Effect of lipid composition on the stability of cellular membranes during freeze-thawing of Lactobacillus acidophilus grown at different temperatures

Lactobacillus acidophilus CRL 640 grown, at the optimal temperature of 37 d egreesC (M37) appeared more sensitive to freeze-thawing than when it was gr own at 25 degreesC (M25). In the first case, 87% of the cells died, in cont rast to 33% for cells grown at 25 degreesC. All the surviving M37 cells sho wed sensitivity to NaCl. However, among the surviving M25 cells, only 85% w ere sensitive to NaCl. The rest of the cells were considered uninjured. Fre eze-thawing in cells grown at 25 degreesC showed a liberation of nucleic ac ids and proteins. However, the leakage was higher in M37 cells after freeze -thawing. The greater fraction of damaged cells were observed in M25 cultur e after freeze-thawing. A relative increase of 81% in cardiolipid (CL), wit h respect to total phospholipids and 72% triglycosyldiglyceride (TGDG) with respect to the total glycolipids was observed in M37, In addition, a decre ase of palmitoyl (C16:0), oleoyl (C18:0) fatty acids at CL, phosphatidylgly cerol (PG), and diglicosyldiglyceride (DGDG) fractions and the increase of C19 eye and C18:0, 10-OH fatty acids in neutral lipid, and CL fractions was also apparent. In M25 cells, the concentration of DGDG and PG was higher t han in M37 cells. The difference in cryotolerance between the frozen cultur es emphasizes the importance of selecting appropriate conditions of growth of microorganisms for use as dietary adjuncts. (C) 2001 Academic Press.