It is essential to determine the cleanliness of food processing equipment and manufacturing areas before they are used for food production. Luminometers help processors monitor surfaces that may contaminate food products and compromise product safety and quality.
 

Luminometers

Surface cleanliness can be evaluated in seconds using a luminometer to measure residual amounts of the chemical marker adenosine triphosphate (ATP). ATP is a compound found in all types of plant, animal and microbial cells.

The science behind the luminometer is based on the enzyme luciferase – the same enzyme that makes firefly tails glow at night. Residual ATP interacts with luciferase to generate light. This light is measured by the luminometer and is recorded in relative light units (RLU). The amount of light generated is directly proportional to the amount of ATP present – an indication of the total biological contamination level. 

• Swabbing
• Swabbing procedure
• Hygiene monitoring
• Software
• Benefits of luminometers
• Limitations of luminometers
• Factors to consider when buying luminometers 

Swabbing
 

Visually clean surfaces are sampled using cotton or foam tipped swabs that have been moistened with water, a buffer or a solution that extracts ATP from microorganisms and food residue. Sample swabs are put back into swab tubes (which contain liquid luciferase to cause a reaction) and are then put in the luminometer for analysis.       

Most swabs are analyzed onsite, but they remain stable for several hours before luciferase activation which allows greater flexibility in reading times. Once activated, swabs must be analyzed by the luminometer within 60 seconds or less.

There are also a number of commercial swabs available for food processors who require ATP testing for water or for allergens. The presence of ATP in water may indicate a loss in process control. Special swabs are used to detect ATP in clean-in-place (CIP) systems or in water quality assessments for food and beverage processing.  

Commercial swabs to test allergens are a thousand times more sensitive than normal surface testing swabs and detect ATP common to allergenic foods (ex: egg, milk). The ATP detection levels are similar to protein-based allergen tests and indicate potential contamination.  

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Swabbing procedure
 

Processors should follow the swabbing protocol outlined in manufacturers’ instructions. However, there is common surface testing protocol:

• Identify a small surface area for sampling (four by four inches or 10 by 10 centimetres).
• Maintain constant pressure when swabbing the area.
• Slowly rotate the swab to ensure maximum surface contact. Apply 10 zigzag strokes over the surface – back and forth and then up and down across the area.

Hygiene monitoring
 

Luminometers show RLU test results on a screen as either a number or a pass/warning/fail reading.   

Numbers:

Numbers are often considered superior, because they demonstrate the degree of sanitation effectiveness and provide measurable targets for continued sanitation improvement. As the processor’s sanitation process improves, the luminometer test result number decreases.  

Pass/warning/fail:

• Pass indicates low levels or no ATP, which means the sanitation process is working.
• Warning means ATP counts are higher than expected and the cleaning procedure needs to be reviewed and/or sanitation staff need to be re-trained.
• Fail means there are high ATP counts and the cleaning process requires immediate corrective actions.

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Software
 

Data management software is provided with most luminometers and provides several benefits:

• Information on swabbing locations and test results are stored on the luminometer and can be downloaded to a personal computer for later trend analysis. 

• Trend analysis capabilities –  including data sorting, charting and graphing – help processors comply with audit requirements by clearly demonstrating that the sanitation process is working correctly.
• Identification of re-test data, alongside original results demonstrates corrective actions and due diligence.
• Testing locations may be tracked over a period of time to identify priority areas, problems with the sanitation process and/or the early detection of biofilms.   
• Setting benchmark numbers promotes ongoing improvement in hygiene standards and cleaning processes.   

Benefits of luminometers
 

• Results can be generated within seconds, unlike the most rapid microbial testing kits which normally require several hours or days.
• Luminometers provide numerical results that support hands-on training. Staff can visually compare surface cleanliness with data from the luminometer.     
• Luminometer swabs are easily applied to most types of food processing plants, field applications and food service or retail sites as well as delivery vehicles and incoming materials (ex: packaging).  
• Luminometers do not require dedicated laboratory space, specialized staff or extensive training.
• Luminometers help validate sanitation standard operational procedures (SSOP) and help cut costs by reducing unnecessary sanitation chemicals and labour.

Limitations of luminometers
 

• ATP luminometer testing is not a direct replacement for microbiological testing. Routine microbiological testing, which provides complementary information on the monitoring or screening of background or specific microorganisms is still required.
• Luminometer test results are commonly thought to reflect only the presence of microorganisms. This non-specific test detects ATP in various components (ex: microorganisms, protein, carbohydrates, etc.) of any given soil.
• Although ATP may not be detected, some other types of contamination may exist.
• Luminometers differ significantly in detection limits and reproducibility.
• Processing operations that use dry cleaning procedures require caution during testing because the cleaning procedures do not always remove all product residues (ex: milk powder, flour).

Factors to consider when buying luminometers 
 

• Cost is always a factor. Luminometers that have photomultiplier tubes definitely have superior sensitivity, but they are more expensive than the more common, less expensive luminometers that have photodiodes.
• Processors will want to consider the instruments size, battery life and general durability and buy from reputable suppliers.
• Guaranteed adequate, timely technical support is required to ensure the luminometer operation, interpretation and analysis are always accurate.  
   

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For information on the Food Safety Program contact the CVO/Food Safety Knowledge Centre.  For technical information, call 204-795-7968 in Winnipeg; or e-mail foodsafety@gov.mb.ca. For general information, contact your local GO Centre.