초록
Clostridium sp. BS-1 produces hexanoic acid as a metabolite using galactitol and enhanced hexanoic acid production was obtained by in situ extractive fermentation with Clostridium sp. BS-1 under an optimized medium composition. For medium optimization, five ingredients were selected as variables, and among them yeast extract, tryptone, and sodium butyrate were selected as significant variables according to a fractional factorial experimental design, a steepest ascent experimental design, and a Box-Behnken experimental design. The optimized medium had the following compositions in modified Clostridium acetobutyricum (mCAB) medium: 15.5gL<SUP>-1</SUP> of yeast extract, 10.13gL<SUP>-1</SUP> of tryptone, 0.04gL<SUP>-1</SUP> of FeSO<SUB>4</SUB>.7H<SUB>2</SUB>O, 0.85gL<SUP>-1</SUP> of sodium acetate, and 6.47gL<SUP>-1</SUP> of sodium butyrate. The predicted concentration of hexanoic acid with the optimized medium was 6.98gL<SUP>-1</SUP>, and this was validated experimentally by producing 6.96gL<SUP>-1</SUP> of hexanoic acid with Clostridium sp. BS-1 under the optimized conditions. In situ extractive fermentation for hexanoic acid removal was then applied in a batch culture system with the optimized medium and 10% (v/v) alamine 336 in oleyl alcohol as an extractive solvent. The pH of the culture in the extractive fermentation was maintained at 5.4-5.6 by an acid balance between production and retrieval by extraction. During a 16 day culture, the hexanoic acid concentration in the solvent increased to 32gL<SUP>-1</SUP> while it was maintained in a range of 1-2gL<SUP>-1</SUP> in the medium. The maximum rate of hexanoic acid production was 0.34gL<SUP>-1</SUP>h<SUP>-1</SUP> in in situ extractive fermentation.