Location: Characterization and Interventions for Foodborne Pathogens
2022 Annual Report
Objectives
Objective 1: Complete the industrial/commercial implementation of the Radio Frequency (RF) technology (with partners) to enhance the safety of shell eggs. Ensure that the technology is optimized, appreciating the complexity of the intervention process, the processing conditions, the equipment necessary, and the sensory and nutritional qualities of the food product.
Objective 2: Utilization of Cold Plasma, a novel non thermal technology to inactivate microbial contamination on various food products, which can include and is not limited to produce, nuts, meats and ready-to-eat foods. Optimize the technology to allow scale-up to commercial treatment levels, appreciating the complexity of the intervention process in terms of the food to be treated, the processing conditions, the equipment necessary, and the sensory and nutritional qualities of the foods types to be treated.
Sub-objective 2.A: Develop and optimize combined treatments of cold plasma with high-intensity pulsed light-based technologies and/or other antimicrobial processes, including chemical sanitizers to enhance microbial food safety and quality.
Approach
Our research will develop and optimize interventions for reducing the microbial load associated with produce, meats, shell eggs, and other food products. The ARS-patented radio frequency pasteurization (RFP) process for shell eggs is 3X faster and produces a higher quality egg than currently available commercial technologies. We will optimize the existing RFP process to improve efficiency and throughput, leading to a commercial-scale prototype. Research will focus on RFP operating parameters such as: power applied; RF pulse frequency and duration; electrode contact profile; cooling water conductivity, temperature, and flow rate. For many other foods, sanitizing technologies currently available fall short of desirable efficacy goals, such as the FDA’s target of a 5 log kill for fresh and fresh-cut produce. Cold plasma is a novel nonthermal sanitizing process which uses ionized air to inactivate pathogens on a variety of foods and food contact surfaces. We will build on our existing cold plasma expertise to develop and optimize applications, focusing on sanitizing protocols suitable for commercially promising commodities such as meats, fruits and vegetables, and low-moisture foods. We will optimize several different types of cold plasma in parallel, as dictated by the most suitable commodity/pathogen application. The treatments will establish commercialization potential for cold plasma as a standalone process and in combination with other antimicrobial treatments, including a primary focus of combining cold plasma with high-intensity light-based treatments. After we evaluate the combined intervention strategies for their effects on product quality and shelf-life, the most effective, practical treatment combinations will be transferred to industry to reduce the risk of foodborne illness. The outcomes of this project will be new validated means/technologies for producers, processors, and distributors to produce safer shell eggs, meats, fruits and vegetables, and other food related commodities.
Progress Report
Progress has been made on the project objectives, with research proceeding toward approved milestones and deliverables. The project research is directed toward the development of radio frequency (RF) treatment of eggs and the development of cold plasma and cold plasma-based combination treatments with nonthermal processes such as pulsed light, novel chemical treatments, etc. A new SY was hired in FY22 tasked with taking up the RF egg research previously conducted by a former FSIT SY (retired 2019). Research activity has involved onboarding to the RF project and in-depth coursework and certification in RF systems analysis, design, and development. A critical aspect of this research as it develops from the current lab-scale prototype system to a larger pilot-scale pre-commercial system is the ground-truthing of temperature profiles inside the egg. The mode of action of the process is heat generated within the egg fluid by the RF pulsed energy. In a large, multi-egg system, process validation requires temperature profiles to be obtained at the yolk, the yolk/albumin interfaces, and in the albumin during RF treatment. Several approaches are being evaluated for this, including microchip thermoprobes to be inserted into the egg, and/or fiber optic probes. A model egg system with thermo-responsive dye is also being developed. The advantage of this approach is that it would provide a permanent record of highest temperature reached, akin to a “max/min” recording thermometer. Standardizing of heat response D-values for Salmonella is being conducted. Also, mathematical models of the microbial inactivation curves are being developed to facilitate the improvement of the RF process for in-shell egg pasteurization. Previous results showed the effective inactivation of Salmonella Typhimurium 53647 inoculated in eggs after 20 minutes of treatment. So far, four