Improvement of lipase biochemical properties via a two-step immobilization method: Adsorption onto silicon dioxide nanoparticles and entrapment in a polyvinyl alcohol/alginate hydrogel.

In this study, the factors affecting lipase adsorption onto SiO nanoparticles including SiO nanoparticles amounts (8, 19 and 30 mg/mL), lipase concentrations (30, 90 and 150 μg/mL), adsorption temperatures (5, 20 and 35 °C) and adsorption times (1, 12.5 and 24 h) were optimized using central composite design. The optimal conditions were determined as a SiO nanoparticles amount of 8.5-14 mg/ml, a lipase concentration of 106-116 μg/mL, an adsorption temperature of 20 °C and an adsorption time of 12.5 h, which resulted in a specific activity and immobilization efficiency of 20,000 (U/g protein) and 60 %, respectively. The lipase adsorbed under optimal conditions (SiO-lipase) was entrapped in a PVA/Alg hydrogel, successfully. FESEM and FTIR confirmed the two-step method of lipase immobilization. The entrapped SiO-lipase retained 76.5 % of its initial activity after 30 days of storage at 4 °C while adsorbed and free lipase retained only 43.4 % and 13.7 %, respectively. SiO-lipase activity decreased to 34.43 % after 10 cycles of use, while the entrapped SiO-lipase retained about 64.59 % of its initial activity. Compared to free lipase, the K values increased and decreased for SiO-lipase and entrapped SiO-lipase, respectively. V value increased for both SiO-lipase and entrapped SiO-lipase.