Protein-starch interaction plays a key role in controlling starch digestion and postprandial glucose increases for moderately milled quinoa grains

Abstract

Whole grains were reported to exhibit positive effects on management of T2D. However, the components of whole grains are complex. To clarify which factor played a key role in reducing starch digestion and postprandial glucose increase, quinoa grains with different milling time (MT-0s, 20s, 40s, 80s) were used. As the MT increased, starch digested ratio in vitro and postprandial glucose in vivo increased. Different factors contributed to this result were further investigated. For starch itself, damaged starch increased from 6.2% in MT-20s to 9.13% in MT-80s. During in vitro gastrointestinal digestion, a maximum of 13.05 mg/g polyphenols were released from quinoa, which was not able to inhibit the activity of α-amylase and α-glucosidase to reduce starch digestion. Besides, the starch digested ratio increased in MT-0s, 20s and 40s as the amount of added trypsin increased, indicating that protein-starch interaction was important for starch digestion. This was also observed in CLSM images. Spearman correlation analysis confirmed that protein content strongly correlated with starch digested ratio compared with other factors. Our results would provide guidance for food processing industry to produce low GI food products.