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 modi
fi
ed 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 forti
fi
ed with spirulina powder
showed a coarse and a compact less porous structure in comparison with the freeze-dried yoghurt samples for-
ti
fi
ed with whey protein concentrate. All Additives signi
fi
cantly decreased adhesiveness and signi
fi
cantly
increased cohesiveness, springiness, gumminess, and chewiness in both fresh and rehydrated yoghurts.