(Editor’s Note: This is an online-only article attributed to the April/May 2014 issue.)
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.