Trans-Resveratrol As A Dietary Supplement Ingredient - A Question Of Shelf Life And Laboratory Potency Determination
By Ted Waszkuc, NOW Methods Development Scientist
Trans-Resveratrol is one of the active ingredients in NOW Foods Pometrol V-caps. Although Resveratrol is well known for its antioxidant capacity, it possesses certain molecular structure features that have raised concerns about its stability. Resveratrol belongs to the class of non-flavonoid polyphenolics of the stilbene family. Its molecular structure reveals two phenolic rings combined with carbon atoms linked to each other by the rigid double bond, making the compound possible to exist in two different geometric forms: trans and cis.
Chemically speaking, stability, or for that matter instability, of a compound depends upon its reactivity. The practical question to be answered here is how easily the ingredient of interest reacts with, or is affected by environmental agents like moisture, air, UV light, or elevated temperatures.
In liquid media (alcohol or aqueous alcohol solutions), resveratrol has a tendency to form the trans/cis mixture in which the proportion of each isomer depends on physico-chemical condition of storage. Such transformation may be considered as degradation because most of the reported health benefits, including protection against atherosclerosis, coronary heart diseases and cancer have been attributed to trans-resveratrol. On the other hand, the biological properties of cis-resveratrol are generally unknown.
One interesting study has indicated the instability of trans-resveratrol in wine after the bottle has been opened, partially used and resealed, suggesting that presence of cis form in wines may simply be an artifact of storage and manufacturing conditions. Alternatively, because resveratrol is susceptible to oxidation, exposure to air may lower a product’s total content.
Chemical reactions, including degradation, result from collision of the reacting molecules. For a reaction to occur, the reacting compounds should acquire certain degree of mobility to be able to collide with sufficient energy. This explains why the rate of degradation reaction in case of resveratrol is much higher in liquid phase (compound dissolved) as compared to solid phase (powdered extract). The stability of the pure trans-resveratrol dissolved in most popular laboratory solvents and used as reference standard for analytical determination has been reported in literature.
Trials in methanol, conducted under various conditions showed that trans-resveratrol remained stable for about one month in refrigerator when completely protected from light. Conversion to cis-resveratrol occurs after exposure to direct daylight and can be accelerated by UV irradiation. Temperature had no detrimental influence on trans-resveratrol. On the contrary, when the mixture containing both isomers was heated in ethanol, substantial reconversion of cis- to trans- took place without loss of either isomer.
In order to establish product expiration date, storage stability studies are conducted. These studies usually entail measurement of the starting potency of the most unstable active ingredient just after finish product is made, subjecting it to the carefully design conditions at which ingredient of interest may undergo degradation and measurement of its potency again after predetermined amount of time. At NOW Foods, our Methods Development Laboratory conducts validated analytical procedures during each step of laboratory testing to assure that no decomposition of the compound of interest takes place during quality control analysis.
It is recommended that trans-resveratrol standards and samples in solution should be protected from light during extraction, storage (at lowered temp.), and analysis. The Resveratrol used in NOW Foods Pometrol V-capsules comes from Polygonum cuspidatum root extract and does not exhibit any HPLC detectable amounts of cis-isomer. Furthermore, the HPLC method we use at NOW to measure changes in trans-resveratrol content during accelerated stability study is designed to assure that no loss of potency happens during the analytical laboratory procedure.
The trans-resveratrol content of one Pometrol capsule is equivalent to 5 to 10 glasses of red wine.