Control Salmonella on tomatoes.

The consumption of fresh tomatoes has been associated with outbreaks of salmonellosis. The primary sources of the Salmonella on tomatoes are not known, making prevention of contamination a challenge.

Contamination of internal tissues can also occur when tomatoes with contaminated surfaces are sliced. Since fresh tomatoes are increasingly being marketed in sliced and diced forms, additional control over this hazard would be helpful. One way to control the pathogen is to package tomatoes in an atmosphere containing an antimicrobial that would be effective during their expected shelf life. Scientists at the University of Georgia undertook a study to determine the effectiveness of three volatile antimicrobials, carvacrol, cinnamaldehyde and allyl isothiocyanate, in inactivating or preventing the growth of Salmonella on the skin surface of whole tomatoes and in the flesh tissue of sliced tomatoes.

The investigators tested carvacrol and cinnamaldehyde at 25, 50 and 75 [micro]l per L of headspace. Allyl isothiocyanate was tested at 3, 6 and 12 [micro]l per L of headspace. Tomatoes were inoculated with a mixture of Salmonella serotypes. The Salmonella grew by about 2.4 log CFU per g when tomato slices were stored at 10 C for seven days. Carvacrol and cinnamaldehyde prevented growth at all concentrations tested. All test concentrations of allyl isothiocyanate inactivated the pathogen by 5 log CFU per g.

The population of Salmonella remained constant on whole tomatoes stored at 10 C. Salmonella grew on sliced tomatoes stored at 25 C. Allyl isothiocyanate, but not carvacrol or cinnamaldehyde, inhibited growth at this temperature. Salmonella did not grow on the tomato surface at 25 C. At the lowest concentrations tested, all three antimicrobials decreased populations on the surface by more than 1-log CFU per g.

It may be possible to control Salmonella on packaged tomatoes by permeating the headspace with low levels of volatile plant-derived antimicrobials. These antimicrobials inhibited growth of Salmonella, which was also inactivated on the tomato surface. Other researchers have shown that allyl isothiocyanate has a tendency to cause tissue browning, so this requires additional investigation. Sensory analysis of the treated tomatoes is also needed.

Further information. Michael Doyle, Center for Food Safety, University of Georgia, Griffin Campus, Melton Building, Griffin, GA 30223; phone: [phone]; fax: [phone]; email: [e-mail].

The acidity and pH of the internal tissues of tomatoes are insufficient to prevent the growth of Salmonella. The pathogen can infiltrate tomato tissue as a result of temperature differentials created by immersing warm tomatoes in cold water.