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ARS Home » Northeast Area » Wyndmoor, Pennsylvania » Eastern Regional Research Center » Residue Chemistry and Predictive Microbiology Research » Research » Research Project #420972


Location: Residue Chemistry and Predictive Microbiology Research

2011 Annual Report

1a. Objectives (from AD-416)
To determine sensory, nutritional and/or product quality impacts of efficacious food processing interventions and combinations of interventions. To develop antimicrobial packaging-based treatments for controlling pathogens. To identify compounds of potential concern formed by novel non-thermal food processing interventions. To develop/optimize treatment processes and combinations to control pathogens and to minimize loss of product quality and value.

1b. Approach (from AD-416)
An integrated approach to enhance microbial safety while maintaining product quality will be adopted by combining efficacious treatments and processes with antimicrobial packaging. Current antimicrobial treatments, processes, and intervention technologies that have been demonstrated to be effective in inactivating human pathogens will be modified and evaluated to confirm their effectiveness in obtaining a minimum 3 log CFU/g reduction of E. coli O157:H7 and Salmonella spp. on fresh and fresh-cut produce (mainly leafy green vegetables and tomatoes). Novel intervention technologies with higher efficacy of pathogen reduction will be developed and optimized. The impact of efficacious chemical and physical intervention technologies on sensory properties, nutrients, and shelf-life will be determined using the intensity (time, concentration, dose, etc.) that achieves a 3-log CFU/g reduction of the pathogens. In addition, new antibrowning/antimicrobial formulas will be developed to minimize risk of L. monocytogenes contamination during processing of cut fruit while inhibiting tissue browning. Furthermore, accumulation of chemical by-products as a result of chemical sanitizers and physical interventions will be investigated. Antimicrobial packaging as the final defense against human pathogens will be developed for a variety of food products (fresh-cut produce, meats, etc.) to reduce or control the re-growth of surviving pathogens during storage. Finally, combinations of efficacious intervention technologies with antimicrobial packaging will be evaluated for additive or synergistic inhibition of pathogens and preservation of product quality. Strategies and treatments will be developed to minimize adverse effects of intervention technologies and antimicrobial packaging on product quality. By combining efficacious intervention technologies and treatments with antimicrobial packaging, a 5-log reduction of common pathogens may be achieved. Intervention technologies either alone or in combination with antimicrobial packaging will be transferred to industry to enhance microbial safety of commercial food products.

3. Progress Report
A new coating solution has been developed to apply on tomatoes and cantaloupes. Experimental results showed that the coating treatment effectively reduced the population of Salmonella by more than 6 log-cycles in tomato stem scars and up to 5 log-cycles on cantaloupes. No re-growth occurred during 14 days storage at 10 C in both tomato and cantaloupes. The coating solution can significantly enhance microbiological safety of tomatoes and cantaloupe with no adverse effect on tomato’s quality. Antioxidant activities, organoleptic properties, and consumer acceptance of spinach leaves treated with radiation at doses up to 4 kilogray (the maximum permissible dose) were evaluated. Results showed that none of organoleptic properties were affected by irradiation at doses up to 2 kilogray, and overall antioxidants contents of spinach were not consistently affected by irradiation at any dose. Therefore, low-dose irradiation may be used to enhance microbial safety without affecting consumer acceptance or overall antioxidant values of irradiated spinach. The effects of ultraviolet light (UV-C) treatment alone or in combination with low-dose gamma irradiation on microbial loads and qualities of tomatoes and mushrooms were studied. Results showed that UV-C or its combination with low dose gamma irradiation reduced populations of native microflora and Escherichia coli O157:H7 inoculated on mushrooms and tomatoes. The treatment effectiveness was slightly higher for pathogens located on the skin compared to stem scar sites of tomatoes. UV-C treatments also inhibited development of brown spot on the mushroom surface. Therefore, UV-C radiation or its combination could potentially be used for sanitizing fresh button mushrooms and tomatoes, and extending shelf-life. A novel in-package ozonation system was evaluated for its effectiveness in reducing populations of Escherichia coli O157:H7, Salmonella spp. and Listeria spp. on tomatoes. High levels of ozone were generated within 1 min using the dielectric barrier discharge technology inside the packages containing tomatoes. The treatment effectively reduced the populations of microorganisms by 2-5 log-cycles, even in inaccessible sites such as the stem scar area. Longer treatment times did not further reduce microbial population. This technology will be of potential significance to processors and consumers of tomatoes. A continuous antimicrobial treatment vessel was designed and fabricated to evaluate the effect of continuous treatment on removal of pathogens in fruits and vegetables. It is expected that the new system could more effectively reduce the bacterial loads in treated fruits and vegetables.

4. Accomplishments
1. Use of nanoparticles to inactivate foodborne pathogens. Nanoparticles can be effective antimicrobial agents against foodborne pathogens. ARS researchers at Wyndmoor, PA, investigated the antimicrobial activities of two nanoparticles (magnesium oxide and zinc oxide) against three major foodborne pathogens: Escherichia coli O157, Salmonella Stanley, and Camplylobactor jejuni. The results demonstrated that these nanoparticles dramatically killed those pathogens and, therefore potentially can be added directly in foods or incorporated in packaging materials to improve microbiological safety. This research explores a new application of nano technology and inorganic antimicrobial compounds in the food safety area, and provides useful information to the food and packaging industries. The impact of nanopaticles on environment and human health is not clear. Currently nanotechnology is being evaluated in FDA’s Critical Path Initiative. Further toxicological studies are needed to determine the potential risks to human.

2. Determined irradiation conditions that eliminate pathogens without damaging spinach. Outbreaks of foodborne illness associated with leafy greens highlighted the safety concerns of the produce industry. Ionizing radiation is known to effectively eliminate human pathogens such as Escherichia coli O157:H7 on fresh produce. However, commercial application of irradiation is still limited partially due to concerns about possible damage to product quality. ARS researchers at Wyndmoor, PA, conducted a study to investigate quality of irradiated cut lettuce and spinach (salads) during storage at 4 degree C. Our results suggest that irradiation at doses up to 2 kilogray did not significantly affect overall antioxidant capacity, liking or consumers acceptance of spinach or appearance and texture of cut lettuce. The successful application of this FDA-approved technology on spinach will enable produce industry to reduce the risk of foodborne diseases in the U.S. The cost for commercial development of irradiated spinach is largely unknown and needs to be determined by the industry.

3. Combination of UV and irradiation improves microbial safety of tomatoes. Tomatoes are frequently consumed for their beneficial effect such as reducing risk of cancer and coronary heart disease in human population, but they can be contaminated with foodborne pathogens. ARS researchers at Wyndomoor, PA, found that combined treatment with ultraviolet light and low-dose gamma irradiation can effectively reduce the population of E. coli O157:H7 on tomatoes, thus proving that this technology may be a suitable intervention approach to enhance microbial safety of tomatoes.