The effect of freeze drying of yoghurt and addition of some additives on the physico-chemical, microbiological, texture, microstructure, and sensory quality of yoghurt was studied. Freeze drying of yoghurt had light effects on the viability of Streptococcus thermophilus and no effect on viability of Lactobacillus delbreuckii subsp. bulgaricus and rehydrated yoghurt. Addition of modified starch had a considerable protection effect on Streptococcus thermophilus during freeze drying process. Addition of whey protein concentrate produced different surface structures and caused porous and loos structure. The microstructure of the freeze-dried yoghurt fortified with spirulina powder showed a coarse and a compact less porous structure in comparison with the freeze-dried yoghurt samples fortified with whey protein concentrate. All Additives significantly decreased adhesiveness and significantly increased cohesiveness, springiness, gumminess, and chewiness in both fresh and rehydrated yoghurts.

Effects of Production System, Breed, Parity and Stage of Lactation on Milk Composition of Dromedary Camels in Saudi Arabia

Frozen yogurt is known as ice cream with some properties of yogurt. Frozen yogurts are a rich source of sucrose levels between 15% and 28% of total ingredients. Consumers suffering from lactose intolerance and metabolic syndrome are looking for sugar-free products. The current study investigates the sugar replacements by using sweeteners (stevia, sucralose and sorbitol) on physicochemical, microbiological, microstructural and sensory characteristics of probiotic-frozen yogurt. Four different treatments of probiotic-frozen yogurts were studied (control probiotic-frozen yogurt with sucrose (F1), probiotic-frozen yogurt with stevia (F2), probiotic-frozen yogurt with sucralose (F3) and probiotic-frozen yogurt with sorbitol (F4)). The chemical properties were not significantly present p > 0.05) during storage in all treatments. In the F1 treatment, sucrose value was higher (14.87%) and not detected in the F2, F3 and F4 treatments. The highest values of overrun, hardness and viscosity (p < 0.05) were detected in the F2, F3 and F3 samples, but the lowest value was detected in the F1 treatment. Total Str. thermophilus and Lb. delbrueckii ssp. bulgaricus counts were gradually decreased (p < 0.05) during storage periods. At 1 day, the Bifidobacteria counts ranged from 7.56 to 7.60 log₁₀ CFU g⁻¹ in all groups and gradually decreased during storage, but these bacterial counts remained viable (>6.00 log₁₀ CFU g⁻¹) during storage periods up to 60 d. During storage periods, the highest scores of total acceptability were detected in the F3, F4 and F2 treatments. Scanning electron microscopy (SEM) micrographs of all probiotic-frozen yogurt treatments illustrated that the microstructures showed a difference with a fine network, size pores and structure between the frozen yogurt with sweeteners (F2, F3 and F3) and control frozen yogurt (F1).