New Impact Odorants Related to Specific VOO Odor Notes: Volatile Thiols
Stefania Vichi1, Nuria Cortés-Francisco1, Josep Caixach2 , Agustí  Romero3
1Department of Food Science and Nutrition, University of Barcelona, Barcelona, Spain 
2Mass Spectrometry Laboratory, IDAEA-CSIC, Barcelona, Spain 
3 Olive Production, Oil Processing and Nut Trees, IRTA, Constantí  
(Tarragona), Spain.

Several sensory attributes cannot be directly related to any compound detected until now in the volatile fraction of virgin olive oil (VOO). They could be the result of the interaction between various volatile compounds, or they could be due to a number of compounds that have not been yet identified. Volatile thiols are powerful odor compounds that contribute significantly to the sensory properties of several food products [1].  Due to their extremely low odor thresholds, they exhibit a significant sensory impact even at very low concentrations. The implication of thiols in some of these VOO secondary attributes has been recently pointed out after the development of a simple, reliable, selective and sensitive method for the assessment of volatile thiols at trace levels in lipid matrices [2]. The method consisted of a single-step derivatization/extraction procedure followed by electrospray ionization-high performance liquid chromatography-high resolution mass spectrometry (ESI-LCHPLC-HRMS). By combining derivarization-ESI-LC-HRMS and sensory analysis [3,4], a significant correlation between 4-methoxy-2-methyl-2-butanethiol (4MMB) and the ‘fig tree leaf’ sensory attribute was revealed [5]. This sensory characteristic is frequent in VOO but it could not be previously related to any component of VOO volatile fraction. Although 4MMB was present at ng/kg, it significantly influenced VOO aroma. Moreover, by performing a non-target screening, various volatile thiols were detected for the first time in VOOs. In addition to 4MMB, 3-methyl-2-butene-1-thiol, methanethiol, and benzenethiol were identified in different VOOs on the basis of their elemental composition and by comparison with reference compounds. All of them were quantified and found to be present at ng/kg level. Unlike 4MMB, they have not yet been associated with any sensory note, but given the high sensory impact usually shown by volatile thiols in food, the occurrence and the sensory influence of these new thiols deserves to be further investigated.

[1] McGorrin, R.J.  in: M. Quian et al. (Eds.), Volatile sulfur compounds in foods, ACS Symposium Series, Washington, 2011, pp.3.
[2] Vichi, S. et al. (2013) J. Chromatogr. A, 1318, 180- 188	
[3] Commission Regulation (EC) No 796/2002 of 6 May 2002
[4] Commission Regulation (EC) No 640/2008 of 4 July 2008
[5] Vichi, S. et al. (2014) Food Chem. 149, 313-318