Heat Inactivation of Hepatitis A Virus in Dairy Foods

Abstract

Experiments were performed to determine the thermal resistance of hepatitis A virus (HAV) in three types of dairy products containing increased amounts of fat content (skim milk, homogenized milk; 3.5% MFG, and table cream; 18% MFG). HAV-inoculated dairy products were introduced into custom-made U-shaped microcapillary tubes that in turn were simultaneously immersed in a waterbath, using custom-made floating boats and a carrying platform. Following exposure to the desired time and temperature combinations, the contents of each of the tubes was retrieved and was tested by plaque assay to determine the reduction in virus titer. Our data indicated that Ͻ0.5 min at 85ЊC was sufficient to cause a 5-log reduction in HAV titer in all three dairy products, whereas at 80ЊC, Յ0.68 min (for skim and homogenized milk), and 1.24 min (for cream) were needed to cause a similar log reduction. Using a nonlinear two-phase negative exponential model (two-compartment model) to analyze the data, it was found that at temperatures of 65, 67, 69, 71, and 75ЊC, significantly (P Ͻ 0.05) higher exposure times were needed to achieve a 1-log reduction in virus titer in cream, as compared to skim and homogenized milk. For example, at 71ЊC, a significantly (P Ͻ 0.05) higher exposure time of 0.52 min (for cream) was needed as compared to Յ0.18 min (for skim and homogenized milk) to achieve a 1-log reduction in virus titer. A similar trend of inactivation was observed at 73 and 75ЊC where significantly (P Ͻ 0.05) higher exposure times of 0.29 to 0.36 min for cream were needed to cause a 1-log reduction in HAV in cream, as compared to Յ0.17 min for skim and homogenized milk. This study has provided information on the heat resistance of HAV in skim milk, homogenized milk, and table cream and demonstrated that an increase in fat content appears to play a protective role and contributes to the heat stability of HAV.Hepatitis A virus (HAV), the causative agent of hepatitis A, is a member of the Picornaviridae family. Because of its unique genetic and physical characteristics, HAV has now been assigned to a distinct genus, hepatovirus (17). It is a 27-nm icosahedral, nonenveloped virus, containing a 7.5-kb positive-stranded RNA genome that is enclosed by a capsid protein shell consisting of VP1, VP2, VP3, and VP4 glycoproteins. Despite its successful propagation in cell culture (3,19), wild-type HAV strains are still very difficult to culture, even in primary mammalian cells. Although similar to other enteroviruses in morphology and composition, HAV exhibits greater resistance to inactivation by various chemical and physical agents, including heat (4,6,8,21). Outbreaks of foodborne hepatitis have been well documented epidemiologically with a wide variety of foods, such as shellfish, salads, fruits, and dairy products being implicated (1,2,20). Most investigations have focused on the use of heat as a method of inactivating HAV in shellfish. Koff and Sear (10) indicated that it took 4 to 6 min for the internal temperature to reach 100ЊC in st...

Evaluation of the Persistence of Infectious Human Noroviruses on Food Surfaces by Using Real-Time Nucleic Acid Sequence-Based Amplification

“…Our finding in the present study that NoV survival on turkey was slightly greater than that on lettuce suggests that the food surface may affect the persistence of NoV infectiousness or recovery of the virus by elution. This protective effect of food matrices has already been reported for other studies (4,28,34). As found by Mattison et al (28), the smallest reduction in the FCV titer over 7 days at refrigeration temperature was observed for ham, compared to lettuce, strawberries, and stainless-steel surfaces.…”

Inactivation of Caliciviruses

“…Remarkably, Slomka and Appleton (39) reported a comparable 3 D inactivation in 0.5 to 1 min of FeCV in contaminated cockles at 80°C, indicating that FeCV, unlike hepatitis A virus (2,29), is not significantly stabilized by factors such as fat and high protein content.…”

Effects of Technological Processes on the Tenacity and Inactivation of Norovirus Genogroup II in Experimentally Contaminated Foods

“…Matrix-derived protective effects have been described in connection with heat treatments. An increase in the fat content of milk appeared to have a protective effect on HAV, increasing its heat stability (15,78). In this study, clear protective effects on NV were observed for some heat treatments with various intensities.…”

“…Such studies are limited mainly to shellfish (42, 43) and berries (18,19) or to cultivable enteric viruses, such as hepatitis A virus (HAV) (15,24,42,66,78), poliovirus (PV) (26, 84), or rotavirus (12). Due to the lack of a mammalian cell culture or animal model for norovirus, various studies of persistence and inactivation have been performed with genetically related surrogates of norovirus, including feline calicivirus (FCV) (17,28,32,35,68,82,86) and murine norovirus (MNV) (7,8,10,11,21,51), which are cultivable nonenveloped viruses belonging to the family Caliciviridae.…”