Identification of wine aroma precursors in Moscato Giallo grape juice: a nuclear magnetic resonance and liquid chromatography-mass spectrometry tandem study.

In this work, several aroma precursors present in Moscato Giallo grape juice were identified and characterized using LC-MS and NMR techniques. A preliminary separation of various fractions was obtained using adsorption on Amberlite(®) XAD resin and HPLC chromatography on a reverse phase column. Subsequently, U-HPLC with mass spectrometry allowed the identification of some compounds corresponding to mono- and disaccharides linked to terpenes. The MS-MS fragmentation step indicated which kind of glycosides, the moiety sequence and sometimes which kind of terpene were present. NMR enabled the correct identification of glycosides and terpene when the fraction analyzed was sufficiently concentrated and with few components. Twelve glycosidically bound terpenes were characterized: (E) and (Z)-furanosyl-linalooloxide-7-O-[α-D-apiofuranosyl-(1→6)-1-ß-D-glucopyranoside], (E)-furanosyl-linalooloxide-7-O-[1-ß-D-glucopyranoside], (Z)-8-hydroxylinalool-8-O-[1-ß-D-glucopyranoside], 1,2-dihydroxylinalool-1-O-[1-ß-D-glucopyranoside], linalool-3-O-[α-L-arabinofuranosyl-(1→6)-1-ß-D-glucopyranoside], linalool-3-O-[α-L-apiofuranosyl-(1→6)-1-ß-D-glucopyranoside], linalool-3-O-[α-L-rhamnopyranosyl-(1→6)-1-ß-D-glucopyranoside], nerol-1-O-α-D-apiofuranosyl-(1→6)-1-ß-D-glucopyranoside, geraniol-1-O-[α-L-arabinofuranosyl-(1→6)-1-ß-D-glucopyranoside], geraniol-1-O-[α-L-rhamnopyranosyl-(1→6)-1-ß-D-glucopyranoside], and a geranic acid disaccharide derivative. It is the first time that this kind of compounds are directly detected and identified in a mixture with these two techniques.

Stilbene compounds and stilbene synthase expression during ripening, wilting, and UV treatment in grape cv. Corvina.

The content of selected phenolic compounds including resveratrol (trans-3,5,4'-trihydroxystilbene) and its cis-isomer and glucosides (piceides) were monitored in grape (Vitis vinifera L. cv. Corvina) berry skin during ripening in the vineyard and in response to the post-harvest drying process (wilting). Four wilting conditions were compared (traditional, mixed, low-temperature, and high-temperature) to verify the eliciting effect of drying on resveratrol production. During fruit ripening the cis-piceid was the major stilbene found in berry skins, and a weak accumulation of stilbene synthase (STS) mRNA was observed, whereas UV-light irradiation greatly stimulated STS transcript of unripe berries. A time-course experiment showed the highest STS mRNA accumulation and resveratrol content (34 microg/g fresh weight at 58 days) occurring in berry skins in a mixed wilting process.

The determination of total SO2 in grape juice. A comparison among five methods.

The EC official method of total SO2 analysis in grape juice was modified in 1990. The main improvements concerned the amount and concentration of H3PO4 used during the distillation to recover the combined SO2 and the standardization of the distillation time at 15 min. This comparative study evaluated the total SO2 level of 12 grape juices determined by five methods, including distillation, iodimetric and enzymatic-based methods. Attention was focused on the total SO2 legal limit of 10 mg/l fixed in Europe for grape juice. Analysis of variance disclosed a significant difference among the total SO2 content in grape juices determined by five methods. Each analytical method showed limits in relation of their ability to release the combined SO2. In particular, the SO2 bonded to phenolic compounds is partially released at low pH in the acidified juice leading to higher results.

Resveratrol content of some wines obtained from dried Valpolicella grapes: Recioto and Amarone.

Resveratrol (trans-3,5,4'-trihydroxystilbene), a phenolic substance present in both grape skin and wines, is a phytoalexin involved in grey mould resistance. A new interest has surfaced in recent years related to the antioxidative actions of resveratrol, which in vivo could be related to the prevention of cardiovascular diseases linked to lipid metabolism, particularly HDL production, while the antifungal activity may be of interest in wine production technology. These aspects have led to the publication of a number of papers reporting data on the resveratrol content of several kind of wine: for Italian wines, it ranges between 0.5 and 10 ppm, depending on cultivar, area of cultivation, climate and wine-making technology. In this work, resveratrol was quantified in samples of two unusual Italian wines, Recioto (sweet) and Amarone (dry), produced with the same cultivar mixture in the same area (Valpolicella, Verona, Italy) and with the same grape conditioning technique. After resveratrol extraction, reversed-phase HPLC analysis was carried out and several elution conditions were tested. The resveratrol content of Recioto and Amarone wines was lower than the values reported in the literature for other wines, ranging between 0.05 and 0.8 ppm.