Study On Three Kinds Of Set-type Functional Yogurt

In this paper, Bifidobacterium adolescentis ys01 and Lactobacillus casei ys05 in the form of mixed culture were used to enrich selenium (Se), and applied them to produce Se-enriched yogurt starter. Then the fermentation conditions of Se-enriched yogurt were optimized by single-factor and central composite design experiments. The changes of physicochemical properties of Se-enriched yogurt were investigated during refrigerated storage. The results showed that the content of selenium in B. adolescentis ys01 and L. casei ys05 was 551μg/g, and Se-enriched yogurt starter had good fermentation performances. The optimal fermentation condition of Se-enriched yoghurt was as follows:milk powder 12%, sucrose 5%, isomaltooligosaccharide 1%, sodium selenite 61.8μg/kg, sodium caseinate 1.4%, inoculum 4.5%, fermentation temperature 40℃, culture time 7h. Under this condition, Se-enriched yogurt had a good sensory quality, physicochemical parameters conformed to the relative requirements in national standard GB19302 and the content of organic selenium was 29.2μg/kg. During 25 days' storage, the main properties of Se-enriched yogurt including lactic acid bacteria, pH, protein, fat and non-fat milk solid declined, while the content of organic selenium was relatively stable.Bifidobacterium adolescentis ys01, Lactobacillus delbrueckii subsp bulgaricus 1.1480, and Lactobacillus acidophilus ys2 in the form of mixed culture were used to enrich zinc (Zn), and then utilized the mixed cells to produce Zn-enriched yogurt starter. The fermentation conditions of Zn-enriched yoghurt were optimized by single-factor and Box-Behnken design experiments. Then changes of physicochemical properties of Zn-enriched yogurt were investigated during refrigerated storage. The results indicated that the content of zinc in mixed cells was 550μg/g, and Zn-enriched yogurt starter had good fermentation performances. The best fermentation condition of Zn-enriched yoghurt was as follows:milk powder, sugar, zinc gluconate, modified starch, inoculum, fermentation temperature, fermentation time was 13%,6%,39.1mg/kg,1.3%,4.2%,41℃,6h, respectively. With this understanding, the sensory score was 8.9, physicochemical parameters conformed to the relative requirements in national standard GB19302 and the content of organic zinc was 6.2mg/kg of the yoghurt. During refrigerated storage, the pH and the number of lactic acid bacteria, protein, fat, the non-fat solid and organic zinc of the Zn-enriched yoghurt had a decrease trend, but the syneresis increased.The reconstituted milk was added with hawk tea of 2%,4%and 8%(w/v), and inoculated with B. adolescentis ys01,L. bulgaricus 1.1480,L. casei ys05, S. thermophilus ys14 and L. acidophilus ys2 to obtain hawk tea yoghurts. Effects of hawk tea on lactic acid bacteria and flavor, and other qualities of yoghurt were investigated. Results suggested hawk tea had no significant effect on the syneresis and pH of the yoghurt, but increased the viscosity. Hawk tea promoted the growth of the Streptococcus thermophilus, Lactobacillus acidophilus, and Lactobacillus casei. Thirty kinds of flavour components were identified in the hawk tea yoghurt, and majority were aldehydes, ketones, acids and alcohols. Moreover, some of aldehydes, ketones, acids in the hawk tea yoghurt increased to varying degrees, comparing with the control.Diabetic mice model was established with alloxan, and hypoglycemic effects of Se-enriched yoghurt, Zn-enriched yogurt, and hawk tea yogurt were assessed. Results indicated that Se-enriched and Zn-enriched yogurts could prevent blood glucose increasing, whereas hawk tea yogurt had hypoglycemic effect on diabetic mice.