pH-mediated hydrolysis alters phenolic profiles and biological functions of brown seaweeds

Phenolic compounds in brown seaweeds remain poorly characterized due to their complex associations with cell wall components. This study investigated the effects of pH-mediated hydrolysis (pH 1, 4, 10, and 13) on the release, composition, and bioactivities of bound phenolics from Ascophyllum nodosum, Fucus vesiculosus, and Ecklonia radiata, with their phenolic fractions as baselines. Phenolic content was quantified using complementary assays, and antioxidant, anti-diabetic, and anti-inflammatory activities were evaluated in vitro. Untargeted LC/Q-TOF MS profiling revealed pronounced pH- and species-dependent compositional differences. Alkaline hydrolysis (pH 10-13) released phenolic assemblages with superior radical scavenging and α-amylase inhibitory activity, whereas acidic conditions (pH 1-4) yielded phenolics with enhanced anti-inflammatory efficacy. This pattern demonstrated that extraction pH governs not merely phenolic yield but the functional identity of the liberated fraction. Correlation network analysis further confirmed the selective liberation of functionally coordinated phenolic assemblages upon hydrolysis.