A bulletin for the Australian Food Industry February 1998
Contents: Maximum, safe food cooling times in food service situations | FDA approves irradiation of red meat | Monosodium glutamate revisited | Ochratoxin A in foods | AQIS Imported Food Inspection Program | Chlorine under challenge
Chlorine under challenge
Chlorine has been the biocide of choice for the food industry for many decades. When used correctly, it is regarded as both inexpensive and effective. Many regulations and guidelines applied to the food industry stipulate minimum free chlorine concentrations in water streams.
Its use in can cooling water has possibly been its most important function but it is also widely used in wash waters and in the fluming of fruits and vegetables between processing operations.
Chlorine does, however, have real limitations. The two most common criticisms of its use in this country have been its corrosivity in canning operations and its failure to perform effectively as a biocide in waters with high organic loading. This second deficiency has become a greater issue with the growth in the manufacture and marketing of peeled and sliced or diced vegetable products. Manufacturers have in general relied on the addition of chlorine to wash water to reduce the microbial load on vegetables, both to minimise the risk of food poisoning bacteria being present and to extend the shelf life of these products.
In general the shelf life has been disappointing even when adequate refrigeration is maintained. Also, an increasing number of published studies suggest that if pathogens are present on vegetables before washing, a proportion will remain after washing, even if initial free chlorine concentrations of 50-100 mg/L are employed in the wash water.
Other concerns about chlorine include the fact that chlorine reacts with phenolic compounds and the resultant chlorophenols cause tainting at very low concentrations. There are also environmental concerns about the build up in waterways of other chlorinated organic compounds.
There has therefore been a search for alternatives to chlorine for treatment of waters in the food industry. Of these, the compound which has attracted the most attention is chlorine dioxide which is a permitted water treatment agent in the Australian Food Standards Code.
The recent publication by the Campden & Chorleywood Food Research Association of its Guideline no. 15, Microbiological control of food industry process waters; guidelines on the use of chlorine dioxide and bromine as alternatives to chlorine, is timely. Bromine is not a permitted treatment agent for water which will come in contact with food in Australia but it has been trialled as an alternative to chlorine in can cooling systems.
In a comprehensive review of the properties of chlorine, bromine and chlorine dioxide as they might be used in the food industry, the guidelines make a number of important points about chlorine dioxide.
Amongst the advantages of chlorine dioxide listed are its biocidal activity up to pH 10 - chlorine is largely ineffective above pH 7.5; its low potential to form tainting compounds; and its better tolerance to organics than chlorine or bromine.
However the authors of the guidelines make the point that, as with the use of other halogens, incidence of heavy organic loading in treated waters will require the system to be drained down and replenished. In addition, chlorine dioxide is present in water as a dissolved gas and a proportion of it will be lost to the atmosphere during any process which involves spraying under pressure as is often the case in washing operations.
A number of food processors have expressed disappointment at the performance of chlorine dioxide as a biocide in practical situations. As with all these reactive chemicals, it is necessary to monitor carefully exactly what effective concentration is being achieved if maximum destruction of microorganisms is to occur in any given situation. It must also be realised that for microbial destruction to occur, the chemical must actually come in contact with the microbial cell.
Food Science Australia
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