Killing salmonella, avian flu in eggs

16 November 2005

A consortium led by the Council for Scientific and Industrial Research (CSIR) has developed a new system that pasteurises raw eggs to destroy the dangerous Salmonella enteritidis bacteria – and could kill the virus that causes avian influenza.

Salmonella can cause potentially lethal diarrhoea and is a major concern for the restaurant trade, which uses raw eggs in puddings and sauces.

With increased restrictions on feed antibiotics administered to chickens, the incidence of salmonella is rising. Many countries have recently had to take measures to contain salmonella outbreaks.

The World Health Organisation reports that 40% of food poisoning cases in Europe are a result of infected eggs. In Africa, the higher incidence of HIV can make the consequences of salmonella poisoning more serious in immune-compromised individuals.

To tackle the problem the research consortium pooled the skills of the CSIR, the University of Pretoria, Delphius Technologies and Eggbert Eggs, the country’s second largest egg producer. Financial support came from South Africa’s Innovation Fund.

The process works with low-frequency microwaves and hot air, says Nell Wiid, managing director of Eggbert Eggs. The eggs are placed in a specially designed microwave oven and are heated to between 50°C and 70°C, killing the salmonella bacteria without cooking the eggs.

Pasteurised eggs are sold in the US, but they cost up to three times more than untreated eggs, says Wiid. Moreover, the US system uses an impractical water-bath technique that partly cooks the egg white.

The South African technique requires a specially designed oven cavity and phased process developed by Delphius Technologies, specialists in the development of industrial microwave ovens. The consortium is seeking an international patent for the ovens and processes.

“The most difficult part of the project optimising the heating curve and identifying hot spots,” says Wiid. “Eggs vary in shape, mass, position of the yolk and heating profile and the microorganisms are sensitive to many of these variables.”

The bird flu threat
By the time the consortium’s work had produced results, warnings by the World Health Organisation on bird flu led the team to expand its research to include testing on a low-virulence strain of the avian flu virus.

“Preliminary results from these trials indicate that the new pasteurisation technology also destroys the avian influenza pathogen,” says Dr Gatsha Mazithulela, the CSIR’s executive director for biosciences.

“While all indications are that South Africa is currently free of avian flu, we are encouraged by these results and by the future potential of this technology as one possible preventative measure.”

From December South African consumers will be able to buy pasteurised eggs – clearly marked as “Safe Eggs” and “Pasteurised Eggs” – from supermarkets. They will cost about 8c more than unpasteurised eggs. The eggs also have an extended shelf life of at least double that of unpasteurised eggs, and can be kept for up to six weeks at 18°C to 22°C.

Huge international interest in the technology has taken Wiid to Belgium and France, and he is optimistic that South Africa could significantly benefit from this innovation. reporter

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