Effects of extractable protein hydrolysates, lipids, and polyphenolic compounds from pearl millet (Pennisetum glaucum (L.) R. BR.) whole grain flours on starch digestibility

Abstract

Pearl millet and other minor cereal production is marginalized in the Sahara of Algeria (Tidikelt and Hoggar regions). Their productions in these areas depend on traditional harvesting and processing. Pearl millet seeds are used as animal feed and rarely for human consumption. This work was to assess the starch digestion of pearl millet cultivated in the arid areas of Algeria. The seeds from this cereal could provide broad potential benefits to human health. However, their digestion properties have not been reported. Therefore, in this study, the in-vitro starch digestibility of pearl millet flour and the effect of processing on the expected glycemic index (eGI) were investigated. Grains from six pearl millet samples were chosen from two regions: Tidikelt and Hoggar. Five flours were prepared by dry milling (MF) and different treatments after dry milling such as extraction of phenolic compounds (MF-PP), lipid extraction (MF-L), protein hydrolysate extraction (MF-P) or lipid plus protein hydrolysate extraction (MF-L-P). The flours were then subjected to digestion, and the effects of grain treatments on the in vitro starch digestion were investigated. For all pearl millet samples, the kinetics of in vitro starch digestion displayed first-order model as substrates were digested to different extents; k (kinetic constant), C_∞ (percentage of starch hydrolyzed at infinite time), HI (hydrolysis index) and eGI (expected glycemic index) of the samples were also calculated. Significant increases in C_∞, HI and eGI (P<0.05) of the samples were observed after extraction of proteins or proteins plus lipids from flour. Four flours obtained after lipid extraction and five flours from extraction of phenolic compounds had low glycemic index (<55), with values ranging between 31.36 and 44.97. In contrast, flours obtained from protein hydrolysate extraction or lipids plus protein hydrolysates had the highest glycemic index (>69), with values ranging between 77.50 and 121.44. This study confirmed that some of the processed pearl millet seed flours have acceptable nutritional values suitable for human health and nutrition due to the low glycemic index values.