Grape skin components

During alcoholic fermentation, the degree of maceration is the first factor that affects the extraction of some compounds present in the grape skin, especially phenolic compounds, which are responsible for the color of the wine. However, not only does the maceration affect the extraction of polyphenols but also of other grape components, such as proteins, polysaccharides and, also, amino acids, which are precursors of biogenic amines. In most red wines, alcoholic fermentation takes place... 

Malvin, a major component of the grape skin (Vitis vinifera) is depicted by (4) as a 3,5-diglucoside structure which has been... 

Hydroxystilbenes are found in a variety of plants, many unrelated. They are a prominent component of many species of the Poly-gonaceae family Rheum, Polygonum spp.) but the richest source is found in grape skins and red wine (Creasy and Creasy 1998). 

The most common supercritical medium is CO2 because of its low critical temperature (31°C) and critical pressure (7.3 MPa), its cost effectiveness, its food grade status, and overall environmental friendliness. However, due to its low polarity, supercritical CO2 (SC-CO2) alone did not perform well in the extraction of phenolic compounds and anthocyanins from grape skins (Mantell et al. 2003 Vatai et al. 2009). A cosolvent, usually ethanol, can be added to SC-CO2 during extraction to enhance polarity. Such a mixture can result in a two-fold increase in phenols and three-fold increase in anthocyanins extracted. Isolation of quercetin might also be improved as SC-CO2 can remove the nonpolar components, thus concentrating the quercetin in the feed material. Water and methanol can also be added as cosolvents to increase the polarity of SC-CO2. 

Pinelo, M Amous, A Meyer, AS. Upgrading of grape skins significance of plant cell-wall structural components and extraction techniques for phenol release. Trends Food Sci. Technol. 2006,17, 579-590. 

Grape skin extract (enocianina) is a purplish red liquid prepared by the aqueous extraction (steeping) of the fresh deseeded marc remaining after grapes have been pressed to produce grape juice or wine. It contains the common components of grape juice namely, anthocyanins, tartaric acid, tannins, sugars, minerals, etc, but not in the same proportions... 

The complexity of wine composition is a central reason for the vast variety of wines in the marketplace. In addition to water and ethanol, the major components, a variety of organic acids as well as metal ions from minerals in the skin of the grape are present. Initially, all of these substances remain dissolved in the bottled grape juice. As the fermentation process occurs, the increasing alcohol concentration in the wine alters the solubility of particular combinations of acid and metal ions. Unable to remain in solution, the insoluble substances settle as crystals. Since the process of red-wine making involves extended contact of the grape juice with the skins of the grapes (where the minerals are concentrated), wine crystals are more common in red wines than in white wines. 

As flavonoids and flavanones contribute to the yellow color in both white and red wines, anthocyanins 42 and their mono- and diglucosides are the bright red pigments in grapes, mainly in the skin, but in autumn also in the leaves. These components contribute only slightly to the taste but as... 

Many of the wine macro-components (e.g. carbohydrates, proteins, polyphenols), come from the skins and the pulp of grapes and from the cell walls of the yeast. Although this varies, the molecular weight of the majority of macromolecules is over 10,000 D and their final concentration ranges from 0.3 to 1 g/L (Voilley et al. 1991). Most macromolecules will be eliminated by clarification and stabilization treatments of the wine. Because of their interactions with wine aroma... 

Ripe grapes have relatively low concentrations of pectic substances compared to other fruits. These compounds are the main component of the fine cell walls in grape flesh. In addition to pectic substances, the thicker skin cell walls also contain hemicelluloses and larger amounts of cellulose. 

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