Sunday, September 16, 2007

It’s not rocket science, but…..

How many times do we hear that expression? And anyway, who decided that rocket science should be the datum for the rest of us? The success rate in that field could be improved a lot!

I want to show that simple experiments can be valuable.

Food poisoning doesn’t seem to be going away, in spite of the many articles published, television advertorials and the plethora of antibacterial cleaning agents on the market. The current concern about fresh poultry being a source of Campylobacter in the kitchen has lead to dishcloths being suggested as potential vectors of cross contamination. We all know this already, but we continue use them. Can we make them safer? Should we move to paper towels (not always convenient and perhaps environmentally unfriendly) or should we take the more expensive approach using cloths but discarding them more often? Should we boil them or put them in the dishwasher?

Standard fabric cloths were used in the kitchen for a week in the normal way. The cloths were then cut up and Standard Plate Counts were performed on Plate Count Agar. The samples were then treated by one of the following: economy wash cycle with a mdium load of dishes in a dishwasher; microwaving for 20 seconds on high (1 Kw); washing in hot water containing dishwashing detergent, or treating with hypochlorite solution containing 200ppm free chlorine. The samples were then counted again. Four complete replicates were performed. The results are shown below as a graph of log(APC/g) vs treatment; the error bars represent one standard deviation.

We can take several important points from these results:
• Used for a week, dishcloths become “microbial zoos” and a major source of contamination in the kitchen when the cloth is used to wipe benches etc.
• Hot water washing has little effect on the population size
• Bleach reduces the count by a factor of only10, probably because it is rapidly inactivated by the organic materials
• Dishwashing reduces the count by about 100x
• Microwaving is apparently the best treatment, reducing the count by a factor of over 1000x but there is still a very large population present, which can be spread around the kitchen.

This was a simple experiment that shows us some very important facts about the safety of everyday items in our food preparation areas. It might not be totally original, but that doesn’t affect the interpretation.

Who was the non-rocket scientist who made these measurements? The experiment was planned and conducted by Elisabeth Bakker, an eleven year old schoolgirl in Palmerston North, New Zealand, who submitted her research for a science fair project.

Wednesday, September 5, 2007

Deadly Poison in the Kitchen - updated

February 29, 1984, was an unusual day for New Zealand – it was leap year and the date when the country’s first ever cases of human botulism were confirmed.

Botulism is quite rare in the developed world, (fewer than 200 cases of all forms of botulism are reported each year in the United States) but not a new disease. Emperor Leo VI of Byzantium forbade the eating of blood sausages because the link between their consumption and the disease was recognized. However, it was not until 1895 that it was understood that the disease is caused by the growth of bacteria in the food. Clostridium botulinum can produce one of the most deadly toxins known to man. The toxin is so potent that the lethal dose for humans is approximately 1 μg/Kg body weight.

In the last year there have been several cases of intoxication by foods containing botulin toxin reported around the world – a man in Ireland became ill after eating food sent to him from Poland; bottled carrot juice caused several cases in apparently related incidents; canned chili, stew, hash and other foods were withdrawn from sale after an outbreak, but several days after the recall, the products were still on sale in stores.

In all these cases, the basic rules of food production and distribution had been ignored, or someone had failed to take proper care of the food. The isolated Irish case was probably the result of unsterile food being packaged in an airtight container, resulting in growth of the strict anaerobe C. botulinum and hence production of toxin. In the other cases, the foods were commercially manufactured. The carrot juice may have been pasteurised, but this will not destroy spores of C. botulinum, so the product required refrigeration; the canned products were all low acid foods and should have received a 12D* thermal process, which is sufficient to kill spores and sterilize the product. If this had not been properly delivered, or there had been post-process contamination, spores could have survived and germinated. As for the product remaining on the shelves after the recall, the only comment I can make is that the recall process was flawed, someone was grossly negligent or totally unscrupulous.

One final point: testing of canned foods for C. botulinum is impractical. No sampling plan could detect the one in 10^12 (a 1 followed by 12 zeros) faulty cans, so we are totally reliant on the correct delivery of the thermal process. The fact that the only case we have seen in New Zealand was caused by home-preserved food shows that our canning industry is getting it right.

* A 12D process is one designed to reduce the population by a factor of 10^12. In the case of low acid canned foods, such as canned meats or vegetables, this heating process is based on killing the spores of Clostridium botulinum.

Since I wrote this article, residents of Florida have been advised to throw out products manufactured by Gourmet de Lyon. This company produces food products from a kitchen in a Delray Beach restaurant that has no permit to produce or sell canned products or those sold in jars. It would be fair to say that many of the C. botulinum cases seen in developed countries are caused by consumption of low acid canned foods produced by unlicenced manufacturers or home-canned goods sold illegally. The problem stems from the inability of such producers to control the process sufficiently accurately to ensure the destruction of the C. botulinum spores, which are highly resistant to heat.

For more information on the Florida case, see Bill Marler's website:

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