An extract that has been purified or formulated to contain a consistent, measurable quantity of a target compound (or sometimes class of compounds) in every batch, is referred to as “standardized.” The level of the compound is guaranteed to be within a certain range or above a certain minimum in every batch or lot of the extract that you purchase. The exact level of the compound in a particular batch should be reported on the Certificate of Analysis, which most vendors provide with the extract shipment. Common chemical analytical methods such as HPLC, GC, titration, etc. are generally used to measure the content of the target compound within the extract. Although, in some cases, pharmacological bioassays are used to measure the particular type of biological activity within the extract, for example, enzyme activity.
There are two schools of thought regarding how an extract should be standardized. Some people feel that a virtually pure compound is the most efficacious approach to formulating an effective product. Using one pure plant derived compound eliminates any confounding properties that a more complex extract might have. Botanical extracts can contain extremely complex mixtures of compounds. It is possible that some compounds in the mixture may interfere with or counteract the benefits of the target compound. For example, the polyphenol fraction of St. John’s Wort (Hypericum perforatum) has been found to have immunostimulating activity, whereas the lipophilic fraction had immunosuppressing properties (16). In a complex mixture, you don’t know exactly what you have. Complex extracts may cause difficulties formulating, problems with formula stability, or perhaps occasionally problems with safety such as allergic responses to the final product.
The other school of thought seems to stem mainly from ethnobotanical research. Traditional herbal medicines are usually prepared as teas (aqueous infusions of the fresh or dried plant material). In some cases, different compounds within the tea contribute additional or different therapeutic benefits. For instance, ginger (Zingiber officinale R.) contains anti-inflammatory compounds and anti-nausea compounds (17). Using a pure form of one of the anti-inflammatory compounds will not give the full range of benefits derived from the traditional medicine.
Valarian (Valeriana officinalis), used as a sedative, is another example of an herbal medicine that appears to contain more than one type of compound responsible for the benefits derived from it (18). The volatile oil contains major constituents, including valerenic acid and its derivatives, which have demonstrated sedative properties in animal
models. Valepotriates and their derivatives, which belong to the iridoid class of molecules, have also demonstrated in vivo sedative activity, but they are very unstable and tend to break down over time, making their activity difficult to assess. Valerian extracts also contain gamma-aminobutyric acid (GABA) and aqueous extracts contain glutamine which may be converted into GABA. These compounds may also contribute to valerians sedative effects. In this case, the herbal medicine contains three different classes of molecules, all of which may to contribute to the sedative benefits of the extract.
Another important consideration is whether the extract is standardized to the correct constituent. As can be seen from the previous examples of herbal medicinals, often the compounds responsible for the therapeutic benefits are not well understood, sometimes not known period. For many years the constituents responsible for the antidepressant benefits of St. John’s Wort (Hypericum perforatum) were not understood. It was thought that hypericin was the primary active in the herb. Dietary supplements of St. John’s Wort were standardized to hypericin, and perhaps still are in some instances. Hypericin is known to be a photosensitizer (19). This property was first recognized in cattle that grazed on this plant. Several instances of photosensitization in people using St. John’s Wort herbals have been reported (20-22). Hyperforin is now recognized as the major antidepressant constituent of this plant. Hyperforin has been found to be a strong uptake inhibitor of serotonin, dopamine, noradrenaline, GABA, and L-glutamate (23). Although hyperforin alone is a powerful antidepressant, several other compounds in the plant also appear to contribute to the overall antidepressant benefits from the plant (24). This compound is not a photosensitizer, but it is unstable. Its instability makes it difficult to standardize to and perhaps explains the continued use of hypericin as the marker compound.