Lignosulfonate as biosurfactant for the enzymatic conversion of sisal lignocellulosic fiber into fermentable sugars

Lignocellulosic fibers, such as sisal, have been considered a promising solution to increase sustainable energy production. These fibers can be converted into fermentable sugars to produce ethanol. Here, it was investigated how the efficiency of enzymatic hydrolysis of sisal fibers can be improved by adding a biosurfactant. The action of sodium lignosulfonate (SLS) as a biosurfactant was investigated using different concentrations (5.0 g L⁻¹ and 7.5 g L⁻¹). Adding a biosurfactant is expected to decrease the interfacial tension of the reaction medium and improve the interphase reaction between the enzymes and the fibers’ polysaccharides (cellulose and hemicelluloses). In addition, SLS’s high structural similarity with lignin (one of the components of sisal lignocellulosic fibers) leads to interactions between them, which hinders the unwanted interaction of cellulases with lignin, which, when it occurs, negatively impacts the efficiency of enzymatic hydrolysis. The unreacted fibers, withdrawn from the reaction medium during the hydrolysis, showed different morphology, length, and thickness when SLS was used. Regarding sugar production, by using 5.0 g L⁻¹ of SLS, the xylose and glucose production increased. The sugar production decreased at the higher concentration (7.5 g L⁻) of SLS, probably because this macromolecule and cellulose competed to interact with the enzymes, leading to the ineffective interactions between SLS and cellulases. This study, unprecedentedly, showed that SLS, a product obtained from wood pulping, can increase sugar production from a non-woody source such as sisal.