As a result of the ongoing Coronavirus pandemic, the 11th Annual CPS Research Symposium was conducted virtually over the course of five consecutive weeks in 2020. In Session 1 held on June 23, 2020, we explored the use of computer-based modeling to help address two burning issues for the produce industry: understanding potential Listeria growth and persistence in whole produce commodities and the development of sampling strategies to support microbial testing needs. The second session conducted on June 30, 2020, helps expand our knowledge base on Listeria monocytogenes and its persistence and growth on specific commodities and fresh-cut products and examines novel methods to control Listeria growth on food contact surfaces. These outstanding presentations and discussions generated the following executive summary and more lengthy Key Learnings.
These learnings are meant to inform and provoke thought with an eye towards inspiring readers to examine their own produce safety programs and to use the research to make improvements. They are not meant as a directive on what must be done to produce safe food.
This and other recordings of CPS webinars are available via CPS’s website. The latest information about specific research projects mentioned in this document is available via CPS’s website, including our extensive research database and other produce safety resources.
Key Learnings Executive Summary
- Always check new products for ability to support Lm growth. When new combinations of produce commodities are used in a new product offering, it is important to understand if they represent more or less of a Listeria monocytogenes (Lm) growth risk if subjected to temperature abuse.
- Lm growth supported by novel salad ingredients. Salad ingredients like Brussels sprouts, beet greens, broccoli stalks and kale can support growth of Lm if temperature abused, and while this observation is consistent with the Lm computer-based growth model described in Session 1 of the CPS Symposium, in some items the growth rates are slower than what might have been expected likely owing to the presence of a naturally occurring component of crucifer crops known as glucosinolates.
- Listeria innocua as a Lm surrogate for growth studies. A potential surrogate for Lm is Listeria innocua. Growth studies on salad ingredients indicate that its growth rates very closely mimic those of Lm. L. innocua has been proposed as a surrogate for Lm in other validation scenarios and it seems that it may also have use in crucifer crop studies.
- pH and temperature are the primary determinates of Lm growth on produce. As discussed in Session 1 and elaborated on during Session 2 of the CPS Symposium, pH and temperature are key factors in supporting Lm growth on whole, fresh-cut, and juiced produce items. Generally, pH values near neutral (7.0) and elevated temperatures (above 39°F) support elevated growth.
- Mixed species biofilms protect Lm. Biofilms containing multiple species of bacteria plus Lm are more difficult to eliminate than biofilms containing only Lm. Strains that are efficient biofilm producers can be found consistently in packinghouses, indicating they are adapted well to packing environments. Mixed species biofilms are more resistant to sanitation efforts effectively “protecting” Lm cells that are resident in the biofilm.
- Rough surfaces are more conducive to biofilm stability. Worn equipment with rough surfaces provide niches for biofilm production which can protect Lm from cleaning and sanitation efforts.
- Different sanitation strategies may be needed for different equipment. Equipment made from different materials and in different states of wear may require different cleaning and sanitation strategies to manage the risks of biofilm formation that may result in product cross contamination. Combinations of sanitizers that have different modes of action can be effective tools in developing sanitation strategies to minimize contamination risks.
- The challenge of cleaning and sanitation of reusable totes and bins may be addressed by using plastics infused with antifouling and antimicrobial chemistries. Produce containers, liners and spray-on biocoatings developed with N-halamine chemistry that delivers free chlorine to control biofilms and kill bacteria have been tested and shown to be effective. These products are rechargeable; meaning they can be refreshed multiple times by simple exposure to 1-percent bleach for 15 minutes. Additional antifouling and antimicrobial materials are also being evaluated in an ongoing CPS project.
- Collaboration remains an integral piece of successful produce safety research. The research projects in Session 2 were all supported by industry collaborators that provide researchers access to facilities and products and share knowledge and data to shape the subsequent research priorities and inform interpretation of the results.
This is the Key Learnings Executive Summary only. See the PDF link for more extensive information.