germination. 74 Reduced germination temperature and extended germination duration leads to a significant build-up of amylase.The study of Gimbi 75 reports that probably three isozymes make up finger millet α-amylase.As the germination time increases from 3 to 6 days at 20 °C and from 5 to 9 days at 15 °C, α-amylase activity is gradually higher, starting at very low levels at 15 and 20 °C. At pH values of about 5.4 and temperatures lower than 70 °C, α-amylase is also found to be fairly stable. The endogenous enzymes, the α- amylase responsible for the breakdown carbohydrates into simple sugars thereby improving digestion of carbohydrates. 76 Beta-amylase activity was observed during germination in finger millet seeds. Beta-amylase in finger millet seeds exhibited a high affinity for starch, amylose, and amylopectin, and a reasonable level of affinity for glycogen. The enzyme was also found to be stable in a pH range of 4.0–10.0 and a temperature range of 30–70 °C. However, the enzyme was irreversibly inactivated by heating to 60 °C and 70 °C, which was often related to aggregation. 77 Table 2 shows a enzymes involved in the germination process.
Enzymes Involved in Germination.
Protein Degrading Enzymes
The study conducted by Patoliya 78 found that protease activity in finger millet was 1.77 mg/g. Germination process of finger millet had the highest protease activity (2.15 mg/g). The decrease in proteolytic enzyme activity during roasting was due to enzyme deactivation. Soaking and germination treatments resulted in a significant increase in free amino acid contents, with germination having higher values than soaking. This is due to the partial hydrolysis of storage proteins by endogenous proteases during the germination. According to Ramana 80 De Novo protease synthesis during germination may be the cause of the increase in protease activity. In the study conducted by Vidyavathi, 79 the highest proteolytic activity was seen on the third day of germination. The proteolytic activity was greatest at pH 2.5 when the inhibitor was used as the substrate and was inhibited by diazoacetylnorleucine methyl ester and Pepstatin.
Peroxidase Activity
Peroxidase activity in finger millet undergoes significant changes during germination. Research shows that this activity can increase up to eightfold during the initial 36 h of germination, followed by a decline, but still remaining four times higher than in dry grains after 144 h. 81 The mean values for peroxidase activity in finger millet are reported as 8.79 (ΔOD.mg-1 protein.min.-1), with values increasing to 12.00 (ΔOD.mg-1 protein.min.-1) during germination treatment. 72 This higher activity in finger millet compared to sorghum, pearl millet, and little millet highlights its unique biochemical profile during germination.
Various factors influence peroxidase activity during finger millet germination. Ethanol and lactic acid treatments have been found to reduce peroxidase activity, with different responses observed among cultivars.82,83 These findings underscore the dynamic nature of peroxidase activity during finger millet germination and its potential role in disease resistance.
Impact of Germination on in vitro Protein Digestibility, Starch Digestibility of Finger Millet
In vitro Starch Digestibility
Starch digestibility is a crucial nutritional aspect of finger millet. When consumed, starch is converted into glucose for energy, and its ease of digestion is categorized into three types: Rapidly Digestible Starch (RDS), Slowly Digestible Starch (SDS), and Resistant Starch (RS). A study by Sharma and Gujral 84 revealed significant changes during germination. Non-germinated finger millet flour had low RDS (12.17% dry basis) but high RS (30.17% dry basis) and SDS (28.23% dry basis). As germination progressed up to 48 h, these proportions changed to low SDS (17.96% dry basis) and RS (20.23% dry basis)but high RDS (21.35% dry basis). 84 The RDS increased while SDS and RS decreased, indicating improved digestibility. During germination of finger millet, starch digestibility increases as starch is hydrolyzed into shorter chain polysaccharides by amylolytic enzymes, leading to higher levels of reducing and nonreducing sugars. 24 The process of soaking and sprouting gradually reduced RS and SDS fractions while increasing RDS in all millet flour types. These findings suggest that germination enhances the overall digestibility of finger millet starch, potentially making its energy more readily available to the body. 84
In-vitro Protein Digestibility
The study focused on the in-vitro protein digestibility (IVPD) of finger millet, revealing that unprocessed flour exhibited an IVPD value of 72.01%. Through the process of soaking and germination, there was an enhancement in IVPD, reaching its peak after 48 h of germination at 83.96%, surpassing other types of millet. 84 This enhancement can be linked to the rise in proteolytic activity, the weakening of protein-starch connections, elimination of protease inhibitors, and an increase in protein solubility. 85 Nevertheless, the inclusion of finger millet flour in waffles resulted in a decline in IVPD due to its substantial tannin content, which obstructs proteolytic enzymes and generates protein-tannin complexes. 86 The germination of finger millet brought about noteworthy reductions in phytic acid (45%), oxalates (29%), and tannins (46%), factors that exhibited a negative correlation with the rise in IVPD. Table 3 and Figure 3 shows aImpact of germination on in vitro Protein Digestibility, Starch Digestibility and Predicted Glycemic Index of Finger milletHejazi 34 proposed that the enhancement in protein digestibility was also a consequence of enhanced plant amylolytic activity, especially α-amylase, which aids in the disintegration of starch granules.
