INFLUENCE OF PH AND INITIAL LACTATE CONCENTRATION ON THE GROWTH OF LACTOBACILLUS-PLANTARUM

Fermentation yields of Lactobacillus plantarum were measured at controlled pH between 4.0 and 8.0 and initial lactate concentrations of 0-90 g/l. Optimal growth conditions at pH 6.0 without addition of lactate gave a growth rate of 0.57 h-1 and 20 g dry biomass/mol ATP formed (Y(ATP)). The pH variations resulted in a decrease in growth rate but the effect on Y(ATP) was insignificant. The addition of lactate to the medium at 0 h resulted in linear decrease in the growth rate of the culture, and all the metabolic activities were completely inhibited at 110 g/l. The Y(ATP) and biomass/substrate yield (Y(x/s)) remained fairly steady up to 33 g lactate/l, beyond which both yields decreased considerably.