Application ofbiological activities of grape polyphenols in poultry nutritionThe biologicaleffects of polyphenols have been extensively studied in vitro and in vivio inanimal models (Yu and Ahmedna, 2013).

However, data from poultry is still verylimited. When applied to poultry nutrition, they offer promising possibilitiesas tools for improving certain aspects of meat quality, antioxidant status, immunity and for modifying intestinalmicrobiota. Antioxidant activityAntioxidantactivity is the most notable bioactivity of phenolic compounds from GP (Xia etal. 2010; Georgiev et al. 2014). In vitro and in vivo studies haveshown that flavonoids present in wine by-products behave like free radicalscavengers by acting as powerful antioxidants and metal chelators. Thisinhibits formation of the superoxide ion and indirectly inhibitsredox-sensitive transcription factors and pro-oxidant enzymes (Puiggros etal.

2005). They also activate antioxidant enzymes, reduce ?-tocopherolradicals (tocopheroxyls), inhibit oxidases and increase levels of uric acid andsubstances of  low molecular weight. Theantioxidative properties of polyphenols result mainly from their ability todonate hydrogen from hydroxyl groups positioned along the aromatic ring inorder to terminate the free-radical oxidation of lipids and other  biomolecules (Foti et al. 1994).

Amongthe phenolics, monomeric forms are less potent as hydrogen-donating radical scavengersthan polymeric phenols (Fiueroa-Espinoza and Villeneuve, 2005).           Hajati et al.(2015) reported that grapeseed extract (GSE) supplementation (150, 300, 450 mg/kg) reduced blood levels of total TG, LDL-C and increasedHDL-C in broilers. Themechanism by which dietary GP supplements affect the concentrations of plasmalipids is not fully understood. However, herbs and herbal products are known toinduce hypocholesterolemic effects by reducing the activity of3-hydroxy-3-methylglutaryl-CoA reductase (HMGCoA reductase), the rate-limitingenzyme in cholesterol synthesis (Hong et al. 2012).

Seven et al.(2008) reported that feeding plant extracts rich in phenolic compounds resultedin an increase in blood GSH-Px activity of chronic heat-exposed broilerchickens. The malondialdehyde (MDA) compound is an end product of the oxidativedegradation of lipids and is an indicator of oxidative stress (Del Rio et al.,2005).

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