mathematical models have been fitted to the survivor’s curves (linear, Weibull, four-parameter, and modified Gompertz). Six treatments were analyzed: hot air, hot water immersion, and hot water spraying, with and without radio frequency. All treatments were not uniform regarding the dose of energy applied. The best mathematical fit was observed using the Weibullan-based model (r2 > 0.93), except for hot air treatments. The “b” parameter of the equation clearly showed the effect of radio frequency in speeding the microbial inactivation. The model also shows that the first segment of the microbial population to die from RF are the most sensitive microorganisms. This is in contrast to how heat kills microorganisms, in which cells die in the general population only after they have accumulated damage. Some microbial subpopulations could be present during experiments based on the n values. Radio frequency is similar to other emerging technologies, in which microbial inactivation does not follow the first-order kinetics because of several artifacts. Additional mathematical modeling is being conducted for the microbial growth of Salmonella cells after radio frequency processing and the degradation of quality attributes of eggs during storage. Other research in the RF project is the upscaling of the associated recirculating water bath, which regulates the temperature at the albumin/shell interface. The redesign and reconstruction of the RF electrode paddles will upgrade the electrode support system to commercially acceptable standards for cleanability and robustness. Research in cold plasma as a sanitizing process has centered around the scale-up of plasma treatment in conveyor belt systems. Previous research on food contact surfaces has shown multi-log reductions of biofilms with short (15 second) cold plasma treatments. This speed of treatment is close to that required for commercial throughput requirements. Current research is using polymer unibelt conveyor belts, more comparable to commercial systems, as well as commercial grade stainless steel link belts. Previous research explored temperature control systems using vortex jet cooling systems side-by-side with the cold plasma injection systems, data which forms the basis for ongoing research to expand into pilot-scale treatments. Research efforts are focused on incorporating cold plasma into combination systems with chemical sanitizers and/or light-based treatments to achieve synergistic reductions. Collaborative research using cold plasma is being pursued with partners in industry, sister agencies, academia, and at other ARS locations. Research is being conducted using a noninvasive light-based technology called Pulsed light (PL) which is essentially a non-thermal preservation method. This technology uses short-duration, high-peak light pulses on food or processing/packaging surfaces. It is efficient in inactivating microorganisms, including spores, in a relatively short period of time compared to other technologies. Research is being conducted to optimize the PL processing in various pathogen-food pairing systems to develop a rapid and robust method for a minimum of 99.9% reduction of the most common pathogens such as Salmonella, Escherichia coli O157:H7 or Listeria in common fruits and vegetables like tomato and lettuce without damaging their quality.
Accomplishments
1. Pulsed light activates organic acids to kill Salmonella on tomato. Raw and minimally processed fruits and vegetables are nutritionally healthy diet options but can harbor harmful pathogens, leading to food borne illness outbreaks. Because pathogens on the surfaces of produce can be hard to kill with conventional sanitizers, there is a need for new safe and effective intervention technologies. ARS researchers in Wyndmoor, Pennsylvania, developed a light-based technology called pulsed light, which when combined with a mist composed of tiny droplets of safe organic acids, can effectively kill 99.99% of Salmonella and other pathogens. This waterless, clean technology does not use heat, and can also reduce molds and other spoilage organisms on tomatoes without damaging the quality. As a low-cost “clean label” antimicrobial intervention, this technology holds great promise for market implementation.
2. Mathematical model describes how radio frequency energy makes eggs safer. The radio frequency (RF) treatment system can effectively inactivate Salmonella inside shell eggs, making them safer for consumers. However, there is a need for a more complete understanding of how the system will perform under different combinations of treatment time, power levels, intensity, water temperature, and other factors. ARS researchers at Wyndmoor, Pennsylvania, have developed four advanced mathematical models based on multiple key treatment parameters. The work shows that RF treatment is similar to other emerging nonthermal technologies, in which microbial inactivation follows a complex pattern because of the interaction of the different factors. This improved understanding will allow end users to produce Salmonella-free eggs more reliably and more economically.
