Ionic Liquid-Based Extraction of Fulvic-like Substances from Wood Sawdust: Reproducing Unique Biological Activities of Fulvic Acids Using Renewable Natural Sources

Fulvic acids (FAs) have been commercially used in cosmetics and agronomy due to their unique biological activities, such as plant stimulation and anti-inflammatory effects. However, the extraction sources of FAs, such as peat, are currently limited. Consequently, new extraction methods using renewable resources need to be developed, while reproducing the biological functions. Here, ionic liquids (ILs) effectively extracted fulvic-like substances (FLSs) from wood sawdust. The overall molecular weight distributions of FLSs were similar to those of commercial FAs, and key organic groups (e.g., aromatic, phenolic, and methoxy groups) were also found to be shared between commercial FAs and FLSs. Detailed compositional analysis revealed by high-resolution mass spectrometry showed that the extracts contain both lignin-like and lipid-like molecules, while commercial FAs are biased toward lignin-like and carbohydrate-like molecules. FLSs generally showed better and similar performance in radical scavenging activity against ABTS+· and H2O2. Fibroblast proliferation and lettuce growth enhancements were also observed with the extract containing 1-ethyl-3-methylimidazolium acetate and triethylammonium hydrogen sulfate, respectively, which performed better than commercial FAs. Immunofluorescence staining of in vitro human follicle dermal papilla cells supports that coexpression of hair growth-related proteins can be accelerated with FLSs, and this effect was further evidenced by in vivo mouse model experiments. Finally, the reusability of ILs in the extraction process was confirmed by analyzing the structural features of FLSs from each recycling. Our findings indicate that ILs are useful for obtaining biologically functional fulvic analogs from renewable plant sources.