Folin-ciocalteu reaction

In the Biuret reaction, a purple colour develops when the protein is treated with alkaline copper sulphate. This reaction is dependent on peptide bonds and not on the side chains of individual amino-acids present. In the Folin-Ciocalteu reaction, the protein is treated with tungstate and molybdate under alkaline conditions and the formation of a complex such phenylalanine and tyrosine gives rise to a blue colour. Lowry developed one of the most widely used protein assays in which a combination of the above reactions is involved07, l8). 

The iodometric method was then modified (G23, G24) by changing the final concentration of trichloroacetic acid from 8% to 3.3%, leaving more proteose-like substances in the filtrate, and quantitating the mucosubstances in the filtrate colorimetrically by the Folin-Ciocalteu reaction with the phenol reagent, instead of iodometric titration. This colorimetric reaction determines the tyrosine and tryptophan content after alkaline hydrolysis of the total dissolved mucin. 

Methods used for the detection of PAs in cmde or partially purified extracts can also be adapted for post-column analysis after fractionation (see below). Direct quantitative analysis of PAs in crude grape phenolic extracts is often impossible due to the complex sample matrix. Thus, fractionation or purification is often necessary before analysis. The Folin-Ciocalteu and Pmssian Blue assays are widely used for the quantification of total polyphenols in plants [27,28]. These methods are not specific for PAs due to the reaction of other phenolic compounds with these reagents. 

In vitro tests, used in evaluation of antioxidant properties make use of the ability of antioxidants to quench free radicals. Based on this mechanism, the methods are divided into two groups SET - single electron transfer, and HAT - hydrogen atom transfer. Reactions with antioxidants in assays with the DPPH radical, ABTS and the Folin-Ciocalteu reagent both operate according to the SET and HAT mechanism. Due to the kinetics of the reaction, they are included in the... 

The Falin-Ciocalteu reagent (FCR) is a complex formed in a reaction between sodium tungstate and sodium molybdenate in hydrochloric add and phosphoric acid, which turns yellow after lithium sulphate is added. The reagent reads in an alkaline environment with reducing compounds. Such a reaction gives a blue chromophore which is observed by colorimetry. The Folin-Ciocalteu method is highly sensitive - both to phenolic and non-phenolic compounds, e.g. proteins, vitamin C, vitamin Bj, folic acid, Cu(I). The method is applied most frequently to determine the total content of phenolic compounds [34,35]. If that is the case, a sample for determination should be prepared in a proper manner to minimise the effect of non-phenolic... 

Performing the assay is reduced to putting an alcoholic solution of the analysed sample, Folin-Ciocalteu reagent and solution of sodium carbonate into a reaction tube, which brings the pH of the reaction environment to approx. 10. According to various literature reports, the reaction runs in the darkness for 10 to 120 minutes. After that time, the blue colour of the solution is observed colorimetrically at 725 nm - 760 nm [34, 35, 36, 37, 38]. The results are expressed based on calibration curves prepared for catechol and gallic acid. 

As can be seen from the data, after 30 min of reaction maximum antioxidant power is observed for unmodified silica, with the index being approximately twice as much compared to the control solution. Modified silica also shows an increase in antioxidant power by 30-35% compared to the control solution. The data are in agreement with previous results showing the stabilization of vitamin C on the silica surface, and its slower desorption from the surface of modified samples. Unfortunately, it is not possible to determine the antioxidant activity of vitamin E by the Folin-Ciocalteu method since it is insoluble in aqueous solution. 

Folin-Ciocalteu (Lowry) Assay. The quantitative Folin-Ciocalteu assay (also often called the Lowry assay ) can be applied to dried material as well as to solutions. In addition, the method is sensitive samples containing as little as 5 /Ug of protein can be analyzed readily. The color formed by the Folin-Ciocalteu reagent is thought to be caused by the reaction of protein with the alkaline copper in the reagent (as in the biuret test) and the reduction... 

There are few spectrophotometric methods published to determine ezetimibe in pharmaceutical dosage forms. The first one was established by Mishra et al. [17] by applying colorimetric assay of phenol group. This method was developed based on the reaction between Folin-Ciocalteu s (FC) phenol reagent and phenol group of ezetimibe, which results in a blue chromogen that was then observed at 760 nm. 

