Fermented Milk Manufacture Conditions Affect Bifidobacterium animalis subsp. lactis BB12 Survival as a Result of Membrane Fatty Acid Composition

The effects of the kind of milk (organic and conventional), fermentation temperature (37°C and 42°C), final pH (4.8 and 4.4), intermediate cooling temperature (22°C, 25°C and 28°C) and duration (4, 8 and 12 hours) were investigated on acidification activity, bacterial survival and membrane fatty acids composition of Bifidobacterium animalis subsp. lactis BB12 after fermentation and storage at 4°C. Acidification time was reduced when fermentation was performed at 42°C until pH 4.4. Superior cell counts were achieved in organic fermented milks at the end of fermentation and after storage, independently of process conditions. Cultivability was higher when the cells were fermented at 42°C until pH 4.4 or maintained at 28°C for 12h before being cooled to 4°C. These conditions led to modifications of membrane fatty acid composition, thus resulting in changes of membrane fluidity. However, if the unsaturated fatty acid percentage was higher in organic fermented milks, it was lower when fermentation was conducted at 42°C until pH 4.4 and after cooling at 28°C for 12h. Finally, this study suggests that other biological mechanisms are involved in the bacterial responses to environmental conditions.