Mechanisms of d-Amino Acid Formation During Maturation of Sweet Rice Wine (mirin)

Abstract

Ripened sweet rice wines (mirins) are stored at room temperature for several years to produce a well-balanced sweet flavor. We performed reverse-phase HPLC quantitative analysis of d-amino acids in eight ripened mirins by using derivatization reagents, and investigated the influence of the Maillard reaction on amino acid racemization in mirin during maturation. The relative quantities of d-enantiomers (%d) of Asp, Glu, and Ser in mirins matured for seven years or more were higher than in non-ripened mirins. Based on the calculated correlation coefficient between %D and the amount of Amadori rearrangement products (ARPs) analyzed by LC-MS in ripened mirins for each amino acid, Asp showed a statistically significant strong correlation. Finally, we conducted heating experiments using synthetic ARPs. Our results revealed for the first time that Asp was racemized via ARPs under the influence of pH during mirin maturation.