TRICKS

Tricks to have a quick idea of an extract value:

Taste it ! If this is a food grade extract, ask to taste it. The more bitter and astringent it tastes, richer it is in polyphenols.

Dissolve it in an alcoholic solution : For extracts with a polyphenolic rate close to 100%, dissolve it in an alcoholic solution (ethanol or methanol). If you obtain deposit, this one corresponds to the non polyphenolic part of the extract (generally polysaccharides).

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POLYPHENOLS PROPORTIONING

Worldwide regulation authorities do not recommend the use of a specific method of analysis for polyphenols rate evaluation. Therefore, various methods are used, having more or less precision in their final results. As a consequence, results can not be compared between each other and the choice between different polyphenolic extracts may be biased.

Three of the most commonly used polyphenols methods of analysis are described below to help you choosing which extract will correspond at best to your needs.

UV-Visible spectrophotometry

METHOD TO BE AVOIDED

Although being one of the very first methods used in the estimate of the phenolic compounds quantities, the use of the UV visible spectrophotometry for polyphenol dosage is arguable.
Plant extracts contain many elements (aromatic amino acids, furfurals compounds produce during the plant drying process); and just like polyphenols, all these elements are able to absorb at 280 nm.

The use of this method is possible if the extract does not contain other 280 nm absorbents elements. (Any furfuraldehyde compounds -caramel- or proteins).
Care about the standard used. (Gallic acid or catechin for reliable results).

Colorimetry by FOLIN-CIOCALTEU method

METHOD TO BE GENERALIZED

The dosage by the Folin-Ciocalteu method is based on the reducing properties of the phenolic compounds. More specific, this method gives a reliable polyphenolic rate in plant extracts. This analysis can dose both native and oxidized polyphenols forms (which still comprise reducing phenolic functions).

For dried plant extracts, there is little chance that contaminations by other reducers (such as ascorbic acid or sulphur compounds) can false the results.
Care about the standard used (Gallic Acid or catechin for reliable results)

Chromatography HPLC

METHOD FOR SPECIFIC ACTIVES

The most precise method, when used with at least one phenolic standard per class of compound. The sum of all the native compounds dosages gives a result close to the results obtain by FOLIN-CIOCALTEU method.

As it only measure the native polyphenols forms, this method under-estimate the real polyphenol content (oxidized -but still active-polyphenols forms are not dosed).
The origin of the extract can be determined with this method.

comparison of extracts proportionning by 3 methods.

	Proportioning by UV-Visible spectrophotometry	Proportioning by FOLIN-CIOCALTEU method	Proportioning by chromatography HPLC
Standard	catechin	catechin	One per class of compound
Polyphenols rate of the Pomactiv extracts	between 85 % and 130%	between 35 % and 50%	between 30 % and 45%
Comment	OVER-ESTIMATED RATE !	WITH THE GOOD STANDARD, THE METHOD IS RELIABLE !	THE MOST PRECISE METHOD !