Total phenols assay

Total Phenols Assay (Folin-Ciocalteu Reagent)... 

As phenolics are well-known antioxidant agents, the Folin-Ciocalteau total phenolics assay was performed to assess phenolic content in ginseng roots. This assay was performed as described by Singleton et al. [20] with modifications [21]. Briefly, extract dissolved in 70% methanol was combined with Folin-Ciocalteau reagent, incubated for 5 min, and then 7.5% NaHCOs was added. Samples were transferred into microplate wells in triplicate, incubated in darkness for 2 h, and then absorbance read at 725 nm. Samples were blanked against a treatment with only solvent. A standard curve of quercetin was produced and data were expressed as quercetin equivalents. 

Correlation Between Total Phenols Expressed as Percent Caffeic Acid Equivalents and Ozone Injury. Twelve cultivars of peanuts ranging from low to high ozone sensitivity were examined. Foliage of each of the cultivars was evaluated for content of total phenols before and after ozone treatment. Because of the relatively high concentrations of caffeic acid in peanut foliage, values are expressed as percent caffeic equivalents in the total phenol assay. Experimental results used in establishing the correlation between caffeic acid and ozone injury are shown in Table I. 

Table II. Molar Absorptivity in the Total Phenol Assay and Precipitability with Acidic Formaldehyde ...

Amine and Aminophenol Derivatives. Amines and aminophenols (Table VIII) react with the F-C reagent about as predicted considering the aromatic amino groups equivalent to phenolic hydroxyls. This would be an important interference with total phenol assay in samples with appreciable aromatic amine content. Fortunately, for this and other reasons as well, the major wine grapes and most other fruit and vegetable products are free of significant concentrations of aromatic amines which would interfere. Correction might be made for methyl anthranilate... 

The use of HPLC for quantification of phenols is often limited to a single class of phenolics and then often only to low-molecular weight compounds that are available as standards. It is, therefore, often necessary to use colorimetric assays such as the Folin-Ciocalteau assay which rely on the reducing ability of phenols to quantify the amount of total phenolics in a sample (Waterman and Mole, 1994 Singleton et al, 1999 Schofield et al, 2001). The degree of condensation of polyphenols can be quantified by colorimetric assays such as the acid-butanol assay and the vanillin assay (Waterman and Mole, 1994 Schofield et al, 2001). 

Determination of Total Phenolics Folin-Denis Assay... 

The Folin-Denis assay is used as a procedure for the quantification of total phenolics in plant materials, food, and beverages. Reduction of phosphomolybdic-phosphotungstic acid (Folin-Denis reagent) to a blue-colored complex in an alkaline solution occurs in the presence of phenolic compounds (Folin and Denis 1912). 

Fig. 7.3 Radical scavenging activity as measured in the DPPH assay versus (a) total ginsenoside content (% w/w) and (b) total phenolics (pg quercetin per mg extract) of eight ginseng root samples (n = 3). The log IC50 of each sample was divided by the log IC50 of the standard ascorbic acid to...

Table 5.6 shows the total phenolic content (determined using the Folin-Ciocalteu assay) and antioxidant activity (ABTS radical scavenging capacity) of extracts from morama bean seed coat and cotyledon prepared with acidified mefhanol. If is clear fhaf morama bean seed coat and cotyledon have appreciable levels of fofal phenolics and antioxidant activity. These phenolics are concentrated in the seed coat. It has been reported that the morama bean cotyledon contains high levels of the amino acid tyrosine (Maruatona et ah, 2010) which is phenolic in nature and can therefore confribufe fo fhe fofal phenolic content of the cotyledon as determined with the Folin-Ciocalteu assay. 

Total phenolic compounds content was assayed spectrophotometri-cally using a modified Prussian blue method as described by Graham (28) employing an LKB Biochrom Ultrospec II spectrophotometer (Cambridge, England). Tannic acid was used as calibration standard. 

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