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We hypothesize that the inaccessibility and possible sub-epidermal internalization of targeted pathogens in contaminated leafy greens and cherry tomatoes lies at the heart of the problem of insufficient pathogen and/or spoilage reduction by conventional sanitizing treatments to assure food safety and extend shelf life. Therefore, application of a penetrating gaseous anti-microbial agent to fresh leafy greens and cherry tomatoes within the retail package would appear to represent a distinct advantage in the quest to maximize consumer safety. The overall goal of this work is to establish the degree of efficacy of ClO2 gas applications in disinfecting two different commodity types, fresh leafy greens and cherry tomatoes. The package will become another asset within the sanitation process and improve product safety. The main constraint for this new design is that the current package must be considered such that the interior of the package can be modified. Therefore, this research project will focus in designing a modification of the interior of the present packaging systems that maximizes and assures the treatment of the product, and in determining the effectiveness of the package system in inactivating food-borne pathogens.<P>
Specific objectives include: <OL> <LI>Identify ClO2 gas treatment conditions that can inactivate human pathogens on fresh-cut leafy vegetables and cherry tomatoes without causing treatment-induced quality defects. <LI>To determine a specific package design that ensures and maximizes effective gases distribution inside the package even in hard to reach areas. <LI>Determine the efficacy of the packaging system in inactivating foodborne pathogens and prolonging the shelf life of lettuce, spinach and cherry tomatoes. <LI>Evaluate a pilot scale treatment and scale up to demonstrate technical and economical feasibility.
NON-TECHNICAL SUMMARY: Minimally processed greens and pre-packaged salads are convenient and popular products well suited to modern life styles. However, such products have emerged as important vehicles of transmission for foodborne pathogens. Several large scale outbreaks of pathogens associated with fresh produce have resulted in serious illnesses and even deaths. Conventional washing treatments used to sanitize produce may not remove pathogens that are located in hard-to-reach areas of leafy greens and other vegetables. In this work we will study chlorine dioxide (ClO2) gas as an antimicrobial treatment for leafy greens (lettuce and spinach) and cherry tomatoes for use with current production lines and packaging systems. To inactivate human pathogens with ClO2, the product must be exposed for a prolonged time, and so we will use several strategies to address this problem. <OL> <LI> We will first identify ClO2 gas treatment conditions that can inactivate human pathogens on fresh-cut leafy vegetables while maintaining product quality.<LI>To complement the sanitizing step, a specific package system will be designed that ensures and maximizes effective ClO2 gas distribution inside the package, even in hard-to-reach areas. An insert will be used to modify the conditions inside the package; currently available packaging materials will be used for the external package. <LI>We will evaluate the efficacy of the packaging system for inactivating pathogens and prolonging the shelf life of leafy greens and cherry tomatoes. <LI>A pilot scale treatment will be evaluated and scaled up to demonstrate the technical and economic feasibility of the system design. </OL>
APPROACH: First we will identify ClO2 gas treatment conditions that can inactivate human pathogens using E. coli O157:H7 and Salmonella as comparative benchmarks on untrimmed or fresh-cut leafy greens (lettuce and spinach) and cherry tomatoes without causing treatment-induced quality defects. By exposing the produce to different levels of ClO2 gas and we will evaluate pathogen survival and produce quality. The shelf life and possible treatment-induced defects in product quality attributes will be evaluated and if necessary, ClO2 treatments will be modified to minimize any adverse effects. Un-inoculated samples, untreated controls, and product treated with conventional levels of sodium hypochlorite, nominally 50 mg/L at pH 6.8, will be packaged, using appropriate films and package atmospheres and stored. Color changes (bleaching or browning) by tristimulus colorimetry, volatiles indicative of anaerobic respiration (i.e. acetaldehyde and ethanol) or other sensory defects by analysis of package atmospheres using GC/MS, and for textural defects by use of an Instron or Texture Analyzer testing machine. The second part will be to determine specific package designs that ensure effective CLO2 gas distribution within the package, even in hard to reach areas. The current rigid and flexible package system will used with changes in the internal design. Software to be used will include Solidworks (parametric software for 3D modeling) to develop the package designs and Fluent (computational fluid dynamics) to study the gas distribution inside the packages. The impact of ClO2 on characteristics and performance of the various packaging materials under consideration will be carried out. Mechanical properties such as tensile strength and elongation will be measured and physical properties such as glass transition temperature, melting temperature and crystallinity will be determined. The third part of this work will determine the efficacy of the packaging system in inactivating food borne pathogens and prolonging the shelf life of fresh-cut leafy greens and cherry tomatoes. The prototype rigid and flexible container systems developed will be evaluated by packaging contaminated spinach, lettuce, and tomatoes. Microbiological analysis for target pathogens and spoilage organisms will be conducted. Finally a pilot scale treatment and scale up will be evaluated in order to demonstrate technical and economic feasibility. Factors considered for technical feasibility will include verification of compatibility with current commercial practice, acceptance by packers and consumers of new technology, safety of generating and handling ClO2 gas, ability to meet tolerances of operating parameters, and ability to monitor performance of the disinfection system. The evaluations will be performed jointly by PD, collaborating Extension Specialists, and collaborating production and technical managers from the produce industry using workshops. The economic feasibility will include measurement of processing costs. Research outcomes will be disseminated through regional stakeholder meetings, professional scientific meetings, and extension activities.