Freeze-drying of dairy products poses a challenge due to the susceptibility of probiotic bacteria to the process conditions of dehydration. The influence of three individual freeze-drying protocols on the survival of probiotic bacteria in yogurt has been studied for the purpose of this thesis. The protocols differ in temperature during primary drying and so yogurt samples have been dry-frozen under an aggressive protocol at –25 °C, under a medium-aggressive protocol at –15 °C, and under a conservative protocol at –5 °C. The course of the dry-freezing process has been monitored with the measuring of heat flux. The viability of bacteria in samples of fresh and dehydrated yogurt has been determined by the colony-forming unit method. Results have shown that the medium-aggressive protocol and the conservative protocol ensure comparable viability of bacteria, whereas the medium-aggressive protocol was two hours shorter in duration.
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