Production of Yogurt Powder Using Foam-Mat Drying

Abstract

Yogurt powder was produced by using foam-mat drying method. Two types of foaming agents as methylcellulose and egg albumin were used at different concentrations as 0.5, 1.0, 1.5 and 2.0% for methylcellulose and 1, 2, 3 and 4% for egg albumin, respectively. The mixture of plain yogurt and foaming agent were blended by using high speed mixer (900 W) for 5, 7, 9 and 12 min. Characteristics of yogurt foam, as foam density, foam stability and foam expansion, were determined. Three percentage of egg albumin with the mixing time of 12 min provided better foam characteristics. The yogurt foam was then dried at 50, 60 and 70C for 3 h. The dried yogurt was blended and kept in an air tight container. Characteristic of yogurt powder as moisture content, water activity (aw) and glass transition temperature (Tg) were analyzed. Simultaneously, the food application of yogurt powder in drinking yogurt was studied. Yogurt powder (15%) was dissolved in cold water (85 ml) and then mixed well. Orange flavor (0.1 g) and color (0.1 g) were added into the product. Two physical characteristics of the finished product, viscosity and cohesiveness, were measured. Moreover, sensory evaluation was performed by using 9-point hedonic score and 30 panelists. The highest viscosity product was obtained when 60C yogurt powder was used. Sensory qualities of drinking yogurt of all treatments were not significant (p>0.05) different. The yogurt powder (60C) had aw of 0.348, moisture content 8.5%, Tg 25.51 C and lactic acid bacteria count 5.6 x 107 cfu g-1 . The preference scores of drinking yogurt made by using yogurt powder were 6.7, 6.8, 6.6 and 6.7 for appearance, flavor, texture and overall, respectively.