Food Safety Magazine, February/March 2013

SEAFOODsqueezed juices than heat-pasteurized products. Pressures of250 MPa or higher are commonly used in the processing industryand kill most bacteria. A simple conversion for MPa is that1 MPa = 145 psi of pressure, which is about five times whatis normally used in a car tire. Therefore, 250 MPa is 36,250psi. Pioneering work on enteric virus inactivation using HPPshowed that hepatitis A virus and norovirus surrogates couldbe inactivated using moderate levels of pressure (450 MPa orless). 8, 9 In a collaboration between the U.S. Department of Agriculture(USDA), Emory University and Virginia Tech, it wasdetermined that pressures greater than 400 MPa are requiredto inactivate norovirus particles in oysters using human volunteers.10 However, 400 MPa is higher than pressures used forcommercial HPP treatments of shellfish.Irradiation. Other postharvest processing methods includegamma and ultraviolet light irradiation. Gamma irradiation canbe effective in eliminating some viruses, like hepatitis A virus,rotavirus, poliovirus and the norovirus surrogates feline calicivirusand canine norovirus; however, some studies reported thatthe levels required for inactivation negatively affected shellfish“High-pressure processing...is an alternative method to inactivatemicrobes in foods, including shellfish.”suggests that many of the viruses within oysters may residewithin hemocytes that migrate from the digestive tissues intothe connective tissues of the shellfish. Consequently, shellfishdepuration appears inadequate to purge viruses from shellfish.High-Pressure Processing. High-pressure processing (HPP) is analternative method to inactivate microbes in foods, includingshellfish. HPP has been used to reduce vegetative bacteria infoods to enhance food safety and prolong shelf life. Foods likeguacamole and fruit juices are often pressure treated. Pressureinactivates the spoilage enzymes in guacamole to preserve itsgreen color, while HPP-treated fruit juices taste more like fresh-flavor. 6 Ultraviolet light inactivates viruses on the surfaces ofproducts, but is ineffective in the case of shellfish due to its inabilityto penetrate into the tissues where virus contaminationgenerally resides. Procedures like salting or freezing and thawingappear relatively ineffective in reducing noroviruses.Product TestingVirus Analysis of Foods. Several methods have been developedto extract and test for total norovirus contaminationF e b r u a r y • M a r c h 2 0 1 3 59