Whey fermentation by Lactobacillus delbrueckii subsp. bulgaricus for exopolysaccharide production in continuous culture

An exopolysaccharide (EPS) producing strain of Lactobacillus delbrueckii subsp. bulgaricus isolated from yogurts was grown at dilution rates (D) between 0.06 and 0.8 h−1. Lactose from deproteinized whey was used as the carbon source. Growth conditions were not favorable [biomass yield into ATP equal to 233.55 mmol (g biomass)−1] at dilution rates lower than 0.36 h−1. A significant fraction of the galactose moiety from lactose was metabolized; molar yield of galactose from lactose changed between 0.173 and 0.791 with increasing dilution rates. The process was heterofermentative with highest concentrations of lactic acid (30.7 g L−1), acetic acid (11.7 g L−1) and ethanol (0.96 g L−1) obtained at dilution rates of 0.12, 0.36 and 0.12 h−1, respectively. Maximum EPS concentration (830 mg L−1) was obtained at a dilution rate of 0.36 h−1. The analysis of the experimental data showed that for the strain under study, the specific rate of EPS synthesis was positively related to both the specific ATP production rate and the specific consumption rate of galactose. The highest specific EPS production rate [188 mg (g biomass h)−1] was obtained at a dilution rate of 0.67 h−1.