CONTINUOUS PRODUCTION OF LACTIC-ACID FROM WHEY PERMEATE BY LACTOBACILLUS-HELVETICUS IN 2 CHEMOSTATS IN SERIES

The effect of dilution rate on the production of lactic acid from whey permeate by Lactobacillus helveticus has been investigated. In the first chemostat of a two-stage system, total conversion (98.1%) and maximum lactic acid concentration (43.7 g l-1) were obtained at a dilution rate (DItot) of 0.06 h-1. Maximum volumetric productivities of lactic acid (8.27 g l-1 h-1) and biomass (1.90 g l-1 h-1) occurred at DItot of 0.40 h-1. The fraction of l-lactate in the product was found to increase with dilution rate and reached a maximum of 66% at the same dilution rate. The maximum specific growth rate (μmax) on this medium was 0.7 h-1. A YATP (max) value of 22.4 g dry weight (mol ATP)-1 and a maintenance coefficient of 8.0 mmol ATP (g dry weight h)-1 were determined. The second stage, in series with the first, confirmed these results and further showed that the total residence time could be reduced by 50%, compared with a single chemostat for the same nearly complete level of substrate conversion. © 1990.