Effect of temperature on growth and metabolism of probiotic bacteria in milk

The growth and metabolism of six probiotic strains with documented health effects were studied in ultra-high temperature (UHT) treated milk supplemented with 0.5% (w/v) tryptone or 0.75% (w/v) fructose at different temperatures. The probiotic strains were Lactobacillus acidophilus La5, Lb. acidophilus 1748, Lb. johnsonii LA1, Lb. rhamnosus GG, Lb. reuteri SD 2112 and Bifidobacterium animalis BB12. Fermentation was followed for 48 h at 20, 30, 37 and 45 °C and the samples were analysed for pH, log cfu mL−1, volatile compounds, organic acids and carbon dioxide. All six probiotic strains showed very different profiles of metabolites during fermentation, however, the two Lb. acidophilus strains were the most alike. All strains, except Lb. reuteri SD 2112, showed viable cell numbers above 6.5 log cfu mL−1 after 48 h fermentation at 30, 37 and 45 °C. The probiotic strains produced different amounts of metabolic products according to temperature and fermentation time illustrating the importance of controlling these parameters.