Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
email: Office@practicalwinery.com
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November/December 2008
WINE MICROBIOLOGY
2,4,6-TBA — Next ‘2,4,6-TCA’ in U.S. wine industry
WINE MICROBIOLOGY
BY

Robert Tracy
with Bevan Skaalen
leadingT ver the course of the last 10 years or so, wineries in the U.S. have been dealing with a difficult problem: 2,4,6- trichloroanisole (2,4,6-TCA). The cost of this chemical compound to the wine industry has been tremendous — in wine quality, in negative publicity, and financially.
Generally termed a haloanisole, 2,4,6-TCA is known to cause a musty, mold taint at very low concentrations (parts per trillion [ppt]). It has likely always been a major cause of wine taint but has been recognized as a serious problem only in the past 10 years because scientific instrument technology has advanced to be able to identify 2,4,6-TCA as one of the sources of the musty, moldy taint found in wines.
Another haloanisole, 2,4,6-tribromoanisole (2,4,6-TBA) has recently been identified as a similar contributor to wine taint. 2,4,6-TBA was first identified by Pascal Chatonnet and collaborators in 2004 in French wines.1 Like 2,4,6-TCA, 2,4,6-TBA causes a musty, mold taint in wine at very low concentrations, but it has the potential to be an even more serious problem to the U.S. wine industry because its precursor (2,4,6- tribromophenol [2,4,6-TBP]) can be found in so many sources commonly used in wineries.
This column provides an overview of the emerging 2,4,6-TBA problem and suggests what preventive actions wineries can implement to protect their wines.
Introduction
What is the taint resulting from haloanisole contamination of food and beverages? Taint is a taste or odor that typically arises from an external source, as opposed to off-odors or off flavors, which are attributed to internal changes to a product (such as microbial spoilage).
The taste or odor threshold for a taint is defined as the lowest concentration of the chemical compound detectable by a defined population group. Generally, a food or beverage taint can be tasted or has an odor at extremely low concentrations.
Chemically, 2,4,6-TBA is a derivative of the anisole (or methoxybenzene) family of compounds, which contain at least one atom of a halogen (fluorine, chlorine, bromine, or iodine) and thus are termed haloanisoles. Haloanisoles are formed from halophenol compounds by microbes, such as filamentous fungi, via a process called biomethylation.
Specifically, 2,4,6-TBA is formed from the biomethylation of its precursor 2,4,6-TBP. Figure I shows the chemical structure of 2,4,6-TBA (three bromine atoms attached to the 2, 4, and 6 positions on a benzene ring).
Origin of the 2,4,6-TBA precursor 2,4,6-TBP
Chlorophenols (like 2,4,6-trichlorophenol [2,4,6-TCP], which is precursor to 2,4,6-TCA) are primarily anthropogenic in origin; that is, they are produced by human activity.
Bromophenols (like 2,4,6-TBP) can be produced both naturally in the environment and anthropogenically. In nature, 2,4,6-TBP can be formed in marine environments by brown algae as a way to remove
excess bromine from their surroundings,2 and anthropogenically, it can be produced in wastewater that has been treated with chlorine in the presence of bromine ions and low levels of organic phenols.3
2,4,6-TBP and its derivatives have been used as 1) fire-retardant agents in epoxy resins, polyurethanes, plastics, paper, textiles, and fire extinguishing media; 2) wood preservatives; 3) general fungicides for the leather, textiles, paint, plastics, paper, and pulp industries; and 4) antiseptic agents. 5) They have also been found in detergents containing bromine.
The winery environment has several possible sources of 2,4,6-TBP, such as painted surfaces in the cellar, sealants, barrels, oak adjuncts, wood ladders, wooden catwalks, wood pallets, plywood, wooden rafters, wood beams, water, water hoses, wine hoses, plastic tank liners, plastics, insulation, filter pads, fining agents, packaging materials (cardboard, adhesives, paper bags), cleansers, and sanitizers.
Formation of 2,4,6-TBA
The only scientifically proven molecular mechanism responsible for formation of 2,4,6-TBA (and all other anisoles found in wine — 2,4,6–TCA, 2,3,4,6-tetrachloroanisole [2,3,4,6-TeCA], and pentachloroanisole [PCA]) is the biomethylation (O-methylation) of its precursor 2,4,6-TBP. (See biochemical reaction in Figure I.) In the conversion to 2,4,6-TBA, 2,4,6-TBP is catalyzed by the enzyme chlorophenol O-methyltransferase (CPOMT), and the oxygen group on 2,4,6-TBP is methylated. This enzyme has been shown to methylate several different halophenols, including chlorophenols, bromophenols, and iodophenols.4
Figure I. Biochemical reaction for the conversion of 2,4,6-TBP to 2,4,6-TBA by O-methylation
This biomethylation reaction is performed primarily by filamentous fungi (Trichoderma longibrachiatum, Penicillium spp., Fusarium spp., Cladosporium spp., and Paecilomyces variotii)5,6,7 and has been shown to be catalyzed by the winerydwelling bacteria Streptomyces.8
Biomethylation is a biochemical defense mechanism for microbes. It allows them to detoxify their immediate environment by converting the highly toxic halophenols to non-toxic haloanisoles. In the absence of this defense mechanism, the filamentous fungi and Streptomyces could die or suffer significant physiological damage. It is worth noting that filamentous fungi also have a second defensive strategy to detoxify halophenols: secretion of oxidative enzymes (laccase) that attack and degrade halophenols.
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