Assessment of microbial population dynamics during yoghurt and hard cheese fermentation and ripening by DNA population fingerprinting

The application of Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis of the small subunit ribosomal gene to examine the bacterial dynamics of relatively fast dairy fermentation processes is illustrated. All individual starter strains yielded characteristic terminal restriction fragments (TRFs). Growth independent T-RFLP analysis was used to identify and follow the dynamics of streptococci, lactobacilli, lactococci and propionibacteria in yoghurt and hard cheese production while samples had been stored frozen until analysis. Starter cultures could be differentiated and followed during production and ripening of hard cheese (Gouda type and Maasdam) as well as production of yoghurt. T-RFLP analysis enabled the characterization of bacterial population structure and dynamics between short time spans, i.e., within hours. Eight samples taken at different times within 5.5 h yoghurt fermentation revealed shifting relative signal intensities in TRF peaks between streptococci and lactobacilli, indicating a (semi) quantitative relation of the TRFLP signal with the actual numbers of bacteria.