optimization of formulation fermented drink yoghurt with fruit juice using response surface methodology

in recent years, water or sugar syrup, flavoring agents such as fruit juice or fruit juice concentrates and stabilizers have been added to the acidified dairy beverage composition. nowadays, the popularity of low fat and defatted fruit yoghurt drinks are mainly growing. the purpose of this study was to diversify the acidified dairy products by determining the sensory, rheological and stability attributes of these kinds of dairy products with considering added elements and hydrocolloids as variables and then optimizing the formulation of fermented beverage, being directly flavored with the fruit concentrates. moreover, mutual effects of total solid materials, concentrate, sweetener and stabilizer were inspected using minitab software and response surface methodology. in this regard, consistency, viscosity, ph and acidity, sensory characteristics and yeast and mold counts were assessed. surveys indicated that contrary to flow behavior index, the stability and straightness index increased with adding stabilizer and decreasing water content. according to sensory evaluation, white samples got lower score in comparison with black cherry ones. furthermore, adding high amount of hydrocolloids negatively affected the total acceptance. not only yeast but also mold was grown on the optimal sample after 28 day storage at refrigerator temperature. generally speaking, it can be concluded that highly viscose and extremely sweet products as well as samples with high amount of stabilizer were rejected by panelists whereas the ones with high amount of concentrate were accepted. according to mentioned properties, the optimum amounts of ingredients are as follow: 13% total solid materials, 9.5% concentrate, 6.2% sweetener and 0.78% stabilizer. this sample with 2.3% of serum scored 7.93 in mouth feel, 8.25 in texture, 7.68 in acidic and 7.84 in fruit flavor, 7.89 in color, 7.78 in sweetness and 7.93 in total acceptance and also had 84.36% of total satisfaction.