Principal component analysis of the relationship between the D-amino acid concentrations and the taste of the sake.

We performed sensory evaluations on 141 bottles of sake and analyzed the relationship between the D-amino acid concentrations, and the taste of the sake using principal component analysis, which yielded seven principal components (PC1-7) that explained 100 % of the total variance in the data. PC1, which explains 33.6 % of the total variance, correlates most positively with strong taste and most negatively with balanced tastes. PC2, which explains 54.4 % of the total variance, correlates most positively with a sweet taste and most negatively with bitter and sour tastes. Sakes brewed with "Kimoto yeast starter" and "Yamahaimoto" had high scores for PC1 and PC2, and had strong taste in comparison with sakes brewed with "Sokujo-moto". When present at concentrations below 50 µM, D-Ala did not affect the PC1 score, but all the sakes showed a high PC1 score, when the D-Ala was above 100 µM. Similar observations were found for the D-Asp and D-Glu concentrations with regard to PC1, and the threshold concentrations of D-Asp and D-Glu that affected the taste were 33.8 and 33.3 µM, respectively. Certain bacteria present in sake, especially lactic acid bacteria, produce D-Ala, D-Asp and D-Glu during storage, and these D-amino acids increased the PC1 score and produced a strong taste (Nojun). When D- and L-Ala were added to the sakes, the value for the umami taste in the sensory evaluation increased, with the effect of D-Ala being much stronger than that of L-Ala. The addition of 50-5,000 µM DL-Ala did not effect on the aroma of the sakes at all.