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Wes Kline, Rutgers Cooperative Extension
The Center for Produce Safety (CPS) holds an annual symposium where researchers present findings
from projects funded by CPS. The goal is to present results faster that may help the industry address food safety issues. I selected four summaries that may apply to the industry in New Jersey. There are fifteen summaries in total. If you would like to review the remainder or read a research report go to
https://www.centerforproducesafety.org
Cleaning and sanitation of harvest equipment. The importance of cleaning and sanitation of harvest
containers and equipment has become increasingly clear. However, a project reported at the Symposium [2023 Chen final report] underlines the importance of continued grower/harvester outreach and education. Machine harvest of blueberries has only recently become possible. This project involved a grower survey that found that only 70-75% clean and sanitize harvest equipment “regularly”, 3 % never perform this vital task and the rest were unaware of the need. Previous studies and outbreak investigations have taught the industry that surfaces on harvesting equipment and containers offer Lm and other microorganism’s niches to reside in and deposit biofilms that permits survival and subsequent cross-contamination of products unless effective, immediate, and verifiable cleaning and sanitation is performed at least daily. It is important for the industry to continually create cleaning and sanitation awareness across all sectors of the industry and leverage our accumulated knowledge on best practices.
Product testing – Preharvest, more samples, more mass is better. Sampling for pre- or post-harvest
product testing has been an important and ongoing discussion within the produce industry. Three different sampling models were explored including leafy greens/STECs, tomatoes/Salmonella, and cilantro/ Cyclospora [Stasiewicz final report 2023]. Regardless of commodity and pathogen, preharvest is more powerful than finished product testing for detection of pathogens. Steps (e.g., cooling, sorting, washing) that might reduce the microbial load postharvest serve to reduce the likelihood of detecting already low level, randomly distributed, and sporadic contamination. Preharvest sampling plans need to be based upon the hazard analysis and the types of risks present in any given field. There is no practical “right number” of samples, but sampling power, or the ability to detect low level pathogens, increases with the number of samples taken and the size or the total mass of the samples. So, the more the better within the constrictions of sampling resources. Risk mapping by observation or additional rapid sampling and testing in the production environment [Verma 2023 final report] can help identify potential “hot spots” and permit concentrated sampling in those higher risk areas.
Controlling wash water quality in dump tanks – It is a question of systems control. Dump tanks often
employ re-circulated wash water, handle large amounts raw product, and over time accumulate high
organic loads. In a study focused on wash water control in apple dump tanks, researchers confi rmed
disinfectant concentration, chemical oxygen demand or COD, and contact time as critical variables that
must be monitored closely to ensure pathogen control [Zhu 2023 fi nal report]. In lab-based experiments using dump tank water the results show that as COD increases, free chlorine’s efficacy at controlling Listeria in wash water decreases while PAA was not impacted by COD levels. In commercial-scale experimentation using four different apple packing operations and employing apples inoculated with nonpathogenic Enterococcus faecium (EF) as a surrogate for Listeria, the research team found that each of the four dump tank systems behaved differently and that while elevated levels of free chlorine and PAA at moderate COD levels reduced EF on the uninoculated fruit and wash water, they did not prevent cross contamination from inoculated fruit to uninoculated fruit. This result is a stark reminder to all fruit and vegetable packing and processing operators that “one size, fits all” approaches to controlling wash water quality are not sufficient and that each system and product combination must be tested, operating parameters established (sanitizer concentration, contact time, pH, COD (or even just turbidity), rate of make-up water addition, product load per unit time, etc.), and microbial control validated and continuously verified during commercial operations.
Listeria monocytogenes (Lm) and Salmonella survival. Timing is everything. Listeria monocytogenes
and Salmonella can survive on surfaces found in dry stone fruit packinghouse environments and persist
after the season [Dawson final 2023 report]. It has been shown that Listeria survives in wet conditions
and this research demonstrates that Listeria also persists in dry conditions, even better than Salmonella.
In packinghouses closed after a season, the aerobic plate count was shown to increase over time in the
dry, idle facilities. Therefore, at the end of a packing season, it is best to rigorously clean the equipment
and the production environment with detergents and agitation to eliminate organic residues and sanitize surfaces properly to ensure Lm and other bacteria are killed immediately and biofilm formation is prevented. Importantly, repeat the process immediately before start up the next season.