Synthesis and Stable Isotope Dilution Assay of Ethanethiol and Diethyl Disulfide in Wine Using Solid Phase Microextraction. Effect of Aging on Their Levels in Wine

Abstract

Ethanethiol and diethyl disulfide (DEDS) most often occurred at levels above their olfactive threshold in wines with nauseous sulfur-linked smells. As ethanethiol is very oxidizable and chemically reactive, a stable isotopic dilution analysis of both ethanethiol and its disulfide in wines using solid phase microextraction and GC-MS was developed. The latter involved the determination of the proportion of DEDS formed by oxidation of the thiol during the analysis conditions, which was obtained by the use of two differently labeled disulfide standards. An original synthesis of labeled ethanethiol standards in conditions minimizing oxidation was developed, and the corresponding labeled diethyl disulfides were obtained from these thiols. This analytical method was used to follow the levels of these sulfur compounds during aging in a young red wine spiked with ethanethiol and added with enological tannins, with or without oxygen addition. The total levels of these two sulfur compounds were shown to decrease steadily after 60 days of aging, up to 83%. The effect of oxygen sped this decrease, but the effect of enological tannins was very slight. Residual ethanethiol was detected in its disulfide form from approximately 36% in the nonoxygenated wines to 69% in the oxygenated samples.

Development of stable isotope dilution assays for the quantitation of the food odorants hydrogen sulphide, methanethiol, ethanethiol, and propane-1-thiol and application to durian (Durio zibethinus L.) pulp

“…In particular, hydrogen sulphide occurs in a wide variety of foods [1] and exhibits a characteristic smell usually referred to as rotten egg-like [1][2][3][4][5][6][7] and an odour detection threshold of 10 µg/L [8]. In food, hydrogen sulphide may be formed either enzymatically or thermally from cysteine or cysteine-containing peptides.…”

“…In some foods, e.g. wine [2,5], it adds to off-flavours and in high amounts it may indicate microbial food spoilage [11,12].…”

“…Simultaneous quantitation of hydrogen sulphide and short-chain alkane-1-thiols can be accomplished by gas chromatography with PLOT columns and sulphur-sensitive detectors such as a flame photometric detector (FPD) or a sulphur chemiluminescence detector (SCD) [32]. However, the high volatility of hydrogen sulphide and short-chain alkane-1-thiols and their tendency towards the oxidative formation of disulphanes [2,33,34] may lead to substantial losses during the analytical workup. To compensate for such losses, the application of stable isotope dilution assays (SIDA) has been suggested [30,35].…”

“…Using deuterated analogues of the target compounds as internal standards and gas chromatography−mass spectrometry (GC-MS) of headspace samples, SIDA was successfully applied to quantitate methanethiol in coffee [36], French fries [22], peanuts [28], and fish sauce [23] and ethanethiol in wine [2]. To the best of our knowledge, no reports on the application of SIDA for the quantitation of propane-1-thiol and hydrogen sulphide have yet been published.…”

4,4′-Azopyridine as an easily prepared and recyclable oxidant for synthesis of symmetrical disulfides from thiols or alkyl halides(tosylates)/thiourea

“…[18][19][20][21][22] According to the literature, disulfides can be obtained directly from *Corresponding author. Email: khalili@shirazu.ac.ir thiocyanates, [23][24][25] alcohols [26][27][28] and sulfonyl chlorides. [29] Alternatively, oxidative coupling of thiols represents one of the most convenient and straightforward methods for the synthesis of disulfides.…”