The production of functional γ-aminobutyric acid Malaysian soy sauce koji and moromi using the trio of Aspergillus oryzae NSK, Bacillus cereus KBC, and the newly identified Tetragenococcus halophilus KBC in liquid-state fermentation

Abstract

Soy sauce fermentation was improved using the trio of A. oryzae (AO), B. cereus (BC), and the newly identified Tetragenococcus halophilus KBC (TH) in liquid-state fermentation. The effect of molasses (5%, 10%, and 20%) and type of wheat flour (organic-WFO and commercial-WFC) were tested on the koji-moromi formulation for efficient ɣ-aminobutyric acid (GABA) production. The koji-WFO produced higher GABA (1290 mg/L) compared to koji-WFC (13 mg/L). In the initial moromi mixture, 2 × 10−4 mL of BC inoculum containing 5–20% of molasses was added and replaced the same amount with TH in the second trial. Subsequently, the moromi was mixed with 1 × 10−4 mL of BC and TH, which shortened the 60-day moromi process to 30 days. Meanwhile, BC-moromi cultured in 20% molasses generated significantly lower GABA (118 mg/L) production compared to other percentages, however the concentration boosted for TH-moromi in 20% molasses (159 mg/L). The combination of BC-TH percentages (5%–20%) gave significantly lower GABA (83–137 mg/L) than the singular 20% TH treatment. The results promote the use of TH in producing high-GABA soy sauce.