Quantification of Several 4-Alkyl Substituted γ-Lactones in Australian Wines

Abstract

Stable isotope dilution assays have been developed for gamma-octalactone (1), gamma-nonalactone (2), gamma-decalactone (3) and gamma-dodecalactone (4) in both white and red wines for the first time. (2)H(7)-analogues of each lactone were prepared for use as internal standards via a strategy employing ring-opening, esterification and oxidation of the respective starting lactones. The methods were shown to be highly accurate and reproducible (R(2) > or = 0.999; SD < or = 1%). A large selection of Australian wines (n = 178) were analyzed for the presence of lactones 1-4. Fifty-eight white wines covering the varieties Chardonnay, Riesling, Sauvignon Blanc, Semillon and Viognier, as well as Botrytis style wines, were analyzed and showed broadly that gamma-octalactone (1) was the most common lactone, being observed above its limit of detection in 28 of the wines, followed by gamma-nonalactone (2) in 23 wines. The Botrytis style white wines had the highest concentrations of 1 and 2 (maximum concentrations 8.5 and 59 microg/L respectively). A total of 120 red wines covering the varieties Cabernet Sauvignon, Durif, Merlot, Pinot Noir and Shiraz were also studied and showed gamma-octalactone (1) and gamma-nonalactone (2) to be the most common lactones present, in 56 and 57 of the wines, respectively. gamma-Decalactone (3) was observed in only a small number (13) of red wine samples and not at all in the white varieties. gamma-Dodecalactone (4) was absent from all 178 samples studied. The highest concentrations of lactones 1, 2 and 3 in the red wines were 4.2, 39.7 and 4.0 microg/L respectively.

Quantitative analysis of γ‐ and δ‐lactones in wines using gas chromatography with selective tandem mass spectrometric detection

“…Optimization of the HS‐SPME started with general parameters (temperature, extraction time) published earlier . In the particular situation with the instrumentation used in our hands, we realized a strong dependency of the signal intensity on SPME fiber exposition, as shown in Fig.…”

“…The synthesis of d 7 ‐γ‐decalactone ( d 7 ‐4 ) was carried out according to Scheme . Basically, the synthesis followed the route described by Günther and Mosandl via a radical addition of the corresponding aldehyde and an ethyl ester, forming a 4‐oxoalkanoic acid ester, in which deuterium could be incorporated as had been described by Brown …”

“…The obtained keto ester (4‐oxodecanoicacid ethyl ester, 3 ) was suspended in D 2 O (750 mg, 3.5 mmol in 12 mL) and heated at reflux in a glycol bath with addition of 35%(w/v) DCl/D 2 O solution (2.1 mL) for 5 days as described previously . Then the aqueous phase was extracted with 3 × 15 mL MTBE, dried with magnesium sulfate, filtered, and evaporated.…”

“…This was discussed in detail by Hener and Mosandl and may be found with the ubiquitous mass fragment (C 6 H 13 ) + (from alkyl chains ≥ six carbon atoms), (C 5 H 9 O) + (2‐methylbutanoic acid (esters)) or others, interfering with the base peak of γ‐lactones . For the complex wine matrix, a thorough study on quantitative γ‐lactone analysis has been recently published . In the thesis by Brown (later Cooke by marriage) and the corresponding publication, quantification of γ‐lactones was based on a stable isotope dilution assay (SIDA), which is state‐of‐the‐art in modern flavor analysis .…”

“…Usually, sample preparation was done by headspace solid‐phase microextraction (HS‐SPME). However, in certain wine samples, Cooke observed co‐elutions that were particularly pronounced for γ‐dodecalactone . A workaround was found in a solid‐phase extraction (SPE) method adapted from others, which allowed sample fractionation, thus including a further purification step.…”