Tomato production practices don’t significantly affect bacteria levels and the study’s results point to the need for additional research, according to University of Maryland and Rutgers University researchers.
From July to September 2012, researchers from the College Park-based University of Maryland’s College of Agriculture and Natural Resources’ Center for Food Safety and Security Systems and New Brunswick, N.J.-based Rutgers’ Cooperative Extension collected and tested 422 samples from 24 conventional and organic tomato farms from four growing regions in Maryland, Delaware and New Jersey.
The researchers analyzed 259 tomato fruit samples and also examined irrigation water, compost, field soil and pond sediment for Salmonella enterica, shinga toxin and bacterial indicators in pre-harvest tomatoes.
They didn’t detect any salmonella on the farms and the prevalence of shinga toxin, a byproduct of E. coli, was very low, said Shirley Micallef, an assistant professor who heads the Maryland university’s food safety center and Plant Science and Landscape Architecture department.
One curious finding was an apparent difference in bacteria present on tomatoes that touch the ground vs. tomatoes higher in a vine canopy that don’t contact the plastic or straw mulch.
Researchers found indicator bacteria on the ones that connected with the ground but no pathogens, Micallef said.
That discovery doesn’t mean tomatoes that touch the ground shouldn’t be harvested but only points to the need for additional investigation, she said.
Another finding was groundwater from the end of drip lines possessed higher indicator bacteria counts than the source water, Micallef said.
The difference in microbiological quality of water signals potential risk and points to the need for growers to conduct more frequent drip line system maintenance by testing water at the end of the line, she said.
The research also found no difference in contamination risk between conventional and organic tomatoes and study was also different because it focused on small and medium-sized growers, Micallef said.
“It was encouraging we didn’t find a huge problem because here in the Mid-Atlantic, we have had outbreaks associated with tomatoes,” she said. “It’s good to see growers really paying attention to GAPs (good agricultural practices) and trying to implement food safety practices as best they can in the fields. They probably do help to reduce the risk.”
The study is scheduled to be published in the March issue of the International Journal of Food Microbiology.