Analysis, occurrence, and potential sensory significance of five polyfunctional mercaptans in white wines

A previously developed analytical method has been improved, validated and adapted for the analysis of 2-furfurylthiol (FFT), 4-methyl-4-mercapto-2-pentanone (MP), 3-mercaptohexyl acetate (MHA), 3-mercaptohexanol (MH) and benzylmercaptan (BM) in 136 white wines from different parts of the world. The overall uncertainty of the determinations was found to be around 20%, which was considered satisfactory given the low levels at which these compounds are found. The levels ranged from the method detection limits (0.5; 0.6; 2.0; 8.0 and 0.5 ng/L for FFT, MP, MHA, MH and BM, respectively) to 225; 87.9; 591; 7255 and 131 ng/L, which implies that nearly all of them can reach more than 100 Odor Units in some wines. The levels are significantly linked to both the grape variety (with the exception of FFT) and to the origin (in the case of Sauvignon Blanc samples), however, the range of variation within groups are so large that clear clusters could not be observed. Different sensory tests carried out on white wine models showed that all these compounds, even at low concentration, play an outstanding role on the aroma of wine, contributing to fruity, fresh and green notes. In some wines they are at concentrations high enough to act as genuine impact compounds.