Enhancement of Poly-γ-glutamic Acid Formation and Antioxidant Activity in Cheonggukjang Fermented with Bacillus velezensis CH7P29

초록

This study aimed to isolate Bacillus strains producing poly-gamma-glutamic acid (gamma-PGA), a natural antioxidant biopolymer, from Cheonggukjang, optimize fermentation conditions, improve gamma-PGA production in the food by applying the selected strain, and investigate its potential association with antioxidant activity. Among 157 isolates, Bacillus velezensis CH7P29 demonstrated the highest gamma-PGA production (602.80 +/- 6.55 mu g/mL) and was selected for fermentation. Optimal in vitro conditions for gamma-PGA production were determined as 40 degrees C and 0-2% NaCl. In Cheonggukjang fermentation under optimal conditions, the CH7P29-inoculated group exhibited a marked increase in gamma-PGA content (16.02 mg/g on day 4), which was significantly higher than the uninoculated control (not detected) and reference strain groups (12.25 and 11.38 mg/g, respectively). Simultaneously, its DPPH radical scavenging activity exceeded 60%, and gamma-PGA content strongly correlated with antioxidant activity (R = 0.95). Conversely, total polyphenol content remained stable, indicating that gamma-PGA and microbial metabolites contributed primarily to antioxidant activity. Further analysis supported this by showing that gamma-PGA accounted for 37.40% of the total DPPH radical scavenging activity in the CH7P29-inoculated group at the end of fermentation. These data emphasize that B. velezensis CH7P29 is a promising functional starter culture for enhancing the biofunctional properties of Cheonggukjang and fermented soybean food.

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