Protection of α-amylase from proteolysis by adsorption to feed components in vitro and in the porcine small intestine

The interactions between digestive enzymes and non-substrate feed components, and the impacts these have on enzyme activity, have rarely been studied. The aim of the present study was to determine the ability of granular wheat starch and whole porcine diets to protect porcine pancreatic α-amylase from proteolysis by trypsin both in vitro and in vivo. Granular wheat starch protected α-amylase from degradation in vitro by adsorbing trypsin and reducing its proteolytic activity. This protection was also found for a complete pig diet and corresponded to undetectable soluble-trypsin activity in the presence of the diet. Pancreatic α-amylase from small intestinal digesta of pigs was active from the duodenum to the ileum (~200–330 U/mL) irrespective of the addition of a protease inhibitor immediately after sampling, most likely due to binding with other food components protecting it from proteolysis. We conclude that non-specific binding between pancreatic digestive enzymes and food components may be competitive with enzyme–substrate complex formation, and therefore important in determining differences in the rate of digestion of macronutrients along the small intestine.