Aqueous matrix compositions and pH influence feline calicivirus inactivation by high pressure processing

The individual effects of pH (pH 3 to 8), NaCl (0 to 21%), sucrose (0 to 70%), and whey protein (0 to 2%) on pressure resistance of feline calicivirus (FCV) in Dulbecco's modified Eagle medium with 10% fetal bovine serum were determined. At pH 3 through 8, the virus was more resistant to pressure at a pH of <= 5.2. For FCV samples with sucrose (up to 40%) or NaCl (up to 12%), the amount of FCV inactivated by pressure was inversely proportional to the sucrose or NaCl concentration. For example, a treatment of 250 MPa at 20 degrees C for 5 min reduced the FCV titer by 5.1 log PFU/ml without added sucrose and by 0.9 log PFU/ml with 40% sucrose. Reduced pressure sensitivity with increasing NaCl and sucrose concentrations was not a simple function of water activity. Different PFU reductions were observed for NaCl and sucrose samples with equivalent water activity. Whey protein at concentrations up to 2% did not provide a protective effect. The combined effect of NaCl and sucrose at 4 and 20 degrees C on pressure resistance of FCV also was examined. When both NaCl and sucrose were added to the FCV stock, they had an additive effect on increasing the pressure resistance of FCV. The individual (6% NaCl or 20% sucrose) and combined (6% NaCl plus 20% sucrose) resistance effects did not abrogate enhanced inactivation for pressure treatments at 4 degrees C compared with those at 20 degrees C. Aqueous matrix compositions, in particular different concentrations of NaCl and sucrose or different pH values, can substantially alter the efficiency of virus inactivation by high pressure processing.