Pressure measurement to evaluate ethanol or lactic acid production during glucose fermentation by yeast or heterofermentative bacteria in pure and mixed culture

A rapid and simple technique to follow CO2 release during fermentation of g lucose by heterofermentative bacteria or yeasts was used in order to evalua te ethanol and lactate production in pure and mixed cultures of yeast and b acteria. In pure cultures, good correlations were found between gas pressur e variations (AP) and ethanol or lactate production by yeasts or heteroferm entative bacteria, and ratios between AP and ethanol or lactate produced co uld be established. In mixed cultures, ratios between maximal AP and total amount of glucose consumed were determined. It was thus possible to evaluat e the amount of glucose that was consumed by each strain and then deduce th e bacterial lactate production. Good results were obtained for mixed cultur es of yeast and homofermentative bacteria. This technique may be useful to evaluate the activity of strains in mixed cultures of yeast and lactic acid bacteria.