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California Polytechnic Studies E. coli and Bagged Greens

Researchers will use RFID sensor tags to measure the real-time temperature and humidity levels of lettuce and spinach during shipment from packer to retailer, then replicate those conditions in a lab.
By Claire Swedberg
Oct 09, 2009With a $600,000 National Integrated Food Safety Initiative (NIFSI) grant from the U.S. Department of Agriculture (USDA), a team of researchers from several universities are embarking on a three-year study using RFID sensors to track the temperature and humidity conditions of leafy green vegetables in the supply chain. Led by a group of scientists at California Polytechnic State University, the study—which is expected to be fully underway in the first quarter of 2010—is intended to determine when, and under what conditions, food-borne illness contamination develops in "at risk" product (in this case, bagged spinach and lettuce).

The researchers will place the RFID sensors in produce containers within trucks used to ship the food, in order to measure temperature and humidity levels, as well as when fluctuations occur and how they may correspond with the incidence of Escherichia coli (E. coli) and other pathogens in produce sold by retailers. For example, the humidity level can affect the permeability of the plastic bag in which greens are packaged, thereby reducing the product's shelf-life. Researchers also hope to use the study's results to provide training for packaging and distribution professionals, in order to prevent food-borne illness through the monitoring of fresh products during transport and distribution.

California Polytechnic assistant professor Keith Vorst
The study, part of a project entitled "A Systems Approach to Minimize Escherichia coli O157:H7 Food Safety Hazards Associated with Fresh- and Fresh-Cut Leafy Greens," will include at least four produce packers, as well as major retailers, trucking companies and distribution centers (DCs). The team is employing Sensor Wireless' Active Wireless Sensor (AWS) 2.4 GHz ZigBee RFID tags with built-in temperature and humidity sensors that transmit to a central receiving unit with a GPS receiver to track a truck's location and send that data via a GPRS connection.

The study will focus on leafy greens because E. coli has been prevalent in such produce. Since 1993, at least 25 E. coli outbreaks have been traced to leafy green vegetables—primarily lettuce and spinach. There has been little tracing of temperature or humidity during commercial transport of leafy greens, says Keith Vorst, an assistant professor at California Polytechnic and the study's principal investigator. For that reason, he notes, the team is interested in gaining visibility into the products' temperature under commercial transport and warehouse conditions.

The AWS technology will enable researchers to receive data regarding the conditions of lettuce and spinach shipments in real time, according to Wayd McNally, Sensor Wireless' president—though in the early part of the study, Vorst says, the data will be examined mostly at the end of the shipment.

With the study, California Polytechnic's researchers will place AWS sensors (27 per shipment) in cartons of greens as they are loaded into trucks by the university's researchers, on the West Coast, East Coast and Midwest—with five trucks being tracked in each region. Tracking the temperatures and humidity to which each product is exposed could be made more complex due to the unloading and reloading of products at DCs, including mixed pallets containing products from multiple locations. For that reason, the sensors are being placed within the cartons rather than on pallets.

Every two minutes, the sensors will measure the temperature and humidity within the trucks at various areas around the produce, then transmit that data to a Sensor Wireless Sensor Communication Interface (SCI) unit, which functions as an RFID interrogator. The SCI, in turn, sends the information, including location, to Sensor Wireless' software on its server, via a GPRS signal. Whether the vehicle is at the loading dock or on the highway in transit, as long as there is a cellular connection, the SCI transmits the tag data every two minutes.

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