Direct fermentation of starch to l(+) lactic acid in SSF by Lactobacillus amylophilus GV6 using wheat bran as support and substrate: medium optimization using RSM

Abstract

Wheat bran is an underexploited cheap byproduct obtained during the milling process of wheat. The ability of Lactobacillus amylophilus GV6 to hydrolyze raw starch in wheat bran to produce l(+) lactic acid was studied in solid state fermentation (SSF), opening a novel method for the utilization of these agricultural byproducts. l(+) Lactic acid production by L. amylophilus has been reported by various groups from processed and unprocessed starch but there are no reports available from natural starches in SSF. All amylolytic wild strains reported so far have high yield efficiencies at low substrate concentrations whereas at high substrate concentrations lactic acid production was low. L. amylophilus GV6 showed high yield efficiency at high substrate concentration in SSF. To improve and optimize l(+) lactic acid production by L. amylophilus GV6, response surface methodology (RSM) using central composite rotatable design was adopted in SSF. MINITAB-13 was used for planning the experiments, data analysis, contour diagrams and response optimizations. The optimum media composition was obtained as peptone, 0.9%; yeast extract, 0.88%; tri-ammonium citrate, 0.379%; NaH 2PO 4·2H 2O, 0.769% and Tween-80, 0.30 ml. Under these conditions a maximum of 36 g of lactic acid was produced per 100 g of wheat bran having 54 g of starch. The organism showed 90% yield efficiency based on substrate consumed. Successful optimization of the selected ingredients, led to 100% increase in lactic acid production, i.e. from 18 to 36 g. Due to its high potentiality in conversion of starch to l(+) lactic acid, L. amylophilus GV6 can be exploited industrially for developing a novel technology using inexpensive renewable resources.