Preparation of thermally stable and digestive enzyme resistant flour directly from Japonica broken rice by combination of steam infusion, enzymatic debranching and heat moisture treatment

Abstract

Through a series of gelatinization, enzymatic debranching and heat moisture treatment, unmilled japonica broken rice was applied to prepare thermally stable and digestive enzyme resistant flour. The optimal conditions of gelatinization temperature, enzyme/substrate ratio, and debranching duration were determined by the three-factor three-level response surface methodology (RSM). Raw flour and products processed in each step were collected to test and compare the hydration ability, reheated solubility, pasting property, starch classification (RDS, SDS, RS) and in vitro digestibility. The results of RSM showed that E/S ratio was the main factor influencing the RS formation, while influence aroused by hydrolysis time and gelatinization temperature were minor. Gelatinization broke down the intermolecular bonds of starch molecules, allowed the hydrogen bonding sites to engage more water, and improved the availability of digestion. However, debranching provided an opportunity for the alignment of short-chain and long-chain amylose molecules. Therefore, RS increased to 42%, and digestibility decreased accordingly. HMT could further enhance the molecular rearrangement, while the RS was increased to as high as 55% and the final product met the low GI criteria.