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

• Published in: Food chemistry. Molecular sciences Vol. 6; p. 100166
• Main Authors: Martínez-López, Rosalía, Tuohy, Maria G.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 30.07.2023; Elsevier
• Subjects: Algae; Fast Blue BB salt; Folin-Ciocalteu; from the Special Issue ‘Polyphenols in the development of functional foods and impact on health and nutrition in South and Central Americas’ by Cinthia Betim and Lilian Mariutti; Phenolic compounds; Phloroglucinol; Seaweeds; Algae; Folin-Ciocalteu; Phloroglucinol; FBBB; F-D; Phenolic compounds; F-C; Seaweeds; Fast Blue BB salt; PGE; FBBB, fast blue bb salt; F-C, Folin-Ciocalteu; F-D, Folin-Denis; PGE, phloroglucinol equivalents
• ISSN: 2666-5662; 2666-5662
• DOI: 10.1016/j.fochms.2023.100166

•Optical properties of the FBBB interaction with phloroglucinol were investigated.•FC/FBBB ratios of aqueous and ethanoic seaweed extracts ranged from 1.3 to 3.9.•Reaction FBBB and PG to form tri-azo complex is firstly reported.•FBBB method minimized the detection of non-phenolic reducing interferences.•Up to 48 tests (n = 4) in 1 h (0.24€/test) in aqueous and ethanoic seaweeds extracts. 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.