Location: Microbial and Chemical Food Safety
2019 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
Progress was made on Objective 2, which falls under National Program 108, Component I, Foodborne Contaminants, and National Action Plan Problem Statement 5, Intervention and Control Strategies. Experiments were conducted to determine the synergistic/additive effectiveness of combining pulsed light, antimicrobial packaging, and aerosolized/vaporized antimicrobials to maximize the effectiveness of the interventions against various human pathogens and spoilage microorganisms while maintaining sensory quality of fresh produce. Detailed progress to achieve the overall objective is listed below.
Experiments were conducted to develop and validate a method using low dose/short duration pulsed light followed by aerosolized antimicrobial treatment for greater than 3 logs reductions of common food-borne pathogens in fresh leafy greens and tomato fruits without significant quality deterioration. Among various aerosolized antimicrobials tested, aerosolized formulations containing hydrogen peroxide and organic acids exhibited significant synergistic effects with pulsed light, inactivating > 99.999% of Salmonella and E. coli O157:H7 on tomato and romaine lettuce. The pulsed light - aerosolized sanitizer combination provided not only a pasteurizing effect, but also reduced native microbial populations on these produces and slowed their growth during storage. Furthermore, the color parameters and the firmness of the produce were not significantly affected by the combination of treatments. Overall, results demonstrate that the integrated pulsed light - aerosolized sanitizer treatment technology can be used to enhance microbial safety of produce. Findings from this research will greatly benefit the farmers and small to large produce industries.
Progress was made by combining natural antimicrobials aerosolized into packages of fresh produce in which gaseous chlorine dioxide-releasing film was included. The aerosolized antimicrobials not only inactivated pathogenic microorganisms by themselves, but also helped in facilitating the release of gaseous chlorine dioxide from the films into the headspace of packages. As a result, higher reductions of pathogens such as Salmonella on berries and lettuce were achieved than the individual treatment alone. Further studies will be conducted to improve repeatability of the treatments, and evaluate the impact of these treatments on the quality of treated food products.
Packaging films releasing gaseous antimicrobials into headspace of packaging containers were continuously studied. Films with biopolymers and carvacrol, an essential oil component, were placed on the lid of food containers and their antimicrobial efficacy against foodborne pathogens (Listeria and E. coli) and spoilage microorganisms in cherry tomatoes was investigated. Results show that these antimicrobial films placed inside of food containers effectively killed or inhibited the growth of pathogens and spoilage microorganisms. Further studies will be conducted to evaluate the impact of these treatments on the quality of treated foods.
In addition, significant progress has been made on a NIFA-funded project involving inactivation of Salmonella and quality maintenance of low moisture foods treated with gaseous chlorine dioxide. Result showed that Salmonella populations can be reduced by more than 99.99% with gaseous chlorine dioxide treatments, when combined with mild heating and high relative humidity. Studies on possible formation of chlorine-containing byproducts are underway. Furthermore, in collaboration with an industry partner, the impact of cold plasma on the effectiveness of aerosolized hydrogen peroxide was evaluated. Results showed that cold plasma activated the hydrogen peroxide aerosols and significantly increased the inactivation effectiveness of hydrogen peroxide against Salmonella and Listeria on a number of fresh produce items.
Accomplishments
1. Integrated interventions of processing and coating can provide microbial food safety. Currently the produce industry employs chlorine to avoid cross contamination during processing despite its limited ability to reduce pathogens, and potential of forming possible carcinogenic chlorine by-products in wash water. Hence, there is a need to develop chlorine-free decontamination technologies. Researchers at Wyndmoor, Pennsylvania developed a safe and effective produce safety method combining pulsed light treatment with a sanitizer wash. In a laboratory scale study, this integrated technology inactivated > 99.999% of pathogens such as E. coli O157:H7 in spinach. This combination treatment was also effective in controlling native microbial loads during 21 days of refrigerated storage. Furthermore, firmness and the visual appearance of spinach were not affected by the treatment. Pulsed light is an FDA approved technology while all components of the sanitizer are generally recognized safe compounds. This new integrated method of pulsed light treatment with this new formula sanitizer wash can be used as a replacement for current chlorine-based industrial practice.
