Ultrasound pretreatment as a novel approach for intensification of lipase catalyzed esterification of tricaprylin

The current work deals with ultrasound assisted intensification of synthesis of tricaprylin based on the enzyme catalyzed reaction of caprylic acid and glycerol with novel approach of using ultrasound in only the initial stages of the reaction. Two types of immobilized lipases as Lipozyme RM (Rhizomucor miehei) and Novozym 435 (Candida antarctica) have been used in the work. The effect of ultrasonic conditions such as treatment time and power as well as the reaction conditions such as substrate molar ratio, reaction time and enzyme loading on the yield of tricaprylin has been investigated. It was established that the optimum pretreatment conditions were irradiation time as 30 min with ultrasonic frequency of 20 kHz, supplied power of 240 W, 70% duty cycle (7 s on 3 s off cycle) whereas the optimum reaction conditions were 4:1 molar ratio of caprylic acid to glycerol, enzyme loading as 3% and operating temperature of 50 °C. It was also established that reuse of enzymes for 10 cycles was possible without any significant effect on the activity of lipase. It was also conclusively established that compared to the conventional approach of synthesis, ultrasound pretreatment based approach greatly influenced the rate of reaction and maximum tricaprylin yield of 94.8% was achieved in 7 h of reaction time under the optimum conditions.