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 pH on a medium largely supplemented with yeast extract and peptons has been examined as a function of initial lactic acid addition: these conditions allowed to avoid side effects of cultivation pH and nitrogen source deficiency on coupling. Growth of L. helveticus strain milano was 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-product concentration of 83 g.l(-1), despite the fact that lactose was still available. The extent of autolysis 8 h after growth ceased was practically independent of initial lactic acid concentration: the same conclusion held for the part played by a growth-associated mechanism in total acid production. During the slowing down phase of growth, production was non-growth-associated: production rate remained close to its maximal value, while growth rate declined.