PROTECTIVE EFFECT OF GLUTAMIC ACID AND RELATED COMPOUNDS ON BACTERIAL CELLS SUBJECTED TO FREEZE-DRYING

Abstract

The presence of glutamic acid in a suspending medium prevented remarkably the death of various bacteria (21 species, 26 strains) subjected to the process of freeze-drying. Systematic studies were made of the protective effects of 45 compounds related chemically with glutamic acid, and the following compounds were found to be effective for both Gram-positive and -negative organisms tested: aspartic acid, malic acid, cysteic acid, threonine, pyrrolidone- carboxylic acid, acetylglycine, malonic acid, α-methyl-glutamic acid, N-acetyl- glutamic acid, N-dimethyl-glutamic acid and N-dimethyl-aspartic acid. L- and D-forms of glutamic acid showed equally strong protective activities. Aminomalonic acid, tartoronic acid, α-aminopimelic acid, α-ketoglutaric acid and lysine were effective only for Gram-positive bacteria. The protective effect of glutamic acid and related compounds are considered to be of some physicochemical nature and not of a metabolic one. Chemical structures of the effective compounds seems to be characterized by the presence of a hydrogen-bond generating group (e, g., -NH₂, >NH, -OH or =O) and two acid groups (e. g., α-COOH and γ-COOH).