A new high γ-aminobutyric acid (GABA) producing strain of Bacillus cereus was successfully isolated from soy sauce moromi. This B. cereus strain named KBC shared similar morphological characteristics (Gram-positive, rod-shaped) with the reference B. cereus. 16S rRNA sequence of B. cereus KBC was found to be 99% similar with B. cereus strain OPWW1 under phylogenetic tree analysis. B. cereus KBC cultivated in unoptimized conditions using De Man, Rogosa, Sharpe (MRS) broth was capable of producing 523.74 mg L−1 of GABA within five days of the cultivation period. By using response surface methodology (RSM), pH level, monosodium glutamate (MSG) concentration and temperature were optimized for a high concentration of GABA production. The pH level significantly influenced the GABA production by B. cereus KBC with p-value = 0.0023. GABA production by B. cereus KBC under the optimized condition of pH 7, MSG concentration of 5 g L−1 and temperature of 40 °C resulted in GABA production of 3393.02 mg L−1, which is 6.37-fold higher than under unoptimized conditions. Overall, this study has shown that B. cereus KBC isolated from soy sauce moromi is capable of producing a high concentration of GABA together with the optimal fermentation conditions that have been statistically analysed using RSM.
Evaluation of a Malaysian soy sauce koji strain Aspergillus oryzae NSK for γ-aminobutyric acid (GABA) production using different native sugars