LIMITATION OF GROWTH AND LACTIC-ACID PRODUCTION IN BATCH AND CONTINUOUS CULTURES OF LACTOBACILLUS-HELVETICUS

Continuous and batch cultures of Lactobacillus helveticus operated under different conditions were studied with respect to the limitation of growth and lactic acid production by increasing undissociated lactic acid and hydrogen ion concentrations, respectively. In a single-stage continuous culture without pH control a final pH of 3.8 and 65 mM undissociated lactic acid was obtained. In two-stage continuous cultures provided with different growth media and run at different pH values, 65-70 mM free acid was obtained in the second stage. Further batch-culture experiments showed growth limitation at 60-70 mM lactic acid. After growth ceased, production of lactate continued until a lactic acid concentration of about 100 mM was reached; obviously an uncoupling of growth and acid production had occurred. Examining the effect of different concentrations of either lactic acid or hydrochloric acid, added to growing batch cultures of L. helveticus, it was shown that the undissociated lactic acid concentration was responsible for growth limitation and lactic acid production in this organism, whereas the pH value had only an indirect effect.