Beal C, Fonseca F, Corrieu G
Institut National Agronomique Paris-Grignon, UMR Génie et Microbiologie des Procédés Alimentaires, Thiverval-Grignon, France.
J Dairy Sci. 2001 Nov;84(11):2347-56. doi: 10.3168/jds.S0022-0302(01)74683-8.
The resistance to freezing and frozen storage of Streptococcus thermophilus was related to the fatty acid composition of the cell membrane. The effects of four experimental factors were investigated on the fatty acid concentrations and on the recovery of acidification activity of S. thermophilus stored at -20 degrees C by using a complete experimental design: incorporating oleic acid in the culture medium, fermentation pH, addition of glycerol as cryoprotective agent and duration of storage. The acidification activity decreased during the freezing and the frozen storage of S. thermophilus. The storage time slightly enhanced the unsaturated fatty acid concentrations. The addition of glycerol did not modify the fatty acid composition but increased the resistance to frozen storage. The addition of oleic acid and the decrease of the fermentation pH enhanced the ratio unsaturated:saturated fatty acids and improved the recovery of the acidification activity. These results indicate that the resistance to frozen storage was closely related to the membrane fatty acid composition. We interpreted this as an adaptation of S. thermophilus to the addition of oleic acid and the unfavorable growth conditions that corresponded to a low fermentation pH.
嗜热链球菌对冷冻和冻藏的抗性与细胞膜的脂肪酸组成有关。采用完全实验设计，研究了四个实验因素对嗜热链球菌脂肪酸浓度以及在-20℃储存时酸化活性恢复的影响：在培养基中加入油酸、发酵pH值、添加甘油作为冷冻保护剂以及储存时间。嗜热链球菌在冷冻和冻藏过程中酸化活性降低。储存时间略微提高了不饱和脂肪酸浓度。添加甘油并未改变脂肪酸组成，但增强了对冻藏的抗性。添加油酸和降低发酵pH值提高了不饱和脂肪酸与饱和脂肪酸的比例，并改善了酸化活性的恢复。这些结果表明，对冻藏的抗性与膜脂肪酸组成密切相关。我们将此解释为嗜热链球菌对添加油酸以及对应低发酵pH值的不利生长条件的一种适应。
