Kinetic aspects of ultrasound-accelerated lipase catalyzed acetylation and optimal synthesis of 4′-acetoxyresveratrol

Ultrasonic assistance of lipase (Candida antarctica; Novozym® 435) catalyzed synthesis of 4′-acetoxyresveratrol from resveratrol and vinyl acetate was investigated. Response surface methodology and a three-level-three-factor Box-Behnken design were adopted to evaluate the effects of synthesis variables, including reaction time (4–12 h), enzyme amount (2500–4500 PLU), and ultrasonic power (90–150 W) on the percentage molar conversion of 4′-acetoxyresveratrol. Based on ridge max analysis, the optimum conditions for synthesis were: reaction time 10.78 h, enzyme amount 5492 PLU, and ultrasonic power 147.8 W. With ultrasound assistance, not only the phenolic compound acetylation time decreased, but also a high yield (95.2%) was achieved. The reaction kinetic model agreed with Ping–Pong mechanism, and the apparent kinetic constant V m ′ / K 2 ratio related to enzyme performance was 2.4 times higher in the ultrasound-assisted reaction than in the mechanical-mixing reaction. The apparent kinetic constant K2 indicated that ultrasound enhanced the vinyl acetate affinity to the enzyme. The simplified Ping–Pong kinetic model was employed to simulate 4′-acetoxyresveratrol production in batch reaction. It was found that a good prediction existed between the fitting results and the experimental data.