New Method To Estimate Total Polyphenol Excretion: Comparison of Fast Blue BB versus Folin–Ciocalteu Performance in Urine

Polyphenols are bioactive substances of vegetal origin with a significant impact on human health. The assessment of polyphenol intake and excretion is therefore important. The Folin–Ciocalteu (F–C) method is the reference assay to measure polyphenols in foods as well as their excretion in urine. However, many substances can influence the method, making it necessary to conduct a prior cleanup using solid-phase extraction (SPE) cartridges. In this paper, we demonstrate the use of the Fast Blue BB reagent (FBBB) as a new tool to measure the excretion of polyphenols in urine. Contrary to F–C, FBBB showed no interference in urine, negating the time-consuming and costly SPE cleanup. In addition, it showed excellent linearity ( r 2 = 0.9997), with a recovery of 96.4% and a precision of 1.86–2.11%. The FBBB method was validated to measure the excretion of polyphenols in spot urine samples from Spanish children, showing a good correlation between polyphenol intake and excretion.