Integrated Microbial Bioprocessing of Soybean Hulls for Xylanolytic Enzymes, Xylooligosaccharides, and Cellulose Production from Soybean Hulls

Introduction: Xylooligosaccharides (XOS), valuable prebiotics derived from xylan, hold significant potential in the food and pharmaceutical industries. Traditional methods for XOS production involve the pretreatment of lignocellulosic biomass followed by enzymatic hydrolysis, but these approaches often require harsh chemicals, leading to toxic byproducts, higher costs, and unsustainable practices. Enzymatic hydrolysis, while greener, faces challenges with purification and recovery costs. Soybean hulls (SBH), a by-product of the soy-processing industry, present a promising alternative due to their low lignin content, enabling mild processing for the fractionation of cellulose and hemicellulose.

Objective: In this study, we aimed to leverage fungi as a green bioprocess to produce XOS from the hemicellulosic fraction of SBH, alongside cellulose separation.).

Methods: SBH-derived xylan was extracted using alkali followed by ethanolic precipitation, and the structure was analyzed using FTIR, comparing it with commercial xylan and cellulose standards. The SBH-derived xylan and raw SBH were fermented with Aureobasidium pullulans (Ap) and Aspergillus niger (An) for 6 days, with sampling every 24 hours. Supernatants were analyzed for endoxylanase activity (DNS method) and XOS content (HPLC). Preliminary findings showed that heat sterilization of SBH increased xylan yield by 56.44%. The FTIR spectra of SBH-derived xylan and cellulose aligned with commercial standards. Compared to Ap, higher xylanase activity was observed in An fermentations across substrates, with the maximum activity (197 U/ml) recorded on day 3. Quantification of XOS and analysis of their prebiotic activity are ongoing.

Significance: This study demonstrates an integrated bioprocessing approach for SBH valorization, yielding xylanolytic enzymes, XOS, and cellulose, which have multiple potential applications across industries.