Impact of germination on in vitro protein digestibility, starch digestibility. (IVPD – In Vitro Protein Digestibility, RDS - Rapidly DigestableStarch,SDS - Slowly Digestibility Starch,RS - Resistant starch.).
Impact of Germination on in Vitro Protein Digestibility, Starch Digestibility and Predicted Glycemic Index of Finger Millet.
(SDS, RDS, RS = per cent on dry basis IVPD – In Vitro Protein Digestibility, RDS - Rapidly Digestable Starch, SDS - Slowly Digestable Starch, RS - Resistant starch. PGI – Predicted Glycemic Index).
Source: 84.
Impact of Germination on the Functional Properties of Finger Millet
Bulk Density
Raw finger millet flour had a bulk density of 0.65 g/cm³, while GFMF measured 0.97 g/cm³. 15 This represents a 44.21% decrease in bulk density after germination.
The reduction in bulk density following germination and fermentation can be attributed to the breakdown of complex, dense carbohydrates and proteins into smaller, less bulky molecules. 87 Abioye 36 observed that germination time influences the bulk density of millet flour, with shorter germination periods resulting in higher bulk densities.
Ocheme et al 88 suggested that the decrease in bulk density during germination is likely due to the breakdown of complex compounds such as proteins and starches into smaller constituents.
Water Absorption Capacity (WAC)
Azeez 59 reported that the Water Absorption Capacity (WAC) was increased in GFMF compared to the non germinated millet flour. WAC of raw and germinated millet flour was found to be 3.33 g/g and 4.12 g/g, respectively, rendering an increase in WAC by 33.24% after germination. Water absorption represents the volume occupied by starch after swelling in excess water, which maintains starch integrity in aqueous medium. 15
Higher WAC helps to improve the bulkiness, softness and consistency of products. 89 The WAC is determined by the protein content of the flour, the amount of starch damaged during milling and the presence of non-starch carbohydrates. 90 WAI and OAI increase due to more damaged starch and greater surface area. Damaged starch absorbs more water than regular starch, boosting overall absorption. 91
Water Solubility Index (WSI)
Water Solubility Index (WSI) is an important quality parameter for the development of cereal based drinks. The change in WSI is due to changes in carbohydrates and proteins. Germination decreases amylase content of starch and reducing molecular weight proteins. WSI increases significantly by 15.73% with increase in germination time after 96 h germination period. The increase in WSI may be due to increased sugar content as a result of breakdown of starch. 25 Different finger millet varieties show marked increases in solubility over a 72-h germination period. Axum's solubility rises from 2.70% to 26.83%, Meba's from 3.98% to 26.18%, Tessema's from 3.88% to 30.32%, and Tadesse exhibits the most dramatic change, increasing from 2.68% to 31.01%. 92 This rise in solubility is attributed to starch hydrolysis and increased sugar levels during germination, a finding supported by Kumar, 25 who reported similar increases in WSI with extended germination time.
