Whey and Pea Protein Fortification of Rice Starches: Effects on Protein and Starch Digestibility and Starch Pasting Properties

Rice is rich in starch but low in protein. In countries where rice is the staple food, people are at high risk of protein deficiency. Legumes (such as pea) and milk are an important part of the diet in many developing and developed countries, respectively. For this reason, pea protein isolate (PPI) and whey protein concentrate (WPC) are incorporated into basmati (≈20–25% amylose) and glutinous (≈0–3% amylose) starches to test the effect of protein incorporation on the pasting properties of rice starch, and on starch and protein digestibility. Increasing protein incorporation reduced the peak, breakdown, and final viscosities. The effect is more pronounced for basmati mixtures compared to glutinous mixtures. For starch digestibility, basmati starch mixtures exhibited an increasing trend in the amount of glucose released over 120 min, whereas glutinous starch mixtures show a decrease in the amount of glucose released after 60 min. In addition, samples with the same % protein incorporation (PPI and WPC) shows similar trend in terms of amount of glucose released at each time point. The amylose content appears to have an effect on starch digestibility over time. For pea and whey protein digestibility, basmati starch samples exhibited lower digestion after 120 min compared with glutinous starch samples. The starch amylose content appears to have an impact on protein digestibility. This provides a way of fortifying rice starch with proteins, in which the proteins are effectively digested without significantly increasing blood glucose levels.