ATP detection: The balance between precision and speed

Adenosine triphosphate (ATP) is an indicator molecule for the presence of biological residues used in food production. Burcu Yordem, 3M Food Safety, explains its role in an effective hygiene monitoring programme

Food production managers are relied on to make a critical decision every day: whether to start production or not. The fundamental worry is the hygiene of the facility. Every hour production is stalled for cleaning is potential revenue lost. However, if production is conducted on a surface that hasn’t been adequately cleaned, the risk of contamination and costly recalls increases dramatically.

Manufacturers have traditionally performed either visual inspections (relying on the naked eye) or microbial tests (swabbing surfaces and then testing in a lab) to help evaluate whether environments are safe and free of any potential pathogens. However, visual inspections are imprecise and subjective, and microbial tests are a time-consuming process. Food production managers have increasingly turned to new technologies, most notably to adenosine triphosphate detection (ATP testing), to bridge the gap and earn the perfect balance between precision and speed.

ATP is an indicator molecule for the presence of biological residues. ATP testing solutions work by capturing the molecule from a surface or water sample via a swab.

To measure ATP, the sample is mixed with an enzyme from fireflies called luciferase, which catalyses a reaction where two of the phosphates are broken off from the ATP molecule. The energy from this reaction is captured by the enzyme to create light.

The newly redesigned 3M Luminometer works alongside Clean-Trace Hygiene Monitoring and Management System

The swab is inserted into a device called a luminometer, which reads the amount of light produced by the sample. The light produced is proportional to the amount of ATP in it: the more bacteria or product residue on the surface, the more ATP; the more ATP, the more light produced.

The light is detected in an instrument and displayed in relative light units, or RLUs. The higher the RLUs, the more likely it is that the surface has not been properly cleaned.

Luminometer technology has evolved to a point where food manufacturers can carry a device in their hand and receive results instantaneously.

An RLU is not a standardised unit of measurement like grams or centimetres. Different ATP monitoring systems have different outputs, sensitivities, reagent formulations and light detection systems.

The readings from different manufacturers are not interchangeable. For instance, a reading of 10 RLU from one manufacturer may be equivalent to 50 RLU for a different brand, so pass/fail levels must be independently determined for every system. It also is important to note larger RLU values do not indicate that a system is more sensitive.

Best Practices

ATP testing is a well-established method for measuring hygiene, however it cannot be used as a replacement for traditional microbiology tests.

Conventional microbial tests are often concerned with counting the number of colony forming units (CFU) per area of the surface being tested. ATP test methods detect ATP from all living cells and product residues, so it is not inherently indicative of the measure of bacteria on a surface. RLUs measure the overall cleanliness of a surface rather than the number of bacteria.

Because colony counts and RLU values are determined using different test methods and measure different elements of hygiene monitoring, RLU values do not necessarily correlate to colony forming units when testing an environmental surface.

ATP hygiene monitoring provides a measurement of the direct risks resulting from high levels of microorganisms plus the indirect risks resulting from organic residues that can provide a source of nutrients to microorganisms. An effective hygiene monitoring programme will make use of both ATP and microbial testing technologies.

The most important first step in choosing to use an ATP testing device is understanding how the technology will integrate into a larger environmental monitoring programme.

Food manufacturers should start by mapping their entire facility into multiple areas, or hygienic zones, based on the microbial risk to the product. Once the full environment has been mapped and considered, managers should work with their team to determine the most relevant test points and a testing cadence that makes sense for their specific processes.

The two most important things to consider when evaluating how important a given test point are: how close the surface is to the actual food product, and how difficult the surface is to clean.

Surfaces that are far from the food or very easy to clean thoroughly likely don’t need to be tested as often as surfaces that come into direct contact with the product or surfaces that are particularly difficult to clean properly. For example, conveyor belts or meat slicers could be considered Zone 1 sites because they hold a much higher risk and need to be tested much more frequently than a forklift in a facility, for example; but all surfaces are important to monitor regularly.

The highest risk – Zone 1 – test points should be monitored daily, or ideally, after every time those surfaces are cleaned and again before they’re used in production. Lower risk areas can be monitored much less frequently, but they should still be tested often enough to ensure that sanitation efforts are sufficient to secure the safety of the facility.

While there are a number of adequately sensitive ATP monitoring systems available to food manufacturers to help with food safety, it’s important to evaluate each option to find the system that provides stable and consistent results, including across time and temperature changes.

Choosing a method

While many systems can give manufacturers a reading for their sampling sites’ ATP levels, some hygiene monitoring solutions have been shown to produce different changes of results on the same surfaces when tested at different times or at different temperatures.

In a true food safety environment, the temperature of a surface in a facility that produces a refrigerated product could be well over 35°C directly after it has been power washed, but less than 10°C directly before production starts. It is important for manufacturers to take their environment into account and choose a system that will show consistent, reliable results in any production environments that are likely to occur.

A trial of any rapid hygiene monitoring system is strongly recommended, and this trial should mimic a part of the full sampling schedule. This period is when a food manufacturer can discover if the ATP system produces results that are both stable and consistent.

This is imperative because a business wants to feel comfortable relying on a hygiene monitoring solution that ensures the high-risk decision to start the production process is made with confidence and the operational risk is proactively managed.