Swelling Capacity (SC)
Abioye 36 reported that the Swelling Capacity (SC) of raw and germinated millet flour ranged from 1.80 to 1.87%. The extent of flour swelling is influenced by factors such as particle size, flour type, and processing methods. The micellarnetwork'strengh and makeup within the granule can be seen in the increasing strength. The swelling power of starch stands out as a crucial factor to determining the swelling capacity. 93
As germination progressed, swelling power showed a significant decrease. Nefale 94 reported that un-germinated flour had a swelling power of 4.83 g/g, which dropped to its lowest value of 3.17 g/g after 72 h of germination. Similar results noted by Adadeji et al, 87 in their study of germinated flours. They attributed the reduction in swelling power to two factors: amylases breaking down hydrogen atoms, and proteases hydrolyzing compounds into sugars and amino acids.Lower swelling capacity is beneficial for gut food handling, especially in infants, as reported in the study.
Oil Absorption Capacity (OAC)
GFMF had higher OAC than the non-germinated millet, which ranged from 1.38 to 1.45%. High oil absorption capacity plays an important role for boosting the energy density of complementary foods. 36 An increased oil absorption capacity enhances the flavor, taste, and lipophilicity of food products, which may be caused due to protein dissociation and solubilization, thereby exposing non polar components within the protein molecules during germination. 95 Research by Nefale 94 showed that germination affects the oil absorption capacity of finger millet flour. They found that non-germinatedflour had an oil absorption capacity of 163%, which increased to 178% after 72 h of germination.
In another study, Yensaw 92 observed variations in oil absorption capacity among different finger millet varieties. The range was quite wide, with values between 103.33% for non-germinatedflour (0 h) and 173.33% for flour germinated for 72 h. This indicates that both germination time and variety can significantly influence the oil absorption properties of finger millet flour.
A higher oil absorption capacity for germinated millet flour indicates that it could be used to make gluten free, high oil products. The WAC and OAC are useful markers of a the ability of the grain protein to prevent fluid loss when food is being stored.15,96
Water Absorption Index (ABI) and Oil Absorption Index (OAI)
On sixty hrs of germination, the WAI and OAI was found to increase, after which the WAI and OAI were noticed to reduce linearly. The increasing surface area and damaged starch in the millet flour is the factor leading to the rise in WAI and OAI. Because of its increased hygroscopicity compared to native starch, the damaged starch absorbs more water. 91 The study of Saxena 97 states that germination followed by sonication enhances the functional properties of finger millet milk.
Foam Stability and Foam Capacity
The foaming capacity of the millet flour varied from 36.20 to 38.17%. The study showed that the 96 h germinated sample had higher protein content, foaming capacity and foam stability, which were dependent on the levels of protein, lipids, salt, sugars, temperature and pH of the sample. 36 Foaming capacity increased upto 36 h of germination followed by a significant decrease. A similar trend was observed in foam stability and with increase in germination time, the stability of foam was also increased, which might be due to the increased concentration of sugars and salts. 91 A decrease in protein content might be responsible for loss of foaming properties. 98 Siddiqua 89 reported that germination led to surface denaturized protein and reduced the surface tension of molecules, which gave good formability.
Emulsion Capacity (EC) and Emulsion Stability (ES)
According to navyasree 59 EC of native finger millet is 8.43 ± 0.51% to germinated finger millet is 11.40 ± 0.53%. During germination the emulsion capacity (EC) and emulsion stability (ES) was increased in non-germinatedand germinated finger millets ranged from 19.24 to 23.45% and from 15.21 to 21.03, respectively. 15 Siddiqua 89 reported that hydrophobic protein activity increased that tends to increase in EC and ES of both germinated and non-germinated finger millet. The increase in the EC of GF may be due to hydrolysis and partial unfolding of polypeptides. The lipid droplets interact with the hydrophobic portions of the protein chain. Thereby volume to the surface area of protein was made available. 59
Protein Solubility
The protein solubility of raw finger millet was 37.45%. After germination, the protein solubility increased to 66.30%, and paired germination and fermentation increase the protein solubility to 81.84%. 61 Similar increase in PS after germination (10-48 h) has been reported in sorghum (40.25-84.95%). 98 The improvement in protein solubility has been linked to the breakdown of proteins into peptides and free amino acids, which in turn increases the solubility. 98
Pasting Property
