Modeling of Moisture Crystallization of Bacterial Starter Cultures during Freezing

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.