Quality and microstructure of freeze-dried yoghurt fortified with additives as protective agents

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.