عنوان مقاله [English]
Introduction: There are numerous concerns regarding dietary fat as an additional source of calories, saturated fatty acids, cholesterol, and the association between fat and incidence of cardiovascular disease, cancer and obesity. According lyconsumers tend to use low-calorie and low- fat products such as mayonnaise, yogurt, and egg-free products, while the quality of these products has not changed and is similar to that of high-fat products. Therefore, in case of reduce fat percentage, it is necessary to use compounds that are capable of simulating fat properties. The use of fat substitutes in white sauce will play an important role in producing a high-calorie product. Fat alternatives are mainly based on carbohydrate and protein. Proteins are ideal compounds for simulating fat properties in foods. The transglutaminase enzyme, a protein with a molecular weight of 37, 368 Daltons, contains 331 amino acids that are classified in the group of transferase enzymes (EC 220.127.116.11). It is used to modify the functional properties of proteins in various foods. The function of this enzyme is to bind glutamine amino acid from one protein and lysine amino acid from another protein without adverse effect on biological access of lysine and nutritional value of consequently protein. Purpose: Due to the unique use of transglutaminase enzyme in improving the quality of products, the aim of this study is to evaluate the effect of this enzyme on the production of low fat white sauce and evaluation of physical (thermal and physical stability), rheological (viscosity and shear stress) properties and thermal gravimeteric analysis (free and bonded water) are the product.
Material and methods: To make the sauces, first the flour was poured into the mixer with milkand after complete mixing (45 s) of microbial transglutaminase enzyme with activity 80 units/g was added gradually into the mixer and it was stirred well (one minute), then the butter was added to the mixture and stirring continued for 5 minutes and after emulsion formation and proper texture, the sauce samples were filled in glass containers. In the used treatments, the percentage of fat removal was equal to replacement percentage of milk and flour.The amount of fat reduction was calculated based on the amount of added butter. For this purpose, seven different treatments were produced with different amounts of fat (0, 25, 37.50 and 50 g) and enzyme (100 and 200 ppm). All tests were performed in 3 replications. Duncan test at 5% level was used to compare the mean of treatments. Data were analyzed using GraphPad Prism 5.0 software.
Results and discussion: Minimum and maximum viscosity values were observed in treatments containing 100 and 200 ppm enzymes with 37.50 g fat. High concentrations of transglutaminase enzyme increase the degree of polymerization and and eventually the viscosity increase, compared to the control sample. In this case, the viscosity can increase up to 100 times. The maximum amount of shear stress (166.30 pa) was observed in the treatment containing 100 ppm enzyme with 37.50 g fat. The presence of the transglutaminase enzyme produces polymers with high molecular weightof protein monomers without altering their chemical properties, as a result, the viscosity increases. Reducing the amount of fat in the formulation reduces the shear stress in the final product. The reason for this decrease is attributable to decrease in the viscosity of the product with decrease in fat percentage. By increasing contact level of oil drop, the force of friction between the particles increases, which affects the viscosity. The highest amount of thermal stability (95.10%) and physical stability (95.91%) was obtained in treatments containing 200 ppm enzyme with 37.50 and 0.00 g fat. In thermal and physical stability, cause of increasing percentage of stability in all treatments compared to the control treatment can be attributed to the effect of the transglutaminase enzyme (Protein compound) in cross-linking between protein molecules and creating a coherent network lattice and increased friction that is prevent of phases separation. According to Stoke's law, with increasing viscosity ofcontinuous phase, speed of phase separation will be slower and the emulsion more stable, if the viscosity decreases, the particles move more and leaking water increases. The mechanism of the effect of transglutaminase enzyme on proteins is polymerization, which has led to changes in the hydrophobic molecules of the proteins. Therefore it effects on the functional properties of the enzyme, the solubility effect, gel formation, emulsification, foaming, viscosity and water holding capacity. The treatment containing 200 ppm enzyme with 37.50 g fat had the lowest amount (64.28%) free water. Treatment with 25 g fat containing 100 ppm transglutaminase enzyme had the highest amount of free water. Adding transglutaminase enzyme to foods increases the gel strengthandat the same time, the pores become smaller and texture become denser. More free water is trapped in the gel- like network. Like free water for each treatment, bonded water is reported. But in the 100 and 200 ppm treatments with 37.50 g fat and the 100 and 200 ppm treatments with the lowest fat content, the water content of the bonded water was significantly reduced. Compared to the control treatment, the bonded water decreased significantly. By reducing fat and increasing protein, the protein network is denser and able to bind more water in a given volume.
Conclusion:This study showed that, according to the microbial transglutaminase enzyme has plant origin, it has great potential for practical uses in industryand it can be suggested to sauce manufacturers, especially in the production of mixtures whose fat is reduced, such as formulation of low-calorie white sauce, with maintaining the desired properties.