Effect of parboiling on decortication yield of millet grains and phenolic acids and in vitro digestibility of selected millet products

Parboiling is a common method used in rice processing to improve milling yield and physicochemical properties. The current study evaluates parboiling as a pre-treatment step in millet decortication and its impact on phenolic profile and in vitro digestibility of two traditional millet products, steam-cooked couscous and porridge, made from pearl (Pennisetum glaucum) and proso (Panicum miliaceum) millets. Parboiling increased decorticated yield of pearl and proso millet by 37% and 28% respectively. It resulted in significant (P < 0.05) rise in free and bound phenolic contents and DPPH (2,2-diphenyl-1- picrylhydrazyl) radical scavenging activity of the millet products. This method significantly (P < 0.05) changed starch digestion fractions of both products thereby reducing expected glycemic index (eGI) while the in vitro protein digestibility of products decreased by 14-17%. Parboiling could be an effective way to improve millet decortication yield as well as produce millet products with higher phenolic acids antioxidant activity and lower GI.