Influence of cooling temperature and duration on cold adaptation of Lactobacillus acidophilus RD758.

Abstract The effect of different cooling temperatures and durations on resistance to freezing and to frozen storage at −20 °C in Lactobacillus acidophilus RD758 was studied, by using a central composite rotatable design. A cold adaptation was observed when the cells were maintained at moderate temperature (26 °C) for a long time (8 h) before being cooled to the final temperature of 15 °C. These conditions led to a low rate of loss in acidification activity during frozen storage (0.64 min day −1 ) and a high residual acidification activity after 180 days of frozen storage (1011 min). The experimental design allowed us to determine optimal cooling conditions, which were established at 28 °C during 8 h. Adaptation to cold temperatures was related to an increase in the unsaturated to saturated fatty acid ratio and in the relative cycC19:0 fatty acid concentration. Moreover, an increased synthesis of four specific proteins was observed as an adaptive response to the optimal cooling conditions. They included the stress protein ATP-dependent ClpP and two cold induced proteins: pyruvate kinase and a putative glycoprotein endopeptidase.