Lactic acid production from hemicellulosic hydrolyzate by cells of Lactobacillus bifermentans immobilized in Ca-alginate using response surface methodology

Consumption of hexoses/pentoses and production of lactic acid by Lactobacillus bifermentans were investigated in optimized culture medium and hemicellulosic hydrolyzates. The hydrolyzate used had the following composition (expressed in gL(-1)): xylose 50 +/- 5 gL(-1); glucose 18 +/- 3 gL(-1); arabinose 29 +/- 5 gL(-1). The immobilization experiments were conducted with microbial cells entrapped in calcium alginate beads. The results indicate that maximum concentrations of lactic acid were produced after 54 h of fermentation. All glucose and arabinose in wheat bran hydrolyzate were consumed during fermentation. Only xylose was not completely consumed. The substrate consumption rate was 3.2 gh(-1), 1.9 gh(-1), 1.6 gh(-1) respectively for glucose, arabinose, and xylose. The optimized culture condition gave a lactic acid concentration and metabolic yield of 62.77 gL(-1) and 0.83 gg(-1). These parameters improved to 41.3 gL(-1) and 0.47 gg(-1) respectively, when cell free was used.