RESUMO
Determinations of membrane fatty acid composition and fluidity were used together with acidification activity and viability measurements to characterize the physiological state after freezing of Lactobacillus buchneriâ R1102 and Bifidobacterium longumâ R0175 cells harvested in the exponential and stationary growth phases. For both strains, lower membrane fluidity was achieved in cells harvested in the stationary growth phase. This change was linked to a lower unsaturated-to-saturated fatty acid ratio for both strains and a higher cyclic-to-saturated fatty acid ratio for L. buchneriâ R1102 alone. These membrane properties were linked to survival and to maintenance of acidification activity of the cells after freezing, which differed according to the strain and the growth phase. Survival of B. longumâ R0175 was increased by 10% in cells with low membrane fluidity and high relative saturated fatty acid contents, without any change in acidification activity. Acidification activity was more degraded (70 min) in L. buchneriâ R1102 cells displaying low membrane fluidity and high saturated and cyclic fatty acid levels. Finally, this study showed that membrane modifications induced by the growth phase differed among bacterial strains in terms of composition. By lowering membrane fluidity, these modifications could be beneficial for survival of B. longumâ R0175 during the freezing process but detrimental for maintenance of acidification activity of L. buchneriâ R1102.