OPTIMIZATION OF CULTURE CONDITIONS FOR Bacillussubtilis RGT2 BACTERIA CAPABLE OF PRODUCING POLYPHENOLS BY RESPONSE SURFACE METHOD

Background: Polyphenols are a group of natural compounds with many important pharmacological activities for human health. Objective: This study was conducted to optimize the culture conditions for Bacillus subtilis RGT2 to produce polyphenols. Research subjects and methods: Bacillus subtilis RGT2 used in the study is an endogenous strain isolated from Houttuynia cordata in Kien Giang province. The response surface method with the Box-Behnken design was used to determine the optimal culture conditions. In the study, four variables were investigated: D-glucose content (5-35 g/L), pH level of culture medium (5-8), culture temperature (30-42°C) and incubation time (12-84 hours). The data were collected and analyzed for variance (ANOVA) Results: The coefficient of determination (R2) and the model with significant interaction between all variables are 98.05% and p<0.0001, respectively. In addition, the test for the lack of fit for the model is also not significant, with p=0.4223. The optimal conditions for D-glucose content, pH level, time and culture temperature were found to be 13.93 g/L, 7.6, 51 hours and 34°C, respectively with predicted values of the polyphenol production of Bacillus subtilis RGT2 was 74.58 mg GAE/mL of extracellular fluid. Using statistically optimized conditions showed that the actual polyphenol content was 75.75±1.44 mg GAE/mL of extracellular fluid. Conclusion: In this study, Bacillus subtilis RGT2 produced the highest polyphenols when cultured in potato D-glucose broth with pH 7.6 at 34oC with the extraction time of 51 hours and 13.93 g/L of D-glucose content.