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
Efficacy of antimicrobial agents in inactivating pathogenic microorganisms on fresh and fresh-cut produce surfaces in limited by the accessibility of such agents to the produce surfaces where the microorganisms are residing. Other factors contribute to this problem include biofilm formation by the microorganisms which allows the bacterial cells living within the biofilm to tolerate the harsh environment as well as the antimicrobial agents. Chlorine dioxide (ClO2) gas is able to reach such inaccessible sites on the produce surfaces and to penetrate the biofilm protective layer which gives it a superior efficacy in inactivating bacterial cells. To study the antimicrobial effects of ClO2 on a biofilm, the surfaces of Romaine lettuce were inoculated with Escherichia coli O157:H7 and then were treated with 0.2 mg/L ClO2 for 15 min. The treatment reduced the pathogen population by up to 1.5 logs. Scanning electron microscope pictures taken from both the untreated and ClO2-treated lettuce surfaces showed the noticeable reduction and damages to the biofilm structure following ClO2 treatment. The addition of ClO2 gas to the headspace of food packaging systems could improve the microbial safety and extend the shelf-life of perishable food products. This study considered different flexible package internal designs in which each design released ClO2 in different ways. Also, this study evaluated the impact of packaging design on the inactivation efficiency of ClO2 on shredded Romaine lettuce inoculated with E. coli O157:H7. Samples were taken from different area of the bags, and the results showed that the samples taken from the area next to the releasing spots had significantly higher CFU log reductions (up to 1.5 logs) as compared to those more distant from the releasing ports (up to 0.5 log). The study also indicated that increasing the number of releasing ports per bag and decreasing the amount of ClO2 resulted in a comparable average log reduction to the bag with lower numbers of releasing ports and higher ClO2 concentrations. These important findings are being used to re-design the flexible packaging system that will include ClO2 for improving safety and extend shelf-life of leafy green products. The inadequacy of washing processes to inactivate microorganisms on tomatoes is attributed to biofilm formation and inaccessibility of microbial attachment sites to washing systems. The objective was to develop ClO2 gas treatment capable of inactivating human pathogens attached to inaccessible sites within biofilm on the tomatoes. Tomatoes were inoculated with Salmonella Poona and were treated with ClO2 for 6 h in a closed chamber. This treatment reduced S. Poona populations by more than 4.5 log CFU/gm, extended the shelf life of the tomatoes by reducing the spoilage microorganisms, and did not seem to have adverse effects on the quality of this commodity. This treatment was able to inactivate S. Poona cells attached to inaccessible sites and extend the shelf life of tomatoes without any apparent adverse effects on quality. Progress is monitored through meetings, site visits, conference calls, e-mail exchanges and exchanges of data.