The significance of environmental monitoring to verify effectiveness of sanitation programs and minimize or prevent pathogen food contamination is well recognized. Foods, especially ready-to-eat (RTE) foods, can be contaminated with environmental pathogens such as Salmonella and Listeria monocytogenes through cross-contamination with the plant environment, including contact surfaces, unclean equipment, floor, drains, air, and water. The FDA and USDA expect the industry to have a hygienic zoning and effective environmental monitoring program designed to reduce the potential for contamination.
Many novel rapid and automated methods for microbiological testing of the food plant environment are available commercially and new methods are being introduced regularly. Their acceptance by the industry, however, depends on several factors, including speed (time to result), specificity, selectivity, accuracy and reproducibility. Other things to consider are ease of use, cost, reagents, consumables, need for training, the availability of technical support, and regulatory acceptance.
Microbiological tests designed for detection or enumeration of indicator organisms or environmental pathogens using swabs or sponges and plating are used to obtain quantitative verification of the effectiveness of sanitation procedures. These tests, however, can take days to yield results. Indirect methods like adenosine triphosphate (ATP) testing are a popular option for hygiene monitoring and verification of cleaning and sanitation.
Unlike other methods, ATP testing provides results in seconds and is sensitive, quantitative, effective, and simple. Microbes and product residue contain ATP, an indicator of biological residues that can be easily detected to measure cleanliness because effective cleaning and sanitation remove all ATP from the food plant environment and food contact surfaces. A positive ATP test is indicative of unclean or not adequately clean surfaces.
Many food processors who found hygiene and environment monitoring by swabbing and microbial counts tedious, time consuming, and expensive are considering the ATP bioluminescence system for hygiene monitoring. The proliferation of new kits and luminometers has provided several options for the food processing industry but can cause confusion about the capability and proper application of the technology. The following are some of the main criteria and considerations to keep in mind when selecting an ATP bioluminescence system:
- Intended Purpose: ATP systems are designed to provide a quick idea about the cleanliness of food contact surfaces such as equipment, conveyors, pipelines, pumps and valves, or drains. They are NOT intended for determining a level of residual microorganisms (e.g. < 100/in² ) on a food contact surface.
- Speed (time to result): All ATP systems currently available on the market provide “rapid” results—the reading time may vary, but a reading is obtained in a few seconds. It is also important to consider the time required for an activated swab to be read in the luminometer. Other factors, such as the number of sampling sites per shift, or per day, the location of sampling sites, and operator-related factors will influence the overall speed in obtaining results.
- Reagents and Swabs: The ATP bioluminescence systems employee swab devices already containing rinsing buffer and luciferin-luciferase reagent. The convenience of the swabs is obvious. However, reagent stability, shelf-life expectancy, and storage temperature requirements are important considerations. Also, consider if you have to “read” the test immediately after swabbing or can allow some time lapse before reading. You should also look at the quality control of swabs in terms of background reading (if any) and the batch-to-batch variation.
- Instrument: ATP hygiene monitoring systems are based on one of the two photodetection technologies: photomultipliers and photodiodes. The sensitivity, robustness, accuracy, and precision of the rapid hygiene monitoring device are influenced by these technologies. All ATP bioluminescence systems offer portability, computerized data logging, and visual readout of ATP levels in terms of the RLUs (relative light units) or “zones” of cleanliness. The ruggedness of the instrument, battery life, computer interface with other computers in the plant, and availability of a “hard copy” of the data are other important considerations when selecting a system. For a multiproduct plant, the system’s versatility would also be something to look into. Its ease of operations and user friendliness are also important.
- Training and Technical Service: When you consider adding an ATP bioluminescence system to your plant, keep in mind the training and technical service required for transition from conventional methods. All major vendors of the instruments and kits provide some training for proper operation and maintenance, but you should try to obtain training specific to your plant and situation. Contact colleagues in other companies who may have experience with a particular ATP system to discuss their experiences. Also, technical service and responsiveness should be available following the purchase. In this regard, you may also want to access training opportunities available through professional organizations and universities as well as keep current with professional reading in pertinent scientific journals and trade magazines.
- Cost: I would list cost as the last consideration, although it may be the first thing you ask about. The cost of instruments, reagents, swabs, etc. is definitely a factor to be considered, but many variables influence the true cost. Most luminometers and swab devices are priced competitively and may be compared easily on a cost/test or cost/swab basis, and there may be incentives provided by vendors based on the testing volume or leasing versus purchasing the hardware. You may also consider return on investment or the time it will take to pay for the instrument. Savings resulting from improvements in cleaning and sanitation of plant equipment and environment may reflect in improved quality and shelf life and less time spent managing and monitoring the cleaning process and crew.
The above criteria and considerations are, by no means, a complete list of dos and don’ts when selecting an ATP bioluminescence system. Current ATP bioluminescence methods can be very useful in verifying effectiveness of plant cleaning and sanitation, becoming a valuable part of your food safety management program and sanitation preventive controls implementation.
Remember, though: The results from ATP surface hygiene monitoring are different from those of microbial enumeration methods and are not directly correlated to microbial counts or detection of Listeria or Salmonella. ATP tests are not intended to replace environmental microbial testing, but they can be an excellent way to obtain indication of hygiene efficacy in seconds versus days.
Dr. Vasavada is professor emeritus of food science at the University of Wisconsin-River Falls and a co-editor of Food Quality & Safety. Reach him at Purnendu.C.Vasavada@uwrf.edu.