Masayoshi Sugawara

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

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.

Effect of Raw and Heat-Moisture Treated High-Amylose Corn Starch on Fermentation by the Rat Cecal Bacteria

Resistant starch content of high-amylose corn starch (HAS) was doubled by heat-moisture treatment. Resistant starch content of HAS and heat-moisture treated high-amylose corn starch (HMT-HAS) were 31.8 and 67.3%, respectively, as determined by enzymatic-gravimetric method. Effects of the two types of high-amylose corn starches, HAS and HMT-HAS, on starch fermentation, microflora, pH, short chain fatty acid (SCFA) content and β-glucuronidase activity in the cecal content have been investigated. Rats were given ordinary corn starch (OCS; control), HAS or HMT-HAS at 10% level for 10-13 days. The cecal and colorectal contents weights were larger in HAS and HMT-HAS groups than in the OCS group. The cecal contents weight did not differ between HAS and HMT-HAS groups, while the colorectal contents weight was higher in the HMT-HAS group than in the HAS group. The upper and lower small intestinal and cecal starch contents were significantly higher in the HAS and HMT-HAS groups than in the OCS group, whereas there were no differences between colorectal starch content in group OCS and HAS. Starch excretion in feces was significantly higher in groups HAS and HMT-HAS than in group OCS, the increase in the HMT-HAS group was especially remarkable. The composition of the cecal microflora was not effected by the diet. β-Glucuronidase activities in rats fed HAS or HMT-HAS decreased. SCFA concentration was higher in groups HAS and HMT-HAS than in group OCS, and the cecal pH was lower in groups HAS and HMT-HAS than in group OCS.