1a. Objectives (from AD-416):
This project will focus on the integration of effective intervention technologies and treatments to enhance microbial safety of fresh fruits and vegetables with a holistic approach addressing major elements (safety, quality, and shelf-life), necessary for the implementation of technologies. The ultimate goal is to reduce the risk of foodborne illnesses associated with consumption of fresh produce, while maintaining acceptable food quality and shelf-life. Specific objectives of the research program are: Objective 1 - Develop and optimize single intervention technologies to reduce pathogen populations, maintain quality, and extend shelf-life of foods. Sub-objective 1.1. Develop and optimize aerosolizing technology and pulsed light to reduce pathogen populations, maintain sensorial and nutritional quality, and extend shelf-life of fresh produce. Sub-objective 1.2. Develop new antimicrobial packaging/coating-based technologies by incorporating natural, modified and novel materials to inactivate foodborne pathogens on fresh produce. Objective 2 - Determine the synergistic/additive effectiveness of combining non-thermal processing, antimicrobial packaging and effective chemical interventions utilizing information generated from the first objective.
1b. Approach (from AD-416):
An integrated approach to enhance microbial safety while maintaining product quality and extending shelf life of fresh produce will be adopted by combining aerosolizing antimicrobials, pulsed light antimicrobial packaging and other interventions. The types of fresh and fresh-cut produce evaluated in the project will be those frequently involved in outbreaks of foodborne illnesses, those that are hard to sanitize due to surface characteristics, and those that cannot be washed. During the first part of the proposed project plan, we will develop and optimize new aerosolization systems, pulsed light technology, novel antimicrobial coating with incorporation of nature and bio-based substances, and antimicrobial packaging materials with controlled-release mechanisms triggered with either acids or pulsed light. The optimized/developed interventions and antimicrobial packaging will then be combined with each other, and with other effective antimicrobial treatments to study the synergistic or additive effects on pathogen inactivation while maintaining quality and shelf-life of fresh produce. When selecting combinations, technologies with different pathogen-inactivation mechanisms or synergistic interactions will be desirable. We will utilize the advanced oxidation, photochemical, and photothermal, and triggered-release mechanisms and other hurdle technologies to increase the efficacy of combined antimicrobial treatments. By combining effective intervention technologies and treatments, synergistic effects with a targeted 5-log reduction of common pathogens may be achieved. Pathogens to be included in the proposed project plan are Salmonella spp., E. coli O157:H7, L. monocytogenes and other emerging pathogens (such as non-O157 STECs). We will use a representative cocktail of 3-5 strains from each genera of bacteria that are associated with outbreaks of relevant fresh produce. Scientifically well-established inoculation, recovery, and enumeration procedures will be used. Appropriate controls will be included in each experiment, and experiments will be replicated independently at least three times. Inoculation of fresh produce will be achieved either by surface ‘spot inoculation’ where specific locations on the produce surface will be inoculated or by a ‘dip inoculation’ technique where the whole produce item will be submerged in the experimental inocula. The inoculated fresh produce will be drained and air dried in a laminar flow hood before being subjected to various treatments. After treatment with various chemicals and physical interventions, the total number of viable and injured bacteria will be determined using amended media. The effects of the individual and combined treatments on the physiochemical and sensorial quality and shelf-life will be evaluated during storage. Shelf-life will be determined based on the deterioration in product quality and increasing populations of microorganisms that render the product unacceptable to consumers.
3. Progress Report:
Progress was made on Objectives 1 and 2, which fall under National Program 108, Component I, Foodborne Contaminants, and National Action Plan Problem Statement 5, Intervention and Control Strategies. Experiments were conducted to optimize conditions for the applications of aerosolization and pulsed light technologies and to develop antimicrobial packaging systems. Detailed progress to achieve the overall objectives is listed below. Under objective 1, significant progress was made by optimizing aerosolization technologies for the inactivation of bacteria (Salmonella, E. coli and Listeria) inoculated onto a number of fresh produce items and for the maintenance of product quality attributes. Furthermore, a gaseous ozone treatment system with precise controlling and monitoring of ozone levels was built. The system consists of a computer controlled flow device, ozone generator, ozone analyzer, ozone destruction units, and treatment chambers. The system was tested for the inactivation of Salmonella spp. inoculated onto stem scar and smooth surface of tomatoes. Effects of gaseous ozone on product quality (appearance, color, texture etc.) are being conducted. Tests will be conducted to combine the ozone treatment with aerosolized hydrogen peroxide to produce synergistic efficacy against bacteria. Also under Objective 1, significant progress was made by applying pulsed light (PL), a non-thermal preservation method, to mitigate the safety issues associated with fresh produce. The technology uses short-duration, high-peak light pulses on food or processing/packaging surfaces. Research was conducted to optimize the pulsed light processing to achieve a minimum 3 log reductions of most common food borne pathogens such as Salmonella and E. coli O157:H7 in fresh produce without damaging the quality. Preliminary results showed pulsed light treatment was capable of inactivating greater than 99.9% of a mixed culture of Salmonella and E. coli O157:H7 inoculated on tomato stem scars and on spinach leaves. The native aerobic bacterial load was also substantially reduced, and mold and yeast population fell below the limit of detection. No visual alteration of color and texture was apparent. The result of this optimization reveals the applicability of the method for fresh produce. Under Objectives 1 and 2, significant progress was made by screening and evaluating a number of natural antimicrobials and new polymers for their antimicrobial activities against E. coli and Listeria and for film forming capacity. Furthermore, antimicrobial films, pads and cartridges that release gaseous chlorine dioxide have been developed. Preliminary results show that gaseous chlorine dioxide released from antimicrobial films, pads and cartridges placed inside of food containers is able to kill or inhibit the growth of food pathogens (Listeria, Salmonella and E. coli) and spoilage microorganisms on broccoli, strawberries and tomatoes. More studies will be conducted to evaluate the quality and shelf life of treated foods.
