INTRODUCTION:

In the modern world, due to unfavorable environmental conditions, stress, overload, and malnutrition in the human body, there are not enough internal reserves to maintain homeostasis of the main functional organs and systems. Food products should not only satisfy the physiological needs of the body but also fulfill preventive and therapeutic purposes since in modern conditions the number of diseases associated with nutritional disorders is increasing¹. These diseases are caused by several factors, including the deterioration of the ecological situation, the accumulation of toxic and mutagenic substances in food, and an increase in the consumption of some medications, in particular, antibiotics, without considering their effect on the gastrointestinal tract and the microflora inhabiting it.

One can weaken their influence by eating food that helps the body to normalize functions, prevent the appearance of diseases, and fight them².

The scientific and technical process allows the production of such food in the form of dietary supplements (DS) for a healthy diet, the intake of which should be dosed in such a way that the human body can fully work at a level that promotes preservation and improvement.

Recently, food products containing components capable of correcting various physiological disorders and improving human health have received the name "functional products". These products contain physiologically functional ingredients and are suitable for both therapeutic and prophylactic nutrition^3-5.

Thus, the creation of functional food products is conditioned by the need to protect the human body from adverse environmental factors and provide the body with essential food components.

Sugar substitutes are used in many branches of the food industry^6,7. This is primarily due to the exceptionally high sweetness coefficient, which is 200-600 times higher than that of sugar, and, as a consequence, the possibility of using them to produce inexpensive low-calorie food products with full or partial replacement of sugar^8,9. Secondly, due to the absence of a glucose fragment, they can be used in the manufacture of products for people with diabetes mellitus^10-12. Thirdly, their application will allow solving the problem of national security in the field of healthy nutrition of the population¹³.

Currently, several plants are known that contain components exceeding sucrose in sweetness by hundreds and thousands of times, such as Dioscorephyllum cumminsil, Hemsleya panicis-scandens, Lippia dulcis, Syncepalum dulcificum, and Thladiantha grosvenorii. The commercial use of these plants as raw materials for the production of sugar substitutes for food purposes is limited by the difficulty of harvesting the fruits and low technology (Thladiantha grosvenorii) or toxicity of the extracts. Thus, Lippia dulcis, in addition to the sweet component hernandylcin, which is 1,000 times sweeter than sucrose, contains a toxic monoterpene (camphor). Hemsleya panicis-scandens, along with the sweet glycoside cucurbitan, contains cucurbicin, which is harmful to human health due to its cytotoxin properties¹⁴.

Stevia is a perennial herb of the Stevia genus which includes more than 180 species and belongs to the Asteraceae family¹⁵. Stevia (honey grass) is of interest as a sweetener for food and medicine, the sweetness of which is determined by the complex of diterpene glycosides contained in all aerial organs^16-19. Besides, stevia and its processed products contain a wide variety of valuable substances, including natural antioxidants^20-23.

Honey grass can be grown in Russia. Since 1996, for the first time, a new valuable technical culture of narrow-leaved stevia (Stevia rebaudiana Bertoni) has been included in the State Register of Breeding Achievements Admitted for Use in the Russian Federation. Three varieties of Russian selection are recommended for use: Detskoselskaya, Ramonskaya slastena, Dulsineya²⁴.

Although stevia is a tropical crop, the possibility of its successful cultivation in several regions of the Russian Federation and even the existing possibility of cultivating stevia as a perennial crop in the southern part of the Krasnodar Territory has been proven, provided that varieties adapted to the conditions of the region are developed and zoned. The yield here reaches 2 -2.5 tons of dry leaves per hectare.

Stevia is the youngest agricultural crop in modern plant production in Russia. The technology of cultivation and processing of stevia involves the cultivation of seedlings and plants, harvesting and drying of leaves, processing of stems^14,25.

MATERIAL AND METHODS:

The objects of the study were dry leaves of stevia (Stevia rebaudiana Bertoni), collected during the flowering period and dried at a temperature of 55-60˚С, at which enzymes that destroy glycosides are inactivated.

When carrying out analytical studies, modern methods of physical and chemical analysis were used. The determination of the mass fraction of protein in the objects of the study was carried out according to the Kjeldahl method, the amino acid composition of proteins was determined by the chromatographic method on an automatic amino acid analyzer. The determination of the mass fraction of carbohydrates was carried out on an Agilent 1260 Infinity high-pressure liquid chromatograph (USA) in an acetonitrile/water mixture. The mass fraction of metals was determined on a 240FS AA atomic absorption spectrophotometer (USA). To determine the effect of mechanochemical effects on the properties of plant raw materials, a rotary-roll disintegrator (RRD) of the vertical type was used, with pressure control on crushing-abrasive rolls. The degree of grinding plant raw materials was determined by the current characteristics of the mechanochemical activator.

