Summary
Following recent melon-associated foodborne outbreaks, California cantaloupe growers voluntarily developed and implemented commodity-specific food safety guidelines for the safe handling of cantaloupes and other netted melons. While this document details best food safety practices to reduce the risk of contamination during production, packing, and distribution, science-based metrics describing transfer coefficients for pathogen contamination onto melons during field-packing operations are needed. Cross contamination is a known food safety risk in many environments, and is dependent on many variables, including transfer surface, commodity surface, and contamination level. Cross contamination was highlighted by the Food and Drug Administration as a critical factor contributing to recent cantaloupe-associated outbreaks. To date, no published literature evaluating the cross-contamination potential of whole melons has been established under typical field-packing conditions. Furthermore, there is a lack of data on handling practices related to cross-contamination risks for melons in the retail distribution supply chain, as well as guidance on the safe and uniform handling of melons throughout the retail environment. Through this proposed project, potential cross-contamination points likely to increase risk will be identified, and intervention strategies targeted to reduce the occurrence of pathogen transfer events during the handling of melons at harvest and retail will be developed.
Technical Abstract
Approximately 60% of the outbreaks related to the consumption of melons are linked to contaminated cantaloupe. Several of these outbreaks were attributed to cross contamination. As a result, guidance documents have been developed to assist the industry in the safe production and handling of melons to reduce the risk of cross contamination. A complicating factor in effective guidance is that the production and handling of melons is not uniform. Melons grown on the East Coast are commonly washed after harvest in packinghouses; melons grown on the West Coast are almost exclusively packed in the field without washing. While previous research has focused on cross contamination of melons with foodborne pathogens from contact with other melons and surfaces under wet conditions, little research has examined cross contamination of melons from these sources in dry conditions typical of Western field-packing operations. Specifically, metrics describing coefficients for pathogen transfer between melons and contact surfaces including gloves, knives, packing tables, rags, brushes, and bins. Therefore, the proposed project aims to provide scientific data on which to update/refine melon specific best practice guidance to reduce to likelihood of cross-contamination events in field-packing operations by quantifying the transfer of Salmonella and Listeria monocytogenes onto melons from each potential cross-contamination surface (e.g., stainless steel, polyethylene, or corrugated cardboard–lined packing tables). A series of inoculation experiments will be performed to calculate coefficients for pathogen transfer to melons upon single and subsequent touches to each potential contact surface. Furthermore, the survival of Salmonella and L. monocytogenes will be accessed for each potential cross-contamination surface. Field-pack equipment is regularly cleaned and sanitized at the end of each day, so pathogen survival will be evaluated at several time points to identify which contact surfaces have the greatest pathogen survival over time if contaminated. The effect of different sanitizers will be tested to determine the most effective decontamination regime to reduce the potential transference of pathogens to melons. It is common practice that once melons leave the fields the container lid is not removed until arrival at the distribution center or retail store. Thus, in order to fully understand cross-contamination risks throughout the distribution chain, melon handling in the retail environment will also be evaluated. Information on melon handling practices at distribution centers and or retail stores will be collected via case study methodology including interviews with key personnel and observation of product movement to identify potential cross-contamination points, investigate surfaces and define risk control sites. Mitigation and intervention strategies specific to cantaloupe distribution, storage, handling and display will be developed for retailers to limit these identified cross-contamination points to ensure the continued safety of melons from harvest to consumer. At the conclusion of the proposed project, we will have identified “high risk” cross-contamination points during the handling of melons at harvest (field-pack) and retail, and guidance aimed to reduce the occurrence of such cross-contamination events. This guidance will be communicated by hands-on trainings and a report to the industry, as well as supported by peer-reviewed publications that will detail the science-based data derived from the project.
Research Objectives
1. Quantify the transfer of Salmonella and Listeria monocytogenes onto melons in field-packing operations from each potential cross-contamination surface.
2. Compare the effect of different sanitizers on Salmonella and Listeria monocytogenes survival on potential cross-contamination surfaces.
3. Assess melon handling practices at retail through case study methodologies including interviews and observation to identify potential risk factor points.
Findings & Recommendations
• Transfer of Salmonella and L. monocytogenes was highest for rubber gloves compared with all other field-pack contact surfaces. Over time, due to wear, the rubber gloves cracked and allowed better attachment of pathogens.
• Less transfer of Salmonella and L. monocytogenes was observed between contaminated cantaloupe and surfaces (or vice versa) with shorter contact times.
• Less transfer of Salmonella and L. monocytogenes was observed between contaminated cantaloupe and surfaces (or vice versa) with smoother surfaces (e.g., stainless steel or nitrile gloves).
• Pathogen survival was greater on fouled compared with clean contact surfaces, highlighting the importance of robust, frequent sanitation.
• The most effective sanitation protocol for fouled contact surfaces was an overnight application of either chlorine or PAA.
• Listeria spp. were present in retail whole cantaloupe display environments.
• Retail contact surfaces in whole cantaloupe areas that were cleaned and sanitized on a regular basis (e.g., daily) had lower Listeria spp. prevalence than those surfaces that were cleaned and sanitized on a variable schedule (or as needed basis).
• Foam had the highest prevalence of Listeria–positive samples (100%), and is not recommended for use in whole cantaloupe displays (despite its ability to cushion product)