Reduction in the bitterness of protein hydrolysates by an aminopeptidase from Aspergillus oryzae

Abstract

An aminopeptidase was purified from Proteax, a food-grade commercial enzyme reagent derived from Aspergillus oryzae that showed the highest debittering effect on casein hydrolysates among nine such reagents, and its enzymatic characteristics and debittering activities were investigated. Treatment with the enzyme, identified as leucine aminopeptidase A (LapA), on pepsin-degraded casein and cod protein solutions reduced their bitterness and increased the amount of free hydrophobic amino acids such as leucine, valine, isoleucine, and phenylalanine, as well as arginine, tyrosine, and threonine. These results indicated that LapA preferentially released hydrophobic amino acid residues at the amino terminus of peptides including bitter-tasting peptides and reduced the bitterness of protein hydrolysates.