Isolation, Identification, and Optimization of γ-Aminobutyric Acid (GABA)-Producing <i>Bacillus cereus</i> Strain KBC from a Commercial Soy Sauce <i>moromi</i> in Submerged-Liquid Fermentation

• Main Authors: Wan Abd Al Qadr Imad Wan-Mohtar, Mohamad Nor Azzimi Sohedein, Mohamad Faizal Ibrahim, Safuan Ab Kadir, Ooi Poh Suan, Alan Wong Weng Loen, Soumaya Sassi, Zul Ilham
• Format: Article
• Language: English
• Published: MDPI AG 2020-05-01
• Series: Processes
• Subjects: GABA; fermented food; functional food; non-protein amino acid; soy sauce fermentation
• Online Access: https://www.mdpi.com/2227-9717/8/6/652
• ISSN: 2227-9717

A new high γ-aminobutyric acid (GABA) producing strain of <i>Bacillus cereus</i> was successfully isolated from soy sauce <i>moromi</i>. This <i>B. cereus</i> strain named KBC shared similar morphological characteristics (Gram-positive, rod-shaped) with the reference <i>B. cereus</i>. 16S rRNA sequence of <i>B. cereus</i> KBC was found to be 99% similar with <i>B. cereus</i> strain OPWW1 under phylogenetic tree analysis. <i>B. cereus</i> 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 <i>B. cereus</i> KBC with <i>p</i>-value = 0.0023. GABA production by <i>B. cereus</i> 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 <i>B. cereus</i> KBC isolated from soy sauce <i>moromi</i> is capable of producing a high concentration of GABA together with the optimal fermentation conditions that have been statistically analysed using RSM.