Optimization of fermentation conditions for cellulase/xylanase production and hydrolysis conditions for efficient conversion of agricultural residues using Penicillium oxalicum UNN1

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.