TECHNOLOGICAL PROPERTIES OF THE POWDER MADE FROM JERUSALEM ARTICHOKE OBTAINED BY THE METHOD OF DRYING WITH MIXED HEAT SUPPLY

Present work addresses technological properties of powder made from Jerusalem artichoke, formed by the method of drying with mixed supply of heat, compared to traditional convection. It is shown that polysaccharides in the composition of Jerusalem artichoke of MHS-drying undergo less crystallization and hence drying is carried out under milder conditions than these components during convection method. We established capacity for the dispersing of dried Jerusalem artichoke in a traditional ball mill depending on the duration, which makes it possible to obtain dried products for various technological purposes. We demonstrated a capacity to swell in the resulting powder made from Jerusalem artichoke, which predetermines the formation of advanced capillary-porous structure. Results of the tensometric method of studies revealed that the formed structure of powder made from Jerusalem artichoke of MHS-drying is characterized by small pores at temperature 50 °С and by 1.2...1.5 times larger – at 70 °С, which must be considered when they are rehydrated. We examined a complex of basic functional-technological properties of powder made from Jerusalem artichoke: coefficient of water absorption (CW), water-retaining (WRC), fat-retaining (FRC) and emulsifying capacities (EC). During mathematical processing of the results received, we obtained a conceptual model that describes a dependence of the comprehensive indicator of technological properties of powder made from Jerusalem artichoke (by the defined weight coefficients: for CW – 0.2; WRC – 0.2; FRC – 0.3; EC – 0.2) depending on the temperature of MHS-drying and dispersibility.


Introduction
The concept of all fast service enterprises is aimed at meeting the needs of consumers at the highest level, the basic principles of which are: a consumer should not have to wait; the task for the staff at an enterprise is to make a consumer want to visit it again.
However, the products in such enterprises do not always meet the requirements of a balanced nutrition, especially under condition of limited consumption of vegetables and fruits.
Therefore there is a need to use dried vegetable and fruit raw materials, in particular powders, in the technology of culinary products. This will avoid the seasonality in their consumption, simplify operations during mechanical culinary treatment of raw materials, reduce the duration of technological preparation of meals and culinary products, extend their asortment, reduce area of warehouse and production premises.
In order to solve the set tasks, technologies of traditional food profucts employ more and more alternative vegetable raw materials, including vegetable, fruit, and fruit and berry powders, which are a concentrate of biologically active compounds.
Among the variety of alternative vegetable raw materials, special attention must be paid to the Jerusalem artichoke. This is a tuber-shaped plant that is characterized by high yields and unique chemical composition, in particular by the contents of inulin, pectin substances, cellulose, vitamins and mineral substances [1][2][3][4][5].
Tubers of Jerusalem artichoke contain up to 3 % of protein, 2... % of nitrogenous substances, 20 % of mineral salts, micro elements, the entire group of vitamins B, especially, B 7 (biotin), vitamin C and carotene. Protein has amino acids -lysine, histidine, arginine, tryptophan, threonine. The composition of carbohydrates includes the soluble polysaccharide inulin (16...18 % and higher), which in the body is converted into high-calorie easily digestable sugar fructose, much required in a diet of patients with diabetes, however, it does not practically contain starch. Jerusalem artichoke as a source of polysaccharides is a powerful immunomodulator, that is a product that enhances protective properties of the human organism [6,7]. Essential substances of Jerusalem artichoke that enter the human body are actively involved in the metabolism of organs and tissues, providing recovery of metabolic changes in the myocardium perfusion, during heart rhythm irregularities, decrease in tone and damage to the blood vessels at hypertension, diabetes, reduced hemoglobin, increased thrombosis, acidity of gastric juice, etc. [5][6][7].
Taking the aforementioned in account, by using the method of drying with mixed heat supply (MHS-drying), we formed technological properties of dried Jerusalem artichoke with humidity not exceeding 7 % [7].

Materials and Methods
In order to examine technological properties of powder made from Jerusalem artichoke that is obtained by the method of MHS-drying, we determined dispersity of dried Jerusalem artichoke depending on the duration of grinding; capacity to swell; technological properties: coefficient of water absorption, water-retaining, fat-retaining and emulsifying capacities, depending on the temperature of MHS-drying and dispersibility.
As the objects of study we chose Jerusalem artichoke of convection drying in line with TU U 15.3-23913766-002:2005 as a control, and the one, obtained by MHS-drying, as an experiment. Dispersibility of the received powders was investigated by the microscopic method, swelling -by the laser granulometry, technological properties -according to the generally accepted methods. Mathematical processing of obtained results was carried out using the method of least squares.

