Hello,
Why usually we use Gallic acid as standard curve for quantification of total polyphenol? Why we don't use another standard?
Hi Mraihi,
Their results must be expressed in an unit where you will get to compare with literature data.
For example, some authors express total phenolic compounds in apples as chlorogenic acid and others express in cereal as ferulic acid equivalent.
Other important point, it would be to verify the predominant phenolic compound in your sample. In these examples gallic acid can be find in insignificantly quantity.
Best regards
Hello, many phenolic compounds can be used as standards, the criteria to consider in the choice of the phenolic acid to be used are the stability, the price, the solubility in the solvent used.... the most important criteria is the abundance in your sample.
Also, you can and need to use a calibration curve for the compound which is dominant in a given raw material, but if we are convinced after a qualitative research that such a relationship is not dominant and gallic acid.
Acácio has given a very appropriate answer.
Use of any available assay would not reflect the total phenolic content of a sample; the employment of Folin-Ciocalteu assay and other methods of estimation only gives an approximate idea of the total phenolic content of a sample.
Folin-Ciocalteu′s phenol reagent reacts with phenolic (-OH containing amino acids, such as L-tyrosine) compounds and non-phenolic reducing substances (including ascorbic acid) to form chromogens that can be detected spectrophotometrically. If you are measuring phenolics in wine you would use gallic acid as a standard, which is a representative and prominent phenolic acid in wine. Interaction with gallic acid has been found to be equivalent to most other phenolics in wine on a mass basis. When one estimates tea polyphenols one would use (+)-catechin as a standard since catechin is more representative of tea polyphenols.
Singleton, V. L.; Orthofer, R.; Lamuela-Raventos, R. M. Analysis of total phenols and other oxidation substrates and antioxidants by means of Folin-Ciocalteu Reagent. Methods in Enzymology 1999, 299, 152-178.
Welcome,
gallic acid is the one that occurs in most species tested, but nothing prevents to convert to another acid, which is the most in your raw material. The question is whether you can find literature data for discussion in such a situation. Because, of course, the sum of phenolic acids can be expressed in terms of gallic acid, or coffee, usually, in terms of flavonoids quercetin and kaempferol, but St. John's wort converted into hyperozyd. And so one could multiply examples.
thank you all for the reply. I was thinking, for the estimation of phenolic content we need to use standard which contains a phenolic group like tannic acid, gallic acid or even catechol. Structurally they all contain phenol ring. But a standard antioxidant like ascorbic acid cannot be used here for the same reason. Ultimately we can express our results as the equivalence of standard.
Hi everybody,
Some of you know if exists some table of equivalence between the different acids used for quantification of total polyphenols. I need transform gallic acid equivalents (GAE)to chlorogenic acid equivalents (CGAE).
Ferulic acid can be used for standard curve preparation. It gives very good reproducible data. (For cereal total polyphenol estimation)
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