Quick-freezing of raw-materials of animal origin using cryogenic technologies
Annotation
An analysis of the main factors for the expansion of the industry for the production of quick-frozen food products in Russia is presented, including a list of the main methods of quick freezing used all over the world. The classification of the freezing process, regulated by the International Institute of Refrigeration (IIR) in accordance with the levels of the average freezing rate (crystallization), is presented. The physical model of the fast freezing process is considered, according to which the concept of true "shock" during freezing is justified as opposed to the non-official term "shock freezing". The prospects of using a cryogenic method based on liquid nitrogen for rapid freezing of food products are justified, its advantages and the main drawback associated with high consumption and costs of a cryoagent are considered; ways of reducing its significance are presented. The results of experimental determination of the main parameters of the fast cryogenic and combined (nitrogen-air) freezing process, represented by graphic data in the form of thermograms, heat flux density change curves, and heat transfer coefficients, were obtained using the example of processing raw materials from broiler, lamb, and horse meat. A description of the experimental stand is presented, based on a nitrogen mini-chamber, which allowed to create rational conditions for rapid cryogenic freezing of meat raw materials, confirmed by the obtained values of the freezing rate (crystallization). The results of joint studies of indicators of nutritional and biological value of meat raw materials frozen for comparison by traditional air, combined (nitrogen-air), and cryogenic methods are presented, proving the advantages of the latter, including an assessment of the structure of ice crystal formation in the test samples and the level of moisture preservation during thawing, after six months of storage. A draft design has been developed for the unit of combined (nitrogen-air) freezing of broiler carcasses, consisting of two parts – nitrogen and air conveyor apparatuses. The design of a fundamentally new model of a nitrogen tunnel rapid freezing apparatus with optimized geometry of a heat-insulated housing, which provides rational conditions for fast cryogenic freezing with reduced energy consumption, has been developed.
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