Abstract Agricultural residues like sugarcane bagasse and rice straw are rich in cellulose and xylan. Their efficient conversion into (oligo)saccharides and value-added products requires microbial cellulases and xylanases, but low enzyme yields and high production costs hinder industrial application. This study isolated Penicillium oxalicum UNN1, a high-xylanase-producing strain with an initial activity of 51.63 U/mL. Submerged fermentation conditions were optimized using different carbon/nitrogen sources to enhance enzyme production. The optimized xylanase activity reached 191.22 U/mL (sugarcane bagasse xylan as sole carbon source) and 142.32 U/mL (combined with Avicel), with filter paper cellulase activity of 0.76 U/mL. The crude enzymes exhibited optimal activity at pH 5.0 and 50 °C. Cellulase retained over 75% activity after 7 h at pH 4.0–6.0 (4 °C) or 40 °C (pH 5.0), while xylanase activity remained nearly unchanged, even after over 21 days of storage at 4 °C (pH 5.0). However, the half-life of xylanase was less than 1 h at 50 °C, though it exceeded 72 h at 40 °C (pH 5.5). 3–5 mM Ca²⁺ and Cu²⁺ strongly inhibited both enzymes. Crude enzyme addition (about 7 U cellulase and 1,400 U xylanase) effectively enhanced reducing sugar production from agricultural residues. Single-factor and response surface optimization yielded optimal hydrolysis conditions: 480 U/g sugarcane bagasse xylan of xylanase, hydrolysate pH of 5.5, hydrolysis temperature of 40 °C, achieving a maximum reducing sugar yield of 0.355 g/g dry biomass. This work demonstrates the potential of P. oxalicum UNN1 enzymes for efficient and stable saccharification of agricultural residues, offering a viable approach for their valorization and environmental management. Graphical Abstract
Zhong et al. (Thu,) studied this question.