Fractionation and characterization of brewers' spent grain protein hydrolysates

Protein hydrolysates with a low and high degree of hydrolysis were enzymatically produced from brewers' spent grain (BSG), the insoluble residue of barley malt resulting from the manufacture of wort in the production of beer. To that end, BSG protein concentrate (BPC), prepared by alkaline extraction of BSG and subsequent acid precipitation, was enzymatically hydrolyzed with Alcalase during both 1.7 and 120 min. Because these hydrolysates contained many different peptides, fractionation of the hydrolysates with graded ammonium sulfate or ethanol precipitation was performed to obtain fractions homogeneous in terms of molecular weight (MW) and hydrophobicity. The emulsifying and foaming capacities of the resultant fractions were determined. MW distributions and surface hydrophobicities of fractions with protein contents exceeding 75% were investigated to determine relationships between technofunctional and physicochemical properties. It was found that the emulsifying and foaming properties are determined by different physicochemical properties of the proteins or peptides. Neither MW nor hydrophobicity alone determines the emulsifying and foaming properties of protein hydrolysates. BSG protein hydrolysates with good emulsifying properties contained less than 40% of fragments with MW exceeding 14 500. Moreover, these hydrolysates had a high surface hydrophobicity. BSG protein hydrolysates with good foaming properties contained less than 10% of material with MW lower than 1700. Hydrolysates with good foaming properties showed low surface hydrophobicities, except for protein hydrolysates with higher levels of protein fragments with MW exceeding 14 500 than of such fragments with MW in a 1700-14 500 range.