AOAC Official Method 997.17 Microbial Ranking of Porous Packaging Materials
(Exposure Chamber Method)
See Table 997.17A for the re sults of the interlaboratory study support ing ac cep tance of the method.
A. Principle
Test portions of porous materials are subjected to an aerosol of Bacillus subtilis var niger spores (ATCC 9372) within an exposure chamber. Spores which pass through the porous material are collected on membrane filters and enumerated. The logarithm reduction value (LRV) is calculated by subtracting the logarithm of the number of spores passing through the porous material (N1) from the logarithm of the initial microbial challenge (N0).
B. Apparatus
(a) Exposure chamber.—The chamber is con structed of acrylic sheeting and consists of 2 sections as illus trated in Figure 997.17A.
The bottom section contains a 6-place manifold connected to 6 flowmeters, one per port, containing hoses at tached to 6 filtering units. The port to the manifold is at tached to a vacuum source. A vacuum gauge is mounted be tween the manifold and the vacuum source. The upper chamber contains a fan for disper sion of the bacterial aerosol, a port for at tachment of the nebulizer, a port for exhausting the chamber, and a plate for attach ment of dis posable or sterilizable filter units. The chamber may use disposable filter units or reusable filter units, or both.
