1a. Objectives (from AD-416)
The overall goals of the project are to establish the degree of efficacy of chlorine dioxide (ClO2) gaseous application in disinfecting fresh leafy greens and cherry tomatoes, to establish the point of dose-dependent injury to fresh quality and shelf-life so that such injury can be avoided, to evaluate the integration of post-harvest strategies of product sanitizing and exposure to an antimicrobial through packaging to assure the microbial safety of fresh produce, and to further improve, extend and transfer treatment application methods to end-users so that adoption of a commercially feasible process becomes possible.
1b. Approach (from AD-416)
1. Identify ClO2 gas treatment conditions that can inactivate human pathogens on fresh-cut leafy vegetables and cherry tomatoes without causing treatment-induced quality defects. 2. To determine a specific package design that ensures and maximizes effective gases distribution inside the package even in hard to reach areas. 3. Determine the efficacy of the packaging system in inactivating foodborne pathogens and prolonging the shelf life of lettuce, spinach and cherry tomatoes. 4. Evaluate a pilot scale treatment, using ERRC BSL-2 pilot processing facility, to demonstrate technical and economical feasibility.
3. Progress Report
In the first part of our study we determined permeability, diffusion, and solubility coefficients of gaseous chlorine dioxide (ClO2) through the following packaging material: biaxial-oriented polypropylene (BOPP); polyethylene terephthalate (PET); poly lactic acid (PLA); multilayer structure of ethylene vinyl acetate (EVA) and ethylene vinyl alcohol (EVOH) [EVA/EVOH/EVA]; polyethylene (PE); polyvinyl chloride (PVC); polystyrene (PS); nylon. However, strong oxidizing agents such as ClO2 can cause oxidative degradation of these packing materials. The effects of ClO2 on properties, and performance of selected polymeric packaging materials were assessed by their IR spectrum, physical, mechanical, barrier, and color properties. The samples were exposed to 3,600 ppm ClO2 at 23 C for up to14 days. The IR spectra of the exposed samples indicated many changes in their chemical characteristics, such as the formation of polar groups in polyolefins, the changes in functional groups, the main chain scission degradation, as well as, the possible chlorination in several sample types. The exposed PEs samples showed a decrease in tensile properties. Decreases in barrier to moisture, oxygen and/or carbon dioxide were observed in PVC, PET and multilayer EVA/EVOH/EVA. On the other hand, significant increase in barrier to O2 was observed in the exposed nylon, which could be the result of the molecular reordering in the exposed sample, as implied through the increase in the crystallinity of the material. A continuous system for measuring the mass transfer of ClO2 through different packaging material was developed utilizing electrochemical sensor as a detector. Permeability, diffusion, and solubility coefficients of 3600 ppm ClO2 were determined through the following packaging material: biaxial oriented polypropylene (BOPP); polyethylene terephthalate (PET); poly lactic acid (PLA); multilayer structure of ethylene vinyl acetate (EVA) and ethylene vinyl alcohol (EVOH) [EVA/EVOH/EVA]; polyethylene (PE); polyvinyl chloride (PVC); polystyrene (PS); and nylon. Permeability values ranged from below 0.07 x 10-17 kg ClO2.m.m-2.s-1.Pa-1 for EVA/EVOH/EVA to 4.83 x 10-16 kg ClO2.m.m-2.s-1.Pa-1 for PE. Results indicated that BOPP, PET, PLA, nylon, and EVA/EVOH/EVA had better barrier properties for gaseous ClO2 as compared to PE, PVC, and PS. The activation energy of permeation for PET and PLA, were determined to be 56.25 ± 5.02 and 82.49 ± 7.02 kJ/mol, respectively. The activation energy for PET are significantly lower than those for PLA indicating that the permeation of ClO2 trough the latter is less temperature dependent, which is considered beneficial when the packaging system is occasionally subjected to temperature abuses during transportation, or on shelf. Progress is monitored through meetings, site visits, conference calls, e-mail exchanges and exchanges of data via electronic and surface mail.