Identification of potential bacterial surrogates for validation of thermal inactivation processes of hepatitis A virus

Thermal treatment is a method for inactivating pathogens in a wide range of food products. Recent studies have shown that hepatitis A virus (HAV) has a D_72°C [D72 degree celcius] of 0.9 min in buffer which is greater than vegetative bacterial pathogens. Common surrogates, such as Listeria innocua, are not resistant enough to be used as surrogates for HAV, thus, new surrogates need to be identified. The purpose of this study was to compare the thermal inactivation kinetics (D- and z-values) of Staphylococcus carnosus in different foods and different incubation temperatures to identify a potential surrogate for HAV. Thermal inactivation of S. carnosus was performed in phosphate buffered saline (PBS), 2% UHT milk, spinach, mussels, and clams following incubation at 32°C or 40°C. Approximately 7 log CFU/ml of S. carnosus in PBS was added to 2 ml vials. Thermal inactivation studies were performed at 65, 67, and 70°C and 55, 60, 65, and 70°C when incubated at 32 and 40°C, respectively. Vials were removed at various time points, plated on BHI agar and incubated for 72 h at 32°C or 40°C. Each trial was conducted in duplicate and replicated three times. D- and z-values were determined and compared using a first-order and Weibull model. The fit of the models was investigated comparing regression coefficient (R²), root-mean-square error (RMSE), and chi-square (ϫ²) values. For incubation of 32°C and 40°C and treatment temperatures of 55 to 70°C, D-values ranged from 478.35 ± 78.35 to 0.36 ± 0.07 min and from 1.49x10⁶ [1490000] ± 1.19x10⁶ to 0.18 ± 0.15 for the first-order and Weibull model, respectively. No significant differences were detected when incubated at 32°C, but for milk and spinach at 65°C when incubated at 40°C, with the first-order model resulting in significantly higher values. Z-values for both models ranged from 6.17 ± 0.08 to 9.78 ± 7.45°C. Based on inactivation kinetics, ease of incubation, and non-pathogenicity, S. carnosus could be used for validation studies of HAV. Additionally, a significant increase in heat resistance could be achieved by increasing the incubation temperature and both models resulted in a good fit of the thermal inactivation kinetics.