Untargeted Metabolomics Reveals the Diverse Phytochemical Composition of Black Wattle Bark (Acacia mearnsii De Wild) Beyond Tannins

This study applied untargeted metabolomics to investigate the metabolite diversity of Acacia mearnsii (Black Wattle) bark extracts using different solvents. Additionally, it aimed to characterize the proanthocyanidin profile of Black Wattle bark cultivated in southern Brazil. The findings demonstrated that solvent choice significantly influences metabolite extraction and composition. The most pronounced differences were observed between water-based and organic solvent extractions, with organic solvents proving more effective. Among them, 50% and 70% acetone, as well as 70% methanol, yielded the highest metabolite abundances. Annotated compounds included organic acids, phenolic compounds, and coumarins, with several phenolics, such as naringenin, and liquiritigenin, annotated in Black Wattle bark for the first time. These results highlight the richness of its extracts in bioactive compounds, demonstrating a chemical complexity that extends beyond proanthocyanidins and may influence their biological properties. The extracts contained a diverse range of proanthocyanidins, up to pentamers. Monomers such as (epi)catechin and (epi)gallocatechin were identified, while the oligomers were predominantly prorobinetinidins, consisting of catechin or gallocatechin as starter units and robinetinidol or fisetinidol as extender units. The presence of a wide range of bioactive compounds underscores the potential of Black Wattle bark extracts for applications in the food and feed industries.