Chapter 11 - Total Polyphenols Content and Antioxidant DPPH Assays on Biological Samples

Abstract

The Folin-Ciocalteu (F-C) method, measuring the total polyphenol content (TPC), is the reference assay to measure polyphenols in foods as well as their presence in plasma, urine, and even different organs. 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging assay (DPPH assay) is one of the various analytical methods that have been developed to measure the antioxidant capacity mainly in plant and food extracts. Because both methods have proven to be equally simple, low cost, and highly versatile methods appropriate for measuring the presence and activity of polyphenols, in this chapter we explore their use in biological samples analysis. Up to now, the Folin-Ciocalteu method is the basic and most used method to determine the concentration of total polyphenols in biological samples such as plasma, urine, and animal organs. Even though not so widely used for biological samples, the DPPH test can be a choice for the assessment of the antioxidant activity. To eliminate the protein interference in these measurements, the sample deproteinization by protein precipitation is recommended. Some authors also recommend the extraction of uric acid from the plasma before proceeding with the measurement of antioxidant activity following a high intake of total polyphenols. The use of a solid phase extraction (SPE) procedure, aiming to remove the water-soluble compounds from urine samples, combined with the Singleton and Rossi F-C assay, with certain modifications, provides an effective technique for quantifying the total polyphenols excreted in urine; these results can then be related to polyphenol intake. The contrasting results in correlating the TPC with the antioxidant capacity as measured by the decomposition of the DPPH radical may be due to several factors including poor bioavailability of polyphenols from the intestinal tract and large interindividual variations in polyphenols’ absorption efficiency. With all these, both methods constitute valuable tools in screening the TPC and antioxidant activity in biological samples, generally, with a special recommendation for the laboratory and resource-limited field settings.