Thermal and high hydrostatic pressure inactivation of human norovirus surrogates in bivalve shellfish
Date
2016
Authors
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Publisher
University of Delaware
Abstract
Bivalve shellfish, such as oysters and clams, are popular among consumers for their sweet and briny flavor, soft texture and high nutrition values. As shellfish are filter-feeder, they tend to accumulate toxins, bacteria, or pollutants from surrounding waters, which result in high numbers of foodborne diseases. The most common cause of shellfish-borne disease are human enteric viruses, notably noroviruses. Human norovirus (HNV) is considered as most frequent causative agent of foodborne diseases in the US. As there is no in vitro cell culture system or small animal model that can be used for culture of HNV, surrogate viruses, such as murine norovirus (MNV-1) and Tulane virus (TV), have been used to study behavior and intervention of HNV in food products. Thermal processing is one of most effective and easy-accessible method to inactivate viruses in food. High hydrostatic pressure (HHP) is a non-thermal processing that has the potential to kill pathogens in seafood while retaining sensory quality. In this research, thermal processing and HHP were used to inactivate MNV-1 and TV in oysters and clams, respectively. The effective HHP treatments were also evaluated for the impacts on clams’ shelf life quality during refrigerated storage. In the research on thermal inactivation of viruses in oyster meat, our results showed that 3 minutes of boiling can reduce both MNV-1 and TV below detect limitation (<1 log10 PFU/ml). Both viruses were inactivated at a faster rate when temperature was over 58°C. At temperature of 58°C and above, TV was much more heat sensitive compared with MNV-1, which might make it a less comparable virus surrogate as HNV in cooked oyster meats. To better describe thermal inactivation kinetics of viruses, first order and Weibull model were compared and Weibull model gave a better fit. The D values of MNV-1 calculated by first-order model and Weibull model ranged from 28.169 to 0.875 min and 26.636 to 0.777 min at 49 to 67°C, respectively. Meanwhile, the D values of TV calculated by first-order model and Weibull model ranged from 18.181 to 1.56 min and 19.349 to 1.56 min at 49 to 63°C, respectively. In the studying on effects of using HHP to improve clam safety and quality, treatment of 450MPa at 21°C and treatment of over 350 MPa at 4°C had over 3 log10 PFU/g reduction of MNV-1 in clams. When treated at 350MPa and 21°C, TV had a higher reduction (>1.57 log10 PFU/g) than MNV-1(0.85 log10 PFU/g). During the 11 days of refrigerated storage, HHP treated clam samples did not show significant difference in tests water activity, tissue yield, glycogen content, and lipase activity, when compared with the findings in control samples. HHP treated clams had lower aerobic bacteria counts and higher pH values than those of control. Higher L and b value was observed of 450MPa at 21°C treated clam on day1 and day11, respectively. Treatment of 350MPa at 4°C had a higher lipid oxidation values than control on day1 and day11. In summary, treatments at pressure level of 450MPa or temperature of 4°C had a higher virus inactivation efficiency. However, high pressure and low temperature might result in undesired impact on clam quality, such as brighter color or more lipid oxidation.
Description
Keywords
Bivalve shellfish, High pressure, Norovirus surrogates, Thermal processing