A bulletin for the Australian Food Industry    May 2002

Contents: Salmonella in chocolate | Hazards in international trade | Children and microbial foodborne illness | International spread of foodborne illness | Sanitizers and fresh produce | Supplement: Acrylamide detection in starchy foods

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Sanitizers and fresh produce

In February 2002, we discussed foodborne viruses and fresh produce. One major review (Journal of Applied Microbiology 91 2001 759) noted the absence in the literature of information on the effect of chemical sanitizers on enteric viruses present on fruits and vegetables.

A recent research report (Journal of Food Protection 64 2001 1430) attempts to provide information in this area. US workers note that the efficacy of common disinfectants (sanitizers) against Norwalk and Norwalk-like viruses (NLVs) is not known. This is partially due to the lack of methods for propagation of these viruses in the laboratory.

The NLV group is an important cause of foodborne gastroenteritis and, in an attempt to redress this lack of information, these workers have reported experiments using feline calicivirus (FCV) as the target organism. FCV and NLV belong to the same family and are similar genetically and physically. FCV however grows rapidly in cell culture and produces characteristic cell damage effects. It therefore seems a satisfactory model to determine the efficacy of disinfectants against NLVs.

When tested at the manufacturers' recommended concentration, none of the disinfectants was effective on stainless steel surfaces experimentally contaminated with FCV.

None of three QACs tested alone was effective against the virus at the concentration tested. However, when the same compounds were used in combination with sodium bicarbonate, they were able to effect a greater than 3-log (1000 fold) reduction in virus on stainless steel provided twice the recommended concentration of disinfectant was used.

The peroxyacetic acid and hydrogen peroxide combination was effective only at four times the recommended concentration and that for a contact time of 10 minutes. The sodium hypochlorite solution was tested at 200, 400 and 800 mg/L of free chlorine. It was not effective at these concentrations when effectiveness was measured as a reduction of at least 1000 fold in viral numbers.

The iodine based compound was not effective at 300 mg/L, four times the concentration recommended by the manufacturer for environmental surface disinfection. The two phenolic preparations used reduced the virus concentration by more than 5-log (100,000 fold) when used at four times the recommended concentration.

After experimentally contaminating the strawberries and lettuce with FCV, the researchers found that washing with water alone for 10 minutes reduced the recovered population of virus 100 fold. However none of the three sanitizers tested was successful in obtaining a 1000 fold reduction on contaminated strawberries or lettuce when used at the manufacturers' recommended concentration for contact times up to 10 minutes.

When each was used at four times the concentration recommended, only the peroxyacetic acid and hydrogen peroxide combination was successful in obtaining the desired 1000 fold reduction in virus on the fresh produce.

While noting the constraints imposed by the experimental design, particularly the use of FCV as a model for NLV and the arbitrary target of a 1000 fold reduction in recoverable virus, the authors conclude that FCV (and therefore NLV) was resistant to common antimicrobial formulations even when these were used at higher than normal concentrations. They recommend that prevention of outbreaks of foodborne calicivirus, including NLV, depends on maintaining correct hand washing practices and excluding ill food workers from the establishment.