| Abstract |
This dissertation reports the use of NMR spectroscopy and NMR-based metabolomics/chemometrics to study the wine maturation procedure. The wines studied were vinified from four indigenous Cretan grape cultivars (Dafni, Vilana – white and Kotsifali, Mantilari – red) and were left to mature in different types of inox tanks (with or without addition of oak oinosticks) and wooden barrels (French oak, American oak, acacia and chestnut). Maturing wines were sampled and analyzed by quantitative 1H NMR spectroscopy every three months for a total of 12 months, and for two consecutive production years (2012, 2013). Wine samples that had matured in tanks or barrels for 3, 6 9 and 12 months were also bottled and stored for 12 months, before they were analyzed.
NMR spectroscopy was used for the detection and quantification of a large number of non-volatile organic compounds in wine (metabolites), including organic acids (lactic, acetic, pyruvic, citric, malic, succinic, citramalic, fumaric), sugars (α-, and β- glucose, sucrose, fructose, trehalose, galacturonic acid), aminoacids (alanine, proline), alcohols (methanol, glycerol, inositol, isopentanol, 1,3-propanediol), phenolic compounds (trans-caftaric acid, tyrosol, gallic acid, 2-phenylethanol, dihydrorobinetin, robinetin) and other compounds (choline, uridine, uracil, cytidine, trigonelline, histidine and acetaldehyde).
Chemometrics analysis of the 1H NMR-obtained wine metabolic profiles using multivariate statistical analysis models (PCA, OPLS, OPLS-DA) demonstrated that NMR based metabolomics can be used to develop models that a) differentiate between wines from indigenous Cretan cultivars with excellent predicting ability, regardless of maturation time in barrels, b) parametrize the wine maturation procedure for each cultivar in different barrels and predict adequately the duration of maturation used, and c) determine the type of barrel used for wine maturation, especially for acacia and chestnut barrels. The extraction rate of dihydrorobinetin from the wood of acacia barrels to the wine body was determined for two consecutive years, and this compound is proposed as a metabolomic marker of wine maturation in acacia barrels.
A novel methodology for the quantitative determination of wine polyphenolics using 1Η and 31P NMR spectroscopy was also developed, based on the isolation of the phenolic fraction of wine using solid phase extraction. Several categories of phenolic compounds were determined in wine using this approach, including flavonols (quercetin, campferol, robinetin), anthocyans (malvidin, peonidin), phenolic alcohols (tyrosol, 2-phenyl ethanol), stilbenes (cis- and trans resveratrol), flavanols (catechin, epicatechin), phenolic acids/esters (trans-caftaric acid, caffeic acid, protocatechuic acid, gallic acid, vanillic acid, syringic acid, trans-coutaric acid, ethyl gallate) and the flavanonol dihydrorobinetin. Chemometrics analysis of the 1H and 31P NMR spectral phenolic fingerprints using bucketing and multivariate statistical analysis models (PCA, OPLS-DA) showed that phenolic fingerprinting offers superior model performance with respect to barrel type discrimination in th wines studied, compared to metabolite NMR profiling of the whole non-volatile metabolome.
Finally, the correlation between the NMR-obtained non-volatile metabolomic data set and sensory panel analysis data provided by professional wine tasters was examined. Excellent correlation was found between the NMR metabolic profiling and the sensory attributes of wines (acidity, sweetness, bitterness, astrigency) during the first wine production year (2012), especially for panel acidity, and good correlation was also found with the wine total scores attributed by the sensory panel, as a function of wine maturation and barrel type. Finally, NMR-based metabolomics also offered the possibility of correlating and estimating the optimum organoleptic characteristics of the wines based on experimental analytical, spectroscopic and sensory panel data.
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Ανάλυση και βελτιστοποίηση της διαδικασίας παλαίωσης του οίνου με τη φασματοσκοπία πυρηνικού μαγνητικού συντονισμού NMR
