Amylose content modulates maize starch hydrolysis, rheology, and microstructure during simulated gastrointestinal digestion

In this study, the microstructure, rheology, and starch hydrolysis of cooked normal (NAM) and high (HAM) amylose maize starch solutions with various dry matter contents (10, 30 and 50 wt %) were compared before and during simulated gastrointestinal digestion. Prior to digestion, increased rheology (modulus and shear viscosity) and more compact gel network structure were observed for both the NAM and HAM with increasing dry matter content. As compared to the NAM, the HAM with the same dry matter content (50 wt%) showed higher rheology and denser gel structure with remarkable aggregation of relatively intact starch granules after cooking. The extent of starch hydrolysis was similar (similar to 10%) between the two starch systems at the gastric digestion phase, whereas it was significantly lower for the HAM in relation to that for the NAM at the intestinal digestion phase. At the end of the GIT digestion, the in vitro digestibility was about 81% and 90% for the HAM and NAM, respectively. The starch hydrolysis was strongly supported by the rheology and microstructure of the starch digesta. Due to the dilution of digestive fluids and starch hydrolysis, the rheology was both remarkably decreased, but the HAM showed significantly higher shear viscosity than the NAM at each digestion phase due to its greater retention of relatively intact starch granules that would cause higher resistance toward shearing. The results indicate that the amylose content was crucial for modulating starch hydrolysis by forming denser gel structure and increasing digesta rheology that would retard the access of digestive enzymes to the starch granules during digestion.