The C13-norisoprenoid aroma compounds 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) and isomeric 2,10,10-trimethyl-6-methylene-1-oxaspiro[4.5]dec-7-enes, so-called vitispiranes, are considered to be biosynthetically related. They occur at higher concentrations in bottle-aged Riesling wines especially and are important contributors to the varietal aroma of Riesling wines. Because of the variation of the quantitative methods and data reported in the literature, a redetermination of concentration levels for both free and total TDN and isomeric vitispiranes, especially in German Riesling wines, was performed using a stable-isotope-dilution assay (SIDA). For this purpose, a novel six-step synthetic route to TDN and deuterium-labeled TDN was developed. A standardized sample preparation for TDN and vitispiranes and a rapid acid-hydrolysis method at genuine wine-pH conditions for the conversion of the precursors into TDN and vitispiranes were also developed. Automated HS-SPME was applied to 250 wine samples from two wine competitions, and analysis was performed by gas chromatography-mass spectrometry with selected-ion monitoring (GC-SIM-MS) as well as selected-reaction monitoring (GC-SRM-MS).
Keywords: 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN); Riesling; isomeric vitispiranes; kerosene off-flavor; petrol note; stable-isotope-dilution assay; synthesis.