Location: Microbial and Chemical Food Safety
2021 Annual Report
Objectives
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.
Approach
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.
Progress Report
Project (8072-41000-101-000D) has been completed with all objectives achieved. The goal of the project was to integrate effective intervention technologies and treatments to enhance microbial safety of fresh produce while maintaining its quality and shelf life. Novel gaseous and aerosolized delivery of chemical sanitizers, pulsed light technology, and antimicrobial packaging have been developed/optimized individually and then combined to achieve synergistic and additive effects on the inactivation of human pathogens. In addition, the impact of the individual and integrated intervention technologies on sensory properties, nutrients, and shelf-life were also evaluated. Several integrated approaches were able to achieve reductions of human pathogens by more than 99.9% and extend shelf-life by reducing populations of spoilage microorganisms while preserving the quality of fresh produce during storage. Patents on novel bio-based antimicrobials and packaging materials have been applied and/or granted. A number of research collaborations has been established with industry and academic partners during the project cycle.
Due to the COVID-19 pandemic, limited progress was made on the 60 months milestone projects under Objective 2, which falls under National Program 108, Component I, Foodborne Contaminants, and National Action Plan Problem Statement 5, Intervention and Control Strategies. The milestones have been either substantially or partially met based on viable data and results conducted in previous years. Experiments were conducted to evaluate the inactivation efficacy of pulsed light for packaged fresh produce. Polyethylene films of 2.5, 5.1 and 7.6 µm thickness with 54-83% UV light transmissibility were used for packaging. Both direct and in-package pulsed light treatment efficacy were evaluated. Inactivation efficacy did not decline significantly with film thickness. No significant difference (P > 0.05) in E. coli O157:H7 decontamination efficacy between packaged and unpackaged Romaine lettuce was observed due to pulsed light treatment. Research is being conducted to evaluate the impact of aerosolized hydrogen peroxide on blueberries in collaboration with scientists in other ARS locations. Recruitment is underway to hire a headquarter-funded research associate position to study bio-based antimicrobials. Research proposal (#2020-8650) entitled "Antimicrobial Thermosetting Bio-Polymers Derived from Non-Edible Oils” has been funded (2021-2024) by the USDA National Institute of Food and Agriculture.
Accomplishments
1. In-package pulsed light treatment can assure microbial safety of produce. Post-processing contamination with human pathogens such as E. coli O157:H7 is a major contributing factor to foodborne illness outbreaks. Safe and effective methods are needed to minimize the spread of human pathogen contamination. ARS scientists at Wyndmoor, Pennsylvania, developed an in-package high-intensity pulsed light treatment capable of penetrating plastic film and killing E. coli O157:H7 on the surface of Romaine lettuce inside sealed packages. The treatment also reduced native microbial populations by greater than 90%, irrespective of the thickness of the plastic film. Pulsed light treatment is a chemical-free, nonthermal, post-packaging treatment for leafy greens and other fresh and fresh-cut fruits and vegetables.
2. Novel antimicrobial packaging system with gaseous and vaporous antimicrobials. Foodborne pathogens located on rough surfaces of fresh produce are difficult to inactivate. There is a need for more effective intervention technologies to reduce the population of pathogens on surfaces. ARS scientists in Wyndmoor, Pennsylvania, developed a novel in-package treatment system using aerosolized acetic acid to trigger the release of gaseous chlorine dioxide from antimicrobial films inside packages. The integration of aerosolized acetic acid and gaseous chlorine dioxide inactivates Salmonella on tomatoes and lettuce by more than 99.9%, reduces spoilage microorganisms' populations and maintains the sensory and nutritional quality. The accomplishment provides the produce industry a novel method to enhance microbial safety of fresh produce after verification in scale-up studies.
3. Combined nonthermal processing and antimicrobial packaging for juice pasteurization. Heat treatment could negatively impact fruit juice's sensory and nutritional values; hence, non-thermal food processing could be a better alternative solution for juice preservation. ARS scientists at Wyndmoor, Pennsylvania, investigated the effectiveness of pulsed electric fields, pulsed ultraviolet light, and antimicrobial packaging treatments, either individually or combined in the reduction of microbial populations and in maintaining the quality of fruit juices. This study indicated that the combined treatments reduced microbial levels in juices without causing changes in their physicochemical properties, quality, and shelf-life. This accomplishment provides valuable information to juice processors for consideration and design of non-thermal pasteurization of juice products.
Review Publications
Huang, K., Ashby, R.D., Fan, X., Moreau, R.A., Lew, H.N., Strahan, G.D., Nunez, A. 2020. Phenolic fatty acid-based epoxy curing agent for antimicrobial epoxy polymers. Progress in Organic Coatings. 14:105536. https://doi.org/10.1016/j.porgcoat.2019.105536.
Yan, R., Gurtler, J., Mattheis, J.P., Fan, X. 2020. Effect of trichrome removal and UV-C on populations of E. coli O157:H7 and quality of peach fruit. HortScience. 55(6):1-6. https://doi.org/10.21273/HORTSCI15231-20.
Juneja, V.K., Osoria, M., Tiwari, U., Xu, X., Golden, C.E., Mukhopadhyay, S., Mishra, A. 2020. The effect of lauric arginate on the thermal inactivation of starved Listeria monocytogenes in sous-vide cooked ground beef. Food Research International. 134. https://doi.org/10.1016/j.foodres.2020.109280.
Berrios-Rodriguez, A., Ukuku, D.O., Olanya, O.M., Cassidy, J.M., Orellana, L.E., Mukhopadhyay, S., Niemira, B.A. 2019. Nisin based organic acids inactivation of Salmonella on grape tomatoes: efficacy of treatment using bioluminescences ATP assay. Journal of Food Protection. 83(1):68-74. https://doi.org/10.4315/0362-028X.JFP-19-275.
Zhang, X., Li, Y., Guo, M., Jin, Z.T., Arabi, S.A., He, Q., Hu, Y., Liu, D. 2021. Antimicrobial and UV barrier properties of composite chitosan films with curcumin grafted cellulose nanofiber. Food Hydrocolloids.112:106337. https://doi.org/10.1016/j.foodhyd.2020.106337.
He, Qiao, Guo, Mingming, Jin, Z.T., Arabi, S.A., Liu, D. 2021. Ultrasound improves the decontamination effect of thyme essential oil nanoemulsions against Escherichia coli O157: H7 on cherry tomatoes. International Journal of Food Microbiology. 337:108936. https://doi.org/10.1016/j.ijfoodmicro.2020.108936.
Lin, Xian, Chen, Gaohui, Jin, Z.T., Wen, Ming, Wu, Jijun, Wen, Jing, Xu, Yujuan, An, Kejing, Yu, Yuanshan 2021. Extension of shelf life of semi-dry longan pulp with gaseous chlorine dioxide generating film. International Journal of Food Microbiology. 337:108938. https://doi.org/10.1016/j.ijfoodmicro.2020.108938
