Improvement of Yogurt Properties by Microbial Transglutaminase

Yogurt was manufactured from cow s milk which was treated with different concentrations of free and immobilized Streptoverticillium mobaraense transglutaminase. The highest pH and lowest titratable acidity during three weeks of storage were detected in the sample treated with 75 U/l of free transglutaminase before starter addition. The concomitant MTGase treatment with starter addition resulted in significant increase in yogurt gel strength and viscosity and decreased water separation. This effect was continued during storage at 4 ?C. The effect of enzymatic treatment with 45 U/l almost resembled that of adding 3% of skimmed milk powder. Immobilized MTGase treatment had less effects on yogurt properties. Sensory evaluation of yogurt showed that treated samples were superior to untreated sample in all sensory aspects through storage periods. To reveal the occurrence of cross-linking among protein molecules, SDS-PAG electrophoresis was performed for yogurt proteins. New high molecular weight protein bands had occurred accompanied by decreasing in casein and whey proteins bands density.