Stability of Viruses in Low Moisture Foods

Abstract

Reovirus type 1, influenza virus type A, and parainfluenza virus type 3 persisted for ≤ 3 days in the low-moisture foods tested. Then enteroviruses tested persisted > 2 weeks at room temperature and > 2 months in the refrigerator. Where storage temperature was not constant, time-temperature effects were roughly cumulative. Inactivation of enteroviruses proceeded at an intermediate rate in foods stored at an intermediate temperature of 12 C. Polioviruses from feces and from tissue cultures were inactivated at comparable rates in foods. The inactivation rate of another enterovirus (ECHO-6) was similar. Neither the presence of feces nor of the fecal microflora seemed to influence the persistence of food-borne poliovirus. The moisture level in a food did not effect poliovirus inactivation under conditions of these tests. At reduced temperatures, virus was extremely stable in foods at pH ≥ 7. At pH 5.5, there was a complex interaction of protein and salt content upon virus stability. Poliovirus was inactivated 10−2 during freeze-drying of cream-style com. The remaining virus was quite stable during storage of the product at 5 C.

Transmission of viruses through foods

“…His data are very difficult to summarize, but the results were generally as stated above. Similar findings were reported for poliovirus type 1 in several foods of normal moisture content by Heidelbaugh and Giron 102 and for three enteroviruses in low moisture foods by Cliver et al 103 Comparable data are not generally available for other viruses as secondary contaminants in foods.…”

“…This was evident at 5°C with poliovirus in a "bland" food adjusted to pH 5.5 with propionic acid, and the effect was more pronounced at pH 4. 103 Similar results can generally be expected with enteroviruses in naturally acid foods, although the picture is complicated in the presence of significant levels of salts and proteins. We found that these last components have little effect upon enterovirus stability at 5°C in food near pH 7 but that they may (at the tested levels) enhance virus inactivation individually at pH 5.5, yet combine to stabilize the virus.…”

“…103 The same might not be true of reovirus: this model agent (reovirus type 1) is known to be relatively stable but was rapidly inactivated when added to lowmoisture food. 103 There is a rather nebulous distinction between infectivity and inactivation among the reoviruses. A great proportion of apparently complete virus particles does not cause infection in tissue culture.…”

“…Inactivation is not necessarily "first-order" under these conditions, but we have recorded rates as low as -0.0008/day" 1 on a logarithmic scale under these conditions. 103 Heidelbaugh and Giron 102 stored poliovirus at 4°C in a food mixture at pH 7.1 and got inactivation during seven days at a rate I estimate to be -0.06 /day" 1 . Rate constants such as these may not differ significantly from zero where the period of storage and sampling at 5°C is less than eight weeks.…”

“…This probably cannot be answered forthrightly, but here is what I mean: at pH 5.5 and a temperature of 4°C, foot and mouth disease virus has been inactivated a millionfold within 30 minutes, 9 7 while poliovirus type 3 was inactivated at a rate which apparently would have required 11 weeks to produce the same result. 103 These two viruses, at pH 7 and 4°C, would show only limited inactivation over a period of months. I suggest that at pH 5.5, the foot and mouth disease virus is being inactivated chemically (by the acid) at a rate determined by the temperature, whereas the poliovirus is being inactivated thermally at a rate determined by the pH.…”