Various physicochemical factors have been suggested to explain differential rates of digestion of food starches. At the food macromolecular level, components such as lipids, proteins and fiber have been shown to influence starch digestibility. Our laboratory has identified that a protein web-like structure formed in sorghum foods retards starch digestion and is finding ways to recreate this effect in other foods. Understanding such a potential protein method of moderating starch digestion rate may lead to development of slowly digesting starchy foods that will fit future demands for healthier starchy foods. The purpose of the present study was to investigate whether such protein-starch associated slowly digesting complexes exist in other important cereal foods such as corn, wheat and rice. Sample flours (on equal starch basis) cooked for 20 min at 100癈 were subjected to porcine pancreatic alpha-amylase digestion at 37癈 over a period of 240 min. Digestions were stopped at desired time intervals and reducing sugars (maltose) were determined by the DNS assay method. Digested samples were also observed by light microscopy after staining starch with iodine or periodic acid/Schiff stain and proteins with Gelcode Blue Stain Reagent. Results indicated that even though the initial rate of digestion of the cereal samples were similar, moderate differences were perceived at longer digestion times (>120 min). Microscopic observation showed protein network associated dense starch structures that persisted through longer digestion time intervals suggesting much slower digestion than free starch entities.
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