THE PHYSICAL AND CHEMICAL CHANGES OF WATER AND THE HYDRATION OF THE PROTEIN COMPLEX IN CHEESE DURING FREEZING

The use of low temperatures is one of the available factors to inhibit the over-ripening of cheeses and the preservation of their quality. This study reveals the patterns and physical and chemical nature of the phase transition of water into ice, and the state of bound water, when freezing semi-hard cheeses in the range of ultra-low temperatures (-20 ... -50°C). The authors research the cheese's resistance to freezing based on the water retention capacity of the proteins. They study the factors of product stability during storage in the frozen state conditioned by a change in state of tightly bound water in the protein complex during freezing to different temperatures. The paper examines three main subclasses of semi-hard cheeses with a high, low temperature second heating which, based on fat content in dry matter, are considered fat and semi-fat cheeses. The research conducted tests to obtain the basic patterns of rapid freezing at different air conditions. The air velocity in the cooling zone was up to 10 m/s. Samples of the finely packaged cheeses weighing up to 0.2 kg were being frozen at a given volume-average temperature of -20°C. The tests allowed to obtain the data about water phase transformation into ice, depending on the values of the low temperature. The kinetics of the process has shown a gradual transition of heterogeneous water into ice in accordance with its binding energy in descending order. Based on the analysis of the experimental data, the phase diagram of water states, depending on the final volume-average temperature of frozen cheese, has been created, and the data on the degree of hydration of the protein complex in the temperature range of -20 to -70°C has been obtained.