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Microwaves effective in zapping Salmonella on fresh vegetables - study

By Rory Harrington , 12-Jan-2012

Exposing fresh vegetables to short bursts of microwave energy can significantly reduce the presence of Salmonella Typhimurium, according to new research.

Scientists from Mexico said using water-assisted microwave treatments on fresh jalapeno peppers and coriander foliage were highly effective in inactivating the pathogenic bacterium on the green vegetables.

However, while the process affected the colour of peppers and jalapenos, their firmness remained unchanged, said the team from Universidad de las Américas Puebla.

Current methods not enough?

The paper, by M.E. Sosa-Morales et al, acknowledged that a number of treatments - such as thermal of ozone-disinfectants - had already been developed. But they suggested that continued incidences of Salmonella outbreaks in green vegetables could mean that “current disinfecting procedures are not being properly used or are not enough to inhibit the bacteria”.

Microwaves have not previously been used for disinfecting coriander foliage or jalapenos. The object of the study was to develop microwave treatments to for ensure products were not contaminated without affecting their physical and sensory characteristics.

The study - Inactivation of Salmonella Typhimurium in fresh vegetables using water-assisted microwave heating – was published in the journal Food Control.

Method and results

The vegetables were immersed in water and treated in a domestic microwave oven at 950 W to reach up 63C. The jalapeño peppers were exposed for 25 seconds and coriander foliage for 10 seconds. After the microwave heating, samples were cooled in water at 4C.

Prior to microwave exposure the vegetable were immersed in a litre of water that contained 1mL of Salmonella inoculated triptycase soy broth (TSB). This was left to stand for 15 minutes to ensure the bacterium population on the vegetables. The peppers and coriander were then drained under sterile conditions.

Samples were observed with a confocal microscope before and after treatment.

The researchers said the method resulted in a reduction of 4-5 log cycles on the Salmonella population.

“This means that a microbiological safe product, respect to Salmonella presence, can be obtained by a simple microwave treatment,” said the study.

However, the treatment did affect the colour of the products - mainly by darkening in both vegetables and loss of greenness in jalapeño pepper.

But there was no loss in firmness and sensory acceptance of a salsa formulated with the treated vegetables had high scores - 7.21 in a 9-points hedonic scale.

The team said that method had fulfilled its objective by reducing Salmonella counts and making the foods microbiologically safe.

Inactivation of Salmonella Typhimurium in fresh vegetables using water-assisted microwave heating, B. De La Vega-Miranda, N.A. Santiesteban-López ,A, López-Malo,, M.E. Sosa-Morales, Food Control, http://dx.doi.org/10.1016/j.foodcont.2012.01.002

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