Thermal inactivation kinetics of microencapsulated microbial transglutaminase by ultrasonic spray-freeze drying

Partially purified microbial transglutaminase (mTG) was microencapsulated by ultrasonic spray-freeze drying (USFD) as a novel method, using a 48 kHz ultrasonic nozzle. The microencapsulated samples, which used a mixture of inulin and gum arabic as coating materials, were compared to microencapsulated samples by conventional freeze-drying (CFD) and conventional spray drying (CSD) in terms of thermal stability. Thermal inactivation kinetics of the microencapsulated and as well as crude enzymes obtained by USFD process (USFD-crude) were evaluated according to first-order reaction kinetics in the range of 40-60 degrees C at different pH values (5.0-7.0), and the activation energy (E-a, kJ/mol) and free energy for thermal inactivation (Delta G, kJ/mol) were calculated. Furthermore, the specific surface area (SSA, m(2)/g) of the samples was determined, and a relationship between SSA and thermal stability was established. The results showed that the thermal stability of micro encapsulated mTG by USFD was higher than all samples, having smaller rate constants and E-a values with higher half-life times and Delta G values. In addition, the thermal stability of the samples decreased when the SSA increased, as in USFD-crude and CSD samples.