Nutrient distribution, phenolic acid composition, antioxidant and alpha-glucosidase inhibitory potentials of black gram (Vigna mungo L.) and its milled by-products

Black gram belongs to the Leguminosae family. It is one of the less studied legumes, although it is widely used in different parts of the world. Black gram in the form of cotyledon (dhal) is mainly used for the preparation of various food products. During milling of black gram into cotyledon, about 25% of the grain is removed as waste by-products. In the present study, nutrient content, phenolic acid composition, antioxidant activity and α-glucosidase inhibitory properties of total black gram flour and its milled fractions were determined with a view to provide economic importance to these by-products. Protein content in black gram and its fractions ranged from 12 to 42%, while fat content ranged from 0.9 to 3.4%. Germ had the highest content of fat and protein, while seed coat and plumule fractions had the lowest (0.9%). Seed coat had the highest dietary fiber content (78.5%) while cotyledon had the lowest (24.4%). Seed coat, plumule and aleurone layer enriched in seed coat extracts showed a better antioxidant potential compared to other fractions and this may be due to the quantitative and qualitative differences in phenolic acids. Extracts of seed coat, plumule and aleurone layer enriched in seed coat extracts showed good α-glucosidase inhibitory activity. Black gram flour contained phenolic acids like gallic, protocatechuic, gentisic, vanillic, syringic, caffeic and ferulic acids. However, composition and content of these phenolic acids varied in different fractions. Ferulic acid was the major phenolic acid in all the fractions. Protocatechuic acid, ferulic acid, gentisic acid and gallic acid contents in these fractions negatively correlated (P<0.05) to IC₅₀ values of both free radical scavenging and α-glucosidase inhibitory activities indicating their potential antioxidant and antidiabetic properties. As black gram and its fractions are rich in antioxidant compounds and nutrients, they may have potential applications as nutraceuticals and functional food ingredients in various processed foods for the improvement of health benefits.