Resveratrol extract is an industrial derivative, whereby the resveratrol content of a plant or grape skin is removed from the source and maintained in pure form. In the case of resveratrol supplements, most contain resveratrol extract obtained from Japanese knotweed, a plant that can supply a large amount of the compound and is grown commercially.
With some supplements you will also see grape seed extract and grape wine extract included in the formula. They are present for the same reasons as resveratrol; they are high in antioxidant content, there is some indication that they can act to lower cholesterol in humans and may act to reduce inflammation.
The resveratrol molecule can be somewhat unstable and the extraction process may result in two classes of molecule, the trans-resveratrol and the cis-resveratrol. All of the benefits associated with resveratrol are conveyed by trans-resveratrol. The content of various resveratrol capsules and tablets is often debated in marketing materials from manufacturers, who will maintain that their resveratrol extract contains a much higher level of trans-resveratrol than the competition.
In the typical extraction process, Japanese knotweed roots are sliced before being heated up in large metal chambers known as extractors. The roots are tested for contamination with heavy metals or chemicals. A solvent – usually ethanol or methanol – is used to separate the resveratrol from the plant tissue, resulting in a liquid extract.
The separated extract is processed further by being run over a column of silica under high pressure in order to separate impurities. It is then vacuum-dried to remove the solvent, finally producing resveratrol powder. At this stage the filler made from some form of organic cellulose is added. The powder is then utilized in resveratrol pills, in capsules or in powder form and packaged as a dietary supplement.