When comparing bioprocessed finger millet flour to raw millet flour, there was a notable decrease in pasting viscosities of BFM flours, but the pasting temperature was found to increase from 76.70 to 92.95 °C). The break down viscosity was found to be 332 ± 1.10cP which indicated that the flour has good paste stability and strong shearing resistance.61,98 The bioprocessed finger millet flour samples recorded the decreased pasting viscosities which could be partially explained by protease induced protein hydrolysis and α-amylase mediated starch degradation. 99 Protease and α- amylase activity has been shown to increase rapidly during germination, and this results in the breakdown of basic elements as noticed during fermentation. 100 For thickening of food or for food applications needing high gel strength, the pasting temperature of the bioprocessed finger millet flour samples was higher than raw flour. 101 The native and germinated flours had different pasting times, while the GFMF had the shortest pasting time of 4.93 min. 61
Impact of Germination on Therapeutic Properties of Finger Millets
Antioxidant Activity
Phenolic compounds present in the millets contribute to the antioxidative property of the grains and also improve the shelf life of cereal products. 58 Ferulic and p-coumaric acid are the two main bound phenolic acids that make up, respectively, 64–96 and 50%–99% of the total ferulic and p-coumaric acid content of finger millet grains. 11 The potential antioxidant activity of a substance (DPPH) may be defined by its ability for reduction of free radicals.32,61 The studies indicated that the color of seeds impact the phenolic content and antioxidant activity of finger millet. Both raw and germinated millets have enzymatic antioxidant activity. On comparison of the free radical scavenging activity (DPPH) of non-germinated and germinated millets, a significant increase from 71.34 to 80.0% was noticed. 15 The antioxidant activity of phenolic acids present in the germinated finger millet was lower in comparison with synthetic antioxidants. 102 The ABTS (20-Azinobis-3-ethylbenzthiazoline-6-sulfonic acid) radical cation was used to determine the antioxidant capacity of finger millet. The results showed that the range from 9.78–10.32 µM TE/g for DBFM and BFM was 9.76–10.63 µM TE/g. After 24 h of malting, DBFM's ABTS radical quenching activity significantly (p < 0.05) decreased; this effect remained for 96 h without changing. After 24 h, there was no discernible change in the ABTS radical quenching activity in BFM however, after 48 h, there was an increase that remained for 96 h. The iron-reducing activity of the finger millet malt ranged from 0.7975–0.9798 in DBFM and 0.9199–0.9961 in BFM. For up to 96 h of BFM malt, increased iron-reducing activity was noted with increasing malting time. Within 24 and 48 h of DBFM malting, there was a significant decrease in iron-reducing activity, which increased significantly at 96 h. 103 Flavonoids increase anti-oxidant activity in germinated finger millet by enhancing it from 26.66% to 33.33%, as shown in the study, contributing to improved health benefits. 36
Germination significantly enhances the antioxidant properties of millet grains, particularly finger millet. Studies have shown that germinating rye grains for 6 days at various temperatures increases methanol-extractable phenolic compounds, attributed to the synthesis of hydrolytic enzymes that modify cell-wall structure and produce new bioactive compounds this may be reason for increasing antioxidant activity in finger millet. 104 In finger millet, germination for 72–96 h results in increased antioxidant activity due to higher levels of catechin, epicatehin, and protocatechuic acid. This process activates enzymes involved in antioxidant defense mechanisms, leading to enhanced production of phenolic compounds, flavonoids, tannins, and vitamins C and E. Additionally, germination promotes the synthesis of bioactive peptides and proteins with antioxidant effects, capable of inhibiting lipid oxidation and neutralizing free radicals. The activation of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and peroxidase further contributes to the increased antioxidant capacity of germinated millet grains. These changes collectively result in improved antioxidant and potential antidiabetic properties, making GFMF a promising ingredient for functional foods. 57 The recent study of saxena et al reported that germination after sonication increase the phenolic activity as well as anti oxidant activity of finger millet. 97
Antidiabetic Property
Due to Finger Millet Flour's high concentration of dietary fiber, arabinoxylan, phenolic compounds, and ANFs (tannins, phytic acid), FMF has an advantage over other staples because it prevents starch from being hydrolyzed by enzymes. 105 Kim and White 106 also showed in another study that fats and phenolic compounds adsorbed on the starch surface reduces break down by enzymes, that lowering the starch's glycaemic index. Finger millet have low glycemic index, which causes glucose to be released slowly during digestion thereby lowering the risk of diabetes. 107 Germination increase the calcium and magnesium, Due to its high calcium and magnesium content, studies have shown that finger millet can help with type –II diabetes by regulating blood glucose levels. In addition, the insoluble dietary fibers present in finger millet have laxative properties that help prevent constipation, colon cancer, and heart problems. 70 In comparison to the non-germinatedflours, the progressive germinated millets had a significantly higher predicted Glycemic Index (pGI).
