Tomato Salmonella research to study role of plastics and dry biofilms

By Rory Harrington

- Last updated on GMT

Related tags: Bacteria, Salmonella

New research on the safe handling of tomatoes will examine how plastics in food contact materials and gloves used by workers can affect the formation, transfer and survival of salmonella in the fruit.

A team from the University of Massachusetts Amherst, in the US, has received a US$235,000-grant from the Center for Product Safety, Davis, California, as part of a drive to improve food safety in growing and harvesting fresh produce.

The project, due to begin this month, will also seek to yield new knowledge about how and under what conditions bacteria form biofilms on different surface types and provide practical, science-based guidelines on how to prevent cross-contamination.

At the UMass Amherst food lab, the group will set up an experimental tomato-handling station modelled on those found in farm fields in California and Florida. This will allow them to compare bacterial transfer rates on smooth versus abraded plastic packaging tubs and ramps. They will also evaluate contamination rates between work gloves made of a variety of materials. In this way, they can determine where and when Salmonella most often hitches a ride onto the tomato’s outer skin and into the food supply.

Brittle biofilms

"Bacterial cross-contamination from one surface to another is a more complex problem than we once believed,"​ project leader Lynne McLandsborough told FoodProductionDaily.com “Food scientists would like to better understand how moisture levels affect biofilms and bacteria dispersal, for example.”

The researcher added that her pervious work with Listeria monocytogenes had indicated that the dryer biofilms become, the greater numbers of cells break off and are transferred to foods.

“The level of transfer is dependent upon both the biofilm substrate material and the food,”​ she said. “Currently our working hypothesis is that the presence of water is a major component holding the biofilm cells and exopolymeric substances) together, so as the biofilm dries, it becomes less cohesive.”

Plastic factors

The research project will also be looking at whether the type, and condition, of plastics used to manufacture gloves and storage tubs has a food safety implication.

A variety of glove materials, such as nitrile rubber, low density polyethylene, and polyvinyl chloride vinyl will all be examined. The condition of high density polyethylene (HDPE) – used in the harvesting bins and pails - will also be considered to assess the survival, transfer and cleanability on ‘new’ and ‘worn’ surfaces, with varying amounts of organic load.

The ‘worn’ surfaces will be created by abrading the HDPE to varying degrees. Both the gloves and the HDPE will be treated with repeated sanitising treatments

“I believe we will find that on plastic (as with stainless steel) the abraded surfaces harbour more bacteria,”​ forecast McLandsborough. “And it will be interesting to determine if the sanitizer changes the characteristics of the gloves surfaces and bacterial transfer to these surfaces."

She added: “While we’re not sure about the cross-contamination levels we’ll find with these new experiments in Salmonella and tomatoes, it’s clear that growers need to know the facts and how best to carry out a safe harvest.”

Related topics: R&D

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