Effect of stirring on growth and phosphopolysaccharide production by Lactobacillus helveticus ATCC 15807 in milk

The exopolysaccharide production by Lactobacillus helveticus ATCC 15807 in milk fermentations was studied in a 60 h batch culture. Maximum yields of e xopolysaccharide were detected at the beginning of stationary phase (399.4 mg/l) in stirred cultures and at a late exponential growth phase (318 mg/l) in non-stirred cultures. The slime material contained phosphorus and carbo hydrates. Glucose and galactose were the main monomers found. The phosphoru s:carbohydrate and glucose:galactose ratio was dependent on the fermentatio n time as well as on the culture conditions. The molecular weight was estim ated to be up to 10(6) in both assays. The viscosity of the cultures was no t related to the amount of exopolysaccharide produced since no ropiness was developed by stirred cultures. Lactic acid was produced throughout ferment ation despite the reduction in cell viability, remaining about 20% lactose in the culture medium after 60 h of incubation.