Waxing of whole produce and its involvement in and impact on microbial food safety

After harvest many fresh fruits and vegetables are washed and waxed in order to prevent premature rotting and to extend shelf life. The point at which wax is applied differs from one produce type to another. However, for the majority of produce, such as apples and pears, wax is applied a single time just before packing and shipping. In contrast, citrus fruits may be waxed twice after harvest; one time after initial washing and before storage (storage wax) and a second time just before packing and shipping (finishing wax). For lemons, storage waxes are applied and fruit is stored without drying. In contrast, finishing waxes are typically dried with application of hot air. Over the past decade, the influence of commercially-available waxes on fruit and vegetable quality has been investigated and reviewed, however, only a few studies have investigated the impact of waxes on microbial food safety. Recently, this proposal team evaluated the survival of Salmonella and Listeria monocytogenes (LM) in a range of citrus storage and finishing waxes. The composition, pH, and microbial loads of these waxes differed significantly as did the behavior of pathogens inoculated into the waxes. No significant population reductions were observed in some storage waxes while significant population reductions were observed within 30 min in some finishing waxes. These observations highlight the importance of conducting a systematic evaluation of waxes used by the produce industry. To address this need, we are proposing to use citrus fruit (oranges and lemons) as model commodities. Microbial and chemical properties of a wide range of citrus storage and finishing waxes available from industry collaborators will be evaluated. Salmonella and LM will be separately inoculated into the waxes to mimic potential contamination of the wax at a packinghouse and the survival of pathogens will be monitored at ambient temperature and 4 °C. The behavior of pathogens will also be evaluated on fruit surfaces during lemon storage after the application of storage wax and after application and dry heating of finishing waxes. Wax applications that demonstrate significant bactericidal efficacy under laboratory conditions will then be evaluated via pilot scale studies at the pilot packinghouse operated by the University of California Lindcove Research and Extension Center. The outcomes of this study will bridge the knowledge gaps associated with the microbial safety risks of waxing by providing information about pathogen behavior in a range of storage and finished waxes and how the application of storage and finishing wax impacts the survival of pathogens on fruit surfaces.