Gretchen Shearer, Ph.D.
American Laboratory - May 1, 2015
Adulteration and contamination are ongoing concerns in the food and beverage industry, as they can result in unsafe products and damage brand integrity. Small particulate or light filth contamination may not be identifiable based on visual inspection, and in some cases may be misidentified. Brown or black particulate might simply be charred or burnt product, but other types of manufacturing debris may be found. Dark particulate can be rubber or metal debris, or mold or microbiological growth. Larger colorless or light-colored particulate may look like glass, but may in fact be plastic or compressed product material. Microbiological testing is used to confirm and identify certain types of organisms, but a negative result does not identify the contamination. A number of analytical techniques for material identification have been adapted for use on barely visible or subvisible particulates. Identification of foreign material contamination can alleviate safety concerns and identify the root cause of the problem.
The first step in particle evaluation is microscopic examination using a low-magnification stereomicroscope. Particles that can be seen without magnification are usually in the 100‒300 µm range, but in some instances, smaller particles can be observed. Many types of particulate can be classified and identified based on appearance, color and other characteristics; for example, particulates such as glass and metal have distinctive morphology that allows for tentative identification. Stereomicroscopic examination can be used to select the appropriate analytical technique.
Essentials of Polarized Light Microscopy and Ancillary Techniques by John Gustav Delly has been published.
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