Effect of mild heat-moisture treatment for harvested raw paddy rice on physicochemical properties and in vitro starch digestibility of cooked rice

In this study, heat-moisture treatment (HMT) at 60 °C and 65 °C for 12 h and 18 h was applied to harvested raw paddy rice (Oryza sativa L. cv. Toyomeki), and changes in the quality characteristics and starch hydrolysis during simulated gastrointestinal digestion were investigated. The surface color of the treated rice grains was mainly caused by the period of HMT rather than the heating temperature. HMT at mild temperatures caused a minor change with no significant effect in the total starch content of the treated rice, as well as the moisture content and firmness of the cooked rice (P > 0.05). However, the resistant starch content increased with increasing HMT temperature and time, and a significant difference was found between the control and the treated rice subjected at 65 °C. The mild HMT also promoted the reduction trend of starch hydrolysis for the intact cooked rice grain, which could have health benefits. Thus, the mild HMT of raw paddy rice could be regarded as a profitable technique modifying the digestibility of cooked rice but maintaining rice sensory characteristics.