Optimizing l-(+)-lactic acid production by thermophile Lactobacillus plantarum As.1.3 using alternative nitrogen sources with response surface method

The effects of five alternative nitrogen sources, namely, malt sprout (MS), corn steep liquor (CSL), NH4Cl, NH4NO3 and diamine citrate (DC) were investigated on the l-(+)-lactic acid (LA) production by thermophile Lactobacillus plantarum As.1.3. Through the statistical analysis of the results by three steps of response surface methodology (RSM) design, MS and CSL were found to have significant effects on the LA production and their optimal concentrations in the medium should be 16.0 g/L and 12.0 g/L, respectively. The verification of the optimized medium showed that the maximum specific growth rate (μm) was 1.09 h−1, the cell yield coefficient (YX/S) and the l-(+)-lactic acid yield coefficient (YP/S) were 0.233 (OD620/g) and 0.98 (g/g), and the maximum volumetric productivity and the average volumetric productivity were 13.0 g/L h and 3.20 g/L h, respectively. The results indicate that the LA production can also be enhanced with the inexpensive nitrogen source alternatives.