Some articles reported that the total Flavonoid content in a particular extract which was assessed by AlCl3 method using quercetin as a standard, were higher than the total phenolic content which was assessed by Folin- Ciocalteu reagent using gallic acid as a standard. it is true ?
and why?
It may be true. In other plant extracts, the total flavonoid are fewer than total phenolic content, using respective above mentioned evaluation methods.
It should be noted that, the évaluation methods are different for total phenols and total flavonoids; with different reagents, different colorations and different maximum reading wavelenths. The standards are Also differents!!
So, If AlCl3 method is specific to flavonoids, despite the fact that flavonoids are group of phenolic compounds, strict quantitative compparison with Folin- Ciocalteu methods of total phenols would not make sense in my opinion.
I send to you the answer of Alok Nahata to the same question by Ramtin Pakzad at 4 years ago. which in my opinion is a good answer to your question.
Typical phenolics that possess antioxidant activity are known to be mainly phenolic acids and flavonoids. Phenolic acids are a major class of phenolic compounds, widely occurring in the plant kingdom especially in fruits and vegetables. Because of the diversity and complexity of the natural mixtures of phenolic compounds in hundreds of herb extracts, it is rather difficult to characterize every compound and elucidate its structure, but it is not difficult to identify major groups and important aglycones of phenolic compounds. Many medical herbs and spices have been studied and to some extent their phenolic chemistry is known. The contents of phenolic compounds, measured by HPLC after enzymatic hydrolysis, were found to be different from those values measured using the Folin–Ciocalteu method. The amount of polyphenols was also dependent on the extraction method. The samples for HPLC when subjected to enzymatic hydrolysis which, in contrast to methanol extraction, resulted in specific disruption of linkages and deglycosylation of phenolic compounds. Many authors report that aglycones exhibit higher antioxidant activity than do glycosides. It is obvious that the total phenolic content measured by the Folin–Ciocalteu procedure does not give a full picture of the quality or quantity of the phenolic constituents in the extracts.
Pl. see the following papers for more details:
Katsube, T., Tabata, H., Ohta, Y., Yamasaki, Y., Anuurad, E., Shiwaku, K., et al. (2004). Screening for antioxidant activity in edible plant products: Comparison of low-density lipoprotein oxidation assay, DPPH radical scavenging assay, and Folin–Ciocalteu assay. Journal of the Agricultural and Food Chemistry, 52, 2391–2396.
Wu, X., Beecher, G. R., Holden, J. M., Haytowitz, D. B., Gebhardt, S. E., & Prior, R. L. (2004). Lipophilic and hydrophilic antioxidant capacities of common foods in the United States. Journal of the Agricultural and Food Chemistry, 52, 4026–4037.
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