RESULTS:

Table 1 shows the chemical composition of dry stevia leaves (Stevia rebaudiana Bertoni).

Table 1: Chemical composition of dry stevia leaves

Parameter name	Parameter value
Mass fraction, %: Moisture Proteins Lipids Carbohydrates, including: Monosaccharides Disaccharides Starch	10-11 9.40-10.70 0.50-1.90 26.58-28.19 0.82-1.14 0.61-1.40 1.57-1.73
Dietary fiber, including: Fiber content Pectin Extractive substances, including Diterpene glycosides Tannins Oxycoricic acids Ash	23.58-23.92 15.30-16.40 1.62-1.75 37.70-38.10 16.8-17.2 2.10-3.00 2.55-3.07 8.37-8.75
Chlorophyll	0.85-1.53

Dry stevia leaves contain diterpene glycosides, which determine their sweet taste. This makes it possible to use stevia as a sugar substitute in the production of flour confections. Analyzing Table 1, it should be noted that stevia contains physiologically valuable substances.

The study of the composition and content of vitamins in dry stevia leaves showed that stevia leaves in sufficient quantities contain water and fat-soluble vitamins: 71.24-71.87 mg% of vitamin P, 35.42-36.17 mg% of vitamin B₂, 9.07-11.30 mg% of vitaminsB₁ and B₆, 7.80-9.53 mg% of vitamin C, 3.46-4.73 mg% of vitamin PP, 22.85-24.24 mg% of vitamin E, and 4.74-5.46 mg% of β-carotene.

Considering the importance of macro- and microelements for the dietary nutrition of the population at risk and patients with diabetes mellitus, we looked at their quantitative and qualitative composition in stevia leaves as a result of which it was found that the composition of dry stevia leaves in significant quantities included such macronutrients as calcium (2,853-3,035 mg/100g), potassium (1,585-1,915 mg/100g), magnesium (1,097-1,360 mg/100g), and phosphorus (494-603 mg/100g) and trace elements of iron (48.00-61.00 mg/kg), zinc (33.80-34.39 mg/kg), manganese (14.00-14.56 mg/kg), chromium (11.25-11.87 mg/kg), and selenium (0.31-0.33 mg/kg). The data obtained allow us to conclude about the rich mineral composition of dry stevia leaves.

We also investigated the safety ofstevia leaves. The results are presented in Table 2.

Table 2: Safety parameters of dry stevia leaves

Parameter name

Acceptable levels

Value of the parameter

Microbiological parameters:

Quantity of Mesophilic Aerobic and Facultative Anaerobic Microorganisms (QMAFAM) (CFU/g), not more than

5х10⁴

(2.0-2.5)х10²

Coliform bacteria (in 0.01 g)

not allowed

not extracted

Pathogenic microorganisms, including salmonella

in 25.0 g

not allowed

in 25.0 g

not extracted

Mold, CFU/g, no more than

100

30-35

Toxic elements, mg/kg:

Lead

Arsenic

Mercury

Cadmium

0.5

0.2

0.02

0.03

0.085-0.100

not found

Pesticides, mg/kg:

Hexachlorocyclohexane (α, β,γ-isomers)

DDT and its metabolites

0.5

0.1

not found

Radionuclides, Bq/kg:

Caesium-137

Strontium-90

130

4.9-5.6

2.8-3.5

Studies have shown that in terms of safety parameters, dry stevia leaves meet the safety requirements for supplements and products of plant origin.

Taking this into account, it can be concluded that dry stevia leaves are an essential raw material for the creation of DS and the main components of functional food products. However, it is necessary to develop special technological modes of their processing.

We carried out special experiments to study the effect of temperature and mechanochemical activation on the organoleptic and physicochemical characteristics of dry stevia leaves during their processing in a rotary-roller disintegrator.

Mechanochemical activation of dry stevia leaves was carried out in a vertical rotary-roll disintegrator, the design of which was developed by the staff of the Department of Fats Technology, Cosmetics, Commodity Science, Processes, and Apparatus of the Kuban State Technological University.

