Death Kinetics for Escherichia coli Cells Heated in the Presence of Short- and Medium-Chain Fatty Acids.

We investigated the death kinetics for Escherichia coli K12 cells heated at different temperatures in the presence of saturated fatty acids having short and medium alkyl-chain lengths at various concentrations. Apparent first-order death kinetics were observed with cells heated in the presence of caproic acid, caprylic acid, capric acid, or lauric acid. Values of activation enthalpy and activation entropy of the death reaction decreased with an increase in the concentration of caprylic acid, capric acid, and lauric acid, but did not decrease much for caproic acid. Also, the value of dilution coefficient decreased with increasing heating temperature for the former three fatty acids but was not noticeably temperature dependent for caproic acid. These results suggest that there are two distinct modes for the death reaction of E. coli cells heated in the presence of fatty acids and that the hydrophobicity based on the alkyl-chain length of fatty acid molecule is responsible for such a difference in the death kinetics.