Kinetics of lactate fermentation and citrate bioconversion by Lactococcus Iactis ssp. Iactis in batch culture

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Abstract
The growth kinetics of Lactococcus lactis ssp. lactis were studied in batch culture in conditions of non‐limiting lactose and the presence of citric acid. The control of pH modified growth and citrate metabolism but did not change the yield of acid formation. At controlled pH the growth rate was unaffected by citrate metabolism. Lactose was transformed to L‐lactate and assay of the metabolic by‐products showed some heterofermentation at the end of the growth of cultures with low growth rates. This heterofermentation was interpreted as a slowing down of glycolysis with activation of both the pyruvate formate lyase (PFL) and the pyruvate dehydrogenase complex (PDHC). Under these conditions the presence of citric acid affected the activity of both the PDHC and the alcohol dehydrogenase (ADH). L‐Lactate remains the major fermentation end‐product and the sole inhibitor of fermentation, this inhibition was greater on growth than on lactic acid production.