THE EFFECT OF YEAST EXTRACT SUPPLEMENTATION ON THE PRODUCTION OF LACTIC-ACID FROM WHEY PERMEATE BY LACTOBACILLUS-HELVETICUS

Batch and continuous two-stage cultures have been conducted in order to determine the effect of yeast extract (YE) on the homolactic fermentation of whey permeate by Lactobacillus helveticus. Supplementation with YE had a significant effet on lactic acid concentration, volumetric productivity, and substrate conversion, but not on lactic acid yield. Volumetric productivity in the first stage increased from 2 to 9 g l-1 per hour by increasing the YE concentration from 1.5 to 25 g l-1 At the same time conversion improved from 22% to 93% at a dilution rate of 0.2 h-1. The second stage demonstrated the effect of YE at a lower dilution rate (0.14 h-1. A high system conversion (97%) and a high final lactic acid concentration (40 g l-1) were achieved with 10 g l-1 YE. © 1990 Springer-Verlag.