Rice Husk Alkali Lignin: Characterization and Evaluation of Its Antibacterial Limitations

Rice husk (RH), a major byproduct of rice production, represents a significant environmental burden due to its high volume and common disposal through open burning. This study explores the potential of alkali-extracted lignin from Dominican rice husk (RHL) as a value-added bioproduct, with a focus on its characterization and antibacterial properties. Lignin was extracted using alkaline digestion from two rice varieties (Juma 69-20 and Prosequisa 4), and characterized via UV-Vis and FTIR spectroscopy. Extraction yields ranged from 18–23%, with no significant differences among varieties. Further optimization using Juma 69-20 showed that higher temperature (100°C) and smaller particle size (850–425 µm) significantly enhanced lignin recovery, with a maximum yield of 37.6%. Pretreatment had no significant effect. Spectroscopic analysis confirmed the presence of key lignin functional groups, although high oxidation levels and a predominance of ether bonds were noted. Despite literature reports of antimicrobial activity in lignin, RHL showed no inhibitory effects against ten bacterial strains. This may be due to unfavorable structural traits or particle size heterogeneity. Future work should focus on alternative extraction techniques and improved control over lignin structure to enhance its functional potential. This research supports the valorization of RH as a sustainable resource in biotechnological applications.