SURFACE-ACTIVE PROPERTIES OF THE DISTILLERS GRAINS AND THE PECTINS ISOLATED FROM THEM

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Distillers grains are the largest industrial wastes, which have a volume about 10 mln m3 a year [1, 11]; in average there are 13 m3 of distillers grains per 1 m3 of the alcohol produced [9, 10]. The share of distillers grains among the different wastes of alcohol production (concentrate of head admixtures of ethanol, fermentation gas, residue water, fusel-oil) reaches 85% [9, 10]. Perspective of the pharmaceutical use of distillers grains as a secondary raw material resource is conditioned by its practical non-toxicity [4] and high concentration of different bio- logically active compounds (BAS) [3]: proteins and amino acids, reducing sugars, pectins, fatty oil, flavonoids, vitamins, biogenic elements. The most important adsorption characteristics of the substances, which determine the field of their pharmaceutical application include superficial activity, closely connected with the problems of therapeutic activity augmentation of drugs, their rational technology, stabilization, preservation. From the variety of BAS contained in the distillers grains we marked pectins, which show the highest activity, but this fact requires validation. Many-sided study of pectins as adsorbents can be a prerequisite for this [7]. In this connection the study of superficial activity of pectins, isolated from the other components of distillers grains becomes reasonable. The purpose of this work was to estimate the possibilities of pharmaceutical use of distillers grains as an additive agent by means of study of surface-active properties of distillers grains and pectins isolated from it with determination of their molecules sizes in unsaturated adsorption layer. A liquid phase of distillers wheat grains (which amounts to 90% of distillers grains) produced by Kazachye and Suvorovskiy enterprises from Stavropol Krai which use hydro fermentative grain processing was the object of this study [9, 10]. Apart from that we have studied the fraction of pectins, isolated from the sol- id phase of distillers wheat grains by means of their extraction with the solution of ammonium oxalate, concentration, and further processing of an extract with an ethanol, purification of the targeted product, by reprecipitation from water solutions with different solvents [8]. The isolated pectins have the following physical and chemical characteristics [4]: рН 0.5% of water solution 4.25, average molar weight - 1650×10-3 kg/mol, polymerization degree - 10, binding capability amounts to 282.29 mg of lead ions (II) per 1 g of pectin. The study for surface activity of distillers grains was conducted in terms of pectins concentration (6.67 mol/m3 or 1.1% [3]). The research for surface-active properties of the study object was carried out by using the method of the highest pressure of air bubble with the use of Rehbinder’s apparatus [2]. We used the following materials for the study: series of solutions of the liquid phase of distillers grains which contain 0.06÷6.67 mol/m3 of pectins, and pectin solutions, isolated from a solid phase of distillers grains, with concentration 0.5÷6.1 mol/m3 (with water as a solvent). The measurement of the pressure difference for the solvent (s1, mm) and solutions (s2, mm) at temperature (T) 293 K, with the account of superficial tension of solvent (σ1, N/m), al- lowed calculation of superficial tension of sol- vents (σ2, N/m) by using the following equation: The first derivative σ is a measure of surface activity (g, Н•mol/m4) by the concentration of solved substance (С, mol/m3) [2] (equation 2): In this connection, g value was determined with the use of isotherm of superficial ten- sion of water solvents at constant T (293 K): «σ = f (С)», as a tangent of angle of descent to the obtained curve. We have calculated a superficial excess (G, mol/m2) of the solvents under study by the found value of g with the use of Gibbs’s equa- tion [2] (equation 3): Graphic dependence between the reciprocal quantities G and C, according to the isotherm of adsorption of Langmuir [2], is an equation of a line which is parallel to the abscissa and intercepts a section on an ordinate axis, which is equal to the maximum superficial excess (G , mol/m2). Then, we found a value, antilogarithm of which is a critical concentration of micelle formation, in the graphic scheme of dependence «lg σ = f (lg С)» [2] by the hinge point of the curve obtained, which corresponds to the abscissa axis. Using the Langmuir’s view about the structure of superficial layer we have carried out the calculations of pectin molecules sizes in the sat- urated adsorption layer [2]: - cross section square of the pectin molecule (S, m2) in the saturated adsorption layer was calculated as the quantities, reciprocal to the number of molecules which occupy the square unit (equation 4): - pectin mass (m, kg), per the surface unit (m2) unsaturated adsorption layer (equation 5): - pectin molecule length (l, m) in a saturated adsorption layer, equal to the thickness of this layer (equation 6): -volume (V, m3), occupied by the pectin molecule in an adsorption layer (equation 7): - radius (r, m) and diameter (d, m) of a cross section of the pectin molecule were determined by using the calculation formula of area of cir- cle calculation (equation 8): The measured and calculated indices of sur- face-active substances of the liquid phase of pectins isolated from the solid phase of distill- ers grains are shown in the table 1. In accordance with the isotherm of super- ficial