Effects of Ultrasound on the Kinetics and Thermodynamics Properties of Papain Entrapped in Modified Gelatin

Abstract Papain is one of the most promising proteases for hydrolysis and the immobilized papain is widely used in the food industry. The aim of the study was to investigate the effect of different ultrasound conditions on the kinetics and thermodynamics of enzymatic reactions of papain entrapped in modified gelatin. The diffusion of methyl orange pigment in modified gelatin gel was explored to establish the diffusion kinetics of modified gelatin. Results showed that the temperature and ultrasonic had significant effects on the catalytic reaction between papain entrapped in modified gelatin and casein. Kinetics analysis proved that the catalytic reaction of immobilized papain and the release of methyl orange pigment from modified gelatin followed the first order kinetics. The thermodynamic analysis showed that the apparent activation energy, enthalpy and activation free energy were the lowest at 135 kHz and 0.15 W/cm2, which proved that the optimal conditions for the enzymatic hydrolysis of immobilized papain entrapped in modified gelatin gel were 135 kHz and 0.15 W/cm2. The impact of ultrasound on the diffusion showed that the effect of ultrasonic-assisted treatment on the diffusion coefficient (De) of methyl orange pigment in modified gelatin gel was greater than that of ultrasonic pretreatment. In addition, the influence of ultrasonic power on the De was greater than that of ultrasonic frequency. This study reveals ultrasound treatment could accelerate the spontaneous reaction of the enzymatic reaction. This study is important to explain the hydrolysis reaction of immobilized papain to control the progress of the hydrolysis during ultrasound treatment.