Folin-Ciocalteu value

The phenolic content of 50% SSL diluted to 15% w/w samples was determined by Folin-Ciocalteu reagent [22], Each sample (0.1 ml at proper dilution) was added to 4.2 ml of deionized water and 0.5 ml of Folin-Ciocalteu reagent (Sigma). After 1 min of mixing, 1 ml of an 80% solution of sodium carbonate and 4.2 ml of deionized water was added. The mixture was left for 2 h at room temperature in dark, and the absorbance at 760 nm was measured. The concentration of total phenolic content was determined by a comparison with the values obtained with a standard solution of vanillin (Sigma). 

Measuring absorption at 280 nm seems preferable to the Folin-Ciocalteu test, as it presents a number of advantages, including speed and reproducibility. However, certain molecules, such as cinnamic acids and chalcones, have no absorption maximum at this wavelength. However, as they are present in wine at very low concentrations, any error in the value will be very small. 

It is possible to define the relative contributions of phenolic acids and various non-phenolic substances in wine to this value. It is fairly constant at around 7 for both red and white wines, and corresponds to the value defined by Somers and Ziemelis (1985) using the Folin-Ciocalteu reagent. This is an important factor, especially for white and rose wines, as it represents practically 50% of the value. In red wines, it may be considered that... 

White musts and wines contain benzoic and cinnamic acids, catechins, procyanidins and flavonols (Ribereau-Gayon, 1964 Weinges and Piretti, 1972). A recently discovered class of protein-tannin complexes has been shown to contribute towards the phenol content of white wine (Lea et al, 1979 Singleton et al, 1979). This is the reason for the excessively high result of the Folin-Ciocalteu test and the optical density value of 280 nm (Section 6.4.1)... 

The same sample was then analyzed for protein by the modified Folin-Ciocalteu method." A correction was made for the color of the antigen. To test the method ten triplicate analyses were run on purified antibody samples by both the modified Folin-Ciiocalteu and the Nessler method by two analysts. The first method gave values which averaged 1.035 0.035 times the second. 

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. 

There is, however, a caveat for estimating available total phenolic acid concentrations. The estimates of the total available fraction of phenolic acids in soil extracts represent a crude estimate of what actually occurs in soil, not only because of the range of efficiencies of extraction procedures but also because different phenolic acids at the same concentration generate different absorbances with Folin Ciocalteu s phenol reagent (Fig. 3.7 Blum et al. 1991). In addition soil extracts also contain compounds, other than phenolic acids, that react with (i.e., reduce) the Folin Ciocalteu s phenol reagent (McAllister 1969 Box 1983). The assumption, therefore, was that available total phenolic acid values based on the Folin Ciocalteu s phenol reagent expressed as ferulic acid equivalence were relative values that were consistently related to the acmal total available phenolic acids (hereafter just called total phenolic acid) present in soil extracts. The extraction and quantification by HPLC analysis of available individual phenolic acids in soil do not have these particular problems. 

Pro 4 Total phenolic acid concentrations estimated by water-autoclave extraction and Folin Ciocalteu s phenol reagent are not absolute values and thus should not be viewed as such, they are relative values. The following suggest that these relative values for total phenolic acid content can actually be useful and meaningful ... 

Fig. 2 SEC elution profile of apple procyanidins using a Toyopearl HW-40 F column. Experimental conditions the column size was 950 x 25 mm inner diameter mobile phase solvent was acetone-8 M urea (pH 2) (6 4) flow rate was 1.0 mL/min the eluent was fractionated into 3 ml fractions each the total phenolics content (i.e., the value corresponding to the absorbance at 760 nm) in each fraction was estimated by modified Folin-Ciocalteu assay filled circle= chromatogram of apple procyanidins (10 mg/0.5 ml of mobile phase) open c// c/e=chromatogram of a mixture of standard oligomers from monomer to trimer (each 2 mg/0.5 ml of mobile phase) (reproduced from ref. [24] with permission from Elsevier)...

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