Metabolic flux in glucose/citrate co-fermentation by lactic acid bacteria as measured by isotopic ratio analysis

The flux of carbon into lactic acid, diacetyl and acetoin during the co-met abolism of glucose and citrate by Lactococcus lactis subsp. lactis biovar. diacetylactis has been determined using natural abundance isotopic ratio an alysis. During fermentation in the conditions used (glucose, 27.8 mM; citri c acid, 13.9 mM; initial pH 6.2-6.4, anaerobic) it is shown that. approxima tely 65% of the carbon source used for the aroma compounds is derived from the carbohydrate. Equally, citrate contributes approximately 30% of the car bon recovered in lactic acid. Thus, there is no evidence for a metabolic se paration of the catabolism of these two carbon sources. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.