Extraction, structural characterization and functional properties of protein fractions from millet bran†

To promote the development and high-value application of the millet bran protein from Huangjingu, the Osborne sequential extraction procedure was used to extract protein fractions (albumin, globulin, prolamin and glutelin) from defatted millet bran, and the physicochemical and functional properties of the extracted protein fractions were investigated. The results showed that the yield of albumin, globulin, prolamin and glutelin was 1.22%, 0.98%, 3.25%, and 0.49%, respectively, and their purity was 84.87%, 76.02%, 80.80%, and 56.76%, respectively. Albumin and globulin had lower molecular weights than prolamin and glutelin. The amino acid compositions of the four protein fractions were different. FTIR spectra displayed that β-turns and β-sheets were the principal structures in the four protein fractions; ultraviolet absorption spectra showed that the tertiary structures of the four protein fractions were different, with prolamin having the highest absorbance. The denaturation temperature of the four protein fractions was within the range of 85–95 °C. Prolamin and glutelin showed smaller particle sizes than globulin and albumin. Prolamin exhibited the strongest surface hydrophobicity. pH and temperature could affect the functional characteristics of protein fractions. Albumin exhibited the highest water holding capacity and solubility, while prolamin had the highest oil holding capacity and emulsifying capacity, and globulin displayed the best foaming capacity. These results showed that millet bran protein fractions from Huangjingu have the potential to be applied in the food industry as a functional additive.