No it will become wrong because the product form by Folin-Ciocalteu reagent specifically bind with proteins and peptides in solution and provide green color, it usually read under 640 nm absorbence, while Folin-Denis reagent will provide you green color, that will be read under 580 nm absorbance. The detection reulat be different and will not show presence of tannins. 

You can use Folin-Denis reagent for measuring Phenolic compound  but in different manner.

Please refer the link: Some how controversial statement given in wikipedia. For exact method please refer this publication attached herwith.

http://en.wikipedia.org/wiki/Folin%E2%80%93Ciocalteu_reagent

thanx, everyone.

I used Folin Ciocalteu to measure phenlic compounds.  Actually, FC is a improvement of Folin-Denis reaction and it has less interferences than Folin Denis.  As far as i know (i work with polyphenolic compounds in seaweeds)  FC gives a blue color for the presence of these compounds and the reaction occurs in a alkaline medium. Nowadays, there are other methods to measure phenolic compounds such as DMBA assay. 

Dear Puganeswary,

In our lab we use FC for measuring the phenolics in plant extracts at 720nm (blue-purple colors). You may use ultra filtration to get ride of the existing proteins or you may PPt. them.

The content of total phenolic compounds in each extract was determined

according to the Folin-Ciocalteu method with some modification

to minimize the volume of the reactants used to microlitres. An

aliquot of 10 μl of each extract (1 mg/ml) was mixed with 50 μl of Folin–

Ciocalteu phenol reagent (10 x dilutions) and allowed to react for 5

min. Then 40 μl of 20% saturated Na2CO3 solution was added and

allowed to stand for 1 h in the dark before the absorbance of the

reaction mixture was read at 725 nm using a microplate ELISA reader

(BioRad). A gallic acid standard curve was obtained for the calculation

of phenolic content. The total polyphenol content (TPC) of each extract was expressed as mg gallic acid equivalents per gram of plant

extract on a dry-weight basis.

The main difference between F-D and F-C is the proportion of molybdate to prepare the reagment. This change helps to prevent the white precipitation observed in F-D. Also, the F-C assay is more sensitive and reproducible than the F-D

I agree with Jose Avila-Peltroche

thanx, Hanem Awad  and José Avila-Peltroche · 

The condensed tannins can be measured by spectrophotometric method using vanillin assay (Živković et al., 2009).The absorbance is measured at 500 nm and content of total condensed phenolics in investigated samples is expressed as grams of catechin equivalents (CE) per 100 g of the dry extracts ample (%; w/w), 

Rana Mustafa, I tried vanillin-HCl staning for detect phlorotannins (brown algal polyphenols similar to condesed tannins in plants) in situ. Is it the same technique for quantification? Have u usually used vanillin assay for total condesed phenolics for quantification?

For this method please refer to the publication attached to my previous answer "EXTRACTION AND ANALYSIS OF CONDENSED TANNINS.pdf". I used vanillin assay for total condensed phenolics quantification in grape. 

I am currently working at adapting the Folin-Ciocalteu reagent for the estimation of total phenolic compound in my plant extract. I hope to document the result of my finding in the on-going project.

You may consider using the paper by Blainski et al., (Molecules 2013, 18, 6852-6865). It is an open access publication.

I need to know a method to test Folin - Ciocaltu to know if its suitable for Lowry method determination

The Folin–Ciocalteu reagent (FCR) or Folin's phenol reagent or Folin–Denis reagent, also called the gallic acid equivalence method (GAE), is a mixture of phosphomolybdate and phosphotungstate used for the colorimetric in vitro assay of phenolic and polyphenolic antioxidants and bovine serum albumin or lowry method for protein determination

We can also use PE (Polyethylene glycol) for tannin assay.

the main idea of folin reagent in determining proteins is rate of cu+2 reduction into cu+1 in basic medium. Cu+1 can form tetradentate copper complex with protein. The more protein in the sample the more complex formed. This complex react with folin reagent which is (phosphomolybdate + phosphotungstate). This reaction lead to reduction of folin (Mo +6 to Mo+5), which resulted in the formation of blue colour