Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/17/2008
Publication Date: 8/1/2008
Citation: Kingsley, D.H., Chen, H. 2008. Aqueous Matrix Compositions Influence Virus Inactivation by High Pressure Processing. Journal of Food Protection. 71(1):598-603. Interpretive Summary: High pressure processing (HPP) is a promising technology for virus inactivation within certain uncooked foods, such as oysters and produce. The principal advantage of high pressure processing is that foods retain their raw taste and character. Previous publications described virus inactivation as a function of pressure levels, treatment time, and treatment temperature for inactivation of virus directly within food products, such as green onions and oysters. In this publication, we examine the role of salt (w/v, 0-21%), sugar (w/v, 0-70%), and the combination of salt and sugar on inactivation of the norovirus surrogate, feline calicivirus. The effect of protein concentration (w/v, 0-2%), and acidity (pH 3-8) was also evaluated. Results demonstrate that salt concentration, sugar concentration, and pH dramatically alter the amount of virus inactivated by high pressure treatments. For up to 2% whey protein, no inhibitory effect was observed. A plateau effect was observed for higher concentrations of NaCl (15%) and sucrose (40%), beyond which no further reduction in pressure resistance of FCV was observed. Sucrose and salt did not counteract a previously observed enhancement of HPP by application of high pressure at refrigeration temperatures rather than at room temperature. Salt and sugar in combination do not synergistically enhance, or antagonistically reduce, pressure resistance of the solution beyond the individual separate contributions of salt and sugar in solution. This information will provide a greater understanding of how food product composition can influence the amount of virus inactivated and potentially offer guidelines for high pressure treatment parameters for high pressure processed food products.
Technical Abstract: The individual effects of pH(range 3-8), NaCl (0-70%), sucrose (0-21%), and whey protein (0-2%) on pressure resistance of feline calicivirus (FCV) in Dulbecco’s Modified Eagle Medium were determined at 250 Mpa and 20 deg. The combined effects of NaCl and sucrose at different temperatures was also examined in combination with temperatures of 4 and 20 deg C. Over a pH range of 6-8, the virus was readily inactivated, but at = pH 5.2 FCV was more resistant to pressure. For example, a treatment of 250 MPa for 1 min at 20 deg C at pH 5.2 did not reduce the titer of FCV, while the same treatment at pH 6.0 reduced the titer of FCV by 4.1 log PFU/ml. For FCV samples with sucrose and NaCl, the degree of FCV virus inactivated by pressure was inversely proportional to their concentration. For example, a treatment of 250 Megapascal (MPa) at 20 deg C for 5 min reduced the titer of FCV by 5.1 log plaque forming units (PFU)/ml without sucrose added and by 0.9 log PFU/ml with a 40% sucrose concentration. Likewise, a treatment of 250 MPa at 20 deg C for 5 min reduced the titer of FCV by 5.0 log PFU/ml without NaCl and only by 0.3 log PFU/ml with 15% NaCl. Reduced pressure sensitivity with increasing NaCl and sucrose concentrations was not a simple function of water activity, since different PFU reductions were observed for different NaCl and sucrose samples with equivalent water activity. When both NaCl and sucrose were added to the FCV stock, the two factors had an additive effect on increasing the pressure resistance of FCV. This individual (6% NaCl and 20% sucrose) and and combined resistance effect (6% and 20% together) did not abrogate enhanced inactivation observed previously for pressure treatments at 4 deg C as compared to 20 deg C. Whey protein at concentrations up to 2% did not provide a protective effect. This work demonstrates that aqueous matrix compositions, in particular different concentrations of NaCl and sucrose, or varying pH values can substantially alter the efficiency of virus inactivation by high pressure processing.