tension (fig. 1) surface activity of the liquid phase of distillers grains amounted to 11.67. In comparison with other polysaccharides (sodium alginate, polygalacturonic acid), all molecules of which fully crop up to the surface [6], distillers grains activity is less signified: monomolecular layer on the water surface forms at high concentrations. It is worth noting, that distillers grains being a multicomponent system can lower the surface energy of Gibbs by the distribution of the dissolved matter between the phase volume and superficial (border layer). The quantity of surface activity of pectins, isolated from distillers grains, determined with the use of graphic method by the isotherm of superficial tension (fig. 2), amounted to 7.52, which is 2.5-8 times higher the similar activity of beet bin pectin, but 1.5-3 times lower the activity of sodium alginate and polygalacturonic acid [7]. According to isotherm, molecules of the pectins under study fully crop up to the surface. Isotherm of distillers grains adsorption (fig. 3) gives evidence about the fact that ordinate section from the beginning of axes to the crossing with a line is equal to 1/G = 7.8×104 m2/mol, i.e. the G quantity of liquid phase of distillers grains amounts to 1.28×10-5 mol/ m2, which is comparable to the known polyuronides: sodium alginate (1.67×10-5 mol/m2) and polygalacturonic acid (1.11×10-5 mol/m2) [12]. Thus, together with pectins concentration intensification in solution the number of molecules which are located at the superficial layer is increased. This leads to the formation ofunsaturated monomolecular adsorption layer at the border surface, where the pectins molecules are oriented to the max. Pectins adsorption isotherms (fig. 4) gives evidence about the quantity 1/G = 1,6×104 m2/mol, i.e. quantity G of pectins amounts to 6.25×10-5 mol/m2, which is 4 times higher the similar index for sodium alginate, 7.5-44 times higher than beet bin pectin, 5.6 times higher than polygalacturonic acid [7]. The number of molecules, which are located in the superficial layer, increases together with pectins concentration growth in the solution. As the result, there was saturated monomolecular adsorption layer forming, where pectin molecules were oriented to the max. After the original solution colloid ↔ solution pass, the size and number of kinetically active particles (ions, molecules, micelles) changed, therefore there is a salient point (lg C = 0.12) in the dependency graph “σ = f (C)” (fig. 5), which points out CCM of pectins in a liquid phase of distillers grains - 1.32 mol/m3 (or 0.22%). After the balance shift in the system “original solution ↔ colloid solution” to the formation of colloid solution the size and number of kinetically active particles changes, which is shown with a salient point (lg C = 0.17) in the dependency graph “σ = f (C)” (fi 6), which points out CCM of pectins 1.48 mol/m3 (or 0.24%). The calculation of pectin molecules in the saturated adsorption layer allowed obtaining the following data: ─ S = 1 / (6.02×1023 mol-1×6.25×10-5 mol/ m2) = 2.658×10-20 m2 (2.658 Å2) ─ m = 6,25×10-5 mol/m2 ×1650×10-3 kg/ mol = 1.031×10-4 кг ─ l = (6.25×10-5 mol/m2×1650×10-3 kg/mol) / 1.005×103 kg/m3 = 1.026×10-7 m (1026 Å). ─ V = 1.026×10-7 m × 2.658×10-20 m2 = 2.727×10-27 m3 (2727 Å3) ─ r = √(2.658×10-20 m2/3.14) = 9.20×10-11 m (0.920 Å); ─ d = 2 r = 1.84×10-10 m (1.840 Å). The comparison of pectin from distillers grains with other natural polysaccharides [7], which are used for drugs production (table 2), has shown that pectin molecule from distillers grain in saturated adsorption layer has less value of square, volume, radios, diameter of cross section, but more value of mass on a unit of surface and length. Considering the diameter of biological membrane pores (3.5÷4)×10-10 m [7], from all the compared polyuronides only molecules of pectin from distillers grains and molecules of sodium alginate can pass through them. This in some way favors the biological availability of pectin under study. Conclusions 1. We have established the manifestation of the liquid phase of wheat distillers grains, which contained 6.67 mol/m3 of pectins, surface-active properties which were characterized by the surface activity 11.67, maximum superficial excess 1.28×10-5 mol/m2, CCM 1.32 mol/m3 (or 0.22%). 2. We have established surface-active properties of pectins, isolated from the solid phase of wheat distillers grains: surface activity 7.54, maximum superficial excess 6.25×10-5 mol/m2, CCM 1.48 mol/m3 (or 0.24%). 3. Comparability by the surface activity of the liquid phase of wheat distillers grains and pectins, isolated from the solid phase of these distillers grains with natural polysaccharides (sodium alginate, polygalacturonic acid, beet bin pectin) creates a prospect of their pharmaceutical use in drugs technology as auxiliary agents. 4. We have determined the sizes of pectin molecules from the solid phase of distill- ers grains in the saturated adsorption layer, which differs from the known polysaccharides by their less square (2.658 Å2), radius (0.920 Å) with more weight on the square unit (1.031×10-4 kg) and length (1026 Å). The data obtained favor the biological availability of the studied pectin.

About the authors

N. S Kaisheva

Pyatigorsk Medical and Pharmaceutical Institute - branch of Volgograd State Medical University of the Ministry of Health of Russia

Email: caisheva2010@yandex.ru
Pyatigorsk

A. S Kaishev

Interregional department of Russian Alcohol Control in the Northern Caucasus Federal District

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