Grape phenolic

Waterhouse AL, Walzem RL (1997) Nutrition of grape phenolics. In Rice-Evans CA, Packer L (eds) Flavonoids in Health and Disease. Marcel Dekker, New York, p 359... 

A similar effect was observed in other fruits and vegetables, where UV-C treated strawberries showed a higher increment of phenols and PAL activity 12 hours after treatment than unirradiated (control)(Pan and others 2004), which could be the reason for the increment in total phenol constituents (Lancaster and others 2000). UV-C and UV-B caused a two- and threefold increase in content of resveratrol (a grape phenol constituent). Thus, mature Napoleon grapes that had been irradiated with UV-C light can provide up to 3 mg of resveratrol per serving (Cantos and others 2001). Therefore, UV-C treatments clearly cause a benefit effect, increasing total phenol content, which can be mainly attributed to the increment of PAL activity. 

Methods used for the detection of PAs in cmde or partially purified extracts can also be adapted for post-column analysis after fractionation (see below). Direct quantitative analysis of PAs in crude grape phenolic extracts is often impossible due to the complex sample matrix. Thus, fractionation or purification is often necessary before analysis. The Folin-Ciocalteu and Pmssian Blue assays are widely used for the quantification of total polyphenols in plants [27,28]. These methods are not specific for PAs due to the reaction of other phenolic compounds with these reagents. 

Somers, T.C. 1966. Grape phenolics the anthocyan-ins of Vais vinifera, var. Shiraz. J. Sci. Food Agric. 17 215-219. 

Jaworski, A.W. and Lee, C.Y. 1987. Fractionation and HPLC determination of grape phenolics. J. Agric. Food Chem. 35 257-259. 

Caillet, S., Salmieri, S., and Lacroix, M. (2006). Evaluation of free radical-scavenging properties of commercial grape phenol extracts by a fast colorimetric method. Food Chem. 95,1-8. 

Fig. 8A.3 Grape phenolic acid esters, and the chemical bonds cleaved to release odorous volatile phenols...

Therefore, volatile phenols play a minor role in the aroma of most wines, and when their influence is significant in certain wines, they have mostly a negative effect, which can definitely depreciate their aroma in limit cases (phenolic off-flavors). Thus, the corresponding precursors in grape, phenolic acids, as well as the above-mentioned unsaturated lipids, are hardly taken into account to capture an essential characteristic of the varietal aroma, but to avoid their transformation into off-flavors. 

Grape phenolics compounds are important to wine colour, flavour, astringency and bitterness, with red wines generally containing 1200-1800 mg gallic acid equiv-alents/L of total phenolics, six- to ninefold more than present in white wines (Kennedy et al. 2006). Hydroxycinnamic acids (non-flavonoid phenolics) are major phenolic compounds of white wines and are responsible for their colour. Other non-flavonoid phenolics contribute flavour, such as vanillin, vinyl phenols and gallic acid. Vinyl and ethyl phenols, which can be present to variable extents, elicit phenolics, medical, Bandaid , barnyard and spicy characters in wine, which are generally... 

Waterhouse, L.A. and Walzem, R.L. 1998. Nutrition of grape phenolics, in Flavonoids in Health and Disease, eds., C.A. Rice-Evans and L. Packer. New York Marcel Dekker, Inc., pp. 359-385. 

The low concentration of vinyl-phenols in red wines is mainly dne to the inhibition of the CD of S. cerevisiae by certain grape phenols (Chatonnet et al, 1989, 1993b). This inhibition may be demonstrated by adding an extract of grape seeds and skins in ethanol to must containing phenol acids. Procyanidins, the most active componnds (Section 8.4.5, Table 8.5), may inhibit the enzyme completely, resnlting in the total absence of synthesis of vinyl-phenols. 

Rossi, J.A., Jr., and Singleton, V.L., 1966a, Contribution of grape phenols to oxygen absorption and crowning of wines, Amer. J. Enol. Viticul., 17 231. 

Chira K, Suh J-H, Saucier C, Teissedre P-L (2008) Grape phenolics (Les polyphenols du raisin). Phytotherapie 6 75-82... 

Family Red grape Phenolic compound (mg/kg fw) White grape (mg/kg fw) References... 

Gunata, Y.Z., Sapis, J.C. Moutounet, M. (1987). Substrates and aromatic carboxylic-acid inhibitors of grape phenol oxidases. Plytochemistry, 26,1573-1575. 

The study of red grape phenolic compounds requires the manual separation of the skins from the seeds of about 200 berries taken at random in the sampling. Once separated, the skins and the seeds are dried and lyophilized to facilitate the extraction and the determination of their phenolic content. 

Temperature also has an influence on the composition of grape phenolic compounds. Intensely colored wines are known to be difficult to obtain in extreme temperature conditions (too low or high) though the phenomenon involved can at first appear paradoxical. High temperatures stimulate metabolic reactions, whereas low temperatures curb migration. In either case, however, this corresponds with poor grape sugar alimentation and thus increased competition between primary... 

Similarly, fluctuations in grape phenolic content from one vintage to another and for a given variety are less than the variations between varieties. The genotypic effect of the variety is thus preponderant on grape phenolic compound richness. Anthocyanidic and procyanidic profiles vary... 

Laccase transforms the principal white grape phenolic compounds (cafeic and p-coumaric acids—both free forms and forms esterified by tartaric acid) into quinones (Salgues et al., 1986). These quinones tend to polymerize, forming brown compounds. These compounds are most likely responsible for the characteristic chocolate color of pourris pleins grapes. 

If grapes have low anthocyanin and tannin concentrations, only light red wines should be made. These wines, however, should be fresh and fruity. A limited concentration of grape phenolic compounds nevertheless merits an explanation. It can be a varietal characteristic, which must be taken into account. Vine cultivation conditions, favoring crop yields over quality, can also be responsible. 

---