2-Bromo-4-methylphenol, a Compound Responsible for Iodine Off-Flavor in Wines

Abstract

This study focuses on an off-flavor in wines treated by an acidification technique involving ion-exchange resins. Applying reversed-phase HPLC on a C18 column to a contaminated wine extract resulted in 25 fractions in dilute alcohol medium, and only one, fraction 19, presented this off-flavor. Its composition was analyzed using gas chromatography coupled to olfactometry (GC-O) and mass spectrometry (GC-MS), leading to the identification of 2-bromo-4-methylphenol for the first time as a compound associated with an "iodine" aroma in white, rosé, and red table wines. Contaminated wines presented a wide range of levels, with maximum concentrations of 28900, 7556, and 48000 ng/L and minimum values of 260, 35, and 63 ng/L in white, rosé, and red wines, respectively. Sensory studies investigating 2-bromo-4-methylphenol gave very interesting results. Individual thresholds ranged from 0.15 to >77.4 ng/L in reverse osmosis water, from 0.4 to >193.5 ng/L in white wine, from 0.5 to >774 ng/L in rosé wine, and from 0.5 to >774 ng/L in red wine. The very wide distribution of individual thresholds suggested the presence of two populations, sensitive and nonsensitive, with a bimodal frequency distribution. The odor descriptions quoted by the more sensitive group characterized 2-bromo-4-methylphenol using terms with "iodine" connotations in both the reverse osmosis water and red wine matrices. The descriptors for commercial wines naturally affected by this defect were seafood, iodine, mud, and fish.

Molecular determinism of specific anosmia to 2‐bromo‐4‐methylphenol

“…The distribution curve left no doubt about the existence of two populations in terms of 2‐bromo‐4‐methylphenol sensitivity. The percentage of specific anosmics was significant (52%), confirming previous data in the literature . This specific anosmia was apparently linked to the halogenated substitution position.…”

“…The percentage of specific anosmics was significant (52%), confirming previous data in the literature. [15] This specific anosmia was apparently linked to the halogenated substitution position. This assumption was corroborated by a previous study, [42] which found a large proportion of subjects who were insensitive to 2-iodo-4-methylphenol (42% of the panelists tested).…”

“…The range of dilution factors between the two extreme sensitivities was determined to be over 5*10 5. According to the Amoore criterion, some subjects had such high detection thresholds that they may be considered specifically anosmic for this compound. As structurally related compounds are detected at different thresholds, it is possible to assess the chemical determinism of interactions between the receptor system and the odorants involve .…”

“…[2,3] In the same vein, large interindividual differences in sensitivity (over 1,000-fold for some compounds [4,5] and specific hyposmias (or even anosmias) have been measured for various odorants, such as short-chain fatty acids, [6] musk, [7] amines, [8] 2-isobutyl-3methoxypyrazine, [3] 2,4,6-trichloroanisole, [9] diacetyl, [10] and many others. [11] Furthermore, remarkable bimodal distributions of individual detection thresholds have been observed for several compounds: Acetone, [12] Ambroxan, [13] 4,16-androstadien-3-one, [14] 5α-androst-16-en-3-one, [11] 2-bromo-4-methylphenol, [15] Lcarvone, [16] 1,8-cineole, [16,17] Citralva, [3] Exaltolide, [18] β-ionone, [1] Isobutyraldehyde, [11] Methanethiol, [19] Pemenone, [3] ω-Pentadecalactone, [11] Phenylethyl alcohol, [3] 1-Pyrroline, [11] Rotundone. [20] These variations have been interpreted as consequences of variations in the presence or expression of genes encoding for the relevant odour receptors.…”