The evaluation of mixtures of yeast and potato extracts in growth media for biomass production of lactic cultures.

The effectiveness of yeast extracts (YE) and potato extracts (PE) to promote growth of seven lactic cultures was evaluated by automated spectrophotometry (AS). Two aspects of the growth curve were analysed: (1) maximum biomass obtained (using ODmax) and (2) highest specific growth rate (μmax). Eleven lots from the same PE-manufacturing process were examined for lot-to-lot variability. The ODmax values of three of the seven strains were significantly affected by lot source, but μmax was not significantly affected. The growth of bacteria was systematically lower in base medium containing 100% PE than in base medium containing 100% YE for both ODmax or μmax data, which could be related to the lower content in nitrogen-based compounds in PE. In AS assays, highest OD values for Lactobacillus casei EQ28, Lactobacillus rhamnosus R-011, Lactobacillus plantarum EQ12, and Streptococcus thermophilus R-083 were obtained with a mixture of PE and YE. Fermentations (2 L) were also carried out to determine the accuracy o...