Single step fermentation of starch to l(+) lactic acid by Lactobacillus amylophilus GV6 in SSF using inexpensive nitrogen sources to replace peptone and yeast extract – Optimization by RSM

Wheat bran, an inexpensive underutilized agricultural byproduct, was used as support and substrate for production of l(+) lactic acid by amylolytic Lactobacillus amylophilus GV6 in a single step anaerobic solid state fermentation (SSF). l(+) Lactic acid has wide applications in food, pharmaceuticals, leather, textile industries and in synthesis of biodegradable plastics. L. amylophilus GV6 is found to be efficient than reported amylolytic wild strains at higher substrate concentrations with crude starches in SSF. Substitution of peptone and yeast extract with low cost protein/nitrogen sources, red lentil flour (RL) and bakers yeast (yeast cells, YC) was studied. Central composite rotatable design (CCRD) was employed to determine maximum production of lactic acid at optimum values of the process variables, red lentil flour, yeast cells, CaCO3 and incubation period. A satisfactory fit of the model was realized. Lactic acid production was significantly effected by interactions of yeast cells (YC)-incubation period (IP) and CaCO3-IP. YC, CaCO3 and IP had a linear effect on lactic acid production while RL had no significant linear effect. In square terms RL and CaCO3 were significant. The maximum lactic acid production of 46.3 g/100 g wheat bran having 60 g of starch was obtained at optimized concentration of RL, YC, CaCO3 and IP of 0.6%, 0.9%, 1.3 g (per 10 g wheat bran), 5 days, respectively. Peptone and yeast extract were completely replaced by inexpensive RL and YC in modified MRS medium. There are no reports on utilization of inexpensive nitrogen sources for direct fermentation of starch present in wheat bran to l(+) lactic acid at high substrate concentrations in SSF. L. amylophilus GV6 showed 96% lactic acid yield efficiency (g lactic acid produced/g substrate utilized) and 77.6% lactic acid production efficiency (g lactic acid produced/g substrate taken).