Production of γ-Aminobutyric Acid by Cheese Starters during Cheese Ripening

Abstract

Nine mixed-strain starters were examined for their abilities to produce γ-aminobutyric acid. Six commercial starters were found to produce γ-aminobutyric acid in a skim milk culture. The bacterium that produced γ-aminobutyric acid was isolated from the mixed-strain starters, identified as citrate-utilizing Lactococcus lactis ssp. lactis (formerly L. lactis ssp. lactis biovar diacetylactis) and designated as strain 01-7. A cell extract showed glutamate decarboxylase activity, for which the optimum pH was 4.7. In pH-controlled cultivation, γ-aminobutyric acid was generated at pH 5.0 but not above pH 5.5. Cheeses were prepared experimentally using strain 01-7 to determine the relationship between the pH values and the production of γ-aminobutyric acid during cheese ripening. γ-Aminobutyric acid increased linearly in the experimental cheeses as the pH of the cheese decreased. Based on these results, γ-aminobutyric acid was concluded to be produced by the cheese starters during ripening.