Eco-efficient Recovery and Bioactivity of Polyphenol-rich Extracts from Sawmill by-products of Dialium Polyanthum and Dialium Sp. Nov. from Central Africa

Dialium polyanthum Harms and Dialium sp. nov. are african hardwoods generating large volumes of underexploited sawmill by-products. This study explored their valorization through the extraction and characterization of bioactive compounds, and the evaluation of their antioxidant and antimicrobial properties. Three extraction methods solid-liquid extraction, microwave-assisted extraction (MAE), and ultrasound-assisted extraction (UAE) were compared. UAE emerged as the most efficient and eco-friendly technique, yielding polyphenol-rich extracts with high antioxidant (up to 144 mg TE/g DM) and antimicrobial activities. Phytochemical profiling using GC-MS and HPLC identified key compounds such as catechin, epicatechin, syringic acid, benzoic acid, and -sitosterol, along with unreported metabolites like 1H-indole-2-carboxylic acid. Notably, UAE extracts exhibited strong inhibition against Staphylococcus hemolyticus and Candida albicans, with MICs ranging from 0.4 to 4.0 mg/mL. Multivariate analyses revealed strong correlations between antioxidant activity and the presence of syringic acid, catechins, and other yet-unidentified compounds. This study provides the first phytochemical insights into Dialium sp. nov. and confirms the bioactive potential of Dialium residues, supporting their future use in pharmaceutical and cosmetic applications and contributing to the sustainable valorization of forestry by-products.