Those familiar with the science of nutritional supplements have also heard of the antioxidant capabilities of grape seed extract. However, the phytonutrient value of the grape does not begin and end with the seed. In fact, the polyphenolic content of the skin is at least equal to that found in the seed. Further, the diversity of each of the respective polyphenolic sources is such that they each perform distinctively specific tasks. Studies have shown that the synergy between the polyphenols of the skin and seed of the grape is superior, by demonstrating that the combination of polyphenols from both sources significantly outperformed both grape seed extract and grape skin extract separately in terms of anti-platelet activity.
Not Just another Antioxidant
There is a myriad of polyphenols that exist in the skin of the grape surrounding the oligomeric proanthocyanidin (OPC)-rich seeds. One polyphenol abundant in grape skin that has recently come into the limelight is resveratrol. Resveratrol is most often identified as an antioxidant with the capability to hamper free radical damage linked to cancer. It has also been shown to raise the levels of ‘good’ high density lipoprotein (HDL) cholesterol.
First and foremost, full-spectrum grape extract is one of the most potent antioxidants known to science. This is a very profound statement considering the fact that there are well over 5,000 known flavones currently being studied (and more being discovered all the time).
The definition of an antioxidant is that it is a scavenger of reactive oxygen species (ROS). ROS are toxic compounds that are produced during periods of metabolic or environmental stress. Two of the most potent radicals include the hydroxyl radical and the superoxide anion. The toxic side effects of ROS include damage to DNA (cancer-causing effects) or damage to structural components of the brain (neurodegenerative effects, e.g. Alzheimer’s disease). Antioxidants carry free electrons that neutralize ROS, which require an extra electron to become unreactive. By accepting free electrons from peptides, the ROS are neutralized and their toxic side effects may be prevented (an effect referred to as scavenging).
Proanthocyanidins as the Primary Polyphenol
The primary polyphenols in pomace (the pulpy residue remaining after fruit has been crushed) are proanthocyanidins, which come in a multitude of chemical structures and sizes consisting of base units called ‘monomers’. Proanthocyanidins containing two or more monomers chemically linked together are called oligomeric proanthocyanidins or ‘OPCs’, and grape seed extract is the richest source of these. OPCs scavenge free radicals via a different mechanism than traditional antioxidants with respect to the number of free radicals they scavenge.
The metabolism of OPCs by human colonic microflora has been studied in some detail, the proanthocyanidin polymers are catabolized by colonic microflora into low-molecular-weight phenolic acids. These low-molecular-weight aromatic compounds have been identified as phenylacetic, phenylpropionic and phenylvaleric acids. These are the metabolites that are likely responsible for the entire range of health benefits offered by proanthocyanidins because the latter simply cannot be absorbed through the small intestinal barrier due to its relatively high molecular weight.
Another central capability of proanthocyanidins that distinguish them from other antioxidants is their renowned effect on the circulatory system. Metaphorically speaking, proanthocyanidins “turn back roads into freeways”, stimulating the recuperative and regenerative activity of the circulatory system.
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Folts et al. Grape seed and grape skin extracts elicit a greater antiplatelet effect when used in combination than when used individually in dogs and humans. American Society for Nutritional Sciences 132(12):3592-8, 2002.
Leiro J, et al. Effect of cis-resveratrol on genes involved in nuclear factor kappa B signaling. Int Immunopharmacol. 5(2):393-406, 2005.
Scalbert et al. Polymeric proanthocyanidins are catabolized by human colonic microflora into low-molecular-weight phenolic acids. American Society for Nutritional Sciences; 130(11):2733-8, 2000.