- One approach is the use of a specified ratio of raw materials to solvent. Since different specimens of even the same plant species may vary in chemical content, Thin Layer Chromatography (TLC) is sometimes used by growers to assess the content of their products before use.For this purpose although official standards are necessary to control the quality of the crude drugs used, their use does raise certain problems. To accommodate considerable variation that occurs between different batches of a natural product, it is necessary to set low standards which allow the use of commercial material available in any season. This results in the tendency of suppliers to reduce all of their material to the lowest requirement.
- If the ‘active principles’ of an herbal remedy are known or can be discovered, these substances can act as reference standards, and their specified concentration levels can be quantified in chemical quality-control procedures, which are predominantly preformed by High Performance Liquid Chromatography (HPLC). The extract is prepared by adjusting to a high degree of concentration the active ingredient. Such extracts offer the opportunity to use herbs in a more specific way for specific predetermined therapeutic objectives. Ginkgo leaf standardized to 24% flavonglycosides is used to increase blood circulation especially to the brain instead of its more traditional use by the Chinese as a tonic for the lungs.Examples of active constituent extracts are ginkgo (24% flavonglycosides), milk thistle (80% silymarin), grape seed (95% polyphenols), turmeric (95% curcumin), saw palmetto (90% free fatty acids), green tea (60% catechins), cascara sagrada (20–30% anthraquinones), bilberry (25% anthocyanosides), pygeum (12% phytosterol), kava (30–40% kavalactones).This approach regulates a specific biochemical constituent to a level that may not be naturally found in the plant. Concentrating 95% curcuminoids, for instance, in a standardized turmeric extract creates a product that, while derived from the crude herb, is not expected to be naturally found concentrated at that level. This leaves only 5% of the other turmeric constituents with which the curcumin is combined thus displacing other constituents which may be responsible for the biological activity of the herb.One of the principal issues with extracts standardized to a high degree of concentration of an active ingredient is that they limit the range of the herb’s influence. Well-known medicinal herbs such as turmeric, garcinia, milk thistle and commiphora have several indications. A complex range of chemicals gets excluded from these herbs as a consequence of standardizing them to a high concentration of specific active constituents, causing the herb to lose its more varied and diverse traditional functions.Thus turmeric extracts standardized to a high curcumin content cannot be used in the manner Ayurveda prescribes it, i.e., for promoting blood circulation and to improve digestion. This is because while turmeric is classified as a thermogenic drug-stimulating metabolism, standardized turmeric extract with 95% curcumin is more cooling and it is a more effective anti-inflammatory, but is not as effective a digestant or circulatory stimulant.In the case of certain herbs, the active ingredients are not found to be exclusively responsible for the activity. Other constituents are eventually identified to be more active biologically. Thus, promoting an herb as a standardized extract overlooks the spectrum of uses it covers. For e.g. milk thistle extract, though sold specifically as a hepatoprotective, is actually also indicated for promotion of pelvic blood circulation in dysmenorrhoea, amenorrhoea and irregular passive uterine haemorrhages.
- Another method is standardization on a signal chemical. It may be a known active constituent or a marker compound not necessarily the active constituent but that which is satisfactorily measurable. Extracts standardized with respect to a marker chemical are not based on the concentration of an established active constituent. Instead they represent a specified amount of a specifically selected biochemical constituent, characteristic of the plant, so selected for positive identification or to create a higher degree of uniform potency. E.g. Feverfew, Ginseng (5–15% ginsenosides), brahmi (10% asiaticosides), liquorice (12% glycyrrhizin), green tea (20–50% polyphenols), Ephedra (6–8% ephedrine/pseudoephedrine), etc. Marker extracts that contain all constituents in a proportion similar to the herb retain more relationship to the traditional way herbs are used.
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