Characterization of growth and metabolism of commercial strains of propionic acid bacteria by pressure measurement

Dairy propionibacteria are essential starters for Emmental cheese manufacture. The behavior of three commercial strains of Propionibacterium freudenreichii subsp. shermanii (P.f 1, Rf. 2 and P.f 3) were studied in a liquid medium under air and N-2 atmosphere using an on-line pressure measurement technique. Growth kinetics and metabolite production were characterized under conditions usually reported as "optimal conditions" (pH 6.5, NaCl 0 %, temperature 30 degrees C) and also evaluated under "stressful conditions" (pH 5.2, NaCl 2 %, temperature 20 degrees C) simulating the cheese ripening conditions. In both cases, the effects of oxygen on growth were strain-dependent. Under "stressful conditions", two of the three strains were inhibited by oxygen under conditions of air atmosphere, while all three strains grew under conditions of N-2 atmosphere. In the latter case, the duration of the lag phase and the maximum rate of pressure variation were significantly different, however, no significant differences were found between the strains with regard to the total fermentation time. Under "optimal conditions" metabolite production was strain-dependent. In an air atmosphere, all strains produced more acetate and CO2 and less propionate than in a nitrogen atmosphere.