Interaction of brown rice phenolics with starch digestive enzymes and starch-iodine complex: Their effects on rice starch digestion

This study aimed to investigate the interactions of phenolics from three varieties of brown rice with starch digestive enzymes, the starch-iodine complex, and their impact on rice starch digestion. The results indicated that all phenolics markedly inhibited rice starch digestion, with bound phenolics from indica rice showing the most pronounced inhibition. The observation of static fluorescence quenching with a concentration-dependent effect suggested the potential for an interaction between phenolics and starch digestive enzymes. Furthermore, the bound phenolics exhibited enhanced quenching properties in comparison to their corresponding free forms, which is consistent with the starch-iodine binding affinity experiment. The formation of starch-iodine complexes was found to be impeded in the presence of phenolics, which resulted in an alteration of the microstructural arrangement of starch molecules by the phenolics. Moreover, the phenolics resulted in a significant increase in the proportion of resistant starch (RS), accompanied by a concurrent decrease in rapidly digestible starch (RDS). Of these, the effects of indica rice bound phenolics were particularly noteworthy, with a substantial increase in RS content from 7.15% to 24.63%, representing a 2.45-fold increase. The findings highlighted that brown rice phenolics could be an effective means of modulating starch digestibility in starchy foods.