After 48 h of sprouting, the percentageis increases for 30.18% in finger millet. Due to enzyme activity during sprouting led to increased starch hydrolysis and digestibility, which is reason there is an increase in GI. A prolong sprouting period could result in the release of more glucose (more RDS), which would raise the postprandial glycemic response. 84 The germinated finger millet dosa and roti has greater glycemic response in comparison to traditional whole finger millet dosa and roti. The germination process leading to conversion of starch into dextrins and maltose are mainly responsible for the increased glycemic response.Prior studies have isolated the carbohydrates, proteins, enzymes, minerals and secondary plant products such as phenolics from native and germinated finger millet and showed health beneficial effects such as anti-diabetic and anti-inflammatory properties. 108
Anti-Cancer Property
The phytochemicals and antioxidants present in finger millets inhibit excessive cellular oxidation and act as free radical terminators, protecting humans from heart attacks and some forms of cancer. 63 The phenolic components, tannins, and phytate found in millet may have the potential to inhibit the initiation and progression of cancer in multiple tissues. 109 Finger millet contains a wide range of these compounds, which may inhibit excessive cellular oxidation and shield against various cancers that are common in the human population. According to research in breast cancer cells, 110 Ferulicacid may function as chemotherapeutic agent against cancer. Flavonoids possess anti-tumor potential, while saponins possess immunomodulating capabilities, anticarcinogenic qualities, and control over cell division. They also have positive health effects like preventing cancer cell growth and reducing cholesterol. The role of germination in anti-cancer properties of finger millet, still need more studies. Studies have shown that germination of finger millet seeds leads to the release of phenolic compounds, which exhibit antioxidant properties and have the potential to modulate the proliferative potential of breast and colorectal cancer cells. 111
Antimicrobial Property
Germination of finger millet has been shown to enhance its antimicrobial properties, making it a potential natural antibacterial agent. 112 Finger millet is rich in phenolic compounds, flavonoids, and polyphenols, which contribute to its antimicrobial activity. 113 Additionally, germination increases the total phenolic content and antioxidant properties of finger millet, further enhancing its antimicrobial potential. 61 The presence of compounds like tannins, saponins, and cyanide in finger millet also contributes to its antimicrobial effects. 114 The phenolic compounds present in finger millet especially the tannins, may provide protection from fungal infection. The tannins in the outer layer of the grain act as a barrier against fungal infection. Methanol extracts of the seed coat have stronger antifungal and antibacterial properties compared to whole wheat extracts due to their high polyphenol content. 115 Singh 116 provided information on the zone of inhibition rendered by finger millet extracts against various pathogenic microorganisms. The largest inhibition zones were seen against Pseudomonas aeruginosa and Klebsiellapneumoniae. The finger millet extract in ethyl acetate showed inhibitory activity for all microorganisms except Escherichia coli. Rane 112 reported that germinated finger millet seeds have a bactericidal effect on Escherichia coli and can be used to treat infectious diarrhoea. The minimum inhibitory concentration (MIC) for germinated finger millet was 125 mg/ml. More over there is no studies available for how germination affect microbial properties of finger millet.
Other Therapeutic Properties
Children fed the germinated FM diet for six months showed increases in blood ferritin and haemoglobin levels, which suggested potential medical effects. 117 Germinated finger millet promotes increased production of antihypercholesterolemic metabolites (statin 5.24 g/kg and sterol 0.053 g/kg) in a short time (7 days). Germination also improves nutrient availability for Monascus sp. and lowers pH, resulting in higher production of statin and sterol. Additionally, sprouting aids in the degradation of anti-nutrient factors in finger millet grains. 16 Osteoporosis is a “silent disease” which is loss of bone mass. Many times, osteoporosis is not recognized until fractures happen. 118 Increased consumption of naturally occurring calcium through diet helps to prevent bone diseases such as osteoporosis.The FM contain up to 350 mg/100 g of calcium, which is five to ten times more than other cereals.Finger millet is a reasonably good source of the minerals. 119 Finger millet's bioavailability is increased by bioprocessing processes like germination and fermentation. Because finger millet is lactose free and easily digestible, its products can be used to maintain bone mass in growing children as well as to prevent osteoporosis and other bone diseases in adults and the aging population.
