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IntroductionDoogh is a fermented dairy product that is produced by blending yogurt with water and some salt. This fermented beverage is widely consumed as a refreshing drink in Iran and other Middle East countries. Doogh is a source of calcium needed by the body on a daily basis and contains B vitamins that are effective in the health and strength of teeth and bones. In addition, doogh contains a low percentage of fat, which makes it a diet drink. Whey Protein Concentrate (WPC) is a product contains 25 to 89% protein and different amounts of lactose, fat and minerals. Due to the functional properties of whey protein and its nutritional value; whey protein is widely used in dairy products. The development of cross-linking bonds between protein chains by enzymes is very important today. Enzyme cross-linking of proteins can affect some of their functional properties such as solubility, water absorption, rheological and emulsifying properties. One of the most widely used enzymes in the food industry is the transglutaminase enzyme. In this study the effects of WPC in three levels (0%,1% and 2%) and the transglutaminase enzyme in two levels (0 and 1 unit per gram of milk protein) in two method of dough preparation (adding water to yogurt and fermented milk diluted with water) on rheological characteristics, and microstructure of doogh were studied. Material and MethodsRaw milk was provided by Pegah Khorasan Company, WPC from Multi Company) Mashhad (and Trans glutaminease enzyme from BDF Company of Spain. WPC was first added to milk at 45 ̊ C at three levels of zero, 1 and 2%.The milk samples were then pasteurized at 85 ̊ C for 30 min. After lowering the temperature to 45 ̊ C, the enzymatic operation was performed at two levels of zero and one unit (per gram of protein).To complete the enzyme function, the samples were incubated for 180 minutes at 45 ̊ C. Then a temperature of 90 ̊ C was applied for 1 minute to inactivate the enzyme. The samples were then cooled to 45 ̊ C. At this stage, the samples were divided into two parts. In one part of the samples; milk was diluted with water in a ratio of 6% of the total dry matter for direct production of doogh. After adding the starter, the samples were transferred to an incubator and hold at 43-42 ̊ C, until the pH reaches about 4.1.Thefermented samples were then transferred to a refrigerator. In the second part, starter was added to milk to produce yogurt; after adding starter, the mix was transferred to an incubator and hold at 43-42 ̊ C, until the pH reaches about 4.1. Doogh was produced by diluting yogurt with waterto givethe final product with 6% of total dry matter. Results and Discussion In both production methods, in samples treated only with WPC, the average particle size increased with increasing WPClevel. In both methods, the production of only enzymatically treated samples led to the formation of smaller particles with a more uniform shape and distribution. In samples of doogh produced by both production methods, WPC and transglutaminase enzyme changed the flow characteristics of doogh to non-Newtonian behavior. Samples made directly from milk had significantly higher viscosity than samples made from yogurt. In samples without enzymatic treatment, the microstructure was smooth and homogeneous with smaller particles than other samples. These particles settle very quickly. In the samples where WPC treatment was applied, the amount of large particles and non-uniformity increase with increasing WPC level. The distribution of particles in samples made directly from milk was more regular than samples made from yogurt.

In this study, the formulation of fresh low-fat yogurt containing Balangu seed gum was modeled and optimized. In this study, first the independent variables of balangu seed gum (0 to 0.1%) and fat (0 to 2%) were modeled completely randomly in the form of a central composite design and each of the response variables (syneresis, pH, flavor, color, texture, and overall acceptance) were presented in the form of a polynomial regression model as a function of independent variables.The results showed that with increasing balangu seed gum, syneresis and pH of the samples decreased and the flavor, color, texture, and overall acceptance of the samples increased. Also, the increase in fat only decreased the syneresis of the samples. Then, the obtained models were optimized by multi objective particle swarming algorithm and numerical optimization algorithm in response surface methodology, so that minimum syneresis and maximum texture, flavor, color and general acceptance scores were obtained. The results of comparing the mean of three optimal points of the two algorithms showed that in general, in optimizing the formulation of low-fat yogurt containing balangu seed gum, the multi-objective particle swarming algorithm has a better performance than the numerical optimization algorithm in response surface method. The average optimal amount of balangu seed gum and fat in the multi-objective particle swarm algorithm was 0.85 and 1%, respectively, and in the method of optimization algorithm in response surface methodology, was 0.89 and 1.94%.

In this research, the effects of three variables, Konjac Glucomannan gum (KGM) (0-0.4% w/w), Xanthan gum (XG) (0-0.4% w/w) and Butter (3-9% w/w) on firmness, flavor, spread ability, color, total acceptance and pH of spreadable processed cheese were investigated. The central composite experimental design (CCD) was used and the data were analyzed using response surface methodology (RSM). Coefficients of determination (R2) of fitted regression models for firmness, flavour, spreadability, colour, total acceptance and pH were 0.834, 0.852, 0.959, 0.886, 0.813 and 0.871, respectively. The Results of analysis of variance (ANOVA) table showed that the lack of fit was not significant for all response surface models at 95%. Therefore, the models for all response variables were highly adequate. The results showed that the effects of adding hydrocolloids and butter content were significant for sensory and chemical specifications. The optimum processing conditions for producing spreadable processed cheese with the best overall values for response variables were 0.066% (w/w) KGM, 0.024% (w/w) Xanthan gum and 8.53% (w/w) butter. The response values for such product were: firmness: 2.88, flavour: 3.99, spreadability: 4.88, colour: 4.11, total acceptance: 4.03 and pH: 5.51 and the desirability value was 93.06%.