УДК 637.14

Korotkaya E.V., Korotkiy I.A., Maltseva O.M.

Kemerovo Institute of Food Science and Technology

Fractional Freeze Separation in the Processing of Dairy Products

Processing of raw milk products into long-term storage food products is an important focus of the dairy industry. Scientists use a variety of tools and techniques to extend the shelf life of dairy products. Modern methods of dehydration can solve the problem of maintaining the quality of perishable foods for a long time.

Concentration is used to extend the shelf life of products for isolation of specific components with a view to their future use, in order to reduce the volume of liquid food products and reduce the cost of their packaging, storage and transportation. Concentration process consists in the partial removal of free water while maintaining the system in a fluid state at a predetermined temperature.

Methods for water removal may be different: those of evaporation, molecular filtration and freezing (cryoconcentration) [1]. As public policy objectives are to provide the public with healthy biological foods, condensed milk and milk products should not be accompanied by irreversible changes in the composition and properties of raw materials irrespective of the concentration process.

Evaporation is a common method in which moisture is removed from the solution in a vapor state by boiling. In the process of evaporation, the product becomes more dense and viscous. Correctly selected modes provide a high degree of preservation of initial properties of the product. Evaporation may be carried out both at atmospheric pressure and under vacuum conditions [2]. Concentration of products by evaporation is quite energy-intensive technology, since a large amount of energy is consumed for heat supply to the finished product. Furthermore temperature increase sometimes affects quality factors of the product.

Membrane filtration processes are separation processes which take place under pressure using porous polymeric or inorganic materials. They are classified according to particle size, delayed or passed through by filters: standard particle filtering (used in the allocation of particles larger than 10mkm); membrane filtration processes, namely, microfiltration (separates particles of 0.05-10mkm size); ultrafiltration (separates colloidal particles and macromolecular substances of 0.001-0.05mkm size); nanofiltration (separates molecules of 0.0005-0.001mkm size); reverse osmosis (separates molecules and ions smaller than of 0,0005mkm size) [3]. While using membrane filtration the volume unit thickening cost is 2-2.5 times lower than it is by evaporation. The main disadvantage of this process is the difficulty in cleaning the membranes themselves. To eliminate this disadvantage the devices with periodic cleaning of the membranes from the precipitate are being developed.

Cryo concentration method (freeze concentration) is based on the moisture content freezing (water in the material crystallizes in the form of pure ice) followed by the removal of ice and the increase of non-frozen product concentration to 30-40%. The process consists of two stages: the crystallization of moisture carried out in special equipment (crystallizers) and separation – the separation of ice from the concentrated solution [4].

Studies of methods and devices concentrating the liquid products used in domestic and foreign practice showed that cryoconcentration is one of the most effective processes. The main advantage of this method is the high degree of conservation of quality factors of products, more complete preservation of biologically valuable components - vitamins, micro and macro elements, and aromatic substances, as the entire process takes place at temperatures below 0º C. Produced concentrates are of high quality, and the pure water separated after cryoconcentrating can be used in the further process.

Low energy costs for cryoconcentration make this method more cost-effective compared with other methods of condensation. For example, compared with evaporation, it can be noted that the specific heat of ice formation of water (334 kJ/kg of frozen moisture) is about 7 times smaller than that of its vaporization (2258,2kJ/kg of water), and solid losses are less than 1%. To divert 334 kJ of heat is required to transfer a kilogram of water into ice. The refrigerating machines having an effective cooling rate of 2-2.5 and used for heat removal, help to reduce these costs.

It is also possible to use a cheaper construction material, since at temperatures below 0° C equipment corrosion processes undergo slowly [5]. In colder climates, where there is the possibility of using natural cold to reduce the cost of electricity, freeze concentration is of particular value [6].

Currently, due to the fact that the refrigeration and electronic equipment is being modernized, more and more high quality vehicles and industrial designs are invented and more attention is paid to the processing of raw materials using cheaper methods, saving the original properties of the product. This method is relevant and can compete with the major known methods of fractional separation of colloidal solutions.

Thus, together with the high quality of the resulting product, and low cost of processing equipment, the use of fractional freeze separation is the most effective method for milk and dairy product concentration.

Lterature:

1. Panchenko, S.L. issledovanie protsessa kontsentrirovaniya tvorognoy syvorotki metodom vymoragivaniya: diss.kand.teh.nauk: 05.18.12/ Panchenko Sergey Leonidovich. – Voroneg, 2010. – 187s.

2. Taubman, E.I. Vyparivanie / E.I. Taubman. – M.: Himiya, 1982. – 327s.

3. Krus, G.N. Technologiya moloka i molochnyh produktov / G.N.Krus, A.G.Hramtsov, Z.V.Volokitina, S.V.Karpychev. – Izd: Kolos, 2008. – 456s.

4. Pap, L. Kontsentrirovaniye vymoragivaniem: per. S veng./ L.Pap; pod red. O.G.Komyakova. – M.: legkaya I pischevaya promyshlennost, 1982. 96s.

5. Luginin, M.I. Razrabotka I issledovaniestruinogo kriokontsentratora gidkih produktov: diss.kand.teh.nauk: 05.04.03/ Luginin Mihail Igorevich. – Krasnodar, 2008. – 138s.

6. Lobasenko, B.A. Protsessy gidromechanicheskogo razdeleniya pischevyh sred / B.A. Lobasenko, Yu.V.Kosmodemyanskiy. – Kemerovo: KemTIPP, 1999. – 103s.