Key odorants responsible for the sensory spaces defining the different aroma potentials of Grenache and Tempranillo grapes

There are yet many gaps in our knowledge about the aroma potential of winemaking grapes and its measurement. Trying to bring some light into this question, a new general strategy based on the accelerated hydrolysis of reconstituted phenolic and aromatic fractions (PAFs) extracted from grapes has been developed. In this paper, we present results obtained by applying such PAFs strategy to the study of 33 different lots of grapes from grenache and Tempranillo from different areas of Spain and different qualities. 

Grapes were first crushed and macerated in the presence of ethanol to avoid fermentation. The ethanolic must was pressed and filtered, then, an aliquot was centrifuged, dealcoholized and extracted in a C18 cartridge. Phenols and aroma precursors, PAFs, were eluted with ethanol. This ethanolic fraction was then reconstituted with water and tartaric acid to make a reconstituted wine model (r-PAF; 13.3% ethanol, pH 3.5). Aroma was developed by storing the r-PAFs in complete anoxia at 75ºC for 24h. The 33 ar-PAFs were subjected to different sensory analyses. First, a sorting task to define sensory categories and to select the most representative samples, which were characterized by flash profiling and by gas chromatography-olfactometry (GC-O). 

Samples developed strong aroma nuances over a background of vegetal and dry fruit odors and were classified into six different sensory categories: 1) citrus & floral; 2) dried fruit & floral; 3) wood, toast & red fruit; 4) red fruit, black fruit & dried fruit; 5) vegetable & dried fruit; and vi) vegetable. Vegetal notes were attributed to aroma compounds derived from lipid oxidation (Z-3-hexenal, Z-2-nonenal, E-2-nonenal and 1-octen- 3-one), while the dry fruit background was attributed to β-damascenone and to massoia lactone. Citrus notes were associated to the surprising presence of 3-mercaptohexanol, whose origin has been exclusively associated to fermentation. Woody and toasty character were attributed to guaiacol and 4-allyl-2-methoxyphenol while furaneol and an unknown ester-like odorant could be linked to red fruit notes. Samples from Grenache were more often classified as floral, citrus and dry fruit, while samples from tempranillo were more often classified as woody, toasty, red fruit and vegetal. 

Overall, the procedure provides a new insight into the aroma potential of winemaking grapes, which should be helpful in understanding and managing grape quality. 

Acknowledgments: Work funded by the Spanish MCIU AGL2017-87373-C3-1R. Y.A. and LAAE acknowledge the Diputación General de Aragón for a predoctoral fellowship, as well as the European Social Fund.

Authors: Yohanna Alegre, SaraFerrero-del-Teso, María-Pilar Sáenz-Navajas, Purificación Fernández-Zurbano, Purificación Hernandez-Orte, Vicente Ferreira 

Laboratorio de Análisis del Aroma y Enología (LAAE), Department of Analytical Chemistry, Universidad de Zaragoza, Instituto Agroalimentario de Aragón (IA2) (UNIZAR-CITA), Associated unit to Instituto de las Ciencias de la Vid y el Vino (ICVV) (UR-CSIC-GR) 

Email: yohannaalegre@unizar.es 

Keywords: Phenolic and aromatic fractions (PAFs), accelerated hydrolysis, sensory analysis ,GC-O 

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