Folin-Ciocalteau procedure

The total phenols in an anthocyanin preparation can be routinely determined using the Folin-Ciocalteau procedure (Singleton and Rossi, 1965). 

A method that has been the standard of choice for many years is the Lowry procedure. This method uses Cn ions along with Folin-Ciocalteau reagent, a combination of phosphomolybdic and phosphotnngstic acid complexes that react with Cn. Cn is generated from Cn by readily oxidizable protein components, such as cysteine or the phenols and indoles of tyrosine and tryptophan. Although the precise chemistry of the Lowry method remains uncertain, the Cn reaction with the Folin reagent gives intensely colored products measurable spectrophotometrically. 

A standard Lowry-based protein assay has been adjusted to the special conditions encountered with skin [126], Basically, proteins reduce an alkaline solution of Cu(II)-tartrate to Cu(I) in a concentration-dependent manner. Then, the formation of a blue complex between Folin-Ciocalteau reagent (a solution of complex polymeric ions formed from phosphomolybdic and phosphotungstic heteropoly acids) and Cu(I) can be measured spectrophotometrically at 750 nm. A calibration curve can be obtained by dissolving known amounts of stratum corneum in 1 M sodium hydroxide. A piece of tape that has not been in contact with skin is subjected to an identical procedure and serves as negative control. The method was recently adapted to a 96-well plate format, notably reducing analysis times [129],... 

The Folin-Ciocalteau (FC) procedure is one of the standard procedures in wine analysis, as well as in tea analysis (Wiseman et al., 2001). One drawback in interpretation is that different classes of phenolics have varying taste attributes, and tests for chemical astringency based on precipitation of proteins have been recently developed (Adams et al., 1999). In addition, if the food product contains sugar, it can mask the bitterness and astringency, as observed in ripe fresh fruit, sweetened chocolates, and tea. 

The Folin-Ciocalteau Assay of Protein Concentration. The Folin-Ciocalteau assay is one of the most sensitive and most commonly used assays to determine protein concentration (sensitive to about 10 /rg/m I protein). This procedure employs two color-forming reactions to assay protein concentration photometrically. In the first reaction (a biuret reaction), compounds with two or more peptide bonds form a dark blue-purple color in the presence of alkaline copper salts. In the second reaction, tryptophan and tyrosine side chains react with the Folin solution to produce cuprous ions. This reaction is most efficient under basic condi-... 

The following procedure will be used for all protein assays performed in this experiment. Because of day-to-day variation in the assay, you must prepare a standard curve each day that you perform the Folin-Ciocalteau assay. 

The Folin-Ciocalteau analysis of total phenols was performed using the method of Singleton and Rossi (35). This procedure used Folin Ciocalteau s reagent (Sigma) and a saturated aqueous sodium carbonate solution to produce an absorbance at 765 nm. Gallic acid was used to make the standard curve and results are expressed as gallic acid equivalents (GAE). 

The most commonly used methods for determination of total phenolics in foodstuffs are the Prussian Blue assay and the Folin-Ciocalteau method. Although these procedures have undergone numerous modiiicalions, the version adopted by the American Oil Chemists Society (AOCS) is most commonly used nowadays. These assays are not specific for phenohc compounds, although they are widely used to get a global concentration of phenolic compounds present in foods. 

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