Optimization of microencapsulation conditions of transglutaminase by freeze drying.

Transglutaminase (TG), which is an important enzyme for food processing, can enhance the firmness, viscosity and water binding capacity of food products by catalyzing the cross-linking reaction of proteins. Since preservation of the enzyme activity is essential, the production of microencapsulated powder form of TG can be a great challenge to maintain its initial activity. In this study, TG was microencapsulated using a freeze drying technique and the effects of homogenization conditions and coating material ratios on the enzyme activity were investigated using D-optimal combined design. Mannitol, gum arabic and casein were chosen as coating materials and different homogenization times (1-5 min) and homogenization rates (11,200-20,000 rpm) were applied. The optimum conditions which ensure the maximum enzyme activity have been determined as 11,200 rpm of homogenization rate, 1.27 min of homogenization time, and in addition a mixture of mannitol, gum arabic and casein with ratios 38.2, 40.2, and 21.6%, respectively. Most of the activity loss occurred in the homogenization stage and the coating materials preserved enzyme activity during freeze drying. At the optimum point, the remaining activity of the microencapsulated TG was 93% while that of the crude (without coating materials) TG was 64% at the same drying conditions. Moreover, the effects of the microencapsulation conditions on the physical properties of powder such as moisture content, color, particle, bulk and tapped densities, porosity and flowability were determined.