Composition and protein profile analysis of rice protein ingredients

The objective of this study was to investigate the nutrient composition and protein profile of a range of rice protein ingredients containing 32–78% total protein. Rice protein ingredients had significantly (P < 0.05) lower levels of calcium and total essential amino acids compared to selected dairy protein ingredients, i.e., skim milk powder, whey protein isolate and whey protein hydrolysate. Protein profiles of the ingredients were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion-high pressure liquid chromatography (SE-HPLC). Since the dominant rice protein fraction (i.e., glutelin) is extensively aggregated and crosslinked through disulfide bonds, a strong reducing buffer was developed in order to solubilise the rice protein ingredients prior to analysis by SDS-PAGE. Intact rice protein ingredients (n = 3) contained proteins with molecular weight (MW) ranging from ∼11 to >250 kDa, while rice protein hydrolysates (n = 4) were composed mainly of low MW peptides. In parallel, enriched protein fractions were extracted from defatted rice flour based on their solubility and characterised by SDS-PAGE to facilitate the identification of protein bands in the rice protein ingredients. The results of this study underpin the understanding, prediction and control of physicochemical functionality of rice protein ingredients.