Comparison of three methods for quantifying brown algal polyphenolic compounds

Area of Science:

• Marine Biology
• Analytical Chemistry
• Phytochemistry

Background:

• Accurate quantification of total phenolic compounds in marine brown algae is crucial for understanding their biological activities and ecological roles.
• Existing methods for phenolic compound analysis can be affected by interfering substances, such as proteins, impacting measurement accuracy.
• Marine algae, particularly brown algae, are rich sources of phenolic compounds with diverse applications.

Purpose of the Study:

• To compare the accuracy and reliability of three distinct methods for quantifying total phenolic compounds in marine brown algae.
• To evaluate the interference of proteins, specifically bovine serum albumin (BSA), on phenolic compound measurements using different assay conditions.
• To determine the most suitable assay for precise phloroglucinol quantification in the presence of interfering biomolecules.

Main Methods:

• Comparison of three quantification methods: Folin-Ciocalteu assay in 80% methanol, Folin-Ciocalteu assay in 75% methanol-25% trichloroacetic acid (TCA), and a polyvinylpolypyrrolidone (PVPP) precipitation assay.
• Known concentrations of phloroglucinol were measured in the presence of bovine serum albumin (BSA) to assess method performance and protein interference.
• Analysis of the impact of TCA on solution pH and protein solubility, and assessment of PVPP's effectiveness in removing phenolic compounds.

Main Results:

• The Folin-Ciocalteu assay using 80% methanol yielded the most consistent results and exhibited the least interference from BSA.
• The presence of TCA decreased solution pH and increased protein interference in the Folin-Ciocalteu assay, particularly at high protein concentrations.
• The PVPP assay demonstrated unreliable phloroglucinol removal, with results varying significantly based on phloroglucinol concentration.

Conclusions:

• The Folin-Ciocalteu assay in 80% methanol is the recommended method for accurately quantifying total phenolic compounds in marine brown algae, offering superior consistency and minimal protein interference.
• Trichloroacetic acid (TCA) can exacerbate protein interference in phenolic assays, compromising measurement accuracy.
• While the 80% methanol Folin-Ciocalteu assay may quantify minor nonphenolic substances, their contribution is minimal in species like Fucus gardneri (≤5%).