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.[3] The reagent has also been shown to be reactive towards thiols, many vitamins, the nucleotide base
guanine, the
triosesglyceraldehyde and
dihydroxyacetone, and some inorganic ions. Copper complexation increases the reactivity of phenols towards this reagent.[4]
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"[5] was the most
cited paper in the 1945â1988
Science Citation Index, with 187,652 citations.[6]
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.[7][8] 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United States Department of Agriculture were withdrawn in 2012 as biologically irrelevant to human health, referring to an absence of physiological evidence for polyphenols having antioxidant properties in vivo.[9] Consequently, the ORAC method, derived only from in vitro experiments, is no longer considered relevant to human diets or
biology.
^Ikawa M, Schaper TD, Dollard CA, Sasner JJ (2003). "Utilization of FolinâCiocalteu phenol reagent for the detection of certain nitrogen compounds". J. Agric. Food Chem. 51 (7): 1811â5.
doi:
10.1021/jf021099r.
PMID12643635.
^Ou B, Hampsch-Woodill M, Prior R (2001). "Development and validation of an improved oxygen radical absorbance capacity assay using fluorescein as the fluorescent probe". J Agric Food Chem. 49 (10): 4619â26.
doi:
10.1021/jf010586o.
PMID11599998.
^Prior R, Wu X, Schaich K (2005). "Standardized methods for the determination of antioxidant capacity and phenolics in foods and dietary supplements". J Agric Food Chem. 53 (10): 4290â302.
doi:
10.1021/jf0502698.
PMID15884874.