Mirko De Rosso

Advanced knowledge of three important classes of grape phenolics: anthocyanins, stilbenes and flavonols

Grape is qualitatively and quantitatively very rich in polyphenols. In particular, anthocyanins, flavonols and stilbene derivatives play very important roles in plant metabolism, thanks to their peculiar characteristics. Anthocyanins are responsible for the color of red grapes and wines and confer organoleptic characteristics on the wine. They are used for chemotaxonomic studies and to evaluate the polyphenolic ripening stage of grape. They are natural colorants, have antioxidant, antimicrobial and anticarcinogenic activity, exert protective effects on the human cardiovascular system, and are used in the food and pharmaceutical industries. Stilbenes are vine phytoalexins present in grape berries and associated with the beneficial effects of drinking wine. The principal stilbene, resveratrol, is characterized by anticancer, antioxidant, anti-inflammatory and cardioprotective activity. Resveratrol dimers and oligomers also occur in grape, and are synthetized by the vine as active defenses against exogenous attack, or produced by extracellular enzymes released from pathogens in an attempt to eliminate undesirable toxic compounds. Flavonols are a ubiquitous class of flavonoids with photo-protection and copigmentation (together with anthocyanins) functions. The lack of expression of the enzyme flavonoid 3′,5′-hydroxylase in white grapes restricts the presence of these compounds to quercetin, kaempferol and isorhamnetin derivatives, whereas red grapes usually also contain myricetin, laricitrin and syringetin derivatives. In the last ten years, the technological development of analytical instrumentation, particularly mass spectrometry, has led to great improvements and further knowledge of the chemistry of these compounds. In this review, the biosynthesis and biological role of these grape polyphenols are briefly introduced, together with the latest knowledge of their chemistry.

Study of Grape Polyphenols by Liquid Chromatography-High-Resolution Mass Spectrometry (UHPLC/QTOF) and Suspect Screening Analysis

Suspect screening analysis is a targeted metabolomics method in which the identification of compounds relies on specific available information, such as their molecular formula and isotopic pattern. This method, coupled to liquid chromatography-high-resolution mass spectrometry, is effective in the study of grape metabolomics, in particular for characterization of flavonols, stilbene derivatives, and anthocyanins. For identification of compounds expected in the samples, a new database of putative compounds was expressly constructed by using the molecular information on potential metabolites of grape and wine from the literature and other electronic databases. Currently, this database contains around 1,100 compounds. The method allows identification of several hundred grape metabolites with two analyses (positive and negative ionization modes), and performing of data reprocessing using “untargeted” algorithms also provided the identification of some flavonols and resveratrol trimers and tetramers in grape for the first time. This approach can be potentially used in the study of metabolomics of varieties of other plant species.

Changes in Chemical Composition of a Red Wine Aged in Acacia, Cherry, Chestnut, Mulberry, and Oak Wood Barrels

Aging in wooden barrels is a process used to stabilize the color and enrich the sensorial characteristics of wine. Many compounds are released from wood into the wine; oxygen permeation through the wood favors formation of new anthocyanin and tannin derivatives. Recently, polyphenols and volatile compounds released from acacia, chestnut, cherry, mulberry, and oak wood used in making barrels for spirits and wine aging were studied. Here, changes in volatile and polyphenolic compositions of a red wine aged for 9 months in acacia, cherry, chestnut, mulberry, and oak barrels are studied. Mulberry showed significant decreases of fruity-note ethyl esters and ethylguaiacol and a great cession of ethylphenol (horsey-odor defect). Cherry promoted the highest polyphenol oxidation, making it less suitable for long aging. LC/ESI-MS(n) showed the relevant presence of cis- and trans-piceatannol in mulberry-aged wine, a phytoalexin with antileukemia and antimelanoma activities.

