An economic approach for l-(+) lactic acid fermentation by Lactobacillus amylophilus GV6 using inexpensive carbon and nitrogen sources

Development of cost-effective production medium by applying statistical designs for single-step fermentation of starch (corn flour - CF) to l-(+) lactic acid, using inexpensive nitrogen sources as substitutes for peptone and yeast extract in MRS medium by amylolytic Lactobacillus amylophilus GV6. A two-level Plackett-Burman design was employed for screening various available crude starches (flours) for l-(+) lactic acid production by Lact. amylophilus GV6 using red lentil flour (RL) and bakers yeast cells (YC) as substitutes for commercial peptone and yeast extract in MRS medium in anaerobic submerged fermentation. Of all the tested flours, CF was found to be the most significant. Central composite rotatable design was employed to determine maximum production of l-(+) lactic acid at optimum values of process variables, CF, RL, YC, CaCO₃ and incubation period (IP). minitab analyses showed that lactic acid production was significantly affected by the linear terms CF, RL, CaCO₃ and IP. The interactions of CF-RL, CF-YC, CF-CaCO₃, RL-YC and RL-CaCO₃ and the square terms CF and IP were significant. The maximum lactic acid production of 29 g/37 g of starch present in 50 g of CF was obtained at optimized concentrations of CF 5%, RL 0·7%, YC 0·8%, CaCO₃ 0·8% and IP 2·9 days. Successful application of Plackett-Burman design helped in identifying CF as the best carbon source among the tested flours for l-(+) lactic acid production using inexpensive nitrogen sources. Further optimization of the process variables by response surface methods (RSMs) led to maximum production of lactic acid (29 g lactic acid from 37 g of starch present in 50 g of flour). Lactobacillus amylophilus GV6 showed 78·4% lactic acid production efficiency (g lactic acid produced/g starch taken) and 96% lactic acid yield efficiency (g lactic acid produced/g starch utilized). Information from the present studies provides a better understanding on production of l-(+) lactic acid on fermentation of CF using inexpensive nitrogen sources and on changes in the production as a response from interaction of factors. Use of inexpensive nitrogen sources and starch as substrate in MRS medium for single-step fermentation of lactic acid can become an efficient, economic and viable process. This report is on optimization of inexpensive nitrogen sources completely replacing peptone and yeast extract in single-step submerged fermentation of starch (present in CF) to lactic acid with high production efficiency.