L-Prolyl-L-leucine Anhydride A Bitter Compound Formed in Aged Sake

Abstract

A cyclic dipeptide with a bitter taste, compound B–1, was isolated from sake and its properties were characterized. Compound B–1 was chromatographically purified by the use of Amberlite XAD–2, silicic acid, Dowex 50–X4 (H type), Amberlite IR–45 (OH type) and silicic acid again, and crystallized from ethanol, From the decomposition point (159~165°C) and the ultraviolet and infrared spectra, the compound was identified as l-prolyl-l-leucine anhydride. The content of this compound in sake samples aged under various conditions was determined by gas chromatography and it was found that the amount of this compound increased with the time of storage of sake. Furthermore, the contribution of the bitter compound to the flavor of sake was evaluated from its content and the threshold taste value.