Heat sensitization of human enteric viruses by plant extracts and validation of their thermal inactivation by bacterial surrogates

Human enteric viruses including hepatitis A virus (HAV) and human noroviruses (HNoV) predominantly are linked to foodborne outbreaks worldwide. Heat has been historically used to inactivate foodborne pathogens and spoilage microorganisms to increase safety and also prolong shelf-life. Recent foodborne viral outbreaks have enhanced the need for research to determine optimal processing approaches and thermal inactivation parameters such as D- and z-values, for their control. Heat-sensitization of foodborne viruses by "generally recognized as safe''(GRAS) substances can potentially reduce their time-temperature inactivation parameters during processing. HAV reportedly has higher resistance to heat (in buffer the D72°C was 0.9 min) than known vegetative bacteria. Therefore, non-pathogenic surrogates with higher thermal resistance are required for process validation. This present study determined and compared the D- and z-values of HAV (~7 log PFU/ml) and Tulane virus (TV; ~6 log PFU/ml), a cultivable HNoV surrogate, with curcumin (0.015 mg/ml), gingerol (0.1 mg/ml), or grapeseed extract (GSE; 1 mg/ml) at 52 to 68 °C in 2-ml glass vials. Decreased D-values (52 to 58 °C) for TV with curcumin from 4.32±0.25 to 0.62±0.17 min, gingerol from 4.09±0.18 to 0.72±0.09 min and GSE from 3.82±0.18 to 0.80±0.07 min, from initial 4.59±0.28 to 1.08±0.16 min in buffer wre observed by both linear and Weibull models, with similar trends for HAV (56 to 68 °C). This study also determined the D- and z-values of Staphylococcus carnosus strains (CS-299 and CS-300) as potential HAV surrogates under modified growth conditions (higher temperature, salt and low pH). D-values (by the linear model) of CS 300 grown at 37 °C at 56 to 68 °C in 2-mL glass vials were 6.18±0.25 to 0.54±0.12 min and increased to 7.09±0.15 to 0.59±0.06 min when grown at 42 °C, in 4% NaCl, pH 6 and further increased as a lawn. A similar trend was observed for CS 299. Overall, this research determined the decreased time-temperature parameters needed to inactivate enteric viral surrogates and the increased heat resistance of bacterial surrogates for application in process validation for the thermal inactivation of HAV.

Chapter 2 of this document will be submitted to Journal of Food Microbiology