Comparison of Texture of Yogurt Made from Conventionally Treated Milk and UHT Milk Fortified with Low-heat Skim Milk Powder

ABSTRACT: The textures of yogurt made from ultra-high temperature (UHT) treated and conventionally treated milks at high total solids were investigated. The yogurt premixes, fortified with low-heat skim milk powder to 16%, 18%, and 20% total solids, were UHT processed at 143°C for 6 s and heated at 85°C for 30 min using the conventional method. The onset of gelation was delayed in the UHT-processed milk compared with conventionally heated milk. During fermentation, the viscosity of yogurt made from UHT-treated milk at 20% total solids was close to that of yogurt made from conventionally treated milk with 16% total solids. However, after storage for ≥ 1 d, the yogurt made from UHT-treated milk had lower viscosity and gel strength than the yogurt made from conventionally treated milk. The solids level had no influence on yogurt culture growth.     

Survival of probiotics encapsulated in chitosan-coated alginate beads in yoghurt from UHT- and conventionally treated milk during storage

Survival of the microencapsulated probiotics, Lactobacillus acidophilus 547, Bifidobacterium bifidum ATCC 1994, and Lactobacillus casei 01, in stirred yoghurt from UHT- and conventionally treated milk during low temperature storage was investigated. The probiotic cells both as free cells and microencapsulated cells (in alginate beads coated with chitosan) were added into 20 g/100 g total solids stirred yoghurt from UHT-treated milk and 16 g/100 g total solids yoghurt from conventionally treated milk after 3.5 h of fermentation. The products were kept at 4 °C for 4 weeks. The survival of encapsulated probiotic bacteria was higher than free cells by approximately 1 log cycle. The number of probiotic bacteria was maintained above the recommended therapeutic minimum (10⁷ cfu g⁻¹) throughout the storage except for B. bifidum. The viabilities of probiotic bacteria in yoghurts from both UHT- and conventionally treated milks were not significantly (P>0.05) different.     

Effect of addition of inulin and galactooligosaccharide on the survival of microencapsulated probiotics in alginate beads coated with chitosan in simulated digestive system,yogurt and fruit juice

Galactooligosaccharides (GOS) and inulin were added during microencapsulation of Lactobacillus acidophilus 5 and Lactobacillus casei 01 in alginate beads coated with chitosan at the concentrations of 0, 0.5, 1.0 and 1.5%. Addition of prebiotics significantly (p < 0.05) increased the bead size by approximately 3.8%. The presence of GOS (0.3%) in the microencapsulation provided the best protection with only 3.1 and 2.9 logs reduction for L. acidophilus 5 and L. casei 01, respectively, after incubation in simulated gastric juice (pH 1.55), followed by simulate intestinal juice containing 0.6% bile salt. The viabilities of microencapsulated probiotics containing 1.5% GOS in commercial yogurt and orange juice were also performed at refrigerated storage for 4 weeks. In yogurt, the numbers of cells with GOS were higher than those of without GOS by approximately 1.1 and 0.4 logs for L. acidophilus 5 and L. casei 01, respectively. In orange juice, the numbers of cells with GOS were higher than those of without GOS by approximately 0.5 and 0.4 logs for L. acidophilus 5 and L. casei 01, respectively. The numbers of probiotic bacteria were maintained above the recommended therapeutic minimum (10⁷ cfu g⁻¹ or mL⁻¹ of product) throughout the storage in both products.