We constructed carboxypeptidase O deficient strains(⊿
ocpO)from a koji mold, the
Aspergillus oryzae industrial strain, and examined their brewing characteristics. Acid carboxypeptidase(ACP)activities of the rice-koji prepared with ⊿
ocpO strains were significantly reduced to approximately 35% of that of the wild type parent strain, while other important enzyme activities,(glucose forming activity, α-amylase, and acid protease)were almost identical. Sake brewed using the ⊿
ocpO strains had almost the same general analytical values as that produced with the parent strain with the exception of a slightly lower amino acidity. All amino acids were present at lower concentrations in sake using the ⊿
ocpO strains except for L-arginine, which was significantly increased. The ACP substrate specificity of rice koji differed between the ⊿
ocpO and parent strain, which likely explain the observed increase in L-arginine. The finding that the amino acidity was only slightly lower in sake brewed with ⊿
ocpO strains despite significant decreases in the ACP activity of the rice koji is likely caused by the functions of the other ACP isozymes and enzymes to produce amino acids in the sake mash. Finally, a taste sensor of sake brewed with the ⊿
ocpO strains suggested that carboxypeptidase O affects the taste balance of the sake.
View full abstract