Practical validation of surface pasteurization of netted melons.

No one wants to take cantaloupes off the shelf or foodservice menu offerings. Since 1990, cantaloupes have been associated with 36 outbreaks and pathogen-based recalls recorded in the public health database. Preventive controls are viewed as the best strategy to combat this burden on consumers and public health, the general economy, and the sustainability of this important fruit category. This project will seek to translate well and established laboratory findings that support the effectiveness of hot water pasteurization of cantaloupe and other netted-rind melons into a validated and verified process. This research will be conducted in controlled experimental farm and model process studies and at newly constructed, essentially identical, rind pasteurization and disinfection lines in major commercial facilities in CA and AZ across two seasons. The outcome of these studies, using a combination of applied environmentally fit and adapted bacterial strains and native indicator bacteria, common to all melon production fields, will assist in the design and implementation of preventive controls and postharvest interventions for netted melons. This research data is viewed by many diverse stakeholders as vital to establish meaningful and verifiable food safety control measures to regain and enhance consumer confidence so badly shaken by the listerias tragedy of 2011.

No one wants to take cantaloupes off the shelf or foodservice menu offerings. Since 1990, cantaloupes have been associated with 36 outbreaks and pathogen-based recalls recorded in the public health database. Preventive controls are viewed as the best strategy to combat this burden on consumers and public health, the general economy, and the sustainability of this important fruit category. The essential functionality of thermal surface-pasteurization of netted melons has been recognized at the basic and applied research level for over a decade, primarily as hot water immersion and hot water brush washing. The reported inactivation of inoculated pathogens, predominantly Salmonella enterica serotypes, has exceeded a 4.5 log reduction. With the recurring economic losses and human tragedy associated with the most recent outbreak, we seek to assist in converting these bench-top studies to a validated and verified high-throughput commercial system across extended seasons, growing districts, varieties, netted rind traits, and other commercial variables. In addition to meeting food safety goals, killing heat shocks may also positively or negatively impact the post-treatment keeping quality of cantaloupes and other more sensitive netted melons. Therefore, our proposed research plan will develop ‘real-world’ data for this postharvest disinfection treatment to arrive at a balance in which food safety objectives do not compromise the quality and arrive at a set of Best Practice options for the industry. To achieve this goal, experimental farm trials using an attenuated isolate of Salmonella Typhimurium and Listeria innocua, a surrogate for Listeria monocytogenes, will be conducted at the UC Davis Research Farm Facility. Fruit from these open environment trial will be subjected to hot water surface pasteurization alone or in combination with a sequentially applied labeled disinfectant to achieve at least a 4-log reduction of applied pathogen surrogates and retain or improve fruit shelf-keeping properties. The recognized scarcity of detectable populations of pathogens, such as Salmonella, on cantaloupe in arid western production regions essential precludes verification of hot water pasteurization with non-inoculated fruit in either a lab pilot system or commercial system. Based on our experience from prior studies, we have targeted log reduction of indigenous Total Coliform as the appropriate benchmark for future commercial verification studies on-site that can be correlated with 4-log reductions of stress-adapted inoculated strains from model studies at Time:Temperature regimes that both define and parallel the commercial process design and operational parameters. Therefore, hot water surface pasteurization alone or in combination with a sequentially applied labeled disinfectant in the twin commercial process systems will be verified to achieve a regional and temporally reproducible success criterion of at least a 2-log reduction of indigenous Total Coliform on netted melon rind and retain or improve fruit shelf-keeping properties. The outcomes of this research project will be very valuable for the cantaloupe industry and template SOPs should be extendable to other types of melons and durable fresh produce. We believe that a public information resource of this disinfection technology may be scalable, easily transferred, and successfully implemented by the global cantaloupe and netted melon supply and fresh processing industry.

1. Evaluate the quantitative and qualitative survival of attenuated S. enterica and L. innocua during cantaloupe in controlled open-field experimental production. 

2. Validation of postharvest mitigation treatments and effects of delays of cooling after sanitizing and temperature fluctuations during postharvest storage on pathogen survival. 

3. Verify, by on-site studies, the efficacy of an evolving commercial process utilizing heat immersion as a rind pasteurization treatment across multiple time-points in each of two seasonal production intervals.

With proper system design and management, we find that a thermal-shower partial pasteurization of the netted rind of cantaloupe, though costly to implement on a large scale in a manner to most closely reflect the supporting validation studies, is possible to achieve without compromising quality. It was not possible, nor anticipated to be a project outcome, that any verification standard could be designed for validated or verifiable reduction of naturallycontaminating Salmonella or Listeria. In a separate survey study within the same project period, our lab tested over 4,000 cantaloupes collected from CA shippers after packing, including more than 400 from our cooperator’s facility, and found no detectable presence of either pathogen. Therefore, our studies focused on the more ubiquitous general bacterial indicators but still found limited levels and consistency in log reduction, relative to lab validation outcomes. Based on our outcomes in assessing the thermal wash temperature tolerance of native indicators compared to applied pathogens, we recommend using total Enterobacteriaceae as the routine process verification standard in addition to water temperature monitoring. Infrared imaging is a viable nondestructive option for monitoring the uniformity and peak rind temperature exposure of the process. Regardless, commercial handlers should carefully evaluate this option before embarking on installation of system based on thermal washing alone or in combination with an approved adjunct antimicrobial process aide.