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Advancement of Non-Thermal Process Technologies that Produces Safe Fresh Foods with High Consumer Acceptance

Lee, Ken
Ohio State University
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The objective of this project is to test e-beam irradiation on fresh products that are produced for sale by Ohio companies and determine those with the highest promise for further development. Potential candidates for testing include cabbage, green beans, spinach, collard greens, parsley, and garlic. The hypothesis is electron beam irradiation will reduce or inactivate pathogenic microorganisms to safe levels in fresh Ohio produce.

This hypothesis is based on prior research and preliminary data reviewed here. Fresh produce samples will be provided by Sandridge Food Corporation or Greenline Foods. E-beam irradiation will be conducted at NeoBeam in Middlefield, a unique facility in Ohio that is part of Kent State University.

This project has a high likelihood of success as it is based on promising preliminary data, uses the unique commercial e-beam facility in continuous operation at Kent State, and pools the irradiation, food safety and microbiological expertise of the collaborators.

Key hypotheses will be tested via these two objectives:

Objective 1: Measure inactivation of food-borne bacteria on fresh produce by electron beam irradiation. The hypothesis is that indigenous microflora and Escherichia coli K12, a non-pathogenic surrogate, will be susceptible to irradiation treatment.

Objective 2: Determine the radiation susceptibility of a food-borne virus surrogate. The hypothesis is that murine norovirus, a surrogate for human norovirus, will be more resistant to irradiation than bacteria, but will be susceptible to irradiation at increasing dosages.

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NON-TECHNICAL SUMMARY: Consumer demand for minimally processed foods creates the need for novel, non-thermal food processing systems that maintain quality attributes. These attributes, which would normally be lost during thermal processing, include appearance, texture, nutrients, or flavors. Novel non-thermal processing technologies show promise for maintaining high quality attributes, as well as controlling pathogenic and spoilage microorganisms. Irradiation was approved by the FDA to treat fresh produce, among numerous other food products. With regards to fresh produce, the dosage of ionizing radiation to control food-borne pathogens may not exceed 4.0 kGy (kilogray) for iceberg lettuce and spinach, and may not exceed 8.0 kGy to control pathogens on seeds for sprouting. We use e-beam irradiation, where an accelerator produces beams of accelerated electrons that can be aimed at the food directly. The electron beam can either be directed at a heavy metal target to produce X-rays, or can be aimed at the food itself. Unlike gamma irradiation, e-beam irradiation can be switched off when not needed, but it has a limited penetration depth of < 3.3 cm. All irradiation technologies kill microorganisms by causing covalent breaks in genetic compounds, or disruption of enzymes, plasmids, and membranes. Water is very important during irradiation because water molecules lose an electron (H2O → H2O+ + e-) and easily produce reactive compounds that disrupt chemical bonds in DNA. The susceptibility of various organisms to e-beam is dependent on their physiological characteristics. Non-sporeforming bacteria tend to be more susceptible to irradiation, with Gram negative enteric bacteria being the most susceptible. Spore-forming bacteria and viruses are much more difficult to kill with irradiation. Spores have a much lower water content thus making them resistant. Viruses are also low in moisture content and have a much smaller physical and genomic size than bacteria making them difficult to inactivate. Another drawback is consumer acceptance of irradiated food products. Consumers tend to associate irradiation with cancer, weapons, or x-rays. Although consumers are skeptical of irradiated goods, research has found a positive correlation between consumer knowledge and irradiation acceptance. After being educated about irradiation, consumers are more willing to try an irradiated product once, and will continue to provided that the products are acceptable and safe for consumption. Research on e-beam irradiation has shown great promise for uncooked and ready-to-eat produce.

APPROACH: Objective 1: Measure inactivation of food-borne bacteria on fresh produce by electron beam irradiation. Produce samples will be provided by Sandridge Food Corporation or Greenline Foods. Samples will be placed into polyethylene pouches, and will either be inoculated with E. coli K12 (to achieve 106 CFU/g) or uninoculated. Pouches will then be sealed with a heat sealer. Pouches will be assigned to treatments of 0 (positive control), 1, 2.3, or 4 kGy in duplicate. Samples will be placed in coolers with ice packs and transported to NeoBeam in Middlefield, Ohio for e-beam treatment, then be transported back to OSU for microbial analysis. Samples will be diluted (1:10) and stomached with 0.1% peptone water. Serial dilutions will be performed, with subsequent plating to tryptic soy agar (TSA) and MacConkey agar (MAC), to determine total aerobic bacterial counts and Gram negative counts, respectively. Interpretation. Three replicates reveal differences in bacterial populations after treatment that are tested with one-way analysis of variance (ANOVA) at the ƒ¿=0.05 level. The results determine the most effective irradiation doses to inactivate spoilage and pathogenic microorganisms on fresh produce. This information will be shared with the Ohio food industry to help improve the safety of food. Results will also be shared with the scientific community and the public through presentations and peer-reviewed articles. Potential problems with the research could include contamination of the TSA or MAC plates. If contamination occurs, the experiment will be terminated, and performed again. If E. coli K12 grows poorly or not at all in control samples, the inoculation levels can be altered accordingly. Although irradiation is FDA approved, consumer acceptance is evolving. . Objective 2: Determine the radiation susceptibility of a food-borne virus surrogate. Samples of produce will be inoculated with approximately 106 PFU/g murine norovirus (MNV-1). The experimental design will be identical to the design described in Objective 1, except that samples will be treated at 0, 1, 2, 4, 6, 8, 10, and 12 kGy. The reason for the higher doses is because viruses are much more difficult to inactivate with irradiation. Methods. Samples will be diluted (1:1) with PBS and stomached. Serial dilutions will be performed and applied to plaque assays to determine viral populations remaining on samples. If no virus is detected, reverse transcriptase PCR (RT-PCR) will be used to detect if viral RNA is still present. Three replicates reveal differences in viral populations after treatment will be tested with one-way analysis of variance (ANOVA) at the ƒ¿=0.05 level. Currently, no research has been conducted on the effect of electron beam irradiation on food-borne viruses. Data generated from this study will be disseminated through scientific presentations and peer-reviewed articles.

Funding Source
Nat'l. Inst. of Food and Agriculture
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Chemical Contaminants
Bacterial Pathogens