An Analytical Technique for Identifying Tribromoanisole

Combining olfactometry analysis with multidimensional gas chromatography–mass spectrometry provides an extremely useful analytical method for identifying aroma or odor notes from a sample.
Nov 01, 2011
Volume 2011 Supplement, Issue 6

In the past several years, pharmaceutical companies have recalled some of their products due to the presence of a musty, moldy, earthy odor (1–5). When a consumer opens a product container and smells an unusual odor, it indicates that the product has been compromised. Subsequent analysis of the recalled products determined that 2,4,6-tribromanisole (TBA) caused the odor.

TBA has been found to cause odor problems in the past. Whitfield and coworkers identified TBA as a possible source for a musty odor in sultanas that were packaged in polyethylene bags (6). They demonstrated that when these food packages were stored in the presence of TBA-contaminated fiberboard, the food could acquire the off odor or off flavor after only one week.

Chatonnet and colleagues also identified TBA as the compound responsible for a musty off odor in wine (7). The compound was present in wines that had a musty character during tasting. The wine acquired this flavor from being stored in an atmosphere contaminated with TBA.

TBA belongs to a group of organic compounds called haloanisoles, which are extremely powerful and can add musty, moldy, or earthy odors to many materials, such as food, beverages, and packaging. Haloanisole compounds contain at least one halogen atom (i.e., fluorine, chlorine, bromine, or iodine) as part of their chemical composition.

Other haloanisole compounds, such as 2,4,6-trichloroanisole (TCA), 2,3,4,6-tetrachloroanisole, and pentachloroanisole have similar odor characteristics and have been associated with cork taint in wine (8). They are extremely aromatic and have low odor-threshold concentrations i.e., (the minimum amount necessary for the compound to be smelled by the majority of people).

Figure 1: Biomethylation reaction where 2,4,6-tribromophenol is converted to 2,4,6-tribromoanisole. (ALL FIGURES ARE COURTESY OF THE AUTHORS)
The minimum concentration necessary to produce the characteristic off odor of TBA and TCA is approximately 30 parts per quadrillion (9). These haloanisole compounds are a byproduct of microbial metabolism in products that have been treated with halophenols. The biomethylation process is performed by various types of filamentous fungi primarily as a biochemical self-defense mechanism. Figure 1 shows the chemical reaction during which the hydrogen of the hydroxyl group is replaced with a methyl group. The fungi convert the usually toxic halophenol compounds into less toxic haloanisole compounds.

Haloanisoles can be present in many manufacturing and shipping areas. Trichlorophenol can be formed when chlorine reacts with the natural phenolic compounds found in wood and water. Cleaning or sanitizing materials are a possible source of chlorine. Tribromophenol (TBP) can be used as a flame retardant in brominated plastics, papers, and textiles. The compound also is used as a fungicide, a wood preservative, and an antiseptic agent.

TBP is also a synthetic intermediate used for producing many types of brominated flame retardants (10). In some parts of the world, TBP continues to be used as a fungicide and wood preservative. The compound is not a registered pesticide with the Environmental Protection Agency, and its use as a fungicide has been banned in the United States, Canada, and Europe (11).

For contamination to occur, TBP and the filamentatous fungi must be present. As the fungi consume the TBP, the local concentration of TBA increases as a function of time. Only after the odor-threshold concentration for TBA is exceeded does the characteristic odor of TBA become apparent.

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