Chiang Mai Journal of Science

 The production efficacy of L-lactic acid production by Lactobacillus salivarius L105 was improved by statistical optimization. Plackett-Burman design was used to screen for the most influencing factors effect on L-lactic acid production. Among eight nutritional parameters including glucose, beef extract, yeast extract, sodium acetate, trisodium phosphate, ammonium citrate, magnesium sulfate and manganese sulfate, yeast extract and trisodium phosphate were found to be the most significant effective factors (p<0.01) which were further optimized using central composite design (CCD) and response surface plot. A second order polynomial regression model estimated a maximal lactic acid production of 11.09 g/l whereby the levels of yeast extract and trisodium phosphate were 22.10 g and 11.09 g, respectively. The experimental value of 12.0 g/l lactic acid with the productivity of 0.63 g/l/h was achieved after cultivation in the optimized medium. Cultivation L. salivarious L105 using the optimized medium in 2.5-L jar fermenter under the controlled pH 6.5 at 37°C without aeration gave higher L-lactic acid approximately 1.5 times. L. salivarious L105 showed the osmotolerant characteristic at the high concentration of sugar up to 200 g/l. However, the improvement strategies i.e. medium composition, fermentation operation and bacterial strain improvement is necessary for achieving the higher productivity.