Summary
After harvest, fresh oranges and lemons are sorted, washed and packed for further distribution and sale in packinghouses. Because green and blue molds result in significant losses of citrus fruit during storage and shipping, fungicides are often applied to during packing. Recirculating drench applications are common because they significantly increase fungicide efficacy but they also provide an opportunity for cross contamination or movement of microorganisms throughout the facility which can be a food safety issue if not appropriately managed. The overall goal of this project is to provide data that the California fresh citrus packinghouse industry can use to support the controls that reduce or eliminate foodborne pathogen cross contamination where citrus fruits are comingled or where recirculating materials come into contact with the fruit. A laboratory component is included to determine for the most common fungicides, minimum compatible sanitizer concentrations that are effective in eliminating Salmonella and Listeria monocytogenes. The laboratory data will be verified in a pilot scale citrus packing facility and the results of these studies will be used to prepare documents the industry can use to support the efficacy of their food safety practices.
Technical Abstract
After harvest, fresh oranges and lemons are sorted, washed and packed for further distribution and sale in packinghouses. In California, the growth of Penicilium species that cause green and blue molds results in significant losses of citrus fruit during storage and shipping. To reduce these losses, one or more fungicides (e.g. sodium bicarbonate, imazalil) are applied to citrus fruit during packing often in recirculating, in-line drench applications that significantly increase efficacy when compared to low-volume spray applications. However, recirculation of fungicides that are not also bactericidal may can result in increased bacterial loads and a potential for cross contamination among fruit and on equipment surfaces. The proposed project focuses on two important fungicide treatments that are often used by the citrus industry in sequential application. While chlorine is routinely added to sodium bicarbonate (SBC) to maintain water quality in fruit immersion tanks or recirculating systems, data are lacking to support the efficacy of chlorine at the generally high pH (>8.0) of these solutions. The fungicide imazalil is widely used in the citrus industry but is incompatible with chlorine. Documented efficacy of alternative water sanitizers such as peracetic acid in combination with imazalil are lacking. Under laboratory conditions the minimum free chlorine concentrations at higher pH levels for SBC solutions and minimum peracetic acid concentrations in imazalil solutions will be determined for rapid elimination of Salmonella and Listeria monocytogenes. These data will be used to establish pilot scale packinghouse trials where minimum operational sanitizer levels will be established by monitoring microbial loads in fungicide solutions, on fruit, and on equipment surfaces. The survival of Salmonella and L. monocytogenes on the surface of oranges and lemons will be determined as a function of surface location, inoculum carrier, microbial concentrations, and commercial storage conditions. The overall goal of the proposed research is to improve the ability of the citrus industry to successfully apply validated preventive controls that prevent the spread of bacterial foodborne pathogens in recirculating fungicide applications used by the packinghouse industry.
Research Objectives
The overall goal of the project is to provide data that the California fresh citrus packinghouse industry can use to support preventive controls that reduce or eliminate cross contamination where citrus fruits are comingled or where contact materials are reused. Specific objectives are:
1. Determine the potential for Salmonella and Listeria monocytogenes to survive in float tanks, drench systems, and systems where the fungicides sodium bicarbonate, imazalil, and soda ash are recirculated/reused.
2. Determine minimum levels of compatible sanitizers or thermal treatments that control, reduce, or eliminate Salmonella and L. monocytogenes in recirculated/reused sodium bicarbonate, imazalil, and soda ash solutions.
3. Determine the potential for survival of Salmonella and L. monocytogenes on citrus fruit (predominantly Navel and Valencia oranges and Eureka lemons) during pre-shipping storage under typical and sub-optimal conditions. NOTE: Items in red were added to the original objectives.
Findings & Recommendations
This project has generated significant new findings, relative to factors affecting pathogen reduction in citrus fungicides. The key findings and recommendations are as follows:
• In 3% SBC, 18 ppm free chlorine resulted in a >5-log reduction of L. monocytogenes and Salmonella within 20 s at both pH ~8.0 and ~9.5. Similar results were achieved in end-ofuse SBC solutions.
• In 300 ppm imazalil at 16°C (60°F), >5-log reductions of Salmonella and L. monocytogenes were achieved with 30 and 60 ppm of PAA, respectively, within 1 min; 10 and 20 ppm of PAA, respectively, were sufficient at 40°C (104°F). Cross contamination from inoculated to uninoculated fruit was prevented at these PAA levels.
• No significant difference was observed in the reduction of L. monocytogenes in lab-prepared and end-of-use imazalil solutions from two packinghouses, and initial reductions of L. monocytogenes were significantly greater in one end-of-use imazalil solution.
• In 3% soda ash, no significant reduction of L. monocytogenes was observed at 16°C for 8 h, but a 2.5-log reduction was obtained at 40°C in 30 min. Reduction of Salmonella was more rapid in soda ash; a >5-log reduction of Salmonella was observed in 3 min at 40°C and in 8 h at 16°C. A >5-log reduction in L. monocytogenes was achieved in 1 min when the soda ash was heated to 60°C.
• Under de-greening conditions over 7 days, L. monocytogenes and Salmonella declined by 1.26 and 2.1 log CFU on lemons, respectively, and by 1.6 and 3.12 log CFU on oranges, respectively. L. monocytogenes populations declined by >5 log on lemon surfaces after 26 days at 12°C (54°F) and 80% relative humidity, conditions that simulate commercial storage in a packinghouse.