Determination of optimal conditions for γ-aminobutyric acid production by Lactococcus lactis ssp. lactis

The biocompatibility of nine proteinase-negative strains of Lactococcus lactis ssp. lactis with the ability to produce γ-aminobutyric acid (GABA) and four proteinase-positive (Prt+) strains of Lactococcus lactis ssp. cremoris under simulated Cheddar cheese manufacturing conditions resulted in the selection of the Prt+ strain L. lactis ssp. cremoris W62 for mixed cultures with the nine GABA strains. Of the nine mixed cultures inoculated in milk enriched with glutamate, two blends produced between 7.0 and 7.5 mg of GABA per 100 mL of milk. The effect of pH, salt-to-moisture (SM) ratio, and glutamate concentration on the production of GABA was evaluated using cheese slurry models. The production of GABA increased with glutamate concentration but was lower for a SM level of 4.5%. Low pH was the key factor for GABA production. Combining the optimal factors (pH 4.8, 3.0 mg glutamate, SM 3.0%) gave 23 mg GABA per 30 g of cheese curd.