초록
Feruloyl esterase plays an indispensable role in hydrolyzing plant cell walls, and ferulic acid will be released as by-product, which has potential applications in food and medicine industry. This study presents immobilization of partially purified feruloyl esterases from the fermentation liquor of recombinant Pichia on magnetic Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles. Furthermore, the optimal conditions for the immobilization and some characteristics of immobilized enzyme were studied. The optimal immobilization conditions observed were enzyme 0.2 mg (1 mg/mL, 0.2 mL), magnetic Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles 4 mg, pH 6.0, immobilization time 3 h. The results showed that the optimal reaction temperature of immobilized enzyme was increased from 45<SUP>o</SUP>C to 55<SUP>o</SUP>C. Thermal stability of the immobilized enzyme also had an improvement, the residual activity retained 80% and 69% after 120 h at 40<SUP>o</SUP>C and 50<SUP>o</SUP>C, respectively, while free enzymes only showed 45% and 40% remnant activity at the same condition. The immobilized enzyme also exhibited good operational stability and 52.4% of its initial activity was observed during the fifth cycle. In terms of the thermal and operational stability, the immobilized enzyme could be better used in many more applications than the free enzymes. At last the destarched wheat bran was taken as substrate for immobilized and free feruloyl esterases to produce ferulic acid, the maximum ferulic acid yield was 11.2% and 12.3%, respectively, indicating a great potential in industrial application.