Summary
Tomatoes are a nutritious food and an important crop for the state of Florida and the US economy. Yet, foodborne illness outbreaks associated with tomatoes have negatively impacted public health, consumer confidence in tomatoes, and the industry’s economic well-being. The Florida tomato industry has taken an active role in establishing tomato-handling standards to prevent pathogen contamination and infiltration. However, due to lack of scientific data applicable to commercial handling conditions, some of the standards rely upon recommendations previously developed for tomato quality maintenance. Therefore, scientific studies to evaluate pathogen contamination and infiltration under realistic commercial handling conditions are critical for developing handling practices to effectively reduce pathogen contamination. Proposed research will focus on evaluating current tomato post-harvest handling practices on Salmonella contamination and infiltration, and providing answers to the queries raised by the industry. Goals include defining operational limits for dump tank water management, identifying cost-effective dump tank water quality monitoring parameters, and developing/optimizing an overhead spray sanitation system to minimize tomato surface contamination while reducing water and chemical use. Project outcome will provide data for developing science-based guidelines to reduce food safety risks, and avoiding setting up costly regulations that may not necessarily advance food safety.
Technical Abstract
Tomatoes are a nutritious and valuable food crop that is important to Florida's economy as well as that of the US. About 71% of fresh tomatoes are grown in Florida and California, of which Florida's share amounted to $630 million (AMRC, 2009). Unfortunately, the tomato industry has been troubled with several foodborne illness outbreaks associated with consumption of tomatoes contaminated with Salmonella spp. in recent years. The overall goal of this project is to provide tomato growers and packers specific information that will allow the improved food safety of fresh tomatoes. Information gained will allow “functional limits” to be set, which “an operator can use to ensure that effective sanitizer concentrations are present in the dump tank,” and provide an answer as to when “the addition of additional chlorine is ill‐advised or ineffective and the water needs to be partially or fully changed?” Other impacts of this work will include reduced water use by utilizing fine mist sprayers as opposed to large-volume flume tanks that require daily filling, draining and cleaning. Additionally, since the water used in the overhead spray system is not recirculated, less chemicals could be used, reducing the overall cost of operation and lowering the environmental impact of a packing operation. The overall outcome of this work will be to answer fundamental questions. Information gained will provide answers to set “functional limits an operator can use to ensure that effective sanitizer concentrations are present in the dump tank,” and answer the question as to when “the addition of additional chlorine is ill‐advised or ineffective and the water needs to be partially or fully changed?” Other impacts of this work included reduced water use utilizing fine mist sprayers as opposed to large-volume flume tanks that require daily filling, draining and cleaning. Additionally, since the water used in the overhead spray system is not recirculated, less chemistry could be used, reducing the overall cost of operation while lower the environmental impact of a packing operation.
Research Objectives
1. Determine the effect of tomato dump tank water management standards on Salmonella infiltration.
2. Determine the correlation among water quality measurement parameters, and assess functional limits where wash water replenishment or replacement is needed.
3. Determine whether a dry-dump system utilizing an overhead spray rinse with a brush washer, is equal to or better than a flume system in removing surface pathogens from the surface to tomatoes.
4. Develop specific operation limits and monitoring recommendations for implementation in commercial settings, and ensure this information is disseminated to growers, packers and other stakeholders.
Findings & Recommendations
1) Internalized S. enterica cells were found only within tomato core tissue segments immediately underneath the stem-scars. The internalization incidence and populations of S. enterica declined in the core tissue samples with distance from the stem-scar.
2) The incidence of S. enterica internalization was a function of tomato variety, post-stem removal time, and immersion time, as well as the interaction between tomato dump tank temperature differential and immersion time.
3) Three large packinghouses in Florida were surveyed in 2010 and 2011. It was observed that water quality declined continuously during packing house operations, with a significant increase in chemical oxygen demand (COD) and turbidity. Free chlorine and ORP vary largely among different packing houses, as influenced by the specifics of the packing house operations, including the rate of tomatoes washed, and the dosage of chlorine into the dump tank etc. However, all of them maintained at least 25 ppm free chlorine in the dump tanks during our visits.
4) Laboratory simulation studies indicate that there is a relationship between free chlorine, pH and ORP in water containing a typical organic load. In general, ORP decreases with the increase in pH and decrease in free chlorine concentration. However, this correlation was only maintained within a small range of free chlorine concentration, suggesting a limitation in using ORP as a chlorine indicator.
5) Free chlorine is degraded rapidly by organic loads; although free chlorine concentrations can be brought back to the 60 ppm range, increasing amounts of sodium hypochlorite are needed with increasing organic load in the wash solution.
6) Pathogen cross-contamination occurred readily during tomato washing in the absence of free chlorine (or any other sanitizer). Cross-contamination was found on tomatoes washed in solution containing up to 5 ppm free chlorine, but not in the solutions containing 10 ppm free chlorine. This suggests that maintaining sufficient sanitizer concentration in the wash solution is critical to prevent pathogen cross-contamination.
7) The overhead spray system could achieve a 3- to 5-log10 unit reduction of Salmonella from tomato surfaces with specific sanitizers and spray times.
8) The overhead spray system could provide benefits over conventional flumes including higher pathogen reduction, and less sanitizer and water use, all of which help to decrease tomato packing costs and keep the tomato industry a viable part of Florida’s economy.