The food safety landscape continues to change in the produce sector. Producers normally use microbial testing to measure water quality and potential issues related to a process and environment. Produce testing is mainly conducted to meet customer requirements.

It is well known that produce testing cannot guarantee produce safety alone. However, there is still confusion about what product testing can and cannot ensure. Produce testing can only ensure the product tested is pathogen-free if 100 percent of the product is tested rendering it a cost-prohibitive, impractical option.

There are still several technical and operational challenges that producers deal with when performing produce testing on raw or finished product. Some of these challenges include: the highly perishable nature of most fresh produce items (results are needed as soon as possible), the lack of a statistically valid sampling protocol (sampling is not representative) as well as the selectivity and sensitivity of commercial pathogen tests (the ability of tests to detect when pathogens are present—especially at low levels).

Up to this day the biggest barrier to having a robust product testing program is the lack of statistically valid sampling protocols, stated Dr. Trevor Suslow, an extension specialist from UC Davis in a recent Western Growers webinar related to the subject. He also confirmed that determining the appropriate number of samples to test and the level of confidence those samples represent is a major limitation. This is true because microbial contamination loads vary greatly among different produce commodities, and pathogens are normally found at low and non-homogenous levels at the field level.

In the last few years, the sensitivity (ability to detect bacteria if they are present) and selectivity (ability to distinguish closely related bacteria) of testing methods have improved significantly resulting in fewer issues related to false positives and negatives. This is good news considering both sensitivity and specificity play a big part when selecting a specific test type. While selecting the right test type is a key consideration, the use of a robust sampling protocol and data analysis are also essential for product testing to minimize risk and contribute to the overall improvement of a company’s food safety system.

Currently, commercial testing programs for fresh produce rely on rapid methods (with different sensitivities and specificities). The Probability of Detection (POD) and Limit of Detection (LOD) are affected by factors such as sample enrichment and concentration, which in turn are affected by the status of the pathogen cells and sampling distribution. This is why it is important to work with the service providers to understand the POD and LOD of testing kits as well as the target detection limit and methodology.

Test kit validation can improve POD and other technologies on the horizon can also address and enhance the sensitivity and specificity of detection. One promising technology currently used at the public and regulatory levels is whole genome sequencing (WGS). Whole Genome Sequencing may still be unfamiliar to many people, but the term simply refers to a laboratory process that determines the entire set of genes or genome of an organism (complete DNA make-up).

According to U.S. Food and Drug Administration (FDA) representatives, WGS enables the agency to better understand variations within and between species and organisms with more precision than other technologies. While more widely used at the regulatory level, WGS holds potential as a valuable tool for industry in monitoring pathogens and spoilage organisms as well as sanitary control effectiveness.

Regardless of the technology to be used, Dr. Suslow believes that the validation of pathogen detection platforms for fresh produce should be performed in a context that considers the following: 1) the phyllosphere (the above-ground part of the plant) interactions on target pathogens that affect their survival and adaptation; 2) the sample mass and processing matrix, 3) enrichment protocols; and 4) extended enrichment to minimize the risk of false negatives.

The use of microbiological testing is a tool for the development and verification of a food safety program, a produce testing program must have a defined purpose, clear procedure, use validated methods and clear actions to address results. While new tools continue to advance to overcome current technical and operational limitations, it is still true that if product testing is not properly designed and/or implemented, it may provide false assurances and misleading interpretations. This fact has not changed.