Impact of matrix variables and expertise of panelists on sensory thresholds of 1,1,6-trimethyl-1,2-dihydronaphthalene known as petrol off-flavor compound in Riesling wines

1,1,6-Trimethyl-1,2-dihydronaphthalene (TDN) is known to elicit the perception of "petrol off-flavor" in wine, most prominent in the variety Riesling. This study was focused on the impact of matrix variables such as ethanol and carbonation on the odor detection threshold of TDN. Increasing carbonation nearly doubled the detection threshold in water, however, this effect could not be observed in alcoholic matrices. Ethanol enhanced detection thresholds presumably due to diminished volatilization, which was only partially supported by measurement of partition coefficients using GC-MS. Overall, the impact of matrix changes was small ranging from 1.1 mu g/L in still water to 4.0 mu g/L in Riesling sparkling wine. Consumer detection threshold of 14.7 mu g/L TDN determined with 156 consumers exceeded the threshold of the trained panel by a factor of five and varied by consumers' age and gender. Rejecting a Riesling wine due to its petrol off-flavor, 60 mu g/L TDN were required in a young and 91 mu g/L in an eight-year-old Riesling wine. Based on analytical data for more than 250 commercial Riesling wines, geographic origin and to a smaller extent wine age contributed to large differences in TDN concentrations. About half of the investigated wines exceeded the detection threshold of the trained panel, whereas consumers would have noticed TDN in only less than 15% of the Riesling wines. Merely 3% of the wines actually exceeded the consumer rejection threshold of TDN. For both, detection and consumer rejection thresholds, the applied methodology contributed considerably to the final values, which is discussed critically.