Purpose: The study objective was to determine the heat inactivation kinetics (D- and z-values) of TV in inoculated spinach within vacuum bags, using linear and Weibull models.
Methods: TV, (at 7.25 log plaque forming units (PFU)/ml) inoculated into frozen chopped spinach and sealed in vacuum bags, was heated at 50, 54, 58°C for up to 8 min in a circulating water bath. Survivors were eluted by polyethylene glycol precipitation and assayed using LLC-MK2 host cells in six-well plates. Treatment were replicated thrice and assayed in duplicate. Data were statistically analyzed using PROCREG and NLIN in SAS 9.4 for linear and Weibull models, respectively.
Results: D-values at 50±1°C (± standard error; come-up time=44.5s), 54±1°C (79.5s), and 58±1°C (168.7s) were 7.94±0.21 (R2=0.6; RMSE=0.3), 4.09±0.04 (R2=0.6; RMSE=0.7) and 1.43±0.02 min (R2=0.81; RMSE=0.65), respectively, with a z-value of 10.74°C (R2=0.98; RMSE=0.25) and 6-D values of 47.64, 24.54 and 8.58 min, respectively, using the linear model. The Weibull model showed Td=1 of 4.89±0.02 (R2=0.99; RMSE=0.15; α [scale parameter]=2.24; β=0.17, where β=shape parameter of >1 means survivors are damaged, =1 linear, <1 resistant survivors are present), 3.11±0.45 (R2=0.83; RMSE=0.67; α=1.09; β=0.78) and 0.25±0.38 min (R2=0.96; RMSE=0.61; α=0.04; β=0.43) and Td=6 of 55.87, 32.05, and 15.94 min, for the same temperatures, respectively. Previous studies showed that hepatitis A virus had a D-value of 34.4 min at 50°C and z-value of 13.92°C when inoculated into spinach in vacuum bags. D-values for murine norovirus (MNV-1) and feline calicivirus were 14.57 and 17.39 min, respectively, in inoculated spinach in 2-ml glass vials. This indicates that TV is not as heat resistant as earlier tested cultivable, foodborne viral surrogates.
Significance: Alternate surrogates that mimic the heat inactivation behavior of HNoV in foods need to be explored to ensure adequate thermal processing to maintain food safety.