Health-promoting
properties

Initially,
molecular mechanisms of polyphenol health-promoting properties were related to
their antioxidant properties. This assumption seemed to be supported by
numerous in vitro model studies (Andriantsitohaina et al. 2012).
Flavonoids can prevent injury caused by free radicals by the following mechanisms
(Prochazkova et al. 2011): direct scavenging of reactive oxygen species
(ROS), activation of antioxidant enzymes, metal chelating activity, reduction
of ?-tocopheryl radicals, inhibition of oxidases, mitigation of oxidative
stress caused by nitric oxide, increase in uric acid levels, increase in
antioxidant properties of low molecular antioxidants.

           Emerging findings suggest a large
number of potential mechanisms of action of polyphenols in preventing disease,
which may be beyond their conventional antioxidant activities (Rodrigo et al.
2011). Therefore, it seems likely that antioxidant activity is not a major
mechanism for benefits of flavonoids on endothelial function, atherosclerosis
and cardiovascular disease risk (Hodgson, 2008), as inhibition of
atherosclerosis in animal models is not associated with markers of change in
oxidative damage. On the other hand,there is consistent data indicating that
flavonoids can enhance nitric oxide status and improve endothelial function,
which may be at least partly responsible for benefits on cardiovascular health
(Hodgson and Croft, 2010).

           In
poultry production, it is very important to improve immunity to prevent
infectious diseases. A variety of factors such as vaccination failure,
infection by immune-suppressive diseases, and abuse of antibiotics can induce
immunodeficiency. The use of immune stimulators is one solution to improve
immunity and to decrease susceptibility to infectious disease. GP is
particularly rich in a wide range of polyphenols. Konowalchuk and Speirs (2009)
reported that grape seed proanthocyanidins show up to 50 times more antioxidant
activity than vitamin E.     Immunity is
influenced by oxidative stress and improving antioxidant status of the animal
may enhance their immunity. Similar to our data, Iqbal et al. (2015)
found that broilers fed the grape polyphenols diets showed higher (P<0.05) antibody titers against Newcastle disease virus (NDV) than in those fed the control diet. Also, Acamovic and Brooker (2005) reported immunostimulating activity of polyphenols and oregano essential oil with respect to the system of mononuclear phagocyte system, cell, and humoral immunity.

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