Automatic method for evaluating the activity of sourdough strains based ongas pressure measurements

A new method is proposed for the evaluation of the activity of sourdough st rains, based on gas pressure measurements in closed air-tight reactors. Gas pressure and pH were monitored on-line during the cultivation of commercia l yeasts and heterofermentative lactic acid bacteria on a semi-synthetic me dium with glucose as the major carbon source. Relative gas pressure evoluti on was compared both to glucose consumption and to acidification and growth . It became obvious that gas pressure evolution is related to glucose consu mption kinetics. For each strain, a correlation was made between maximum ga s pressure variation and amount of glucose consumed. The mass balance of CO 2 in both liquid and gas phase demonstrated that around 90% of CO2 was reco vered. Concerning biomass production, a linear relationship was found betwe en log colony-forming units/ml and log pressure for both yeasts and bacteri a during the exponential phase; and for yeasts, relative gas pressure evolu tion also followed optical density variation.