Reduction reaction with Folin-Ciocalteu s (EC) reagent... 

The color produced in the Lowry method results from the biuret reaction plus the reduction of the phosphomolybdate-phosphotungstate reagent (Folin CiOcalteu phenol reagent) by tyrosine residues. The Lowry method is suitable for solutions containing 20 to 400 /rg protein/ml. 

Chromatofocusing of the purified FG converter yielded a single peak of protein corresponding to converter activity. Elution of the converter off the column at pH 5.1 indicates a weakly acidic molecule. The converter gave positive reactions with biuret and Folin-Ciocalteu reagents but not with Coomassie blue G-250 reagent. The absence of a reaction with Coomassie blue probably explains why... 

Briefly, 25 pL of a red and rose wine sample or 250 pL of a white wine sample, 15 mL of distilled water, 1.25 mL of the diluted (1 2) Folin-Ciocalteu reagent, 3.75 mL of a sodium carbonate solution (20%) were mixed and distilled water was added to make up the total volume of 25 mL. The solution was agitated and left to stand for 120 min at room temperature for the reaction to take place. The calibration curve was prepared with gallic acid solutions in the concentration range from 0 to 1000 mg/L. The results are expressed as mmol gallic acid per litter (gallic acid equivalents - GAE). 

Colorimetric Indirect Method based on the typical reaction of polyphenols with formaldehyde, Singleton " proposed an assay for the quantification of phenolic material condensable with formaldehyde. He described a colorimetric procedure, instead of the gravimetric method, combining the Folin-Ciocalteu assay wifii the method of Stiasny (Fig 2). First, the total phenol content of the extract was measured before the precipitation reaction by the Folin-Ciocalteu method following the... 

Lowry method The biuret reaction is incorporated with the reduction reaction of Folin-Ciocalteu s reagent and the resulting phosphomolybdenum blue is quantitated spectrophotometrically at 750 nm 2-100 ng ml" ... 

The Folin-Ciocalteu (F-C) index is a more reliable indicator of polyphenol content and is extensively used. The reaction mixture consists of phospho-tungstic and phosphomolybidic acids, which in alkaline medium, are reduced by the polyphenols to a mixture of blue oxides of tungsten and molybdenum, the absorbance of which is read at 750 nm. The F-C index is expressed as 100-fold the absorbance of the sample typical values are in the region of 25-35. 

Semen is generally detected by identifying acid phosphatase or choline. The suspected stain is cut and incubated for 30 min at 37°C with two drops of a 0.1% aqueous solution of disodium phenyl-phosphate the phenol resulting from the enzyme-catalyzed hydrolysis can be detected with the Folin-Ciocalteu reagent. Phenol forms molybdenum blue on reaction with the molybdophosphate or tungstophosphate incorporated in this reagent. 

Most studies in TLC have been qualitative, and considerable experimentation may be necessary to obtain quantitative results, although excellent commercial layers and new equipment have aided the problem. Phenolic compounds have been analyzed by spectrophotometry off the plate at 725 nm (133) by means of Folin-Ciocalteu reagent, essentially sodium tungstate and molybdate with lithium sulfate (134). Chlorophenols have been quantified after reaction with dansyl chloride and separation (135). Channel TLC (linear relationships between spot lengths and concentration between 1 and 8 pg/spot) has been used (136). The phenols in cashew nut shell liquid have been quantified by off and on the plate methods with a flying-spot scanning procedure and densitometry (137) and the distribution of unsaturateds by TLC/MS (138). Catecholamines and their metabolites in urine have been quantified (12) and determined by on the plate fluorimetry (139). Hindered phenols have been analyzed by densitometry (140). Semiquantitative determinations of the coupling products of 4,4 -... 

Compared with other methodologies, there are only a few examples in the literature that describe the FRAP assay adapted to the FIA system. Drawbacks of the method, such as nonspecific reaction to some antioxidant compounds or irregular reaction times (Pulido et al., 2000 Huang et al., 2005 Prior et al., 2005), can be the main reasons for few studies of this assay. Nevertheless, other methods based on electron transfer, such as Folin-Ciocalteu, and those based on radical scavenging also have drawbacks and are widely studied and adapted to several flow injection systems (Magalhaes et al., 2009). 

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