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''
assay
An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of a ...
of phenolic and
polyphenolic
antioxidant
Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...
s, also called the gallic acid equivalence method (GAE). It is named after
Otto Folin,
Vintilă Ciocâlteu, and
Willey Glover Denis
Willey Glover Denis (February 26, 1879 – January 9, 1929) was an American biochemist and physiologist. She was noted particularly for her collaborations with Otto Folin, including studies of protein metabolism. She was a pioneer in the field ...
. The Folin-Denis reagent is prepared by mixing
sodium tungstate and
phosphomolybdic acid in
phosphoric acid. The Folin–Ciocalteu reagent is just a modification of the Folin-Denis reagent. The modification consisted of the addition of
lithium sulfate and
bromine 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, and will also react with some nitrogen-containing compounds such as
hydroxylamine and
guanidine. The reagent has also been shown to be reactive towards thiols, many vitamins, the nucleotide base
guanine, the
trioses glyceraldehyde and
dihydroxyacetone, and some inorganic ions. Copper complexation increases the reactivity of phenols towards this reagent.
This reagent is distinct from
Folin's reagent, 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 paper in the 1945–1988
Science Citation Index, with 187,652 citations.
Physiologic significance
Because it measures anti-oxidant capacity ''
in vitro'', the reagent has been used to assay foods and supplements in
food science. The
oxygen radical absorbance capacity (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 were withdrawn in 2012 as biologically irrelevant to human health, referring to an absence of physiological evidence for polyphenols having antioxidant properties ''
in vivo''.
Consequently, the ORAC method, derived only from ''in vitro'' experiments, is no longer considered relevant to human diets or
biology.
The
Trolox equivalent antioxidant capacity assay – also based on the presence of polyphenols – is an alternative ''in vitro'' measurements of antioxidant capacity.
See also
*
Gallic acid
References
External links
Folin–Ciocalteu's phenol reagentFluka data sheet. *This link is broken*
{{DEFAULTSORT:Folin-Ciocalteu Reagent
Chemical tests
Analytical reagents