I was analysing a paper for an article I was doing for Nourish Magazine and noticed this comment:
"...by using the Folin–Ciocalteu assay, which is largely adopted to estimate the overall amount of phenolic compounds. It is well known that the phenolic determinations based on such reagents may often over-estimate phenolic concentration because many non-phenolic substances (for example, vitamin C or protein carbonyls) having reducing ability also give a positive reaction.
Nevertheless, the Folin–Ciocalteu assay has been widely applied for the analysis of phenolic compounds in vegetables and it is still useful to compare data from different studies..."
Would be interested to get your thoughts? Thanks.
Dear Susan,
Go to the below link that provides comprehensive answers to your question.
http://www.scepscoridea.org/southeastideameeting/Presentations/BC-O5%20Wangila.pdf
The reagent is not specific to phenolics alone. It also reacts with a number of non-phenolic compounds.
Hope this information is useful
Indeed it is known that the original F-C assay, developed in 1927, is not selective towards phenolics. However certain modifications (reagent complex,pH and detection wavelength) were made which renders the assay more specific (Singleton, V. L.; Rossi, J. A. Colorimetry of total phenolics with phosphomolybdic-phosphotungstic acid reagents. Am. J. Enol. Vitic. 1965, 16, 144-158). However, some interferences still exist (Everette, J. D., Bryant, Q. M., Green, A. M., Abbey, Y. a, Wangila, G. W. and Walker, R. B. 2010. Thorough study of reactivity of various compound classes toward the Folin-Ciocalteu reagent. Journal of agricultural and food chemistry 58 (14): 8139–8144.) Nevertheless, the assay proves its usefulness in many plant extracts as phenolics are often the major contributors to overall antioxidant activity. In some cases, interference of ascorbic acid has been overcome by thermal treatment of the samples (Georgé, S., Brat, P., Alter, P. and Amiot, M. J. 2005. Rapid determination of polyphenols and vitamin C in plant-derived products. Journal of agricultural and food chemistry 53 (5): 1370–1373.).
I agree with the answers given here. That's why if possible, you do F-C assay along with phytochemical screening and characterization. That way, you can also detect other phytochemicals present in your samples.