Thermal inactivation kinetics for Acidovorax citrulli on watermelon seeds as influenced by seed component, temperature, and water activity

Abstract

Knowledge of the thermal inactivation kinetics of Acidovorax citrulli is essential to design an effective heat treatment protocol for its control on watermelon seeds. The coat and embryo of watermelon seeds were selected as two components to compare the heat resistance of A. citrulli. The embryo was chosen to investigate the influence of different water activity levels using a heating block system under a fixed heating rate of 5 °C min−1, which aimed to simulate radio frequency heating. By combining the thermal death kinetics of A. citrulli with the germination rate curves of the seeds, practical treatment protocols were proposed. The results indicated that the heat resistance during A. citrulli inoculation for seed embryo increased with decreasing water activity. The inactivation data for A. citrulli inoculated on the embryo fitted the Weibull model (R2 = 0.965–0.999, RMSE = 0.023–0.304) better than a first-order kinetic model (R2 = 0.927–0.988, RMSE = 0.164–0.467). The Mafart's modified Bigelow model and the cumulative lethal time model showed that under given conditions thermal death kinetics could be applied to reliably predict population reductions of A. citrulli. Thermal treatment protocols were proposed under different heating uniformity index values. These findings could be used to develop an effective treatment protocol based on the germination rate of watermelon seeds and microbial inactivation level.