Rihua Xu, Shimin Ma, Yang Wang, Lisha Liu and Pinglan Li*
The exopolysaccharides (EPS) producing ability was evaluated by phenol -sulphuric acid method and the Lactobacillus HCT was the highest yield EPS-producing strain, which was isolated from feces of Bama centenarian in Guangxi of China. It was identified as Lactobacillus paracasei HCT with carbohydrate assimilation profiling and 16S rRNA gene sequencing. L. paracasei HCT was found to be a novel EPS producing strain. Preliminary one factor tests were employed to obtain the favorable conditions for EPS yield and microorganism growth in a chemically defined medium and found that carbon nitrogen ratio (C/N ratio), cultivation time and temperature had the most significant influences. Box–Behnken experimental design and response surface methodology (RSM) were adopted to further study the interactive effects of these three variables on EPS yield and cells growth. The optimal culture conditions for EPS production were: C/N ratio 9.090, cultivation time 60.67 h and temperature 29.2°C. In these conditions, the maximum EPS yield was 39.0736 mg/ml which was 4 times more than the original yield. But the optimal conditions for cell growth were: C/N ratio 8.643, 58.75 h and 31.9°C, logarithm value of viable cell count reached 7.921. These predicted values were also verified by validation experiments.
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