| Abstract: | Membrane fatty acid composition and thermal resistance (D value) of Pediococcus sp. were determined for mid-exponential-phase (ME) and stationary-phase (ST) cells grown in tryptic soy broth (TSB) and tryptone-glucose-yeast extract (TGY) at 28 and 37°C. As the cells entered the stationary phase of growth, the unsaturated fatty acid, C18:1 n11c, produced during the exponential phase of growth was converted to its cyclic form, C19:0Δ9c. This shift in membrane fatty acid composition was accompanied by an increase in the D values of this bacterium. Data from this study suggest that the membrane fatty acid composition of Pediococcus sp. is dependent on the growth conditions and that membrane fatty acid composition plays a critical role in thermal resistance. Thermal inactivation curves of Pediococcus sp. cells grown in TGY at 28°C indicated the presence of a cell population that is heterogeneous in thermal resistance. The growth of this bacterium in TGY at 37°C and in TSB at 28 and 37°C resulted in cell populations that were uniform in thermal resistance with a lag time for thermal inactivation. Thermal inactivation curves of ME and ST cultures were similar. The data presented here suggest that the cell population’s uniformity of thermal inactivation is independent of the growth phase of the culture. |
