|
Click to listen to this article
|
Studying Pre-Harvest Contamination Risks and Managing Cross-Contamination During Post-Harvest Storage and Handling
By Joy Waite-Cusic, Associate Professor of Food Safety Systems, Oregon State University
Jason Racine, Erik Ohman and Sasha Nerney, Graduate Research Associates, Oregon State University
The number of multistate foodborne illness outbreaks linked to the consumption of contaminated produce has increased over the last two decades. In 2020 and 2021, two of the largest Salmonella outbreaks in more than10 years (each with more than 1,000 confirmed cases) were linked to the consumption of red onions. Outbreak investigations have not yielded a clear cause but have identified routes of contamination during growing and field curing as well as cross-contamination risks during post-harvest storage and handling.
Joy Waite-Cusic’s Food Safety Systems Laboratory at Oregon State University has multiple research projects underway with the goal to help the produce industry better understand practices that may have contributed to contamination as well as practices that might reduce contamination and cross-contamination risks. Graduate students Jason Racine, Erik Ohman and Sasha Nerney are leading these efforts and share updates on each of their projects and next steps in this article.
Assessing Potential for Production Practices to Impact Dry Bulb Onion Safety
The 2022 field trials in Ontario, Oregon, and Pasco, Washington, focused on quantifying the contamination rate and survival of generic E. coli (a surrogate for Salmonella) on onions contaminated by a variety of late-season water applications.
In Ontario, Oregon, a pesticide (Pristine) and a kaolin clay (Surround) application were prepared with contaminated water and applied to fields of Redwing and Cometa onions in late August to contaminate each onion plant with ~300 cells of E. coli. Immediately after contaminated pesticide or clay applications, 52-88 percent of the onion bulbs had detectable levels of E. coli. Contamination levels rapidly decreased, with only 5-20 percent of onion bulbs having detectable E. coli six hours after the spray applications. After two, seven and 16 days of field curing, E. coli was not detected on any onion bulbs tested (n = 160/day). On day 29 of field curing (harvest day), one onion out of 320 was positive for E. coli on enrichment.
Results suggest that risks associated with late pesticide and clay applications prepared with contaminated water were mitigated by field curing under the conditions present during the 2022 Oregon field trial.
In Pasco, Washington, water was contaminated with 1,600-2,000 E. coli/100 ml and applied to Calibra onions via drip and overhead irrigation that delivered 0.38 acre-inches in mid-August. Drip irrigation resulted in minimal contamination, with detection of E. coli on 12.5 percent of onion bulbs on day one. E. coli was not detected on any drip-irrigated onion bulbs on days two, seven, 15 or 28 (n = 40/day). Overhead irrigation with contaminated water initially resulted in over 95 percent of the onions having between one and 22 E. coli cells per bulb. Detectable E. coli persisted on a small number of the onions (one out of 40) for two weeks. By the end of field curing (28 days), E. coli was not detected on onion bulbs (n = 80); however, viable E. coli was detected on two onion tops (leaves) at the end of curing.
Results demonstrate high contamination rates associated with overhead irrigation using contaminated water; however, conditions during field curing in Pasco in 2022 led to substantial die-off. Field trials for 2023 will likely focus on contamination risks associated with overhead irrigation with contaminated water.
Cleaning, Sanitizing Surfaces on Produce Farms
The Food Safety Modernization Act (FSMA) was signed into law in 2011 with the goal of decreasing the detrimental effect of foodborne illness by focusing on the source of the outbreaks. A key component of FSMA is the Produce Safety Rule (PSR), which establishes comprehensive, science-based minimum standards for the safe production of fruits and vegetables to reduce the risk of contamination leading to foodborne illnesses. As we entered the inspection and enforcement period of the PSR beginning in 2019, on-farm inspections identified inadequacies occurring in many operations’ cleaning and sanitizing practices.
The goal of this project is to identify the current cleaning and sanitation practices and evaluate their efficacy. One aspect of this project was to quantify the efficacy of cleaning and sanitation programs in commercial fresh produce operations.
We visited five fresh produce operations between March and August of 2022 and sampled produce contact surfaces such as conveyors, buckets, storage containers and wash tanks to measure microbial and organic loads before and after completion of their cleaning and/or sanitation process. Four operations used wet-cleaning practices, while only one (an onion packinghouse) utilized a dry-cleaning program. One mixed vegetable operation and a blueberry harvesting operation cleaned and sanitized all food contact surfaces regularly. The berry packinghouse had a wet cleaning process with no sanitization step, and one mixed vegetable operation sanitized its food contact surfaces without prior cleaning steps.
The blueberry harvesting operation had the most robust cleaning and sanitizing program for its plastic harvest buckets, which included manually scrubbing each bucket with warm water and dish soap, submerging in a dunk tank containing 50-100 ppm of free chlorine for 30 minutes, followed by a rinse and air dry. This process effectively reduced the organic and microbial load on buckets, resulting in consistently low levels, averaging at 100 relative light units (RLU) and 22 cells/100 sq. cm, respectively.
The berry packinghouse used an automated bin washer to clean its plastic storage trays. Cold pressurized water and trisodium phosphate were used in the washing system, and no sanitizer was applied. This cleaning procedure moderately reduced the microbial load from an average of 20,000 cells/100 sq. cm to an average 3,500 cells/100 sq. cm. Cleaning alone was consistently effective in reducing the organic load on plastic to an average 160 relative light units (RLU).
Dry cleaning procedures in the onion packinghouse had no impact on the microbial or organic loads in the onion packinghouse, averaging 170,000 cells/100 sq. cm. Organic load (ATP RLU results) were inaccurate due to the high level of soil and dust particles that likely interfered with detection of fluorescence. Laboratory experiments are underway to evaluate the impact of soil on the validity of ATP testing in these types of settings.
Dry Cleaning, Sanitation Strategies for Onion Industry
FDA’s outbreak response, resulting recalls and investigation report of the 2020 Salmonella outbreak linked to onions indicated concerns about the effectiveness of dry cleaning to minimize cross-contamination between production lots. Without a wet cleaning and sanitation procedure, a “clean break” between production lots could not be confidently established, and the recall expanded to include hundreds of thousands of pounds of red, white and yellow onions handled in the same facility.
The overarching goal of this new project is to support food safety and risk management needs of the dry bulb onion industry, specifically in post-harvest storage and handling environments. Objectives for this research include: 1) characterizing growth and/or survival of E. coli in onions during post-harvest storage, and 2) defining optimal dry cleaning and/or sanitation of food contact surfaces to minimize cross-contamination risk.
The initial phases of this work will estimate microbial contamination levels of onions at harvest, throughout storage, as well as the transfer of these bacteria to and from food contact surfaces. This information will provide the foundation for subsequent experiments on transfer from surfaces to onions with and without the use of dry cleaning and/or sanitation. Visualization and simulations will be used to estimate cross-contamination risk under different scenarios.
We plan to share our findings through workshops in 2024 as well as sharing the modeling tool as a web-based application that facilities can use for evaluating potential changes to their cleaning and sanitation practices.
For this research to be successful, we need to have a clear understanding of the diverse surfaces, conditions and cleaning/sanitizing practices in post-harvest onion storage and handling facilities. During the first half of 2023, we will be conducting phone interviews and site visits to post-harvest facilities throughout Washington, Idaho and Oregon to characterize food contact surfaces, dry cleaning and sanitation methods, chemicals and tools, as well as potential barriers or concerns that the industry is willing to share. If you are interested and willing to be interviewed or host a site visit, please email joy.waite-cusic@oregonstate.edu or sasha.nerney@oregonstate.edu.
