Study of the process of freezing and thawing out of the fruit juices

UDC 664.857.3

Study of the process of freezing and thawing out of the fruit juices

Ovsyannicov V. YU., Kondrateva I. I., Bostynets N. I., Denezhnaja A. N.

The process of freezing and thawing out of the fruit juices is investigated. It is shown that the crystallization of moisture in the liquid food media, which are been complex multicomponent solutions, depends on the presence of a large quantity of eutectic mixtures, which appear with reduction in the temperature of food medium and isolation of the solvent in the form of clean ice. It is noted, that the minimum temperature of melting is differed from the maximum temperature of complete solidification and it is considerably higher than it, which is caused by the fact that in the process of freezing the intermediate eutectic mixtures are super cooled, detaining further crystallization; therefore fruit juice must be cooled to the lower temperature. Is carried out the experimental determination of eutectic temperature zones for the apple, cherry and cherry juice by the method of the differential thermal analysis, based on the principle of comparative observation of the motion of changing temperatures during the uniform cooling and heating of identical quantities of the juice being investigated and substance, indifferent to the phase transformations in the working temperature range. It is established that the presence of several sharp fractures in the differential curve, of corresponding to temperatures phase transitions, designated by the sections of the simple record, is characteristic for the process of freezing fruit juices: super cooling, the formation of the crystal seeds of ice and the beginning of crystallization and further intensive crystallization of moisture. It is shown that the process of melting the fruit juices depending on its form, contents of dry matter and chemical composition occurs at a different temperature and with different intensity. For the process of melting the characteristically smooth beginning of process, smooth passage to the zone of intensive melting and the zone of the intensive melting of ice. Are explained the special features of the mechanism of freezing and melting ice in fruit the juices from the position of the molecular-kinetic theory of the motion of molecules being investigated. The conducted investigations made it possible to determine the energy of the activation of the processes of crystallization and melting the moisture in the juices being investigated.

Keywords: freezing, melting, differential-thermal analysis, fruit juices

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