Effect of raw and heat-moisture-treated high-amylose corn starches on the process of digestion in the rat digestive tract

Abstract

High-amylose corn starch (HAS) is widely known as a resistant starch foodstuff. We developed heat-moisture-treated high-amylose corn starch (HMT-HAS) that was more resistant to enzymatic hydrolysis. Resistant starch contents of HAS and HMT-HAS using the enzymatic-gravimetric method were found to be 30% and 65% respectively. Rats were given 10% ordinary corn starch (CS), HAS or HMT-HAS by meal feeding for 10 days. The caecum contents increased and the caecal pH was lower after their diets were supplemented with HAS and HMT-HAS. Starch contents increased in the upper and the lower small intestine with HAS and HMT-HAS. Caecal starch with HAS and HMT-HAS was more than that with CS. Particularly, caecal starch with HMT-HAS was seven times more than that with HAS. There were no differences in starch content in the large bowel between CS and HAS, but the content increased with HMT-HAS. These results suggested that HAS and HMT-HAS were resistant to digestion and absorption in the small intestine, and any indigestible starches reached the caecum. In the caecum, HAS was hydrolysed almost completely by intestinal bacteria; however, some HMT-HAS escaped bacterial hydrolysis. This escaped HMT-HAS reached the large bowel and was excreted in the faeces.