Immobilization of Lactobacillus salivarius ATCC 11741 on loofa sponge coated with chitosan for lactic acid fermentation

Abstract

Lactic acid (LA) fermentation by Lactobacillus salivarius ATCC 11741 immobilized on loofa sponge (LS) was evaluated. To increase the surface area of LS for cell immobilization, H2O2 and chitosan were introduced as surface modifying reagents. Four chitosan of different molecular weight were separately coated on LS. All experiments were conducted in shaking flask mode at 100 rpm rotating speed and 37 degrees with 5% CaCO3 as a pH regulating agent. The effects of initial glucose concentration were investigated in the range of 20-100 g L-1 on LA fermentation by free cells. The results indicate that the maximum concentration of LA was produced with 50 g L-1 glucose concentration. The immobilized cell system produced 1.5 times higher concentration than free cells for 24 h of fermentation. Moreover, immobilized cells can shorten the fermentation time by 2 fold compared with free cells at the same level of LA concentration. At 1% w/v chitosan in 2% v/v acetic acid, Yp/s and productivities of various molecular weight of chitosan were insignificantly different. Repeated batch fermentations showed 5 effective recycles with Yp/s and productivity in the range of 0.55-0.85 and 0.90-1.20 g L-1 h-1, respectively. It is evident that immobilization of L. salivarius onto LS permits reuse of the system under these fermentation conditions. Scanning electron micrographs indicated that there were more intact cells on the chitosan-treated LS than on the untreated LS, thus confirming the effectiveness of the LS-chitosan combination when being utilized as a promising immobilization carrier for LA fermentation.