Accurate determination of total biophenols in unfractionated extra-virgin olive oil with the fast blue BB assay

The phenolic compounds of extra-virgin olive oil (EVOO) are key contributors of nutritional and sensory quality as well as chemical stability. The reference method for their determination is the HPLC-UV, which is cost-/time-expensive. In this work, total phenolic compounds were evaluated in unfractionated EVOO adapting the Fast Blue BB (FBBB) assay, which involves the spectrophotometric (absorbance at 420 nm) determination of azo derivatives resulting from the coupling of phenolic compounds with FBBB diazonium salt in alkali pH. When tested on 26 EVOO samples, the FBBB assay and HPLC-determinations were strikingly correlated (R2 = 0.9653), differently from FBBB and Folin-Ciocalteu assays, which showed poor correlation. The assay is simple, repeatable, robust, rapid and cheap, and results might be evaluated on a printed colorimetric scale. This protocol of the FBBB assay could be routinely used to categorize EVOO according to the health claim allowed by EFSA concerning the content of phenolic compounds.