Impact of processing on the phenolic profiles of small millets: Evaluation of their antioxidant and enzyme inhibitory properties associated with hyperglycemia

The effects of germination, steaming and microwave treatments of whole grain millets (barnyard, foxtail and proso) on their phenolic composition, antioxidant activities and inhibitory properties against α-amylase and α-glucosidase were investigated. Compositional analysis of phenolics by HPLC revealed that vanillic and ferulic acids were the principal phenolic acids and kaempferol was the predominant flavonoid found in raw millets. Different processing treatments brought about relevant changes in the composition and content of certain phenolic acids and flavonoids in processed millets. Phenolic extracts of raw and processed millets exhibited multiple antioxidant activities and are also potent inhibitors of α-amylase and α-glucosidase. In general, germinated millets showed highest phenolic content as well as superior antioxidant and enzyme inhibitory activities. These results suggest that germinated millet grains are potential source of phenolic antioxidants and also great sources of strong natural inhibitors for α-amylase and α-glucosidase.