Optimization of Preparation Technology of Blueberry Candied Syrup-based Set Yoghurt

The concentrated blueberry candied syrup and the whole milk sterilized pure milk were used as raw material to prepare set yoghurt. The influence of addition amount for blueberry candied syrup, sugar content, starter inoculation quantity and fermentation time on the yogurt sensory quality, whey exhalation rate and acidity were investigated. Furthermore, the response surface experiment was carried out on the basis of single factor experiment to optimize the set yoghurt preparation technological parameters. Then the texture parameters of yoghurt were compared with those of commercial yoghurt. The results showed that the optimal preparation technology of blueberry set yoghurt was as follows: The addition amount of concentrate blueberry candied syrup (concentration ratio 2 with the total sugar content 0.679 mg/mL) in the yoghurt 7%, custer sugar 4%, starter inoculation amount 0.6%, whey protein powder 2%, and fermentation control time 11 h. Under these conditions, the whey release rate was 12.43%, the acidity was 83.66°T and the sensory score reached the highest score 88.13. The blueberry set yoghurt was purple with strong frankincense and blueberry flavor. The hardness, cohesiveness and adhesiveness of this product were lower than those of commercially available fermented milk, but the water holding capacity was stronger. It was more delicate and refreshing, which tasted better than the commercially available products with thickening agent addition. In this study, the basic preparation conditions of set yoghurt of blueberry preserved fruit syrup were determined, which provided useful reference for improving the comprehensive utilization value of blueberry preserved fruit syrup and developing new fruity set yoghurt.