عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Introduction: the production of milk with different flavors causes people, especially children to buy and consume milk more and to get the required amount of dairy daily. Flavored milk is a dairy drink prepared from milk, flavors and a sweetener which is often enriched with vitamins and calcium (Dadgostar 2013). Chocolate milk is the most popular and accepted type of flavored milk. Prevention of physical instability of chocolate milkis an important challenge in the dairy technology (Prakash etal 2010), The main cause of instability of this product is the incorporation process in which the particles of the cocoa milk are joined each other and form a larger particle, and dispersion is divided into two phases. One of the ways to increase sustainability and to prevent sediment and two phases during the maintenance of this product is adding a stablilazer. Hydrocolloids or gums have a wide range of applications in the food industry, such as by increasing the apparent viscosity of the product or by the colloidal interactions of space barrier and electrostatic repulsion which stabilize some food systems (Foroughinia etal 2007). The native Tragacanth gum is an extruded gum of the Astragalus species, which is chemically containing two parts soluble and insoluble in water, which is called tragacanthine and bassorin (tragacanthic acid), respectively (Mohammadifar etal 2006). This gum is a anionic polysaccharide, non-uniform and high molecular weight (Chenlo etal 2010). In the year 1961 by the US Food and Drug Administration (FDA) has been accepted as a healthy food additive (GRAS) (Balaghi 2009).
The present research was thus aimed optimizing the formulation of chocolate milkto achieve a product with Desirable physical, chemical and sensory properties.
Material and methods: Optimization of Chocolate milk formulation using response surface methodology and in the form of a central composite design was performed. The desired design was set up using two variables of cocoa powder and Tragacanthin gum. According to primary tests, the range of each of the independent variables was determined and then 5 levels of each independent variable and 13 treatments were presented by Design Expert Software (version 8) (table 3). The samples of Chocolate milk based on the formulations specified in the preparation test plan and were evaluated from the viewpoint of different characteristics. In order to prepare different treatments of Chocolate milk, first 15% of the initial milk volume with 2.5% fat in the hot water bath up to 20°C temperature.Then, the different percentages of cocoa powder, tragacanthin gum according to experiments plan and sugar (7%) and tragacanthin gum According to treatment, was slowly added to the milk and Became uniform by magnetic stirrer (model-Ikarh making Germany).
The mixture was heated up to 50 ° C for 20 minutes and finally added to the total volume of milk and was stirred by magnetic stirrer for 20 minutes (Ostadzade etal 2012). Samples were tested after Homogeneisation by Homogenaizer (FG Model 200-S – Hong Kong Country) with a circumference of 1200 per minute, from viewpoint on the physical, chemical and sensory properties of chocolate milk. Also in order to separate the soluble (Tragacanthine) and insoluble (Basorine) parts, one gram of tragacanth powder with one milliliter of ethanol mixed and 200 milliliter of distilled water was added to it. In order to absorb water, the mixture was stirred inside the container for 12 hours by a magnetic stirrer at 4000 rounds per minute. The mixture the was centrifuged at 1700 g for 3 hours (Mohammadifar etal 2006). Thus, the soluble and insoluble sections of tragacanth were separated from each other and the water soluble part was used after drying by spray dryer (Dorsa model- Made in Iran).
Results and discussion: The results showed that increase in gum tragacanthin or cocoa powder was accompanied by increase of pH (p˂0.05). and The acidity of the samples decreased with increasing the amount of tragacanthin gum (p≤ 0.05), while adding cocoa powder had no significant effect on the amount of acidity. Addition of any foreign matter to milk can cause change its physical and chemical properties, including pH and acidity. Consequently, the reason for the significant increase in pH with the addition of cocoa powder can be attributed to the higher pH of cocoa (7.49) compared to milk. increase in level of formulation ingredients caused an increase of viscosity of the chocolate milk (p˂0.05). Both independent variables, their interaction with each other and the square cocoa powder had a significant effect (P ≤ 0.05) on the viscosity response. results show an increase of sedimentation amount once the cocoa powder increased. While by increasing the gum tragacanthin concentration, there was a twofold effect in sedimentation amount and in average level of gum, the minimum amount of sediment was observed. So that it increased up to approximately 0.225% of the amount of sediment and its increase from the mentioned value to 0.3% increased sediment content. In justification the results of the present study According to Syrbe etal 1998 theory, the phenomenon of depletion flocculation may occur when the concentration of free hydrocolloid occurs. when the concentration of free hydrocolloid exceeds the required amount and the hydrocolloid is no longer able to absorb water and thus in the form of sediment out. Also, the sensory evaluation of chocolate milk samples showed that most desirability was to be found in samples containing the average level of cocoa powder, but according to panelists, gum tragacanthin did not have a significant effect in general acceptance.
The results of particle size distribution analysis of optimum sample size showed that the particle size of chocolate milk without gum and chocolate milk containing gum were 377.38 and 410.88 nm, respectively.
Conclusion: The use of native tragacanthin gum in suitable concentration can be used in addition to stabilization without causing adverse effect on the sensory properties of Chocolate milk. Also, the result of optimal sample particle size showed an increase in the sample particle size by adding this gum. Optimization results also show that, the best sample with the desirable physicochemical and sensory properties was obtained by 5.12 % cocoa powder and 0.10 % of gum tragacanthin in chocolate milkformulation.