Light it up

Fireflies light it up

Nature came to the rescue with a unique application of the enzyme luciferase that is present in the tail of the firefly.

Why is cleaning important?

Cleaning is carried out to remove product remaining on the production and/or processing surface. Product residues provide a nutrient base for microbes to grow. Therefore food residues represent a risk of introducing contamination from spoilage and pathogenic organisms. The cleaning process often includes a detergent and sanitising step.

How can we measure clean?

Nature came to the rescue with a unique application of the enzyme luciferase that is present in the tail of the firefly. It was discovered luciferase harnesses the energy released when ATP (Adenosine Tri-phosphate) loses one or more phosphate groups as illustrated in Fig. 1. The question follows, what is ATP? ATP is a molecule that is present in all living cells including microbes, food products, plants, animals and bodily fluids. The relationship between ATP and the measurement of cleanliness is simple. An increase in organisms and protein residues lead to an increase in ATP levels and this leads to an increase in bioluminescence detected. The technique of using the enzyme and substrate of the firefly (luciferase and luciferin) to detect and measure ATP was first described in 1974.

Application and method of ATP detection

ATP bioluminescence detection can be applied as a first line hygiene measurement tool to provide an instant indication on the cleanliness of a surface. A summary of the difference between a visual assessment, microbiological testing and ATP testing is presented in Table 1. Using ATP as a marker allows for rapid indication of the presence of material of biological origin. If cleaning has been effective there should not be much ATP left behind.

The light signal is measured in a sensitive light meter called a Luminometer. Results are expressed in Relative Light Units (RLUs). The higher the RLU value the higher the contamination. ATP bioluminescent detection is a fully quantitative method. Results are obtained in seconds making ATP testing a real-time test. Pre-determined pass/fail levels can be loaded into the software of the Luminometer and corrective action is taken immediately. Data can be stored for analysis over time.

Important to note is that RLU does not equal CFU (colony forming units) that are obtained with microbiology testing. RLU is a measurement of microbes AND food residues and it provides a total picture of the hygiene levels in a plant or production facility.

ATP bioluminescence is a widely used method and the key advantage is the speed of result. It provides important information on the effectiveness of the cleaning in a production facility or processing plant.

What to look for in an ATP testing system?


Repeatability is ESSENTIAL for effective cleaning verification as poor repeatability results in re-cleaning when you don’t need to. This leads to wasted time, money and production capacity.


The sensitivity of ATP systems are measured in femtomoles. A billionth of a millionth (10-15) of a mole is one femtomole (1 fmole ~ 0.5 picograms). Low amounts of proteins can be measured in femtomoles. Essentially all ATP systems on the market are ~0.5-2 fmoles ATP sensitivity. Food applications require ~5-20 fmole sensitivity and you will never get to zero fmole ATP. All systems on the market have enough sensitivity based on pure ATP. Environmental samples are NOT PURE ATP. Beware of making decisions based on sensitivity studies using pure ATP.

Data collection, analyses and storage

Get more value from your ATP data by creating reports to present your data. Make sure that the instrument you choose allows you to manage the data effectively and that the software has the ability to assist you in assessing the efficiency of the sanitation team. ATP testing will allow the tracking of factors (both positive and negative) influencing the cleaning regime.


ATP bioluminescence can be a valuable tool in conjunction with visual assessment to ‘positively release’ a plant after cleaning. Its use allows corrective action to be taken before production starts and reduces the risk of poor cleaning resulting in a product quality problem.

Other uses are to optimise cleaning regimes and therefore contribute to cost-effective chemical use. However, ATP Bioluminescence is not a direct replacement for microbiological testing. Microbiology testing should still be carried out for monitoring background flora or checking for the presence of specific spoilage or pathogenic organisms. If used in conjunction with other control measures, a proactive and effective hygiene management system can be developed with the use of this technology and with regular review of results, the system can evolve and improve.


Dr Louise Maré

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