Microcalorimetric study of growth of Lactococcus lactis IL1403 at low glucose concentration in liquids and solid agar gels

Growth of Lactococcus lactis IL1403 in liquid cultures and solid agar gels at different low glucose concentrations starting from 2 g L−1 up to 10 g L−1 with a stepwise increase by 1 g L−1 was studied using thermal activity monitor TAM III. In parallel to calorimetric measurements the changes of glucose and lactic acid concentrations and pH of culture media were measured in order to obtain additional information for the interpretation of calorimetric power–time curves. The data obtained together with calculated heat yield coefficient YQ allowed to analyze the growth of bacteria in colonies in solid agar gels in detail. The variation of glucose concentration at low levels allows analyzing and describing growth deceleration phase and growth stopping mechanisms both in liquid cultures and in solid-state fermentations.

► μmax is the same in broth and in agar gels independently on glucose concentration.
► Number of bacteria in the exponential phase is 1.5× higher in liquids than in solids.
► Homofermantative metabolism in broth cultures changes to heterofermentative in solids.