Thermal inactivation kinetics of Aeromonas hydrophila in soymilk of varying pH and sugar concentrations

Tackling microbial risk in food requires a good knowledge of the behavior of an organism in specific foods. The effect of temperature (50, 52.5, 55, 57.5, 60, 62.5, and 65°C), pH (6.0, 6.5, and 7.0) and sugar concentration (0, 5.0 and 10% w/v) on survival of A. hydrophila in soymilk was investigated. Heat resistance studies were carried out using conventional screw-capped tube procedure with heating at constant temperature. Survival plots were made from experimental data, and D- and z-values obtained ranging between 18.15–0.57 min and 9.71–9.55°C respectively. Significant effects were observed in D- and z-values with variations in pH and sugar concentrations of soymilk. This hurdle combination proved effective in preserving soymilk, aimed at optimizing nutrient retention, organoleptic quality and destruction of A. hydrophila. The data obtained would be useful in effective thermal processing, establishing appropriate pasteurization schedules with reference to A. hydrophila contamination in soymilk. Novelty impact statement Aeromonas hydrophila has increasingly been recognized as an emerging food borne pathogen that poses threat to human health. Although inactivation studies of A. hydrophila in several foods have been reported, there is limited information on its inactivation in soymilk using multiple hurdles. In this study, thermal inactivation kinetics of Aeromonas hydrophila from a water source was carried out in soymilk of varying pH and sugar concentrations and was observed to exhibit apparently linear survival curves, and higher decimal reduction times (D-value) and z-values than reported for other studied liquid foods. The parameters obtained in this study will be useful in the optimization of thermal processing of soymilk in combination with other hurdles to ensure safety from this organism and similar gram-negative bacteria.