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 glucose by heterofermentative bacteria or yeasts was used in order to evaluate ethanol and lactate production in pure and mixed cultures of yeast and bacteria. In pure cultures, good correlations were found between gas pressure variations (deltaP) and ethanol or lactate production by yeasts or heterofermentative bacteria, and ratios between deltaP and ethanol or lactate produced could be established. In mixed cultures, ratios between maximal deltaP and total amount of glucose consumed were determined. It was thus possible to evaluate the amount of glucose that was consumed by each strain and then deduce the bacterial lactate production. Good results were obtained for mixed cultures 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.