Winemaking from red and white grape flesh and skins produces substantial quantities of organic residues, collectively called
pomace (also "marc"), which includes crushed skins, seeds, stems, and leaves generally used as
compost. Grape pomace – some 10–30% of the total mass of grapes crushed – contains various
phytochemicals, such as unfermented sugars, alcohol,
polyphenols,
tannins,
anthocyanins, and numerous other compounds, some of which are harvested and
extracted for commercial applications (a process sometimes called "valorization" of the pomace).
Skin Anthocyanins tend to be the main
polyphenolics in purple grapes, whereas
flavan-3-ols (i.e.
catechins) are the more abundant class of polyphenols in white varieties. Total phenolic content is higher in purple varieties due almost entirely to anthocyanin density in purple grape skin compared to absence of anthocyanins in white grape skin. In muscadine skins,
ellagic acid,
myricetin,
quercetin,
kaempferol, and trans-resveratrol are major phenolics. The flavonols
syringetin, syringetin 3-O-galactoside,
laricitrin and laricitrin 3-O-galactoside are also found in purple grape but absent in white grape.
Seeds Muscadine grape seeds contain about twice the total polyphenol content of skins.
Resveratrol Resveratrol, a
stilbene compound, is found in widely varying amounts among grape varieties, primarily in their skins and seeds.
Muscadine grapes have about one hundred times higher concentration of stilbenes than pulp. Fresh grape skin contains about 50 to 100 micrograms of resveratrol per gram.
Grape and raisin toxicity in dogs The consumption of grapes and raisins presents a potential health threat to dogs. Their toxicity to dogs can cause the animal to develop
acute kidney failure (the sudden development of kidney failure) with
anuria (a lack of urine production) and may be fatal. == Gallery ==