1. Aerosolized antimicrobials to enhance microbial safety of fresh produce. Washes with sanitizers such as chlorine have limited effectiveness against human pathogen on fresh produce, partially due to the inability of aqueous antimicrobials in reaching bacteria. ARS researchers at Wyndmoor, Pennsylvania aerosolized a number of FDA-approved sanitizers and activated hydrogen peroxide aerosol using cold plasma to inactivate E. coli, Salmonella and Listeria inoculated onto spinach leaves, tomato, and cantaloupe. Results showed that populations of the bacteria on the surfaces of the fresh produce items could be reduced by more than 99.99% depending on types of inoculated bacteria and produce items. The aerosolization technology represents a novel and effective method to enhance microbial safety of fresh produce.
2. Novel edible antimicrobial coatings for the reduction of foodborne pathogens. Ready-to-eat foods, such as deli meat and fresh fruits, could be contaminated with foodborne pathogens. ARS researchers at Wyndmoor, Pennsylvania developed edible antimicrobial coating to inactivate foodborne pathogens on deli meat and fresh strawberries, using the combination of high pressure homogenization technology and bio-emulsifiers from plant byproduct. The coating treatments reduced 99% - 99.9% of foodborne pathogens (Listeria, Salmonella and Escherichia coli O157:H7) on deli meat and strawberries and hence could enhance the safety of ready-to-eat food.
3. New safety method for produce industry. The microbial safety of fresh fruits and vegetables continues to be a major concern. Fruits and vegetables frequently implicated in outbreaks include tomatoes, leafy greens and melons. Currently, the produce industry relies on washes with sanitizers such as chlorine to minimize the contamination risk. However, chlorine based chemical sanitizers have very limited effectiveness and can form potentially carcinogenic byproducts. Therefore new methods are required. ARS researchers at Wyndmoor, Pennsylvania developed a safe and effective method by integrating non-thermal UV light with a novel antimicrobial formulation developed by ARS scientists. In a laboratory scale study, this method inactivated more than 99.99% of pathogens. This new integrated method can be used as a replacement for the current chlorine-based method to ensure consumer safety.
4. Combination of non-thermal processing and sanitizer solution improves food safety and quality. Blueberry, fruit rich in nutrients, can be contaminated with pathogenic or spoilage microorganisms. ARS researchers at Wyndmoor, Pennsylvania developed a method using the combination of pulsed electric fields (PEF) and a sanitizer solution to achieve up to 99.9% reduction of E. coli and Listeria as well as 99% reduction of spoilage bacteria without causing any change in color and appearance of whole blueberries. Anthocyanins and phenolic compounds in blueberries increased by 10 and 25%, respectively, after PEF treatments. These results demonstrate the possibility of PEF to be used to enhance the safety and to improve the quality and nutritional value of fruits and derived products.
5. Packaging films releasing antimicrobial vapor. Controlled release of volatile antimicrobials exhibits more antimicrobial efficacy than their liquid phase against foodborne pathogens or spoilage bacteria in fresh produce. ARS researchers at Wyndmoor, Pennsylvania, teamed with a collaborator, developed antimicrobial polylactic acid (PLA) films releasing allyl isothiocyanate (major component in mustard oil) vapor. The antimicrobial film had more flexibility, lower gas permeability, and higher UV blocking ability than pure PLA film. The vapor released from antimicrobial films inhibited bacterial growth in fresh vegetables stored at 4 and 10 degrees C for 15 days and has the potential to be utilized for extending the shelf-life of various perishable fresh produce.
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