Summary of Awards to Date

Characterization and mitigation of bacteriological risks associated with packing fresh-market citrus


Jan. 1, 2017 - Dec. 31, 2018

Award Number


Amount Awarded



Linda J. Harris, Ph.D.
University of California, Davis


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.