An innovative approach to grape metabolomics: stilbene profiling by suspect screening analysis

Suspect screening analysis is a targeted metabolomics approach in which identification of compounds relies on specific available information such as their molecular formula and isotopic pattern. This method was applied to the study of grape metabolomics with an UPLC/MS high-resolution Q-TOF mass spectrometer (nominal resolution 40,000) coupled with a Jet Stream ionization source. The present paper describes the detailed qualitative and quantitative study of grape stilbenes, the principal polyphenols associated with the beneficial effects of drinking wine. For identification of compounds, a new database was expressly constructed from the molecular information of potential metabolites of grape and wine from the literature and other electronic databases. Currently, GrapeMetabolomics contains about a thousand putative grape compounds. If untargeted analysis of a sample provides identification of a new compound with a sufficiently confident score, it is added to the database. Thus, by increasing the number of samples studied, GrapeMetabolomics can be expanded. This method is effective for identification of the molecular formulae of several hundred metabolites in two runs (positive and negative ionization) with minimal sample preparation, and can also be used to analyse some single classes of compounds involved in cell and tissue metabolism. With this approach, a total of 18 stilbene derivatives was identified in two grape samples (Raboso Piave and Primitivo) on the basis of accurate mass measurements and isotopic patterns, and identification was confirmed by MS/MS analysis. The approach can also potentially be applied to the metabolomics of other plant varieties.

Mass spectrometry in the analysis of grape and wine proteins

Wine proteins play an important role in the quality of wine, because they affect taste, clarity and stability of product. The majority of wine proteins are in the range of 20–30 kDa. Different mass spectrometry (MS) techniques have been successfully applied to study the grape and wine proteins. By liquid chromatography (LC) electrospray ionization (ESI) MS and nano-LC/MS, nine dipeptides and 80 peptides were unambiguously identified in Champagne and Sauvignon Blanc wines, respectively. Using matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) and surface-enhanced laser desorption/ionization TOF, the protein and peptide fingerprints in Chardonnay, Sauvignon Blanc and Muscat of Alexandria wines were determined. MALDI-TOF identified the mesocarp proteome of six Vitis grape varieties. Proteins in different grape tissue extracts were also studied. The major grape pathogenic-related proteins are chitinases and thaumatin-like proteins, which both persist through the vinification process and cause hazes and sediments in bottled wines. ESI-MS, LC/ESI-MS and MALDI-TOF analysis of these proteins in grape and wine were also used to characterize different grape varieties.

Effects of Elicitors, Viticultural Factors, and Enological Practices on Resveratrol and Stilbenes in Grapevine and Wine

The ability of grapevine to activate defense mechanisms against some pathogens has been shown to be linked to the synthesis of stilbenes by the plant (inducible viniferins). Metabolized viniferins may also be produced or modified by extracellular enzymes released by the pathogen in an attempt to eliminate undesirable toxic compounds. Due to the important properties of resveratrol, there is increasing interest in producing foods with higher contents of this compound and higher nutritional value. The production of high resveratrol-containing grapes and wines relies on quality-oriented viticulture (suitable terroirs, sustainable cultural practices) and wine-making technologies which avoid degradation of the compound. The technique of skin extraction and enzymatic hydrolysis of glucoside forms in wine-making plays an important role in resveratrol wine concentration. Other factors affecting its final concentration and balance in wine are conditions for promoting trans-cis isomerization of aglycones, the type of yeast used, and the presence of lactic bacteria with β-glucosidase activity. In general, the enological practices commonly used to stabilize wine after fermentation do not significantly affect resveratrol concentrations, which show considerable stability.

Chemical Characterization and Enological Potential of Raboso Varieties by Study of Secondary Grape Metabolites

DNA studies supported by matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis of seed proteins showed that the Vitis vinifera red grape variety Raboso Veronese is the progeny of a spontaneous cross between Raboso Piave (red) and Marzemina Bianca (white) varieties. In the present work, the main secondary grape metabolites of Raboso varieties were studied, and their enological potential was evaluated and compared with that of other red varieties reported in the literature. In general, Raboso grapes had high flavonoid contents and high percentages of polyphenols extractable in winemaking and substantial contents of norisoprenoid aroma precursors. Raboso Veronese stood out for its high content of cyanidin and had higher (+)-catechin and (-)-epicatechin contents than Raboso Piave and abundant quercetin glucoside, indicating substantial plant biosynthesis toward compounds dihydroxylated in the B-ring. Study of secondary grape metabolites is confirmed as an effective tool in differentiating similar varieties, in particular on the basis of polyphenol profiles.

Seed oil triglyceride profiling of thirty-two hybrid grape varieties.

