Survival of hepatitis A virus on modified atmosphere-packaged (MAP) lettuce

Experiments were designed to study the effect of various modified atmospher es (MA) on the survival rate of hepatitis A virus (HAV) on lettuce. Pieces of lettuce inoculated with HAV were incubated at room temperature (RT) and 4 degreesC for 12 days in ambient air and under various modified atmosphere s (CO2:N-2 at 30:70, 50:50, 70:30 and 100% CO2) inside plastic bags of low O-2 permeability. Samples were removed on days 1, 3, 6, 9 and 12 and the vi rus was recovered and plaque-assayed to determine residual titer. incubatio n for 12 days at 4 degreesC showed that the lowest HAV survival rate (47.5% ) was on lettuce stored in a petri-dish (atmospheric air), whereas the grea test survival rates (83.6%) was on lettuce stored under 70% CO2. Statistica l analysis of virus survival at 4 degreesC indicated that HAV titers decrea sed for all packages, but without a significant (P > 0.05) difference betwe en the package types. Ar RT; however, a significantly (P < 0.05) lower HAV survival rate (0.01%) was evident on lettuce stored in a petri dish, wherea s survival rates as high as 42.8% were observed on lettuce stored under 70% CO2, much lower survival rates (<less than or equal to>8.6%) were obtained on lettuce stored under other MAP environments at RT: Statistical analysis of the RT data indicated that there was a highly significant (P < 0.05) de crease in HAV titre with,increasing storage time and between package types, except for lettuce stored under 70% CO2. These data indicate that MAP does not influence HAV survival when present on the surface of produce incubate d at 4<degrees>C. A slight improvement,in virus survival on lettuce was see n in the presence of high CO2 levels at RT This may have been attributed to the inhibition of spoilage-causing enzymatic activities in the lettuce, wh ich may have reduced exposure of the virus to (C) 2001 Academic Press.