EFFECT OF MICROBIAL TRANSGLUTAMINASE TREATMENT ON SOFT CHEESE PROPERTIES

Abstract

Microbial transglutaminase (MTGase) was isolated from the bacteria Streptoverticillium mobaraense and used to improve the yield and properties of soft cheese manufactured from cow milk by enhancing the cross-linking reaction among milk proteins. The enzyme was applied at different concentrations and at various addition times. Results indicated that the addition of the enzyme before rennet prevented milk coagulation while the simultaneous addition of MTGase and the rennet significantly decreased curd strength and cheese hardness and increased the loss of proteins and fat in the whey. It was found that the most suitable way of adding the enzyme was after coagulation and curd cutting. This treatment enhanced the cross-linking of whey proteins with the curd proteins which was proportional to the concentration of the added enzyme up to 60 enzyme units/liter. The cross-linking reaction was verified by SDS-PAG electrophoresis experiment which showed a high molecular weight band accompanied by a decrease in the density of α s -casein, β-casein and whey proteins bands. Transglutaminase affected the produced cheese composition noticeably by increasing protein content, total solids and decreasing the protein content of the whey. Sensory evaluation of the obtained product showed that the enzyme treated cheese was superior to the untreated cheese throughout all storage period (8 days). INTRODUCTION Cheese production is rising sharply and so is whey. Several billion pounds of fluid whey are produced annually as a by-product all around the world. It is not efficiently utilized and more than 80% of this whey ends up as pollutant. In conventional processes for cheese making, a considerable amount of protein is lost with the whey, as protein is a valuable component of milk and milk products. One of the efforts to reduce cost of cheese production has been to keep the whey proteins from being lost in the manufacturing process. Several methods have been proposed to recover whey proteins. They included the concentration or drying the whey proteins and adding it to the cheese curd, heat or pressure treatment of the milk, and concentration of the milk by ultrafiltration, evaporation or reverse osmosis (Ernstrom et al., 1980; Hinrichs, 2001; Kosikowski, 1977; Lo and Bastian, 1998; O'Reilly et al., 2001). Most of these methods are inefficient due to the lost of whey proteins during curd pressing stage. One of the most attractive methods of recovering whey proteins is the enzymatic treatment of milk or curd with transglutaminase which links whey proteins with curd proteins leading to a noticeable increase in protein and yield of the cheese accompanied by a decrease in whey protein content. This treatment has economical, nutritional and environmental importance.