PRODUCTION OF GAMMA-AMINOBUTYRIC-ACID BY CHEESE STARTERS DURING CHEESE RIPENING

Nine mixed-strain starters were examined for their abilities to produc e gamma-aminobutyric acid. Six commercial starters were found to produ ce gamma-aminobutyric acid in a skim milk culture. The bacterium that produced gamma-aminobutyric acid was isolated from the mixed-strain st arters, 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, gamm a-aminobutyric acid was generated at pH 5.0 but not above pH 5.5. Chee ses were prepared experimentally using strain 01-7 to determine the re lationship between the pH values and the production of gamma-aminobuty ric acid during cheese ripening. gamma-Aminobutyric acid increased lin early in the experimental cheeses as the pH of the cheese decreased. B ased on these results, gamma-aminobutyric acid was concluded to be pro duced by the cheese starters during ripening.