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1 Tashkent chemical institute of technology (Uzbekistan)
2 Rovno State Humanities University (Ukraine)
This work is devoted to the study of a simple method of preservation of the drying process. Problems and methods of optimal drying of vegetables. Analyzed the duration of the drying of capillary-porous materials as well as the effect of temperature on the drying process in two ways: thermal radiation and convection. And also studied the effect of infrared rays on the capillary-porous materials, and changes in volume (shrinkage) in the drying process. With the parameters set, the oven and the results of an experiment conducted in the laboratory.
Keywords: drying, cabbage, vegetable, convective, thermo radiation, humidity, convective, infrared, moisture.
Vegetable raw materials as the object of drying, is characterized by a large amount of water and the small content of solids. The main part of water is in a free look and only about 5% are connected with cellular colloids and strongly keeps. Ease of drying of fruit and vegetable raw materials to humidity of 12- 14% is explained by it and complicates removal of residual moisture .
The vegetable raw materials have capillary and porous structure. Its chemical composition is presented by carbohydrates, proteins, lipids. Small amounts contain biologically active agents which define taste and biological value of raw materials: polyphones, vitamins, organic acids, mineral substances. These components are most subject to adverse changes by preparation of a material for drying, and also in the course of to drying, as leads to decrease in biological value of a ready-made product.
The vegetable raw materials consist of cages. Hydrophilic substances in a cage are in a type of water solutions, hydrophobic - in the form of emulsions and colloidal solutions. Water in a cage is Wednesday in which all reactions proceed. It is distributed unevenly. The greatest number of water contains in pare chemical fabrics; it is less in integument and very little - in seeds. Therefore the cleared raw materials prepared for drying contain more water, than initial.
The most part of solids of vegetable raw materials is made by carbohydrates. They cause flavoring qualities, a consistence and technological features of processing of raw materials [2, 3].
Leaves of cabbage consist of epidermis with the oyster device of palsied and spongy fabrics and vascular carrying-out bunches, and also of water-bearing cages. Products of photosynthesis are postponed in policed and spongy fabrics and in water-bearing cages. White cabbage - a biannual plant. The bulk mass of heads of cabbage makes 650 kg/m3, a thermal capacity of 3,9 kJ/(kg hail) .
Drying parameters at convective a way (BINDER)
We made experiments on drying white cabbage of a grade of "Jaydari" in an electromagnetic field of the infrared range, radiated special lamps, previously betraying a rectangular shape, a certain size. Drying carried out in two dryers which work convective and radiation in the ways.
Cut cabbage with sizes of 20x20 mm. drying of cabbage was made in conditions identical to both drying installations.
The initial mass of cabbage cut made 12,52g; 12,05g. It is established in weighing bottle, and weighing bottle in a drying cabinet of BINDER ED 53 and in IR - vacuum drying installation at a temperature of 50°С. Distance between a power source (IR-a lamp) and бюкса 15 sm. Capacity of IR-of a lamp 1 kW. Each hour checked moisture reduction. Decrease of moisture looks like given (in fig. 1 ).
For drying of plant food materials practical application was received by short-wave IRL with a length of wave about 1,6 - 2,2 microns. When drying IRL the thermal stream is brought to a material some tens (from 30 to 70) time more powerful, than at convective drying.
Speed of drying by infrared beams increases in comparison with convective, on not in proportion to increase in a thermal stream. So, for example, for fruits and vegetables IR drying by beams is accelerated in comparison with the intensified methods of convective drying for 25-95% [5, 6]. It can be explained to that the speed of drying depends not so much on the speed of transfer of heat, how many on the speed of movement of moisture in a material. For an intensification of thermo radiation drying it is necessary that IR beams got into a material on probably deep water that depends both on material capacity, and on length of a wave of IR of beams. The less length of a wave, the more penetration of infrared beams. Permeability of food plant materials increases with reduction of thickness of a layer and with fall of humidity of a material. We give comparison of results between two ways of drying of cabbage (tab. 1, 2).
When drying particles of the food materials, being characterized fast drying of a blanket can happen small permeability, and considerable gradients of temperature and humidity in particles of a material will lead to a buckling and material cracking .
Drying parameters to infrared-vacuum installation
When drying by infrared beams in a material there are differences of temperatures under the influence of which moisture moves in the direction of a thermal stream in a material. Besides, moisture partially evaporates from a surface, as a result, there is a gradient increase moisture content and moisture starts moving to an external surface.
Thus, the gradient of temperature has braking effect on moisture movement. There fore for materials at which the size of particles more than depth of penetration of infrared beams is recommended faltering radiation. Drying under vacuum with a residual pressure over 1,33 kN/ m2 apply for the purpose of improvement of quality of a ready-made product as process is carried out at lower temperature, than in atmospheric conditions. At vacuum drying the speed of evaporation of moisture increases as the speed of removal of moisture is proportional to a difference of pressure of water vapor at a surface of a material and in surround. Profitability of process increases also due to the lack of heat loses with leaving air. Heat for moisture evaporation at vacuum drying is transferred by infrared beams .
Fig. 2. Change of humidity of cabbage in IR - vacuum drying installation at 50-60-70 °С temperature
In the course of drying to products there are considerable changes. They depend, first of all, from the chosen way and a drying mode. Main changes it: shrinkage, coloring change, hardening, violation of restoring ability, loss of flying substances.
In the course of drying the majority of materials decreases in sizes. It is natural process when drying. Shrinkage - reduction of volume and the material sizes in the course of drying. Vegetables, fruits and grain are among capillary and porous materials therefore when drying gives considerable shrinkage, decreasing in volume by 3-4 times. Shrinkage to happen evenly during all process of drying.
At uniform drying and small differences of moisture in a material shrinkage of particles happens to form preservation. Uneven drying leads to distortion of a form of particles. At big differences of moisture in a material gaps and cracks are formed.
Moisture change on time is experimentally investigated when drying cabbage of a grade of
The comparative analysis of drying of cabbage between two ways is carried out.
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