Isomers and homologues of l-glutamic acid 5- n-butyl ester as promoters of sediment formation in raw soy sauce

Abstract

Soy sauce was found to contain promoters of sediment formation at 60°C (1, 2), one of which has previously been identified as l-glutamic acid 5- n-butyl ester (3). Isomers and homologues of l-glutamic acid 5- n-butyl ester ( n-propyl, isopropyl, n-butyl, isobutyl, and sec-butyl esters of l-glutamic acid) were synthesized using 80% (w/w) sulfuric acid as a catalyst and identified by 1H-NMR and the ninhydrin test. The yields of l-glutamic acid 5- n-propyl, isopropyl, n-butyl, isobutyl, and sec-butyl esters from 10 g l-glutamic acid were 25, 101, 72, 130, and 134 μmol, respectively. For maximum sediment formation in 1 ml soy sauce, 1.2, 8.6, 22.0, 22.0, and 26.5 μmol/ml of n-butyl, n-propyl, isobutyl, sec-butyl, and isopropyl esters were respectively required. Sediment-forming activity was not observed with l-glutamic acid and l-glutamic acid 5-methyl, ethyl and tert-butyl esters.