Heat inactivation of hepatitis A virus in dairy foods

Experiments were performed to determine the thermal resistance of hepatitis A virus (HAV) in three types of dairy products containing increased amount s of fat content (skim milk, homogenized milk; 3.5% MFG, and table cream; 1 8% MFG), HAV-inoculated dairy products were introduced into custom-made U-s haped microcapillary tubes that in turn were simultaneously immersed in a w aterbath, using custom-made floating boats and a carrying platform. Followi ng exposure to the desired time and temperature combinations, the contents of each of the tubes was retrieved and was tested by plaque assay to determ ine the reduction in virus titer. Our data indicated that <0.5 min at 85 de grees C was sufficient to cause a 5-log reduction in HAV titer in all three dairy products, whereas at 80 degrees C, less than or equal to 0.68 min (f or skim and homogenized milk), and 1.24 min (for cream) were needed to caus e a similar log reduction. Using a nonlinear two-phase negative exponential model (two-compartment model) to analyze the data, it was found that at te mperatures of 65, 67, 69, 71, and 75 degrees C, significantly (P < 0.05) hi gher exposure times were needed to achieve a 1-log reduction in virus titer in cream, as compared to skint and homogenized milk. For example, at 71 de grees C, a significantly CP < 0.05) higher exposure time of 0.52 min (for c ream) was needed as compared to less than or equal to 0.18 min (for skim an d homogenized milk) to achieve a 1-log reduction in virus titer. A similar trend of inactivation was observed at 73 and 75 degrees C where significant ly (P ( 0.05) higher exposure limes of 0.29 to 0.36 min for cream were need ed to cause a 1-log reduction in HAV in cream, as compared to less than or equal to 0.17 min far skim and homogenized milk. This study has provided in formation on the heat resistance of HAV in skim milk, homogenized milk, and table cream and demonstrated that an increase in fat content appears to pl ay a protective role and contributes to the heat stability of HAV.