Thermodynamics of Heat Inactivation of <i>Aeromonas hydrophila</i> in Soymilk of Varying Initial pH and Sugar Levels

Abstract

The thermodynamics of thermal inactivation of <i>Aeromonas</i> <i>hydrophila</i> in soymilk of varying pH (6.0-7.0) and sugar concentration (0-10%) were studied at a temperature of 50-65°C using kinetic parameters generated through the Classical thermobacteriology assumption of a log-linear relationship between <I>A</I>. <i>hydrophila</i> survivors and heating time. The activation enthalpy (ΔH<sup>#</sup>), activation entropy (ΔS<sup>#</sup>), activation energy (E<sub>a</sub>) and frequency factor (K<sub>o</sub>) for thermal inactivation of <i>A. hydrophila</i> in the soymilk samples were also obtained. Thermal inactivation of the organism followed first order reaction kinetics. The heat destruction rate constant (k) decreased with increase in heating temperature. The activation energy ranged from 210.98 to 215.28 kJ/mol increasing with decrease in pH and increase in sugar concentration of soymilk. The isokinetic temperature (T<SUB>C</SUB>) obtained varied from 55.95 to 56.62°C with inactivation of <I>A</I>. <i>hydrophila</i> exhibiting true compensation effect, with a Gibbs free energy of 82.86 kJ/mol. A combination of temperature, pH and sucrose significantly influenced inactivation of <I>A.</I> <i>hydrophila</i> in soymilk, following a similar mechanism being driven by entropy. Optimum safety from <I>A</I>. <i>hydrophila</i> can be achieved through application of multifactorial hurdles in soymilk processing. The thermodynamic data obtained will be useful to optimize thermal processing conditions for soymilk targeting <I>A</I>. <i>hydrophila.</i>