Evaluation of Novel Rapid Analytical Methods to Categorize Extra Virgin Olive Oil Based on the Coulometrically Determined Antioxidant Capacity and on the Spectrophotometric Assessment of Phenolic Compounds.

The lack of a practical "fit for the purpose" analytical protocol is the main limitation that has hampered the exploitation of the EFSA analytical health claim on the extra virgin olive oil (EVOO) biophenols, more than ten years since its introduction. In this work, two analytical methods recently developed in our laboratories for categorizing EVOO have been evaluated on a set of 16 samples from Cilento (Campania Region, southern Italy) and compared to other commonly used quality indexes. The Coulometrically Determined Antioxidant Capacity (CDAC) is associated with the component responsible for the health-promoting properties and oxidative stability of EVOO. The Fast Blue BB (FBBB) assay consists of the spectrophotometric (420 nm) determination of biophenols-FBBB diazonium coupling products generated in unfractionated EVOO. The FBBB assay and HPLC-UV reference method provide values highly correlated to each other. Fourteen of sixteen EVOO samples with CDAC > 10 mmol kg-1 and FBBB absorbance > 0.5 had HPLC-determined biophenols > 250 mg kg-1, and therefore eligible for the EFSA health claim. Consistently, two EVOO samples with HPLC-determined biophenols < 250 mg kg-1 had CDAC values and FBBB absorbance below the respective thresholds. CDAC and FBBB assays are proposed individually or in combination as methods to categorize EVOO samples in alternative to HPLC-UV.

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.