Plant proteins mitigate in vitro wheat starch digestibility

Wheat is a major staple food in North America. The rapidly digestible nature of cooked wheat starch is linked to a greater incidence of health issues regarding insulin resistance. Plant proteins and their hydrolysates have shown insulinotropic activity and inhibitory activity against targeted metabolic enzymes, however, their direct effects on the susceptibility of wheat starch to amylolytic hydrolysis have not been systematically investigated. The objective of our study was to determine the in vitro amylolysis of wheat starch in the presence of wheat, corn, soybean, pea and rice proteins in their native, denatured and/or enzymatically hydrolyzed forms by pressure cooking or boiling. Native proteins (except rice) showed no significant effect on the RDS content of protein-starch mixtures. Denatured and/or hydrolyzed plant proteins significantly reduced the RDS content, while this effect could be influenced by the cooking method and protein origin. Confocal laser scanning microscopy and differential scanning calorimetry studies on selected starch-protein mixtures suggest that protein denaturation or protease hydrolysis promotes starch-protein interaction, and thus restricts starch hydration and enzymatic cleavage. Our study suggests the possibility of using this protein-based strategy to formulate low glycemic food products.