As a consequence of insufficient study of water phase change in meat accompanied by water crystallization, its modeling is currently based on the empirical dependence of the frozen water portion on temperature. Such model does not allow answering a number of questions such as of metrological order, and also of physicochemical interpretation of processes occurring in meat during water crystallization. In this paper, we propose an approach to modeling the phase change process of meat during its freezing on the basis of the phonon theory of Debye crystallization, which allows to obtain physically justified dependences of heat capacity on temperature in the phase change region. The obtained dependences may serve as a simple method for calculating the heat capacity of meat in the temperature range of 113 K to the cryoscopic temperature of the given meat type, or as a basis for the analysis and correction of factors affecting the meat freezing in the temperature range of the phase change.

In the temperature range from 45 °C to 90 °C the process of thermal denaturation of a whole complex of muscle proteins in meat takes place. An effective mode to register the thermal denaturation process is the method of differential scanning calorimetry (DSC). As a result of studies the differences during the process of thermal denaturation of muscle proteins of pork, beef, chicken and turkey were defined by the appearance of endothermic peaks in DSC thermograms. The main variances are associated with the process of denaturation of myosin and sacroplasmic proteins and indicate indirectly their quantitative ratio in meat. The values of effective specific heat capacity in the temperature range from 20 °C to 90 °C are obtained as well as those of heat spent on the denaturation process. At reheating, the values of specific heat capacity increased by 0.1 J/(g*K) on the average, and peaks of thermal denaturation were not detected, that certifies the irreversibility of the denaturation process and the decrease in the bound moisture proportion in meat after thermal processing. Knowledge of the nature of protein thermal denaturation of each kind of meat product is one of the necessary tools for developing the technology of meat product thermal processing. FOR CITATION:Agafonkina I. V., Korolev I. A., Sarantsev T. A. The study of thermal denaturation of beef, pork, chicken and turkey muscle proteins using differential scanning calorimetry. Theory and practice of meat processing. 2019; 4(3): 19-23.

With the development of food processing and storage at near-cryoscopic temperatures, more and more attention is being paid to the development of methods for frozen out moisture and cryoscopic temperature calculating based on their component composition data. There is a significant dispersion among the existing experimental data of various researchers and calculation methods for beef thermophysical properties. In the study given, the authors determined the enthalpy of phase transitions, beet heat capacity with different moisture content and its cryoscopic temperature with the method of differential scanning calorimetry. With the analysis of the phase transitions enthalpy, it was found out that the share of non-freezing water for beef is n = 0.35 (g of water per 1 g of dry matter). The presence of the vitreous phase in the temperature range of about -85 ° С was established, most noticeably manifested when the moisture content of the samples is w = 37–45.8%, which indicates the formation of amorphous solutions in the process of food products freezing. Beginning of moisture melting peak Tm.b. takes place at temperatures range from -35 ° C till -25 ° C for the samples with low and normal moisture content respectively. Acccording to the theoretical Heldman ratio, a dependence for cryoscopic temperature calculating was proposed . The given semi-empirical dependences of the phase transitions enthalpy and the frozen moisture fraction provide an increase in the accuracy of calculations at low values of moisture content in the product. The research results can be used as input data in mathematical modeling of heat exchange processes and the development of calculating methods for the thermophysical properties of food products based on their composition.

The paper proposes a model for the process of free moisture crystallization in beef within the framework of the Debye concept with establishment of dependencies of model parameters on the initial moisture content. Model adequacy was validated by comparison of the calculation results with the results of the experiments on determination of values of heat capacity and phase transition enthalpy in beef with different initial moisture obtained by the differential scanning calorimetry method. It is shown that the end of free water phase transition in beef with initial moisture in a range of 37% to 80% occurs at a temperature of 243 К. Calculation dependencies of parameters of the model used for calculation of beef heat capacity are presented.

Проведен ряд экспериментов с применением дифференциальной сканирующей калориметрии с целью определения доли вымороженной воды в образцах говядины и свинины. Проведен анализ известных зависимостей для расчёта вымороженной влаги в мясе таких как формулы Нагаока, Максвелла-Эйкена, Леви, Чижова, Рютова, а также преобразованной формулы Авраами, известной как формула расчёта доли закристаллизовавшейся массы при фазовом переходе одномерных полимеров. Анализ показал отсутствие универсальной формулы. Все зависимости имеют эмпирический характер, а константы каждой из них отражают влияние отдельных теплофизических характеристик замораживаемого продукта или процесса замораживания. Это обусловило необходимость предложить теоретически обоснованный вывод зависимости доли вымороженной воды в мясе с позиций формальной кинетики процесса замораживания как аналога химической реакции, в которой учтены влияние влажности исходного образца по Рютову, а также интенсивность процесса, т.е. темп охлаждения при замораживании. Полученная расчётная формула показала достаточно хорошую сходимость с результатами эксперимента.