Microwave treatment eliminates salmonella on vegetables: Study

Exposing fresh vegetables with water-assisted microwave treatments can significantly decrease the presence of salmonella typhimurium, according to researchers at the Universidad de las Américas Puebla, Mexico.

The study, which was led by M.E. Sosa-Morales, was aimed at developing microwave treatments to inactivate salmonella on vegetables, without affecting their sensory or physical characteristics.

While there are several treatments such as thermal or ozone disinfection, instances of salmonella outbreaks because of the contamination of green vegetables indicate current disinfecting procedures are either not being properly implemented or are not enough to limit the bacterial growth.

For the study, researchers immersed jalapeño peppers and coriander foliage, in a litre of water that contained 1ml of salmonella inoculated triptycase soy broth (TSB) for a period of 15 minutes to ensure bacterium growth on the vegetables.

Following, the vegetables were drained under sterile environment, immersed in water and treated in a domestic microwave oven at 950W to reach 63°C.

The jalapeño peppers were exposed for 25 seconds and coriander foliage for ten seconds. After the microwave heating, samples were cooled in water at 4°C and then evaluated using a confocal microscope.

The researchers found that microwave exposure led to a reduction of 4-5 log cycles on the salmonella population, a microbiologically safe level. While the treatment affected the colour of vegetables, as darkening was observed in jalapeño peppers and loss of greenness in coriander foliage, the firmness and sensory characteristics remained the same.

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

Caption: Salmonella contamination of green vegetables is still a major problem even though several treatments are available. Image courtesy of National Institutes of Health.