K. Vorst’s research while affiliated with Iowa State University and other places

There have been very limited time and temperature profiles published for the United States indicating the conditions experienced by fresh-cut, bagged leafy greens during U.S. cold chain transport and distribution. The objective of this study was to monitor and fully characterize truck trailer temperatures during the transport of fresh-cut leafy greens shipped from Salinas, CA and Yuma, AZ, to distribution centers across the United States. A total of sixteen shipments were monitored for trailer temperature from June, 2010 to May, 2011, utilizing trailers provided by multiple major Western processor/shippers. Twenty-four or thirty temperature loggers, total, were placed on six pallets and along the sidewalls during the loading of each trailer. Sensors were placed on pallet stacks at the front, middle and rear of each trailer. Two pallet stacks positioned side-by-side were monitored at each location. Additional sensors were placed 4 feet above the floor on each sidewall adjacent to the monitored stacks. In five of the sixteen shipments, an additional sensor with a probe was placed in each monitored stack at the middle position and the probe was inserted 24 inches into the center of the stack. Data was analyzed for the effect of location within a trailer, on a sidewall, or on or within a pallet; and on a pass/fail basis where any sensor in a trailer recording temperatures above 5 °C subjected the entire load to rejection. Analyzing sensor data on a pass/fail basis yielded highly skewed results as the analysis indicated all trailers failed to maintain adequate temperature during transit. However, only 16.7% of the 431 sensors used in the study recorded temperatures greater than 5 °C and nearly twice as many (47) were found on sidewalls than pallets (25). The FDA standard for pre-cut leafy greens appears to overestimate high temperature abuse as it does not consider where the abuse is occurring in a trailer. Cold temperature abuse was less extensive with only 39 of 431 sensors recording temperatures below -0.17 °C. The data suggests that the product was also under-heated in fall as 22 of 39 sensors recording temperatures <-0.17 °C did so during this period. Though the interior was not greatly different in temperature than the exterior of pallet stacks (2.87 vs. 2.09 °C, respectively), the results indicate the importance of proper stacking and good air-flow around boxes of product in a trailer. For some runs, localized freezing of pre-cut greens may have occurred but, overall, the trailer refrigeration units appeared to be efficient though there was large variability in trailer performance. Microbial modeling utilizing Escherichia coli O157:H7 and Listeria monocytogenes should be conducted based on the cold-abuse profiles generated in this study to determine the potential for the growth of these microbes on pre-cut leafy greens during subsequent retail storage and display.

Agencies such as the Environmental Protection Agency and Agency for Toxic Substances and Disease Registry are pushing for increased use of recycled polyethylene terephthalate. Packaging materials made from recycled polyethylene terephthalate are used for direct food contact in recycled rigid containers and films. Most recycled polyethylene terephthalate packaging materials contain heavy metal catalysts, the most common being antimony. The recycling process has the potential to increase degradation products, chemical additives and polymerization side-products. Recent studies using inductively coupled plasma-atomic emission spectrometry confirmed the presence of cadmium, chromium, lead, nickel and antimony in food packaging. These heavy metals have the potential to migrate onto and into food products, and limited governmental regulation of these contaminants in recycled polyethylene terephthalate packaging materials increases public health risks. In this study, 22 samples of known heavy metal content were tested for heavy metal migration of lead, cadmium, chromium, nickel and antimony into a 5% aqueous citric acid solution or deionized water. Samples were exposed for 5 min to microwaves from a 1700 W microwave oven set to 70% power, or were stored at 7.2 or 22.2℃ for 1, 7 or 14 days before testing. The samples were analyzed for heavy metal content per ASTM E1613-04, the standard test method for the determination of lead by inductively coupled plasma-atomic emission spectrometry. Neither the storage nor the microwave treatments had a significant effect on heavy metal migration, while exposure to 5% aqueous citric acid resulted in a higher rate of heavy metal leaching from the recycled polyethylene terephthalate compared to samples exposed to deionized water. A very low percentage of the samples tested had heavy metals migrate above detectable levels indicating that most recycled polyethylene terephthalate packaging materials are relatively safe for direct food contact.

Polyethylene terephthalate food-product containers made with post-consumer materials have been found contaminated with heavy metals due to the recycling and sorting process. The increased use of recycled plastic flake from international suppliers, and subsequent commingling with electronic waste, has been suspected as the source of the increased levels of heavy metal contamination. In this study, nickel, chromium, cadmium, antimony, and lead were quantified in post-consumer polyethylene terephthalate extruded sheet and thermoformed samples, using inductively coupled plasma-atomic emission spectrometry. Recycled polyethylene terephthalate samples were digested using trace-metal grade hydrochloric, perchloric, and nitric acids. Samples were analyzed per ASTM E1613-04, standard test method for determination of lead by inductively coupled plasma atomic emission spectrometry, flame atomic absorption spectrometry, or graphite furnace atomic absorption spectrometry techniques. Two hundred samples were tested of which 29 were found to be contaminated with heavy metals. Chromium and cadmium were found in all 29 sample replicates. Nickel was found in 96.4% of the sample replicates and when it was found, the concentration averaged 11.59 ppm. Lead was found in 90.4% of the sample replicates and the average concentration was 0.15 ppm. Antimony was found in 97.6% of the sample replicates and concentrations were higher in rigid recycled polyethylene terephthalate containers compared to films. It was noted that the total contamination in all 29 samples was well below the threshold level set for the incidental presence of heavy metals in packaging materials as set forth in California’s Toxics in Packaging Prevention Act of 2006. The percentage of each heavy metal that would actually leach from the plastics to contaminate food products during normal processing, packaging, marketing, and consumer use was not determined in this study.