The Folin–Ciocâlteu reagent (FCR) or Folin's phenol reagent or Folin–Denis reagent, is a mixture of
phosphomolybdate and
phosphotungstate used for the colorimetric ''
in vitro
''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called " test-tube experiments", these studies in biology ...
''
assay of phenolic and
polyphenol
Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some o ...
ic
antioxidants, also called the gallic acid equivalence method (GAE). It is named after
Otto Folin
Otto Knut Olof Folin (April 4, 1867 – October 25, 1934) was a Swedish-born American chemist who is best known for his groundbreaking work at Harvard University on practical micromethods for the determination of the constituents of protein-f ...
,
Vintilă Ciocâlteu, and
Willey Glover Denis. The Folin-Denis reagent is prepared by mixing
sodium tungstate
Sodium tungstate is the inorganic compound with the formula Na2WO4. This white, water-soluble solid is the sodium salt of tungstic acid. It is useful as a source of tungsten for chemical synthesis. It is an intermediate in the conversion of tungs ...
and
phosphomolybdic acid
Phosphomolybdic acid is the heteropolymetalate with the formula . It is a yellow solid, although even slightly impure samples have a greenish coloration. It is also known as dodeca molybdophosphoric acid or PMA, is a yellow-green chemical compound ...
in
phosphoric acid
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...
. The Folin–Ciocalteu reagent is just a modification of the Folin-Denis reagent. The modification consisted of the addition of
lithium sulfate
Lithium sulfate is a white inorganic salt with the formula Li2 S O4. It is the lithium salt of sulfuric acid.
Properties
Physical properties
Lithium sulfate is soluble in water, though it does not follow the usual trend of increasing solubil ...
and
bromine
Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
to the phosphotungstic-phosphomolybdic reagent.
The reagent does not measure only phenols, but will react with any reducing substance. It therefore measures the total reducing capacity of a sample, not just phenolic compounds. This reagent is part of the
Lowry protein assay
The Lowry protein assay is a biochemical assay for determining the total level of protein in a solution. The total protein concentration is exhibited by a color change of the sample solution in proportion to protein concentration, which can then be ...
, and will also react with some nitrogen-containing compounds such as
hydroxylamine
Hydroxylamine is an inorganic compound with the formula . The material is a white crystalline, hygroscopic compound.Greenwood and Earnshaw. ''Chemistry of the Elements.'' 2nd Edition. Reed Educational and Professional Publishing Ltd. pp. 431–43 ...
and
guanidine
Guanidine is the compound with the formula HNC(NH2)2. It is a colourless solid that dissolves in polar solvents. It is a strong base that is used in the production of plastics and explosives. It is found in urine predominantly in patients experie ...
. The reagent has also been shown to be reactive towards thiols, many vitamins, the nucleotide base
guanine
Guanine () ( symbol G or Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is c ...
, the
trioses glyceraldehyde
Glyceraldehyde (glyceral) is a triose monosaccharide with chemical formula C3 H6 O3. It is the simplest of all common aldoses. It is a sweet, colorless, crystalline solid that is an intermediate compound in carbohydrate metabolism. The word comes ...
and
dihydroxyacetone
Dihydroxyacetone (; DHA), also known as glycerone, is a simple saccharide (a triose) with formula .
DHA is primarily used as an ingredient in sunless tanning products. It is often derived from plant sources such as sugar beets and sugar cane, an ...
, and some inorganic ions. Copper complexation increases the reactivity of phenols towards this reagent.
This reagent is distinct from
Folin's reagent
Folin's reagent or sodium 1,2-naphthoquinone-4-sulfonate is a chemical reagent used as a derivatizing agent to measure levels of amines and amino acids. The reagent reacts with them in alkaline solution to produce a fluorescent material that can ...
, which is used to detect amines and sulfur-containing compounds.
A 1951 paper entitled "Protein measurement with the Folin phenol reagent" was the most
cited
A citation is a reference to a source. More precisely, a citation is an abbreviated alphanumeric expression embedded in the body of an intellectual work that denotes an entry in the bibliographic references section of the work for the purpose of ...
paper in the 1945–1988
Science Citation Index
The Science Citation Index Expanded – previously entitled Science Citation Index – is a citation index originally produced by the Institute for Scientific Information (ISI) and created by Eugene Garfield. It was officially launched in 1964 and ...
, with 187,652 citations.
Physiologic significance
Because it measures anti-oxidant capacity ''
in vitro
''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called " test-tube experiments", these studies in biology ...
'', the reagent has been used to assay foods and supplements in
food science
Food science is the basic science and applied science of food; its scope starts at overlap with agricultural science and nutritional science and leads through the scientific aspects of food safety and food processing, informing the development ...
. The
oxygen radical absorbance capacity
Oxygen radical absorbance capacity (ORAC) was a method of measuring antioxidant capacities in biological samples ''in vitro''. Because no physiological proof ''in vivo'' existed in support of the free-radical theory or that ORAC provided informat ...
(ORAC) used to be the industry standard for antioxidant strength of whole foods, juices and food additives. Earlier measurements and ratings by the
United States Department of Agriculture
The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of com ...
were withdrawn in 2012 as biologically irrelevant to human health, referring to an absence of physiological evidence for polyphenols having antioxidant properties ''
in vivo
Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...
''.
Consequently, the ORAC method, derived only from ''in vitro'' experiments, is no longer considered relevant to human diets or
biology
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
.
The
Trolox equivalent antioxidant capacity
The Trolox equivalent antioxidant capacity (TEAC) assay measures the antioxidant capacity of a given substance, as compared to the standard, Trolox. Most commonly, antioxidant capacity is measured using the ABTS Decolorization Assay. Other antioxi ...
assay – also based on the presence of polyphenols – is an alternative ''in vitro'' measurements of antioxidant capacity.
See also
*
Gallic acid
Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acid with the formula C6 H2( OH)3CO2H. It is classified as a phenolic acid. It is found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. I ...
References
External links
Folin–Ciocalteu's phenol reagentFluka data sheet. *This link is broken*
{{DEFAULTSORT:Folin-Ciocalteu Reagent
Chemical tests
Analytical reagents