CONTINUOUS PRODUCTION OF LACTIC-ACID FROM WHEY PERMEATE BY LACTOBACILLUS-HELVETICUS IN A CELL-RECYCLE REACTOR

The production of lactic acid in a cell-recycle reactor has been investigated. Studies were conducted with Lactobacillus helveticus on a supplemented whey permeate medium. At 42-degrees-C and pH 5.5, the biomass was kept constant at 21.3 +/- 2.7 g l-1. The volumetric lactic acid productivity was approximately doubled from 7.8 to 15.8 g l-1 h-1 by increasing the dilution rate from 0.18 to 1.05 h-1. At the same time, the L(+)-lactate fraction increased from approximately 60% to 70%. Using this recycled system, the volumetric lactic acid productivity was about twice as much as with a nonrecycled system. At a temperature of 45-degrees-C, the performance of the system was significantly lower than at 42-degrees-C. Replacing 60% of the yeast extract by skim milk the decreased productivity by only 25%. Therefore a replacement of yeast extract by skim milk could be economically interesting.