Isolation, screening, and production of poly-γ-glutamic acid by Bacillus sp. KMUTT06 using glucose syrup from cassava starch and monosodium glutamate

Poly-γ-glutamic acid (γ-PGA) is a versatile biopolymer characterized by its non-toxic, water soluble, biodegradable making it suitable for a wide range of application. However, the high cost of production remains a major challenge. This study aimed to isolate Bacillus sp. strains from fermented soybean products for γ-PGA production, evaluate production using glucose syrup and monosodium glutamate (MSG), and assess antioxidant activity. Seven isolates of Bacillus sp. were obtained from fermented soybean samples. The isolate KMUTT06 showed that 99.93% similarity to B. tequilensis KCTC13622T, B. inaquosorum KCTC13429T, B. cabrialesii TE3T and B. cabrialesii TSO23T and exhibited the highest γ-PGA production at 1.116 mg/ml, with highest relative viscosity. Using 2.5% (w/v) glucose syrup concentration (w/v) showed that highest of γ-PGA (16.546 ± 2.988 mg/mL) compared to 2.0% (w/v) dextrose and 2% (w/v) MSG produced the highest of γ-PGA (2.589 ± 0.328 mg/mL) compared to L-glutamic acid. Antioxidant activity of γ-PGA produced by Bacillus sp. KMUTT06 had IC50 values of 0.650 ± 0.022 mg/mL (DPPH), 3.050 ± 0.148 mg/mL (ABTS), and a FRAP value of 8.806 ± 0.358 μmol Fe2+/g. In conclusion, Bacillus sp. KMUTT06 may be regarded as a candidate strain for γ-PGA production, demonstrating that glucose syrup and MSG can be used instead of dextrose and L-glutamic acid respectively, for producing γ-PGA with discernible antioxidant activity, further study needed suggesting its potential for various functional industrial applications.