Thursday, September 16, 2010


Eggs are in the news lately for all wrong reasons. There was the massive recall of more than half a billion eggs suspected of salmonella contamination in the US. Packed battery cages used for housing the birds in industrial poultry farms became an emotive issue attracting the attention of a wide segment of consumer population forcing some governments to ban such practices and prescribe mandatory standards for such cages. Considering that eggs are invariably consumed after cooking, minor bacterial contamination should not pose any serious health hazard. But in western countries there are "cold" products that do not undergo the required 72C heating during preparation and they can be risky to consumers, especially those whose immune system is not strong and other vulnerable population. Pasteurized eggs are now available in some markets though they are more expensive. Similarly organic eggs also are supposed to be safe though how they get rid of poultry house contaminants without using chemicals is not known.

Detailed investigations into the egg contamination episode in the US by the authorities concerned revealed how negligent the poultry farms were in managing the operations and the feed storage areas as well as nearby facilities which were heavily infested with rats, considered a major source of Salmonella contamination. The cages were not sterilized periodically as required under good manufacturing practices and birds were over packed in cages giving no room for them even to stand. Under such primitive conditions it is no wonder the eggs from these farms were contaminated. The consequences of such tainted eggs getting into the kitchen raises the possibility of cross contamination to other foods stored together. The egg washing operations which are supposed to remove bulk of the contamination also could have been compromised. It is supposed to be a standard practice for the freshly laid eggs to be washed using detergents and chlorine to disinfect them before sending to the market.

Pasteurized eggs are produced by exposing the eggs to a temperature of 62C to 72C for a period go 3-5 minutes but it requires great caution as just 15 cells of a pathogen would be adequate for causing food-borne illness. It generally takes 6 hours to 48 hours after consuming an infected egg, to see the manifestation of sickness through symptoms like nausea, vomiting, stomach cramp, head ache and diarrhea. As per FDA rules a 5-log reduction is necessary if it takes 3-log reduction to destroy the pathogens. Standard practices of washing followed by coating of the eggs with special mineral oil formulations can be expected to keep the egg free of contamination and arrest quality deteriorating changes at a temperature of 4C. Natural egg has a bloom that covers the surface, protects the contents from ingress of pathogens through the micro pores and development of air cells with aging, deteriorating the over all quality of the egg. Development of egg coating oil formulations is intended for use after the egg is washed and dried which replaces the natural bloom that decomposes with time and affords same protection as the bloom. How ever very few practice egg coating because of the tediousness of the process and productivity constraints.

Recent development of a rapid cooling technology with potential for commercial application appears to be a promising new approach for making eggs safe for consumption. According to the present guidelines cooling of eggs is useful in preventing microbial proliferation but the period within which egg has to be cooled is not clearly spelt. It takes almost a week for the eggs in a large pallet to attain a temperature of 4C at which Salmonella can no longer grow. This is because the egg temperature, when they are packed in cartons, remains high around 38C which can be favorable for growth of pathogens. It is estimated that one in every 20,000 eggs would be contaminated and these eggs mostly hail from the center of the cartons where low temperatures are not attained easily during cooling.

The new technology uses conditions around -50 to -70C in a CO2 atmosphere to reach the freezing temperature of albumin when a thin layer of ice is formed in the shell-albumin boundary and under such a condition egg is supposed to be free from pathogens. Besides this rapid cooling which takes hardly 90 seconds doubles the shelf life of the egg, from 6-8 weeks to 12-15 weeks. The cryogenic CO2 cooling is claimed to cost only 2-5 cents per dozen eggs under commercial conditions. According to safety experts if the eggs are cooled to 7C within 12 hours of laying, the Salmonella poisoning can be reduced by almost 80%. Though technically it is a viable process its economic dimensions need to be worked out, especially the investment part of it before it can become the industry standard.


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