Content of Free D-Ala and D-Glu in Traditional Asian Fermented Seasonings

Free D-amino acids have increasingly attracted attention due to their physiological roles and pathological effects on animals, including humans. In this study, using a chiral high-performance liquid chromatography system, we determined free D-amino acids, particularly D-Ala and D-Glu, in traditional seasonings of four soy sauces, three misos, and four fish sauces that are commonly used in Asian cuisine. Examination of the average contents of the free D-amino acids in all the samples revealed that the content of D-Ala was 3.6 times higher than that of free D-Glu, while the average content of free L-Ala was lower (0.8 times) than that of free L-Glu. The average content of free L-Ala was significantly higher in the soy sauces (53 mu mol/g sample) and fish sauces (53 mu mol/g sample) than in the misos (14 mu mol/g sample), whereas the average content of free D-Ala was almost equal among the soy sauces, misos, and fish sauces (0.25, 0.29, and 0.23 mu mol/g sample, respectively). Taken together, neither free D-Ala nor D-Glu content showed a correlation with its free L-form in the samples, suggesting that the D-enantiomers are not necessarily produced by the same factors as those for the L-enantiomers, which originate from raw materials. Thus, factors specific to the production process of the fermented seasonings appear to play a significant role in their enantiomer content.