Editing Grape (section)

=== Skin ===
[[File:Wine grape diagram en.svg|right|thumb|Grape cross-section|upright=1.35|alt=Anatomical-style diagram of three grapes on their stalks. Two of the grapes are shown in cross-section with all their internal parts labeled.]]

[[Anthocyanin]]s tend to be the main [[Polyphenols in grape|polyphenolics]] in purple grapes, whereas [[flavan-3-ol]]s (i.e. [[catechin]]s) are the more abundant class of polyphenols in white varieties.<ref name="hozczp">{{Cite journal
| doi = 10.1021/jf0204102
| last1 = Cantos | first1 = E.
| last2 = Espín | first2 = J. C.
| last3 = Tomás-Barberán | first3 = F. A.
| title = Varietal differences among the polyphenol profiles of seven table grape cultivars studied by LC-DAD-MS-MS
| journal = Journal of Agricultural and Food Chemistry
| volume = 50
| issue = 20
| pages = 5691–5696
| year = 2002
| pmid = 12236700
}}</ref> 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.<ref name="hozczp" /> Phenolic content of grape skin varies with [[cultivar]], soil composition, climate, geographic origin, and cultivation practices or exposure to diseases, such as fungal infections.

[[Muscadine]] grapes contain a relatively high phenolic content among dark grapes.<ref>{{cite journal |vauthors=Ector BJ, Magee JB, Hegwood CP, Coign MJ |title=Resveratrol Concentration in Muscadine Berries, Juice, Pomace, Purees, Seeds, and Wines |url=http://www.ajevonline.org/cgi/content/abstract/47/1/57 |journal=Am. J. Enol. Vitic. |year=1996 |volume=47 |issue=1 |pages=57–62 |doi=10.5344/ajev.1996.47.1.57 |s2cid=98822789 |url-status=dead |archive-url=https://web.archive.org/web/20061119045158/http://www.ajevonline.org/cgi/content/abstract/47/1/57 |archive-date=2006-11-19 |access-date=2006-11-21}}</ref><ref name="Xu">{{cite journal | last1=Xu | first1=Changmou | last2=Yagiz | first2=Yavuz | last3=Zhao | first3=Lu | last4=Simonne | first4=Amarat | last5=Lu | first5=Jiang | last6=Marshall | first6=Maurice R. | title=Fruit quality, nutraceutical and antimicrobial properties of 58 muscadine grape varieties (Vitis rotundifolia Michx.) grown in United States | journal=Food Chemistry |volume=215 | year=2017 | issn=0308-8146 | doi=10.1016/j.foodchem.2016.07.163 | pages=149–156|pmid=27542461}}</ref> In muscadine skins, [[ellagic acid]], [[myricetin]], [[quercetin]], [[kaempferol]], and trans-resveratrol are major phenolics.<ref>{{Cite journal
| last1 = Pastrana-Bonilla | first1 = E.
| last2 = Akoh | first2 = C. C.
| last3 = Sellappan | first3 = S.
| last4 = Krewer | first4 = G.
| title = Phenolic content and antioxidant capacity of muscadine grapes
| doi = 10.1021/jf030113c
| journal = Journal of Agricultural and Food Chemistry
| volume = 51
| issue = 18
| pages = 5497–5503
| year = 2003
| pmid = 12926904
}}</ref>

The flavonols [[syringetin]], syringetin 3-O-galactoside, [[laricitrin]] and laricitrin 3-O-galactoside are also found in purple grape but absent in white grape.<ref name=Mattivi>{{Cite journal
| last1 = Mattivi | first1 = F.
| last2 = Guzzon | first2 = R.
| last3 = Vrhovsek | first3 = U.
| last4 = Stefanini | first4 = M.
| last5 = Velasco | first5 = R.
| title = Metabolite Profiling of Grape: Flavonols and Anthocyanins
| doi = 10.1021/jf061538c
| journal = Journal of Agricultural and Food Chemistry
| volume = 54
| issue = 20
| pages = 7692–7702
| year = 2006
| pmid = 17002441
}}</ref>