Sensory definition of green aroma concept in red French wines. Evidence for the contribution of novel volatile markers

Abstract

The aromatic complexity of a wine results from the perception of the association of volatile molecules and each aroma can be categorized into different families. The “green” aromas family in red wines has retained our attention by its close link with the fruity perception. In that study, the “green” olfactory concept of red wines was considered through a strategy combining both sensory analysis and hyphenated chromatographic techniques including HPLC and MDGC (Multidimensional Gas Chromatography). The aromatic space of this concept was specified by lexical generation through a free association task on 22 selected wines by a panel of wine experts. Then, 70 French red wines were scored on the basis of the intensity of their “green” and “fruity” attributes. The relationship between these two families and chemical markers (2-methoxy-3-isobutyl, 3-isopropyl and 3-sec-butyl pyrazines and C6 alcohol compounds) was assessed. Strong anti-correlation between “green” and “fruity” was demonstrated but no significant correlations could be established with known molecular markers associated with fresh green characters. So, the contribution of other aromatic compounds was formulated in particular with the level of grape maturation. Microvinifications of Cabernet-Sauvignon grapes from Medoc vineyard harvested at two ripeness stages were done during 2014 and 2015 vintages. The so-obtained wines were extracted with organic solvents and the concentrated extracts were fractioned by semi-preparative HPLC. Among fifty fractions collected, one was particularly highlighted for its green aromas. The sensory impact of this fraction was first confirmed by omission and reconstitution tests. To determine the molecules responsible for green flavour of this fraction, GC-O (Gas Chromatography coupled with Olfactometry) and MDGC-O/Time-Of-Flight-MS were considered. 2-Methoxy-3-isobutyl-pyrazine well known as IBMP (bell pepper descriptor) was identified as one of the compounds responsible for the aroma of this fraction with two other odoriferous compounds presenting a green aroma. One belongs to terpene family, 1,8-cineole (herbs, fresh and eucalyptus descriptors), usually associated in wines with eucalyptus trees contamination. 1,8-cineole was definitively evidenced as a Vitis vinifera compound with concentrations assayed in wines from unripe grapes and other wines from Carmenet family close or higher to olfactory detection threshold (1 µg/l). 1,8-cineole concentrations were shown to decrease like IBMP during ripeness. The other compound was identified as methyl salicylate (fresh, leafy and wintergreen descriptors), a derivative of salicylic acid, sometimes quantified in wine samples at concentrations much higher than its detection threshold (40 µg/l). Supplementation tests at assayed concentrations in red wines for these two compounds exhibited a sensory impact on green aromas and a synergic effect was noticed with IBMP on the enhancement of the green flavour in red wines.