Triglyceride profile of seed oil samples from 32 hybrid grape varieties not studied before was investigated. A new method for the analysis of triacylglycerols (TAGs) has been developed based on the direct infusion in the electrospray ionization (ESI) source and employing tetrahydrofuran/methanol/water (85:10:5 v|v|v) as solvent; the formation of [M + Na](+) ions in high yield has been observed. TAGs were identified by ESI-tandem mass spectrometry analysis, and the matrix-assisted-laser-desorption-ionization and time-of-flight profile of samples was determined. Six were the principal TAGs identified in seed oil: trilinolein (LLL) was the most abundant (43%), followed by dilinoleoyl-oleoylglycerol (LOL, 23%), and dilinoleoyl-palmitoylglycerol (LPL, 15%). Compounds present in lower concentration were LSL and LOO (11%), LOP (6%), and LSP (2%). Compared with seed oils produced from V. Vinifera grapes, some significant differences in the relative abundances of TAGs were found, in particular hybrid grape seed oils showed higher LOL and lower LPL content, respectively. Among the samples studied, a particularly high content of LLL (rich in unsaturated fatty acids) was found in seed oils from two red varieties.

A fast and selective method for anthocyanin profiling of red wines by direct‐infusion pneumatic spray mass spectrometry

RATIONALE Anthocyanins confer the color to red wines. During wine aging, new anthocyanin derivatives with peculiar chromatic characteristics are formed. A fast and selective method for screening the anthocyanin composition of wine has been developed. METHODS Direct-infusion electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis of wine extracts has been performed by operating in positive ion mode with a low spray capillary voltage (0.5 kV) to detect only the species already present in ionic form. The method has been called direct-infusion pneumatic spray (DIPS) mass spectrometry. The anthocyanin profiles of thirteen red wines at different aging stages were studied. Using malvidin-3,5-diglucoside as internal standard, the indices of wine color and of wine color evolution were estimated. RESULTS By decreasing the spray capillary voltage a dramatic increase in selectivity toward anthocyanins has been observed and the related peaks are the most abundant in the spectra. Several anthocyanins and anthocyanin derivatives (pyranoanthocyanins and derivatives formed by reaction with flavan-3-ols) have been identified in the wines. The younger wines showed higher total anthocyanin index. The aged wines showed color evolution index higher than 20% while it was lower in the younger samples. CONCLUSIONS The anthocyanin fingerprint is effective for estimating the aging state of wine. The color evolution index can be correlated to barrel conditions during wine aging and used to distinguish between aged and younger wines. The study of pyranoanthocyanins and anthocyanin-flavanol derivatives can be useful to predict wine color stability.

Characterization of Non-Anthocyanic Flavonoids in Some Hybrid Red Grape Extracts Potentially Interesting for Industrial Uses

Previous studies showed that hybrid grapes often have qualitatively and quantitatively higher polyphenolic contents than the common V. vinifera grape varieties. In general, these compounds are studied for grape chemotaxonomy and for nutraceutical purposes due to their relevant antioxidant activity. Non-anthocyanic flavonoid composition of five red hybrid grape varieties produced by crossing of V. vinifera, V. aestivalis, V. cinerea, V. berlandieri, V. labrusca, V. lincecumii, and V. rupestris were studied by liquid chromatography/high-resolution mass spectrometry. Thirty-one compounds were identified, including methylnaringenin, a tetrahydroxy-dimethoxyflavanone-hexoside, two flavonols (quercetin and a pentahydroxyflavone isomer), 20 glycoside flavonols (four quercetin, two myricetin, two kaempferol, three isorhamnetin, one laricitrin, two syringetin, one kaempferide and two dihydroflavonol derivatives; myricetin-glucoside-glucuronide; myricetin-diglucoside; syringetin-dihexoside), three flavan-3-ols (−)-epicatechin, (+)-catechin, (−)-epicatechin gallate) and four proantocyanidins (procyanidin B1, procyanidin B2, procyanidin B3 or B4/B5, procyanidin T2 or T3/T4/C1). Seibel 19881, Seyve Villard 12-347 and Seyve Villard 29-399 were particularly rich in polyphenols. These findings emphasize that these grapes are especially interesting for the production of antioxidant extracts for nutraceutical and pharmaceutical uses.