Results
In order to determine technological properties of Jerusalem artichoke, which are formed by drying using the method of mixed heat supply, we chose a high-yield hybrid of the variety "Interest" with a high content of inulin. Before drying, the artichoke was washed, dried, and ground in Food Science and Technology the form of chips. MHS-drying of Jerusalem artichoke was carried out at temperature 90 °С, 70 °С and 50 °С to the resulting moisture content not exceeding 7 %.
By the kinetics of drying and absorption coefficient we defined rational parameters for drying the vegetable that are: temperature 70 °С and duration of the process 70…60 s, which is associated with a different chemical composition of vegetable raw material, original water content and its chemical composition. At the first stage of research we defined the measure of crystal structure of the dried vegetable, obtained by MHS-drying, in comparison with the convection, using the X-ray structural analysis.
An analysis of the received diffractograms ( Fig. 1) revealed that the samples of Jerusalem artichoke obtained both by convection drying and MHS-drying display a partially organized structure, which is typical for natural polysaccharides whose macromolecules are able to rotate the plane of polarization of light rays and form a double helix [8][9][10][11][12].  (2) However, the sample of Jerusalem artichoke obtained by MHS-drying demonstrates a clearer diffractive reflex at angles of 2θ=20.5 against a wide blurred reflex, in contrast to the sample obtained by convection drying, where a narrow reflex manifests itself not so clearly (Fig. 1, curve 1).
Thus, the method of MHS-drying characterizes milder conditions of drying [7].
At the next stage, we explored technological properties of dried Jerusalem artichoke in order to predict its behavior in a number of technologies for culinary products: dispersibility, the degree of swelling, coefficient of water absorption, water-retaining, fat-retaining and emulsifying capacities.
Results of research into dispersibility of powders from Jerusalem artichoke are shown in   Thus, we established the ability for dispersing of dried Jerusalem artichoke depending on the duration: to obtain a large fraction, the required time is 10 s, a medium -30 s and finely-dispersed -for Jerusalem artichoke 50 s, which is necessary to consider when receiving a vegetable powder to be used in the technological flow during preparation of culinary products at the enterprises of restaurant business.
In order to explain the manifestation of restoring properties of the powders, as well as to predict their swelling in food systems, we determined the intensity of swelling of finely dispersed powder from Jerusalem artichoke that was obtained at the temperature of MHS-drying of 70 °С.
According to the methodology of research, the process of swelling in the powder made from Jerusalem artichoke with dispersibility 1...5 µm was performed in water at temperature (20 ± 2) °C during 6 hours - Fig. 3.  Fig. 3, a shows that around the surface of particles of the vegetable the solvate complexes form and the photograph clearly displays a layer of adsorption-bound moisture. swelling of larger particles, then the heavy fraction of particles settles and there is an increase in the size of suspended, smaller, particles of the powder. Thus, over a period of 6 hours, the process of hydration of dried vegetable raw materials is characterized by intense swelling that is caused by high hydrophilicity of polysaccharides and capillary-porous structure of vegetable raw materials formed during drying. After 6 hours of hydration, the swelling process intensity falls and becomes a constant magnitude.
In order to substantiate the capillary-porous structure of powder made from Jerusalem artichoke, obtained by MHS-drying temperatures of 50-70 °С, we determined the size of the pores by the tensometric method. Fig. 4 shows experimental isotherm of the sorption-desorption of powders made form Jerusalem artichoke, dried by the MHS method and the convection drying. Based on received data on the sorption properties of powders made from vegetables, we built differential distribution functions of pores in the examined vegetable powders by radii (DDFP) (Fig. 5). Table 2 presents calculated parameters of DDFP for the powders made from Jerusalem artichoke. Table 2 shows that PDFR have a fundamentally different character for the powders made form Jerusalem artichoke obtained at different temperatures. Thus, at drying temperature of 70 °С, changes in the capillaryporous structure of powder in the process of sorption-desorption are vividly pronounced, indicating the formation of artificial fine-porous structure of the powder in the process of MHS-drying -the most probable radius of capillaries is less (Fig. 5).
Food Science and Technology a b Fig. 3. Capacity to swell of the powder made from Jerusalem artichoke: a -microstructure of a particle in the powder (×400); b -intensity of swelling of particles in the powder made from Jerusalem artichoke in water during 6 hours While at temperature of drying 50 °С, such changes are less pronounced, capillary-porous structure of the product changes differently: in the course of desorption, pore radius increases from 13.4 to 21.4×10 -9 m, which is typical for the processes of convection drying, in which the sample undergoes shrinkage. The powder, dried at 70 °С, in the process of sorption of vapors, is restored well, the capillaries swell, which is why DFPR expands, the mean radius of capillaries is increased from 2.8 to 11.1×10 -9 m.
The formed structure of vegetable powders during MHS-drying is characterized by small pores at temperature 50 °С and by 1.2...1.5 times larger size at 70 °С, which must be considered when dried products are rehydrated.

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It is shown (Fig. 6) that Yмах=0.68 is achieved at the temperature of MHS-drying (65…68) °С and dispersibility up to 40 µm.
Thus, in the course of multifaceted comprehensive studies we established high technological properties of powder made from Jerusalem artichoke obtained by the method of MHS-drying, compared to the convection method. 3. A comprehensive study on the porosity in the structure of dried products was conducted. It is proved that during traditional convection drying, there occurs a significant narrowing of capillaries due to shrinkage, whereas dried products obtained by the MHS method have highly porous structure, which predetermines their higher rehydration properties. 4. A complex of research into the properties was performed, based on which we conducted mathematical modeling and optimized comprehensive indicators by the given group of properties of dried vegetables depending on the temperature of MHS-drying and the degree of dispersibility.