Detection methods for foodborne pathogens and spoilage organisms have come a long way from traditional cultural methods. Advances in technology have led the evolution into rapid detection methods, whether they are antibody-based or nucleic acid-based (i.e., DNA or RNA). These rapid detection methods have been widely adopted by the food industry. However, with so many assays, kits, and methods available, it can be daunting to know where to start when choosing a rapid detection method that fits all your needs and requirements. While there are many factors to consider, here are five to keep in mind:
1. Method Science
There are several criteria to use to evaluate the performance of rapid detection method (1). Some of these factors include:
- Specificity: the probability of the method giving a negative test result when the sample is truly negative (i.e., true negative rate)
- Sensitivity: the probability of the method giving a positive test result when the sample is truly positive (i.e., true positive rate)
- Detection limit: the lower limit of the method’s ability to detect the target organism under defined conditions (e.g., detection limit of 1 CFU per 25 g of food)
- Inclusivity: the ability of the method to detect the target organism (e.g., the ability of a Listeria monocytogenes-specific assay to positively detect multiple different strains of L. monocytogenes)
- Exclusivity: the ability of the method to generate a negative result for a non-target organism (e.g., the ability of a L. monocytogenes-specific assay to not detect other Listeria species such as L. innocua)
Validation models differ by how they use some of these factors to describe method performance. For example, AOAC INTERNATIONAL, a recognized authority for method validation programs, incorporates these factors into a single parameter called Probability of Detection (POD), which is dependent on concentration (2).
2. Adherence to Customer Specifications
Foods are supplied, produced, or manufactured with exact specifications or standards to meet. For example, there may be a threshold of the amount of spoilage organisms present in the food sample. A result falling above or below a specification will have an impact on the product’s acceptability. Selecting the right rapid assay that can test reliably at that threshold is critical.
3. Validated Matrices
It is important that a rapid detection method is tested against variety of food matrices to demonstrate its ability perform according to its method characteristics (e.g., detection limit). In particular, a customer needs to know if a rapid detection method has been validated or verified against their specific food matrix or product in order to ensure a valid quality result. Many commercial methods will pursue certification from a recognized authority such as AOAC, which has guidelines for different levels of validation (e.g., AOAC Performance Tested Methods Program vs. AOAC Official Methods of Analysis Program).
4. Turnaround Time
The meaning of the word “rapid” may differ from person to person, so it is essential to know when to expect results once your samples have been received at the lab for testing. Keep in mind that “rapid” may refer to the time it takes to run the assay but typically includes the enrichment time. Sample login, preparation, analysis, quality data review, reporting and approvals will also add to the total time to result.
Keeping costs low is applicable is nearly every aspect of business, and food safety testing is no different. Rapid detection methods vary in cost but it should not be the driving factor in deciding which method to go with it. Consider all the factors – method science, customer specifications, validated matrices, turnaround time, and cost – to select the most appropriate method for your food product.
Mérieux NutriSciences offers a variety of rapid detection methods and can work with you to find the right method to fit your needs. Contact us to learn more about our testing services.
- Wiedmann, M., S. Wang, L. Post, and K. Nightingale. Assessment Criteria and Approaches for Rapid Detection Methods to Be Used in the Food Industry. 2014. J Food Prot. 77(4):670-690.
- AOAC International. Appendix F: Guidelines for Standard Method Performance Requirements. AOAC Official Methods of Analysis (2012). Web accessed 29 Jul 2015.