Unlocking xylan’s potential: Coffee husk-derived xylanolytic blend for sustainable bioprocessing

Abstract

Xylanolytic enzymes cleave the β-1,4-glycosidic bonds within xylan, the primary polymer found in the hemicellulosic fraction of lignocellulosic biomass, converting it into xylose. This enzymatic class holds significant applications in various biotechnological processes, particularly within the pharmaceutical, food, and bioenergy industries. This study focuses on a cost-effective method for producing a xylanolytic blend (XB) through the solid-state fermentation of the low-cost coffee husk (CH) by-product, using Penicillium roqueforti ATCC 10110. Optimal bioprocess conditions were identified at 59% humidity and 16 °C, resulting in xylanolytic activity of 13.20 U/g. The XB exhibited favorable thermostability at 40 °C, with maximum activity at 50 °C and pH 5. The effect of solvents revealed significantly enhanced activity with dichloromethane and hexane. The presence of metallic salts, including Pb(C₂H₃O₂), Na₂CO₃, KCl, FeSO₄, CuSO₄, MgSO₄, and ZnSO₄, led to more than a 100% increase in enzyme activity, with Na₂CO₃ demonstrating an outstanding 229.9% enhancement. Similarly, other organic compounds such as EDTA, SDS, Triton X-100, and Trolox significantly increased enzymatic activity (+ 286.69% for Triton X-100), while other salts such as CaCO₃, MgCl₂, and Al(NO₃)₃ led to inhibition. These results differ from previous reports of xylanases from this microorganism and position the developed XB as a promising sustainable catalyst for the saccharification of CH. The bio-based recycling approach elevates the value of CH and proposes an alternative to conventional fertilizer use. The basis developed here serves as guidelines for further investigations exploring the XB application in high-grade pharmaceuticals, food, and bioenergy in large-scale scenarios.