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
Chlorine dioxide gas (ClO2) is a strong oxidizing agent and an effective surface disinfectant. Its disinfecting capacity has been recognized since the early 1900s, and was used initially to treat water, as it causes less organoleptic problems than chlorine. Due to its bacteriocide effects, Cl02 gas is gaining significant interest in the food and pharmaceutical industries. In 2001, the FDA approved the incorporation of ClO2 within food packaging materials to be used for uncooked meats, such as poultry and seafood. If the package is going to be considered as a strategy for the application of Cl02 gas, the impact of package design on antimicrobial efficacy of Cl02 gas for fresh produce needs to be determined. Commercially available bags were modified to create gas reservoirs (GR) allowing gas release from one side of the bag, from both sides, or in the center (1-GR, 2-GR, or mid-GR, respectively). Cl02 was generated in the GR gas at either 4 or 8 mg ClO2 per kg lettuce per day. Fresh-cut lettuce, artificially inoculated with the human pathogen Escherichia coli O157:H7 was packed in the bags and stored at 4 deg C for up to 7 d. Increasing ClO2 gas dose resulted in greater reductions of E. coli O157:H7. Significantly greater reductions in E coli O157:H7 populations were observed in lettuce samples taken from locations adjacent to the GR. The performance of 2-GR bags indicated that the same degree of antimicrobial effect could be achieved with the lower Cl02 dose.Chlorine dioxide (ClO2) is gaining interest in the food industries due to its antimicrobial effects. One of the most promising applications of Cl02 is to be utilized in vapor-phase decontamination either as fumigation gas in the production line or as antimicrobial gas in a food packaging systems. When Cl02 gas is absorbed into the produce, it might react with organic matters, such as plant cells and pigments, and with microorganisms resided on the surface. The reactions typically generate chlorite (Cl02-) as a major byproduct, along with numerous compounds in trace amount. In this study, the absorption behavior of Cl02 gas by Romaine lettuce and cherry tomatoes, as well as processing factors that could affect this behavior, is being investigated by exposing commodities to 3.0 and 6.0 mg/L of Cl02 for 15-90 min, and then determined residual Cl02 and Cl02- in the samples using amperometric titration. For lettuce sample, Cl02-absorption increased as ClO2 concentration and/or exposure time increased. The study also showed that shredding, which introduced cut or bruises, to lettuce leaf increased Cl02-absorption by 100 times, while washing, which added moisture to the sample around 7% wt/wt, did not significantly affect the absorption behavior of shredded lettuce. Further study indicated that allowing enough time after Cl02 exposure, residual Cl02 and Cl02- will reduce to an undetectable amount. Absorption study of cherry tomatoes is being carried out. The study on both commodities will also include influences of temperature, especially at lower temperature (4 deg C), and correlation between antimicrobial efficacy of ClO2 and its absorption.