Effect of four modification methods on adsorption capacities and in vitro hypoglycemic properties of millet bran dietary fibre

Abstract

To improve the adsorption capacities and hypoglycemic properties of millet bran dietary fibre (MBDF), four methods including acrylate-grafting, carboxymethylation, heat assisted with cellulase hydrolysis, and enzymatic hydrolysis combined with acrylate-grafting were used. The results demonstrated that all carboxymethylation, acrylate-grafting, and enzymatic hydrolysis combined with acrylate-grafting improved soluble dietary fibre content, water swelling ability and α-amylase-inhibition activity of MBDF. They also increased oil, cholesterol, sodium cholate, copper ion and nitrite ion adsorption capacities of MBDF. But carboxymethylation, acrylate-grafting and enzymatic hydrolysis combined with acrylate-grafting decreased polyphenol content, glucose-binding ability and glucose dialysis retardation index of MBDF (p < 0.05). The heat assisted with cellulase hydrolysis increased soluble dietary fibre content, polyphenol content, sodium cholate-adsorption capacity, and hypoglycemic properties of MBDF including glucose-binding ability, glucose dialysis retardation index and α-amylase-inhibition activity; but reduced adsorption capacity of MBDF on cholesterol and copper ion (p < 0.05). Changes in structure of MBDF caused by these modification methods were proved by the results of scanning electron microscopy and Fourier-transformed infrared spectroscopy analysis. These results highlight potential applications of these modified MBDFs as ingredients of hypolipidemic and hypoglycemic foods, or scavenger of nitrite and copper ion.