INFLUENCE OF AN INITIAL ADDITION OF LACTIC-ACID ON GROWTH, ACID PRODUCTION AND THEIR COUPLING FOR BATCH CULTURES OF LACTOBACILLUS-HELVETICUS

Growth and production coupling for L. helveticus growing at constant p H on a medium largely supplemented with yeast extract and peptons has been examined as a function of initial lactic acid addition: these con ditions allowed to avoid side effects of cultivation pH and nitrogen s ource deficiency on coupling. Growth of L. helveticus strain milano wa s reduced by half for a free lactic acid concentration of 0.34 g.l(-1) ; both growth and production were fully inhibited for a critical end-p roduct concentration of 83 g.l(-1), despite the fact that lactose was still available. The extent of autolysis 8 h after growth ceased was p ractically independent of initial lactic acid concentration: the same conclusion held for the part played by a growth-associated mechanism i n total acid production. During the slowing down phase of growth, prod uction was non-growth-associated: production rate remained close to it s maximal value, while growth rate declined.