Grape phenolic compounds can be divided into two groups: non-flavonoid (hydroxybenzoic and hydroxycinnamic acids, stilbenes) and flavonoid compounds (anthocyanins, flavan-3-ols and flavonols). Fourteen phenolic compounds classified as hydroxybenzoic acids: gallic acid, vanillic acid, caffeic acid and syringic acid; hydroxycinnamic acid: protocatechuic acid, chlorogenic acid and p-coumaric acid; flavan-3-ols: catechin, epicatechin, epicatechin gallate; flavonols: quercetrin hydrate and rutin hydrate and stilbenes: trans-resveratrol and trans-piceatannol have been proven to be potent antioxidants and to have immense biological, pharmacological and medicinal properties. Grape byproducts are a rich source of phenolics, but usually wasted from juice and wine processing industries.
Grape seed extracts have liver protective and antiallergic properties. The seeds also are an excellent source of phenolic compounds such as:
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- Flavan-3-ols compounds: catechin, epicatechin, epicatechin-gallate have high antioxidant capacity; found in high amounts.
- Procyanidins suppress lipid accumulation in vascular wall, stopping the development of cardiovascular diseases.
- Proanthocyanidins (condensed tannins) have anti-aging, anti-mutagenic, anti-cancer (colorectal cancer, non-small cell lung cancer, head and neck squamous cancer, cervical cancer and skin cancer), anti-atherogenic, and antiviral properties; they also provide significant protection against acute liver injury caused by multiple factors, such as hepatic viruses, excessive alcohol consumption and hepatotoxins (for example, paracetamol, flutamide and carbon tetrachloride).4
- Gallic acid exerts anti-cancer, anti-oxidant, anti-microbial, anti-hyperglycemic, and anti-inflammatory activities; prevents interstitial collagen deposition in fibrosis; prevents cardiac hypertrophy (animal studies);2present in high amount.
- Caffeic acid is a strong antioxidant.
- Syringic acid has been shown to prevent formation of diabetic cataract.3
- Hydroxycinnamic acids: chlorogenic acid, p-coumaric acid are potent antioxidants.
- Delphinidin possesses strong anti-oxidant, anti-inflammatory, and anti-cancer (prostate cancer, breast cancer) properties.6 It is also an inhibior of hepatitis C virus (HCV) infection, delphinidin, that prevents HCV attachment to the cell surface.5
Purple skinned grapes have higher anthocyanin content as compared to the bronze skinned grapes. It is also reported that red grape cultivars contain high levels of cyanidin and peonidin in skin tissues, whereas black cultivars contain high levels of delphinidin and malvidin. Anthocyanin pigments play an important role in protection towards fungal and bacterial infections in grapes.
The stilbene compounds; trans-resveratrol & trans-piceatannol, which are phytoalexins are found in higher amounts in skin and stem extracts than in seeds. The compounds quercetin and its glycoside rutin (flavonols), and trans-Resveratrol (stilbene).
Dietary antioxidants have been associated with the reduced risk of type II diabetes. Flavonoids may also have antidiabetic activity. Recent study showed 2 to 8 fold stimulation in insulin secretion by isolated pancreatic islets at 16.5 mM glucose concentration in presence of grape seed, skin and stems extracts. Grape seed extract's procyanidins directly act on specific components of the insulin and exert a significant anti-hyperglycemic effect, suggesting that grape seeds and skins could be a valuable food derived bioresource that is rich in antioxidants and anti-hyperglycemic compounds which represents a source of potential new oral hypoglycemic agent and may be useful in the treatment of type II diabetes.
- Phenolic compounds, antioxidant activity and insulinotropic effect of extracts prepared from grape (Vitis vinifera L) byproducts. Pooja Doshi, corresponding author Pandurang Adsule, Kaushik Banerjee, and Dasharath Oulkar. J Food Sci Technol. 2015 Jan; 52(1): 181–190.
- Gallic acid prevents isoproterenol-induced cardiac hypertrophy and fibrosis through regulation of JNK2 signaling and Smad3 binding activity. Yuhee Ryu,1,* Li Jin,1,2,* Hae Jin Kee,a,1 Zhe Hao Piao,3 Jae Yeong Cho,1 Gwi Ran Kim,1 Sin Young Choi,1 Ming Quan Lin,1,4 and Myung Ho Jeongb,1 Sci Rep. 2016; 6: 34790.
Published online 2016 Oct 5. doi: 10.1038/srep34790
- Investigation of synergistic mechanism and identification of interaction site of aldose reductase with the combination of gigantol and syringic acid for prevention of diabetic cataract. Jie Wu,#1 Xue Li,#1 Hua Fang,corresponding author1 Yanqun Yi,1 Dan Chen,1 Yan Long,1 Xinxin Gao,1 Xiaoyong Wei,corresponding author1,2 and C-Y. Oliver Chen2 BMC Complement Altern Medv.16; 2016
- Protective Role of Grape Seed Proanthocyanidins Against Ccl4 Induced Acute Liver Injury in Mice. Jinfa Zou,1,A,B,C,E Fengjie Qi,2,B,C,D Liping Ye,1,B,C,D and Suyan Yao1,E,F Med Sci Monitv.22; 2016
- Polyphenols Inhibit Hepatitis C Virus Entry by a New Mechanism of Action. Noémie Calland et al. J Virol. 2015 Oct 1; 89(19): 10053–10063.
- Delphinidin-3-glucoside suppresses breast carcinogenesis by inactivating the Akt/HOTAIR signaling pathway. Xiaohong Yang,# En Luo,# Xin Liu, Bin Han, Xiaoping Yu, and Xiaoli Pengcorresponding author. BMC Cancerv.16; 2016