Effect of oenological tannins on wine aroma before and after oxidation: a real-time study by coupling sensory (TDS) and chemical (PTR-ToF-MS) analyses

Abstract

AIM: Polyphenols are important compounds involved in many chemical and sensory wine features. In winemaking, adding oenological tannins claims to have positive impacts on wine stability, protection from oxidation and aroma persistence. Polyphenols are antioxidant compounds by either scavenging reactive oxygen and nitrogen species or chelating Fe2+ ions (1). However, as tannins oxidation leads to the formation of highly reactive species (i.e. ortho-quinones), it is still unclear if they have an effective role toward oxidation of wine aromas (2). In this work, we aim at studying the effect of two commercial tannins (proanthocyanidins, ellagitannins) on red wine flavour (mainly aroma) before and after air exposition.

METHOD: We coupled a dynamic sensory evaluation technique with a dynamic instrumental nosespace analysis, in order to decipher the impact of oenological tannins on in-vivo aroma release and perception. 17 trained subjects evaluated the temporal dominance of sensations (TDS) of 6 non-oaked Pinot Noir in duplicate, while their nasal cavity was connected to a Proton Transfer Reaction-Time of Flight-Mass Spectrometer (PTR-ToF-MS). Samples followed a Tannin by Oxidation factorial design including the base wine (BW), BW spiked with ellagitannins (BWE) or with proanthocyanidins (BWP), and the three wines after air exposition (OW, OWE, OWP). Each of these 6 samples was evaluated in 3 consecutive sips and this evaluation was duplicated.

RESULTS: TDS sensory results show that red wine oxidation decreases the fruity aroma dominance and increases the dominance of maderised and prune notes (3). The chemical analysis by PTR-MS revealed that the fruity decrease was correlated to the decrease of the fruity ethyl decanoate and the increase of Strecker aldehydes isobutyraldehyde and isovaleraldehyde. The addition of ellagitannins preserves the perception of fruity notes without the appearance of maderised ones after air exposition. This effect was not observed with proanthocyanidins: the TDS curves of OWP was similar to those recorded for OW, both showing dominant maderised and prune aromas, masking the fruity notes. Moreover, the monitoring of in vivo aroma release by PTR-ToF-MS suggests that ellagitannins increase aroma persistence in the non-oxidized wine.

CONCLUSIONS:

Results evidence that the presence of ellagitannins can have a positive impact on the aroma persistence of young red wine and on the preservation of its fruity aroma perception after oxidation. Being red wine oak-barrel ageing a storage in presence of ellagitannins and oxygen, these results could be helpful in managing the sensory shelf-life of fruity red wines with the preservation of these aromas. Indeed, these aromas are able to mask the appearance of oxidative notes, while balancing the sensory contribution of volatiles extracted from wood.