2. Mild heating and gaseous chlorine dioxide enhances microbial safety of almonds. Salmonella outbreaks have been linked to the consumption of raw almonds. As a result, USDA and Almond Board of California mandated pasteurization of almonds with a minimal 99.99% Salmonella reduction. Currently, almonds are mostly treated with propylene oxide, however there is a safety concern over the use of propylene oxide. Therefore, other intervention technologies are necessary in achieving the mandatory goal of the 99.99% reduction. ARS scientists in Wyndmoor, Pennsylvania evaluated the combination of gaseous chlorine dioxide and mild heating in inactivating Salmonella on almonds. Results demonstrated that applying gaseous chlorine dioxide at 55 degree Celsius achieved more than 99.99% reductions of Salmonella on almonds. The study established the condition of chlorine dioxide needed to meet mandatory goal of almond pasteurization.
3. Combination of antimicrobial packaging and sanitizer solution improves food safety and quality. Fresh strawberries have a short shelf life and were associated with foodborne outbreaks. ARS scientists at Wyndmoor, Pennsylvania evaluated the effectiveness of antimicrobial wash and coating treatments, either individually or in combination, in reducing populations of E. coli O157:H7 and Salmonella on strawberries. The combination treatments reduced over 99% of pathogens and native microflora. Both the combination and the antimicrobial coating treatments preserved the color, texture, and appearance of strawberries throughout 3 weeks storage at 4 degree Celsius. The combined method has the potential to improve the microbiological safety, shelf-life, and quality of strawberries.
4. Gaseous chlorine dioxide inactivates Salmonella while maintaining quality of tomatoes. There have been a number of reports on the effectiveness of gaseous chlorine dioxide in inactivating various human pathogens associated with fresh produce. However, studies dealing with both microbial reduction and impact on quality and nutrients of tomatoes are scarce. ARS scientists in Wyndmoor, Pennsylvania determined the efficacy of gaseous chlorine dioxide in inactivating Salmonella, and the impact on sensory and nutritional quality of grape tomatoes. Results demonstrated that gaseous chlorine dioxide that reduced populations of Salmonella by 99.99% on tomatoes did not significantly affect appearance, texture, color, odor, or lycopene and ascorbic acid contents of tomatoes. The study eases concern over damage of the fruit caused by gaseous chlorine dioxide, and may help in facilitating the commercial applications of the gaseous antimicrobial on fresh produce.
Review Publications
Mukhopadhyay, S., Sokorai, K.J., Ukuku, D.O., Fan, X., Olanya, O.M., Juneja, V.K. 2019. Effects of pulsed light and sanitizer wash combination on inactivation of Escherichia coli 0157:H7, microbial loads and apparent quality of spinach leaves. Food Microbiology. 82:127-134. https://doi.org/10.1016/j.fm.2019.01.022.
Guo, M., Jin, Z.T., Gurtler, J., Fan, X., Yadav, M.P. 2018. Inactivation of E.coli O157:H7 and Salmonella on fresh strawberries by antimicrobial washing and coating. Journal of Food Protection. 81(8):1227-1235.
Gurtler, J., Fan, X., Jin, Z.T., Niemira, B.A. 2019. Effects of antimicrobials on the thermal sensitivity of foodborne pathogens: A review. Journal of Food Protection. 82(4):628-644. https://doi.org/10.4315/0362-028X.JFP-18-441.
Gao, H., Fan, X., Chen, H., Qin, Y., Wu, W., Jin, Z.T. 2018. Microbial inactivation and quality improvement of tomatoes treated by package film with Allyl Isothiocyanate vapor. International Journal of Food Science and Technology. 53:1983-1991.
Min, S.C., Roh, S., Niemira, B.A., Boyd, G., Sites, J.E., Fan, X., Sokorai, K.J., Jin, Z.T. 2018. In-Package atmospheric cold plasma treatment of bulk grape tomatoes for their microbiological safety and preservation. 108:378-386.
