Effect of operative variables and kinetic study of butyl butyrate synthesis by Candida rugosa lipase activated by chitosan-reinforced nanocellulose derived from raw oil palm leaves

Abstract

Currently, the chemically-assisted esterification to manufacture butyl butyrate employs corrosive homogeneous acid catalyst and liberates enormous quantities of hazardous by-products which complicate downstream treatment processes. This study aimed to identify the optimized esterification conditions, and the kinetic aspects of the enzyme-assisted synthesis of butyl butyrate using immobilized Candida rugosa lipase activated by chitosan-reinforced nanocellulose derived from raw oil palm leaves (CRL/CS-NC). The best process variables that gave the maximum conversion degree of butyl butyrate by CRL/CS-NC (90.2%) in just 3 h, as compared to free CRL (62.9%) are as follows: 50 °C, 1:2 M ratio of acid/alcohol, stirring rate of 200 rpm and a 3 mg/mL enzyme load. The enzymatic esterification followed the ping pong bi-bi mechanism with substrate inhibition, revealing a ˜1.1-fold higher K_i for CRL/CS-NC (55.55 mM) over free CRL (50.68 mM). This indicated that CRL/CS-NC was less inhibited by the substrates. Butanol was preferred over butyric acid as reflected by the higher apparent Michaelis-Menten constant of CRL/CS-NC for butanol (137 mM) than butyric acid (142.7 mM). Thus, the kinetics data conclusively showed that CRL/CS-NC (V_max 0.48 mM min^-1, K_eff 0.07 min^-1 mM^-1) was catalytically more efficient than free CRL (V_max 0.35 mM min^-1, K_eff 0.06 min^-1 mM^-1).

Keywords: Butyl butyrate; Candida rugosa lipase; Chitosan; Kinetic study; Nanocellulose; Optimization.