Grape Extract -Not Just the Seed

Published on July 03, 2017 by Dr. Traj Nibber

Those who are familiar with the science of nutritional supplements are no doubt familiar with the antioxidant capabilities of grape seed extract, but the phytonutrient value of the grape does not begin and end with the seed. The fact of the matter is that the polyphenolic content of the skin is at least equal to that found in the seed, and the diversity of each of the respective polyphenolic sources is such that they each perform distinctively specific tasks. The synergy between the polyphenols of the skin and seed of the grape was effectively demonstrated in a study where a combination of polyphenols from both sources significantly outperformed both grape seed extract and grape skin extract separately in terms of anti-platelet activity.

From the myriad of polyphenols that are known to exist in the skin of the grape surrounding the oligomeric proanthocyanidins (OPC)-rich seeds, one in particular has been selected very recently for particular scrutiny - resveratrol. Resveratrol is most often identified as an antioxidant with the capability to hamper free radical damage linked to cancer. It has also been linked with the capability to raise HDL cholesterol. However, the largest areas of scrutiny in the most recent clinical trials appear to be focused on resveratrol's anti-inflammatory potential.

Not Just another Antioxidant

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) for their antioxidant properties, with those properties confirmed in several hundred of them already.

The very definition of an antioxidant is that it is a scavenger of free radicals, and two of the most virulent of these are the hydroxyl radical and superoxide anion. Free radicals in general and these types in particular have been implicated as playing a role in the etiology of cardiovascular disease, cancer, Alzheimer's disease, and Parkinson's disease. In fact, they are the most actively prolific free radical by-products of reactive oxygen species (ROS).

Proanthocyanidins as the Primary Polyphenol

The primary polyphenols in this pomace 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. Proanthocyanidins scavenge scavenge free radicals  via a different mechanism than traditional antioxidants with respect to the number of free radicals they scavenge.

Their metabolism 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. An old marketing adage for proanthocyanidins once stipulated that they turn “back roads into freeways”, metaphorically referring to how they stimulate the recuperative and regenerative activity of the circulatory system.

Select references:

Bagchi D, Garg A, Krohn RL, Bagchi M, Tran MX, Stohs SJ. “Oxygen free radical scavenging abilities of vitamins C and E, and a grape seed proanthocyanidin extract in vitro.” Res Commun Mol Pathol Pharmacol. 1997 Feb;95(2):179-89.

Chang WC, Hsu FL. “Inhibition of platelet aggregation and arachidonate metabolism in platelets by procyanidins.” Prostaglandins Leukot Essent Fatty Acids. 1989 Dec;38(3):181-8.

De La Castra CA, Villegas I. “Resveratrol as an anti-inflammatory and anti-aging agent: mechanisms and clinical implications.” Mol Nutr Food Res. 2005 May;49(5):405-30.

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; September 2002.

Leiro J, Arranz JA, Fraiz N, Sanmartin ML, Quezada E, Orallo F. “Effect of cis-resveratrol on genes involved in nuclear factor kappa B signaling.” Int Immunopharmacol. 2005 Feb;5(2):393-406.

Scalbert et al. “Polymeric Proanthocyanidins Are Catabolized by Human Colonic Microflora into Low-Molecular-Weight Phenolic Acids.” American Society for Nutritional Sciences; March 2000.