Abstract
Introduction. The quality of fermented milk products directly depends on the bacterial starter cultures involved, which contain lactic acid microorganisms. One of the most effective ways to store bacterial ferments is freezing as it improves the survival rate and preserves the morphological and cultural properties. Changing the phase state of water affects the chemical and biochemical processes during freezing. The present research dealt with the issue of moisture crystallization during freezing of bacterial starter cultures. 
 Study objects and methods. The study featured bacterial starter cultures of Lactobacillus bulgaricus and Lactobacillus acidophilus. The authors used standard methods to determine their physical and chemical properties; the first buffer method of two temperature and time intervals made it possible to describe the thermal characteristics. 
 Results and discussion. A set of experiments helped to define the mass fractions of total protein and dry matter, the content of lactic acid, as well as cryoscopic temperatures and thermophysical characteristics of the bacterial cultures in question. The values of the thermophysical characteristics of bacterial ferments proved to depend on the amount of moisture in them. The authors constructed a model of moisture crystallization during freezing of bacterial starter cultures, taking into account the content of lactose and lactic acid. The model made it possible to define the cryoscopic temperatures. Their proved close to the experimental ones. The model of moisture crystallization also provided the freezing time and a method for calculating thermal characteristics and their values. The differences between the calculated and experimental values did not exceed 5.3 %. 
 Conclusion. The experimental and calculated values of the thermophysical characteristics appeared similar, which means that the proposed model of moisture crystallization during freezing of bacterial ferments proved effective. The model can be used in commercial freezing to calculate thermal characteristics and freezing time.
Highlights
The quality of fermented milk products directly depends on the bacterial starter cultures involved, which contain lactic acid microorganisms
Conflict of interest The authors declare that there is no conflict of interest regarding the publication of this article
Effect of acids produced from carbohydrate metabolism in cryoprotectants on the viability of freeze-dried Lactobacillus and prediction of optimal initial cell concentration / S
Summary
Изучение особенностей кристаллизации влаги при замораживании бактериальных заквасок представляет практический интерес. Бактериальные заквасочные культуры Lactobacillus bulgaricus и Lactobacillus acidophilus. Для исследованной группы бактериальных заквасок определены массовые доли общего белка и сухих веществ, содержание молочной кислоты, а также криоскопические температуры и теплофизические характеристики. Предложена модель кристаллизации влаги при замораживании бактериальных заквасок, учитывающая содержание лактозы и молочной кислоты. На основании модели кристаллизации влаги рассчитана продолжительность замораживания, предложена методика расчета теплофизических характеристик и приведенных их значения, рассчитанные по данной методике. Сравнение экспериментальных и расчетных значений теплофизических характеристик показало их близость и позволило сделать вывод об адекватности предложенной модели кристаллизации влаги при замораживании бактериальных заквасок, а также возможности её практического использования при моделировании процессов замораживания, расчете теплофизических характеристик и продолжительности замораживания. В. Моделирование кристаллизации влаги при замораживании бактериальных заквасок / Е.
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