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New method to inhibit E. coli in sprouts

By staff reporter , 02-Nov-2009
Last updated the 03-Nov-2009 at 13:24 GMT

A treatment method using supercritical carbon dioxide (SC-CO2) can help ensure the safety of fresh produce such as alfalfa seeds in terms of Listeria, Salmonella and E. coli contamination, claims new research.

Supercritical carbon dioxide (SC-CO2) treatment is a non-thermal food preservation technology that can inhibit foodborne pathogens without or with minimum impact on the sensory and nutritional qualities of solid and liquid foods, say the scientists in findings published in this month’s International Journal of Food Microbiology.

Transit risk

Fruit and vegetables are flown around the world over long periods of time, giving harmful pathogens an opportunity to breed during transit, meaning food processors have to be even more vigilant.

New processing technologies that can increase food safety without the use of destructive chemicals or harmful heat is attractive to processors, along with the possibility of lower costs.

Heat processes can often reduce the quality of foods.

Germination capability

The authors of this study claim that only a few previous studies have applied SC-CO2 to solid foods, including seeds, and the effects of SC-CO2 on microorganism inactivation and the seed germination capability have not been extensively studied.

“We sought to develop a method of decontaminating alfalfa sprouts of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium without altering the seed germination capability using SC-CO2,” explained the authors.

The results show that treating seeds with SC-CO2 at higher pressures, temperatures, or for longer treatment times resulted in greater microbial reductions than treatments at lower pressures, temperatures, or for shorter treatment times.

Method

According to the authors, samples were treated with SC-CO2 at 10, 15, or 20 MPa and temperatures of 35, 40, or 45°C for five, ten or 15 minutes.

The germination percentage was measured after three days of germination

The outcome

The researchers maintain that SC-CO2 treatment clearly reduced the microorganism levels in alfalfa seeds:

“In particular, treatment at 20 MPa and 45°C for 15 minutes reduced levels of the three pathogens by > 7.0 log colony forming units (CFU)/g,” they reported.

However, the researchers conceded that SC-CO2 treatment at a high pressure and high temperature impaired the seed germination capability in some cases.

“Without impairing the germination capability, the maximum reduction level of E. coli O157:H7 was 3.51 CFU/g with SC-CO2 treatment at 15 MPa and 35 °C for 10 minutes.

Maximum reductions of L. monocytogenes and S. typhimurium were 2.65 and 2.48 log CFU/g, respectively, with treatment at 10 MPa and 45 °C for five minutes,” found the authors.

They conclude that their results indicate that SC-CO2 treatment can be used to effectively improve alfalfa seed safety.

Source: International Journal of Food Microbiology
Published online ahead of print: doi: 10.1016/j.ijfoodmicro.2009.08.014
Title: Potential use of supercritical carbon dioxide to decontaminate Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium in alfalfa sprouted seeds
Authors: W.Y. Jung, Y.M. Choi, M.S. Rhee

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