Effect of post-harvest ozone treatments on the skin phenolic composition and extractability of red winegrapes cv Nebbiolo and Barbera

Several winemaking operations, such as filtration, pumping, and racking, are known to potentially facilitate the incorporation of atmospheric O2 into the wine. Control of grape must oxidation is one key aspect in the management of white wine aroma expression, color stability and shelf-life extension. On the one hand, controlled must oxidation may help to remove highly reactive phenolic compounds, which otherwise could contribute to premature oxidation. And on the other hand, in certain cases of extreme protection of the must from O2 (e.g. pressing under inert atmosphere), it can help to preserve varietal aromas and natural must antioxidants.

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Wine aroma is influenced by several viticultural and oenological factors. In this study we used experimental wine making in a full factorial design to determine the impact of grapevine age, must turbidity, and yeast strain on the aroma of Vitis vinifera L. cv. Riesling wines. A recently developed, non-targeted SPME-GC-MS fingerprinting approach for wine volatiles was used. This approach includes the segmentation and mathematical transformation of chromatograms in combination with Parallel Factor Analysis (PARAFAC) and subsequent deconvolution of important chromatogram segments.

Recent studies have demonstrated the role of certain lactones, particularly 2-nonen-4-olide, and volatile thiols (3-sulfanylhexan-1-ol) in the over ripped aromas of noble rot sweet wines (Stamatopoulos et al. 2014ab). These compounds are partly formed during the maturation and under the activity of B. cinerea on grapes. This research was carried out in the vineyard of Sauternes with aim to better understand their genesis depending on the grape over-ripening on two different soil types during 3 vintages. Thus, the study was conducted, with the Sémillon grape, during vintages 2012, 2014 & 2015, at 4 stages of over-maturation of the grapes (healthy, pourri plein, pourri roti, pourri roti + 15 days) considering two vineyard plots with different soil characteristics (calcosol & peyrosol) planted with the 315 Sémillon clone and grafted on 101-14 rootstock respectively in 1981 and 1980 and cultivated with the same vineyard management. Volatile lactones were assayed by liquid-liquid extraction followed by GC/MS analysis and the precursors of 3-sulfanylhexanol by an adaptation of the method by Capone et al. 2010 (SPE-
UPLC/FTMS).

The above-ground parts of plants, which constitute the phyllosphere, have long been considered devoid of bacteria and fungi, at least in their internal tissues and microbial presence there was long considered a sign of disease. However, recent studies have shown that plants harbour complex bacterial communities, the so-called “microbiome”[1]. We are only beginning to unravel the origin of these bacterial plant inhabitants, their community structure and their roles, which in analogy to the gut microbiome, are likely to be of essential nature. Among their multifaceted metabolic possibilities, bacteria have been recently demonstrated to emit a wide range of volatile organic compounds (VOCs), which can greatly impact the growth and development of both the plant and its disease-causing agents.