From: Food Quality & Safety magazine, April/May 2014

Advances in Air Monitoring

by Anne Connors

Advances in Air Monitoring

Food and beverages can become contaminated by contact with infected personnel, as well as unclean surfaces and polluted air particles. As such, environmental monitoring, and air testing in particular, is a critical tool in the food and beverage industry in order to keep production plants clean and minimize the risk of contamination.

This article describes the various ways to monitor potential airborne contaminants in food and beverage manufacturing. A method comparison between traditional membrane filtration and a new air sampling technology, the MAS-100 CG Ex air sampling system (EMD Millipore, Billerica, Mass.) will be provided.


There are several standard ways of monitoring airborne potential contaminants. Traditional membrane filtration passes a sample through a membrane using a filter funnel and vacuum. Any microorganisms in the sample are concentrated on the surface of the membrane, which is then placed in a petri dish with nutrient medium. The passage of nutrients through the filter facilitates the growth of organisms on the surface of the membrane, which are transferred to culture media for counting.

Passive air sampling uses solid media settle plates exposed to the air for a predetermined period of time. Active air sampling utilizes an instrument that draws ambient air and then directs the air stream at an attached agar plate or strip for collection. Particle counters are used to quantify potential contaminants in the air.

Settle Plates. Settle plates usually contain Tryptic Soy Agar (TSA) or Sabouraud Dextrose Agar , and they are placed throughout the test area with their lids removed. After exposure, the plates are closed and incubated. The number of colonies is then counted and the microorganisms are identified. For safe and efficient documentation, pre-barcoded culture media plates are used, enabling each plate to be fully traceable back to its date of use and the location of sampling.

A drawback when using settle plates is that they lose water due to evaporation when exposed, leading to an increasingly dry skin on the agar surface. This can cause poor growth of certain microbes on the media and thus an underestimation of the proportion of these organisms in the air. Over a typical four-hour exposure period in a unidirectional airflow cabinet, TSA plates have been found to lose up to 16 percent of their original weight. However, when such plates were inoculated with typical contaminants and subsequently incubated, all recovery rates were above 70 percent . To enable prolonged exposure and incubation periods while ensuring that the plates still deliver reliable results, settle plates can be poured to a particularly high filling level. However, the maximum exposure time should be validated for each production line, taking into consideration air flow, temperature, relative humidity of the air, and turbulences.

Active Air Samplers. There are several ways to help avoid contamination when using active air samplers in critical areas, including isolators and Restricted Access Barrier Systems. First, it is important that the air flow is not severely disrupted by the instrument’s operation, placement, or removal, as disturbance makes it easier for contaminants to attach to instrument housing. To minimize air flow disruption in isolators and other confined areas, as well as save space, manufacturers have developed variants of their instruments. For example, the air ducting is directed from the sampling points outside the controlled area where all electronic and moving parts remain. To analyze the disruption propensity of an instrument in use, companies can conduct smoke studies that visualize the movement of air in decommissioned cleanrooms. Some air samplers are specifically designed with rounded edges and other features to minimize air flow disruption.

Active air sampling is also used to identify microbial contamination in compressed gasses, which come into contact with product at numerous points in any production process.

Microbial contamination can exist in the valves or lines that are used to feed gas and air into critical, aseptic manufacturing environments. When testing compressed gasses, ensure constant air flow and consistent air sampling for accurate and reliable sampling. Some compressed gas monitors provide automated operation and conversion of the compressed air or gas sample, which can be at pressures of up to 5 bar (73pounds per square inch), to atmospheric conditions. Automated operation and short-duration, high-volume sampling reduces the time and effort required for monitoring and validating aseptic conditions.

Particle Counters. Particle monitoring of ambient air is conducted to quantify non-viable contaminants in the air and to determine the quality of air in controlled environments. Quantitative particle data often also provides an indication of the status regarding viable contaminants because most airborne microbes adhere to particles.

When selecting an air particle monitoring system, companies must choose either preinstalled or portable particle counters. There are pros and cons to both types. In many pharmaceutical production facilities, the particle counters are preinstalled at specified locations. When the infrastructure of the facility allows for preinstalled particle counters, the systems have proved very convenient.

However, many companies opt for the flexibility of portable particle counters.

MAS-100 CG Ex

The traditional membrane filtration method for air monitoring involves numerous steps including sterilization of the membrane, transportation of samples, the setup of the testing environment, and the membrane transfer. Additionally, the membrane apparatus uses a significant amount of energy for the autoclaving cycle, which can prove costly. The MAS-100 CG Ex air monitoring system eliminates associated setup. To validate the method, we have compared the MAS-100 CG Ex air sampling method to the traditional membrane filtration method.

The MAS-100 CG Ex is an air sampling system which is based on the well-known impaction principle of the MAS-100. The microorganisms are directly impacted on a 90 millimeter standard petri dish filled with culture medium. This air sampler is specially used for the microbiological monitoring of pressurized gases that come into contact with finished product. The microorganisms are collected under working pressure, without risking a sublethal damage by the following decompression. The suction volume of 100 liters/minute is electronically controlled over a pressure range of 1.6 to 10 bar absolute pressure. Unlike other systems and methods, sampling is always performed in the defined pressure range. The instrument is delivered as an ex-proof version and thus is suitable for use in explosion-proof zones. By default the MAS-100 CG is calibrated for air, nitrogen, argon, and carbon dioxide, but it can also be calibrated for other gases.

Taking ISO standard 14698-1 into account, the test method using an MAS-100 CG EX and the membrane filter method is compared in a given pressure range. Both methods are applied under identical test conditions. Compressed air is used as the pressurized gas. Since ISO standard Annex B (Guidance on validating air samplers) contains no instructions regarding the generation of aerosols in the pressure range concerned, this methodology has to be self-developed (the spinning-top or spinning-disc aerosol generator cannot be used in this pressure range). By using a self-developed ultrasonic nebulizing chamber, the spore suspension of Baccillus subtilis variation niger given in the ISO standard can be nebulized and then the microbial count is determined by membrane filtration or by the MAS-100 CG.

With both methods, a series of 10 individual samples is tested on each of three different days. The microbial recovery attained with the MAS-CG is expressed – according to the ISO standard – as a percentage of the membrane filtration recovery. Additionally, the differences between the two procedures are checked statistically using the t-test.

As compared to the membrane filter method, the MAS-100 CG EX has an average efficiency of 92 percent. According to the t-test, there is no significant difference between the microbial counts determined by the two procedures.


To protect product integrity, food and beverage companies must take measures to identify contamination events earlier. Air monitoring can increase control in the product manufacturing process and ensure products are manufactured to the desired specifications. Additionally, new technologies for air monitoring can help detect contamination events faster and prevent future instances, while providing comparable results with traditional methods. The relatively low costs of monitoring result in improved quality and increased safety – and in the reduction of overall production risks and expenses.

Connors is regional marketing manager—Environmental Monitoring/Media Fill Testing North America-BioMonitoring at EMD Millipore. Reach her at


  1. Sandle, T. (2011): Microbial recovery on settle plates in unidirectional airflow cabinets. Clean Air and Containment Review 6/2011.
  2. MAS-100, Qualification of air sampler systems: The MAS-100 Meier R. and Zingre H., (Swiss Pharma 1-2/00).
  3. ISO 14698-1 Cleanrooms and associated controlled environments – Bio-contamination control- Part 1: General principles and methods (first edition 2003-09-01).



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