Impact of Germination on Sensory Attributes of Finger Millets
The color value of finger millet was studied. One of the most crucial aspects of food quality is color. Food that has undergone undesirable color changes may lose quality and marketing value.DE is a measure of the overall color change. Germination increased the lightness (L) value from Hunter L 70.10 of un-GFMF to Hunter L 72.83 of germination after 72 h. 92 There was no significant difference on the control (un-germinated) and GFMFs after 24 and 48 h, respectively. The lowest DE is found in unblanched germinated finger millets. For blanched germinated finger millet, it increased by nearly 2.5 times, and for powdered form, it increased by 7 times. The amount of browning is indicated by a hue angle value. Hue angles for every type of finger millet were contrasted. Hue angle dropped as it soaked. Hue angle values compared to BGFM were greater than those from a UGFM sample. The sample that was powdered had the lowest hue angle value. 119
The L value decreased for porridge compared to FMF and GFMF 24 h, 48 h, 72 h. A lower L value indicated brightness loss in finger millet grains during cooking. 92 Mandge 116 found similar results on lightness changes in cooked porridge. Browning reaction during oven drying caused darkness in finger millet grains. An increase in germination period led to an increase in the L value. The yellowness (b*) significantly increased due to Maillard reaction and shear forces during cooking, causing pigment discoloration. 92
Wheat dough in biscuits was replaced by NFMF and GFMF. Biscuits with NFMF and GFMF were harder and stickier but less cohesive and springy. Biscuit dough with NFMF and GFMF had disrupted protein matrix. Replacing 40% with NFMF or GFMF made biscuits with good qualities. GFMF biscuits with SSL scored higher in surface characteristics and crumb color. Overall quality improved, considering the nutritional benefits of germinated finger millet. 120
Conclusion
Finger millets are cereal crops that are rich in macro and micronutrients and can grow in a variety of agro-climatic conditions. Different processing techniques are essential for improving the nutritional value of finger millets. Other research findings showed that as the germination period increased, the pH value, ash content, and fat content decreased while the germination percentage, germination loss, total titrable acidity, and protein content increased. The solubility, oil absorption capacity, and WAC of flour samples increased significantly during germination, but bulk density and swelling power significant decreased. As the germination period increased from 0 to 72 h, the calcium and iron contents increased in all finger millet varieties, while the zinc content decreased. In acomparative study between non- germinated and germinated flours, the tannin and phytate content was noticed to decrease in all finger millet varieties at 24, 48, and 72 h of germination. In addition, all varieties showed a significant reduction in the phytate/calcium and phytate/iron molar ratios at 72 h of germination. During germination, enzymes such as amylase, protease, peroxidise, ATPase were actively synthesized and increase the bio availability nutrients. The germination significantly increased the therapeutic properties of finger millet such as anti–diabetic (type 2), anti-microbial, anti-tumerogenic, wound healing effect, antiulcerative effect,etc.still need more research on this properties.Future research on germinated finger millet should focus on optimizing germination processes tailored to specific end products, maximizing nutritional benefits while considering desired functional properties. Investigating combinations of germination with other bioprocessing techniques could lead to more effective reduction of anti-nutritional factors and enhanced overall nutritional quality. Exploration of novel functional foods and nutraceuticals utilizing germinated finger millet, targeting specific health benefits or consumer needs, represents a promising avenue. Additionally, conducting clinical studies to further validate and quantify the health benefits of germinated finger millet consumption in various populations will be crucial. Finally, research into scalable and cost-effective methods for commercial production of germinated finger millet products could increase market availability and consumer acceptance, ultimately realizing the full potential of this nutritious grain.
Footnotes
Abbreviations
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