The design of the rotary-roll disintegrator allows simultaneous processing of plant materials and their grinding, as well as creating high-pressure gradients from 60 to 100 MPa and pulsating loads with a frequency of up to 400 Hz.

The processing temperature of dry stevia leaves in a rotary-roller disintegrator varied in the range from 20 to 50 C, and the processing pressure varied from 5 to 20 MPa.

The efficiency of technological modes was assessed by the degree of grinding of dry stevia leaves in a rotary-roll disintegrator.

Fig. 1 shows data on the effect of processing modes on the degree of grinding of dry stevia leaves. A pressure of 5 MPa in the contact zone of the working elements does not provide a product with the required degree of grinding. Grinding dry stevia leaves at a pressure of 10 MPa allows achieving a high degree of grinding with simultaneous formation of the main physicochemical characteristics of the crushed product.

Fig. 1: Influence of processing modes on the degree of grinding of dry stevia leaves

Figs. 2 and 3 show the dependences of the effect of mechanochemical activation modes on the content of diterpene glycosides and triterpene saponins. Figs. 4 and 5 show the effect of mechanochemical activation modes on the content of soluble pectin and the water-soluble fraction of proteins.

Fig. 2: Dependence of the influence of mechanochemical activation modes on the diterpene glycoside content

Fig. 3: Dependence of the mechanochemical activation modes on the triterpene saponin content

Fig. 4: Influence of mechanochemical activation modes on the soluble pectin content

Fig. 5: Influence of mechanochemical activation modes on the water-soluble protein fraction content

An increase in temperature to 45°C leads to an increase in the yield of diterpene glycosides, and a further increase in temperature leads to a decrease in their content, which, is associated with partial destruction of glycosides. The maximum reduction in triterpene saponins in the presence of high organoleptic and physicochemical parameters together with the preservation of biologically active substances is achieved when dry stevia leaves are processed in a rotary-roller disintegrator at a temperature of 30°C and a pressure of 5 MPa.

During the processing, a slight decrease in the content of water-soluble proteins is observed, which is associated with a short-term mechanical effect on the product, as a result of which the destruction of polymer protein molecules with the formation of free amino acids occurs. At the same time, the content of soluble pectin increases, since the mechanochemical treatment of dry stevia leaves in a rotary-roller disintegrator leads to the destruction of polymeric carbohydrates, and protopectin, which forms the basis of the pecto-cellulose membrane of cells, turns into soluble pectin. As a result, the following data on the granulometric composition of the crushed product was obtained: no fractions larger than 100 µm were found; fractions from 40 to 100 μm amounted to 1%; from 30 to 39 μm to 3.6%; from 20 to 29 μm to 12.5%; from 10 to 19 μm to 37.4%; from 5 to 9 μm to 39.22% and less than 5 μm to 6.28%.

The granulometric composition of dry stevia leaves obtained by grinding in a rotary-roller disintegrator is represented by the highest content of particles with a size of 5 to 30 μm, which makes it possible to ensure high consumer properties of the obtained DS.

Table 3 shows the organoleptic and physicochemical characteristics of a DS obtained as a result of processing dry stevia leaves in a rotary-roller disintegrator under the indicated modes.

Table 3: Organoleptic and physicochemical parameters of a DS

Parameter name	Parameter value and characteristics
Parameter name	Dry stevia leaves	The product obtained after processing in the RRD
Taste and smell	Sweet, slightly herbal with a bitter licorice aftertaste	Pleasantly sweet, without bitterness and aftertaste
Color	Brown	Dark green
Appearance		Powder
Degree of grinding, μm	–	20-30
Sweetness coefficient	15-17	20-25
Mass fraction, %: diterpene glycosides Lycurazide Soluble pectin Protopectin	16.80 1.20 0.50 1.12	18.10 0.10 0.83 0.80
Mass fraction of protein fractions, % of total protein content: Water-soluble Salt-soluble Alkaline-soluble	24.50 44.20 31.90	23.10 45.10 31.80

CONCLUSION:

The studies showed that the dry stevia leaf contains physiologically valuable substances and is a promising raw material for the creation of DS. The resulting DS contains diterpene glycosides determining its sweet taste, which makes it possible to use it as a sugar substitute in the production of functional food products. In terms of safety parameters, dry stevia leaves meet the safety requirements for supplements and herbal products.

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

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Received on 31.03.2021 Modified on 01.06.2021

Research J. Pharm.and Tech 2021; 14(12):6693-6698.

DOI: 10.52711/0974-360X.2021.01156