Abstract:Compared to liquid yogurt, freeze-dried yogurt blocks offer greater convenience for consumption. The development of freeze-dried soy-based yogurt blocks introduces new product varieties to plant-based yogurt. This study investigated the effects of pre-freezing temperature and mixing temperature on the textural characteristics and viability of lactic acid bacteria in soy-based freeze-dried yogurt blocks, while the properties of freeze-dried dairy-based yogurt blocks were compared with those of freeze-dried soy-based yogurt blocks. The results revealed that the eutectic temperature and glass transition temperature of soy-based yogurt freeze-dried mixture were -9.04 ℃ and -30.73 ℃, respectively, which were comparable to those of dairy-based yogurt mixtures. It was found that higher pre-freezing temperatures resulted in looser and more fragile product texture along with lower viability of lactic acid bacteria. Conversely, excessively low temperatures of pre-freezingreduced bacterial viability and led to structural collapse due to the narrow water vapor sublimation channels. Ultimately, a pre-freezing temperature of -25 ℃ was determined to be suitable. Increasing the mixing temperature could slightly increase the viability of lactic acid bacteria in freeze-dried yogurt blocks without significantly affecting the product texture. Although dairy-based yogurt blocks exhibited higher bacterial viability, freeze-dried soy-based yogurt blocks showed comparable viability of Lactobacillus and Bifidobacterium after 30 days of storage. The viability of Lactobacillus and Bifidobacterium in freeze-dried soy-based yogurt blocks was higher without nitrogen-filled packaging.
