A carboxylesterase isolated from Aeromonas caviae MTCC 7725 was immobilized by entrapping it in chitosan coated calcium alginate beads. This was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR). The activity of the native and immobilized enzyme was measured at various temperatures, pH levels, and organic solvents. The optimum temperature for activity of the native enzyme was found to be 40 °C and this increased to 50 °C on immobilization. The immobilized enzyme showed enhanced stability and high residual activity in various organic solvents as compared to the free enzyme. An environmentally benign approach was used for the synthesis of ethyl salicylate using the immobilized enzyme. The product obtained was confirmed by GC-MS. The kinetic parameters, such as K m and Vmax, were also determined for the native and immobilized enzyme. The immobilized enzyme retained 50% of its activity after vfie cycles. The immobilized enzyme retained 80% and 40% of its activity at 4 °C and at 37 °C, respectively, at the end of 40 days. The results obtained from our study show that the immobilized enzyme can serve as a robust catalyst for industrial applications.
Keywords: Aeromonas caviae; Carboxylesterase; alginate; chitosan coating; entrapment; esterification; ethyl salicylate; immobilization; organic solvents; reusability.