Rapid and cost-efficient microplate assay for the accurate quantification of total phenolics in seaweeds

Rosalía Martínez-López; Maria G Tuohy

doi:10.1016/j.fochms.2023.100166

Rapid and cost-efficient microplate assay for the accurate quantification of total phenolics in seaweeds

Food Chem (Oxf). 2023 Feb 20:6:100166. doi: 10.1016/j.fochms.2023.100166. eCollection 2023 Jul 30.

Authors

Rosalía Martínez-López¹, Maria G Tuohy¹

Affiliation

¹ School of Biological and Chemical Sciences, and Ryan Institute, National University of Ireland, Galway, Ireland.

Abstract

Brown seaweeds (Phaeophyceae) are a rich source of polyphenols (up to 20% dry weight) with a structure based on phloroglucinol (1,3,5-trihydroxybenzene). To-date the determination of total phenolics content (TPC) involves a redox reaction with the Folin-Ciocalteu (FC) reagent. However, side reactions with other reducing substances preclude accurate, direct measurement of TPC. This research reports a novel microplate assay involving a coupling reaction between phloroglucinol with Fast Blue BB (FBBB) diazonium salt, at basic pH, to form a stable tri-azo complex with maximum absorbance at 450 nm. Linear regression correlation values (R²) were ≥0.99 with phloroglucinol as standard. Direct quantification of TPCs (phloroglucinol equivalents, PGEs) in crude aqueous and ethanolic extracts from A. nodosum demonstrated that the new FBBB assay is not subject to side-redox interference and provides a more accurate estimate of TPC (1.2-3.9-fold lower than with the FC assay) in a relatively rapid (30 min), cost-effective (0.24€/test) microplate format.

Keywords: Algae; F-C, Folin-Ciocalteu; F-D, Folin-Denis; FBBB, fast blue bb salt; Fast Blue BB salt; Folin-Ciocalteu; PGE, phloroglucinol equivalents; Phenolic compounds; Phloroglucinol; Seaweeds.