Purpose: The purpose of this study was to (i) characterize the thermal inactivation behavior of HAV in spinach, (ii) compare first-order and Weibull models in describing the data in terms of selected statistical parameters, and (iii) calculate z-values and activation energy using each model.
Methods: Commercial frozen chopped spinach (25-g samples) were homogenized and inoculated with 5-ml of HAV stock (7.20 ± 0.79 log PFU/ml) and held at 4°C for 24h. Inoculated samples (6 ml) were individually vacuum sealed in plastic bags to -100 kPa and heated in a thermostatically controlled water-bath with monitored temperature. Survivor curves (D-values) and thermal death curves (z-values) were generated using different treatment times (0-6 min) at 5 different temperatures (50 to 72°C) by Weibull and first-order models. A comparison test (ANOVA) was used to analyze the effects of temperature and time on survival ratios by the two models.
Results: D-values for HAV in spinach ranged from 37.08 ± 3.37 to 0.93 ± 0.09 min for Weibull and 34.40 ± 4.08 to 0.91 ± 012 min for the first-order model at 50 to 72°C, respectively. z-values for HAV in spinach were 15.07 ± 1.63°C using the Weibull model and 13.92 ± 0.87°C using the first-order model. Calculated activation energies for the first-order and Weibull models were 162 and 151 kJ/mole, respectively. Using this data obtained and the thermal parameters of industrial blanching for spinach as a basis (100°C for 120-180s), blanching of spinach in water at 100°C for 120-180s under atmospheric conditions will provide > 6 log reduction of HAV using either model.
Significance: These results will benefit the frozen food industry in designing blanching conditions to inactivate/control HAV in spinach.