Production of exopolysaccharide by Lactobacillus rhamnosus R and analysis of its enzymatic degradation during prolonged fermentation

The potential of Lactobacillus rhamnosus R for producing exopolysaccharide (EPS) when grown on basal minimum medium supplemented with glucose or lacto se was investigated. EPS production by L. rhamnosus R is partially growth a ssociated and about 500 mg of EPS per liter was synthesized with both sugar s. The product yield coefficient (Y-EPS/S) was 3.15 (0.0315 g of EPS [g of lactose](-1)) and 2.88 (0.0288 g of EPS [g of glucose](-1)). It was clearly shown that the amount of EPS produced declined upon prolonged fermentation . Degradation of EPS in fermentation processes was also assessed by measuri ng its molecular weights and viscosities. As these reductions might have a negative effect on the yield and viscosifying properties of EPS, it was ess ential to examine possible causes related to this breakdown. The decrease i n viscosities and molecular weights of EPS withdrawn at different cultivati on times permitted us to suspect the presence of a depolymerizing enzyme In the fermentation medium. Our study on enzymatic production profiles showed a large spectrum of glycohydrolases (alpha-D-glucosidase, beta-D-glucosida se, alpha-D-galactosidase, beta-D-galactosidase, beta-D-glucuronidase, and some traces of alpha-L-rhamnosidase). These enzymes were localized, two of them (alpha-D-glucosidase and beta-D-glucuronidase) were partially purified and characterized. When incubated with EPS, these enzymes were capable of lowering the viscosity of the polymer as well as liberating some reducing s ugars. Upon prolonged incubation (27 h), the loss of viscosity was increase d up to 33%.