Cross-contamination risks in dry environments

Cross-contamination of fresh produce is a significant risk factor that can contaminate multiple batches of fresh produce and can result in a food safety outbreak. With extensive research, we have developed understanding of the risk factors that promote cross-contamination of fresh produce during wet handling and processing as well as developed tools and technologies to reduce these risk factors. However, there is a lack of knowledge of the risk factors for cross-contamination of fresh produce in a dry environment as well as technologies and tools to reduce these risks. This proposed research plan is aimed at: (a) addressing key gaps in knowledge for managing cross-contamination risks including identification of surface and surface conditions that promote transfer of microbes from a contaminated surface to fresh produce; (b) developing a quantitative risk model to evaluate cross-contamination risks for diverse food contact surfaces and (c) development and validation of novel sanitation technology using food grade light activated antimicrobials. Thus, this comprehensive research approach addresses gaps in knowledge and develop tools and technologies to reduce food safety risks. In addition, development of a novel sanitation technology will address key gaps in sanitation of dry environments for both organic compliant and conventional fresh produce industries.

Cross-contamination during handling and processing of fresh produce is one of the key risk factors that can lead to a major food safety outbreak. Despite significant progress in understanding cross-contamination risk factors during wet handling and processing of fresh produce, there are significant gaps in knowledge regarding cross-contamination risk factors in dry environments. These risks are further enhanced by the lack of comprehensive approaches to improve sanitation and cleaning on food contact surfaces in dry environments. To address these needs, this goals of this research are: (a) quantify transfer coefficients of bacteria from inoculated dry food contact surfaces including various plastics and stainless steel surfaces to model fresh produce (e.g., onions and stone fruits) with and without the presence of organic and soil contaminants; (b) develop quantitative risk model for cross-contamination in dry environments; and (c) deploy novel photo activated food grade antimicrobials for sanitation in dry processing environments and compare its efficacy with conventional physical or chemicals cleaning/sanitization methods for reducing cross-contamination risks. Thus, the proposed research plan aims to develop a comprehensive understanding of cross-contamination risk factors during dry handling and processing of fresh produce and develop novel sanitation approaches to mitigate the risks of cross-contamination in dry environments. Success in this project will aid the fresh produce industry by addressing gaps in knowledge, identification of high relative food safety risk surfaces and conditions and developing novel approaches to address cross-contamination challenges.

1. Quantify transfer coefficients of bacteria from inoculated dry food contact surfaces, including various plastics and stainless steel, to model fresh produce (e.g., onion). 

2. Develop a quantitative risk model for cross-contamination

The data generated in this project address the gaps in knowledge of factors influencing crosscontamination risks in dry environments. The key findings and recommendations are as follows: 

● Salmonella was able to survive on food contact surfaces, such as conveyor belt (polyurethane, PU) or equipment (stainless steel, SS) surfaces, at ~34% RH and ambient temperature for ~3 months. Thus, pathogens once introduced in a facility may survive for the entire harvest season of an onion or stone fruit crop (~3 months). 

● E. faecium survived better than Salmonella on food contact surfaces at ~34% RH and ambient temperature, supporting the use of E. faecium as a surrogate organism for Salmonella in storage challenge studies. 

● In the presence of onion extract, the survival of Salmonella and E. faecium was enhanced on food contact surfaces. 

● In simulated onion handling, the transfer of E. faecium was significantly influenced by the transfer direction (PU-to-onion versus onion-to-PU) but not impacted by the initial inoculation level (high [7 log] versus moderate [5 log]). 

● A higher rate of transfer from onions was observed for E. faecium compared to Salmonella at the high inoculation level, and the transfer of Salmonella was significantly influenced by the inoculation level. E. faecium may potentially be used as a surrogate organism for Salmonella in transfer studies. 

● Transfer of E. faecium was not significantly impacted by the surface material, either as recipient surfaces (PU or SS) in simulated onion handling or as donor surfaces (PU or polyvinyl chloride, PVC) in simulated peach dry handling. 

● Transfer rate was significantly influenced by the presence of organic residues, including onion extract or soil water in simulated onion handling and peach juice or wax in simulated peach handling. 

● In simulated stone fruit dry handling, transfer rates of E. faecium and Salmonella were not significantly different at the high inoculation level. At the moderate inoculation level, populations of E. faecium and Salmonella transferred from surface to peach were below the limit of detection (1.6 log CFU/fruit) but tested positive after enrichment. 

● At a lower level of contamination (~5 log), the amount of transferred bacteria was <1.6 log CFU/peach, although it tested positive in the enrichment. This result underscores the importance of enhancing detection methods for bacteria in produce contaminated at low levels to improve the quantification of transferred bacteria in these experiments. 

● Transfer rates of E. faecium were not significantly impacted by the produce commodities evaluated (peach, nectarine, and onion). 

● No significant difference was observed in the sequential transfer of either E. faecium or Salmonella from a contaminated PU surface to up to 5 peaches. 

● Modeling the contamination of peaches during dry handling indicated that the presence of dry peach juice or wax on the conveyor belt reduced the number of contaminated peaches during processing; however, it significantly increased the contamination level per peach.