Study of the carbohydrate composition in the underground organs of the couch grass

Abstract

Introduction. Today  in Ukraine there is a tendency to expand scientific research on the study of medicinal plants. According to the literature, plants are a source of primary and secondary metabolites that have a wide spectrum of pharmacological and therapeutic effects [1-5]. One of the plants, the use of which is recommended for the prevention of various diseases, is couch grass (Agropyron repens L.). Agropyron repens is a perennial herbaceous plant with a strong rhizome. Couch grass is common in Europe and Asia, and is also found in Africa. The plant is traditionally used as a mild diuretic and pain reliever for diseases of the urinary tract (cystitis, urethritis, prostatitis). It is known that couch grass also exhibits hypoglycemic, hypolipidemic and anti-inflammatory effects. Couch grass contains carbohydrates, mucous substances, pectin, phenolic compounds, flavonoids, saponins, phytoncides, essential oil (0.01-0.02%), vanillin, vanillin glycoside (vanilloside), phenolic acids and silicic acid. It is known that the underground organs of the plant accumulate substances of primary synthesis - carbohydrates. The study of the quantitative content and qualitative composition of carbohydrates of rhizomes and roots of couch grass is expedient due to the fact that these compounds, in addition to important functional value and specific pharmacological activity, also affect the development of the total pharmacological effect of drugs obtained from plant raw materials [6]. The aim of research. To determine the qualitative composition and quantitative content of the component composition of carbohydrates in the subterranean organs of couch grass. Materials and methods. The objects of study were rhizomes and roots of couch grass, which were harvested in the territory of the Rivne region in 2022. To carry out qualitative reactions on polysaccharides (PS), aqueous extracts from medicinal plant raw materials were prepared. 30 g of crushed dry raw materials were poured with 250 ml of hot purified water and infused for a day. The water extracts were filtered, and the raw materials were poured with 100 ml of hot purified water. The operation was repeated 3-5 times. The aqueous extracts were combined and evaporated to 15 ml. The resulting extract was used to detect PS. 30 ml of 95% ethanol was added to 10 ml of the extract. The appearance of floating lamellar clots that precipitated during settling indicated the presence of PS in the studied raw material. The sediment was filtered and a reaction was carried out to detect reducing (neutral) sugars. The sediment was transferred to a test tube and 5 ml of diluted hydrochloric acid was added and boiled for 30 min. 10 ml of Fehling's reagent was added to the cooled hydrolyzate and boiled again. The appearance of a brick-red sediment indicated the presence of renewable sugars [7-8]. The quantitative content of water-soluble polysaccharides (WSP) and pectin substances (PS) in the studied raw materials was determined by the gravimetric method [9-10].

The qualitative composition and quantitative content of monosaccharides and sucrose were investigated by gas chromatography-mass spectrometry (GC/MS). The method is based on the extraction of free monosugars and the preparation of acetates of their aldonitrile derivatives with further analysis by GC/MS [11]. Chromatographic separation was performed on an Agilent 6890N/5973inert gas chromatography-mass spectrometric system (Agilent Technologies, USA). A HP‑5ms capillary column (30 m×0.25 mm×0.25 mkm, Agilent Technologies, USA) was used. Identification was carried out by the retention time of monosaccharide standards and using the NIST 02 mass spectrum library. Sample preparation of plant raw materials consisted in the extraction of total and free sugars under different conditions. Quantitative analysis was performed by adding a solution of the internal standard to the tested samples. Sorbitol solution was used as an internal standard [12]. Results and discussion. The research results confirmed the presence of polysaccharides in water extracts from underground organs of Agropyron repens L.:  with 95% ethanol, the appearance of lamellar clots was observed, which settled down over time;  with Fehling's reagent, after acid hydrolysis, the appearance of a brick-red precipitate was noted, which indicated the presence of neutral (reducing) sugars. The polysaccharide complexes of rhizomes and roots of couch grass were studied and the quantitative content of water-soluble polysaccharides and pectin substances was determined. The obtained water-soluble polysaccharides are light brown amorphous powders that dissolve in water (the pH of aqueous solutions was in the range of 5–6). Polysaccharides give a positive result in the precipitation reaction with 96% ethanol and Fehling's reagent after acid hydrolysis. The obtained pectin substances are brown amorphous powders that dissolve in purified water to form colloidal viscous cloudy solutions, the pH of which is 4–5. Aqueous solutions of  PS are precipitated with a 1% solution of aluminum sulfate with the formation of pectates. The results of the research indicate that in rhizomes and roots of couch grass, the content of PS is (6.57±0.02) %, and the content of WSP is (5.85±0.02) %. The presence and quantitative content of 8 monosugars after acid hydrolysis was determined in the composition of the polysaccharide complexes of rhizomes and roots of couch grass; 4 free sugars were found - glucose, fructose, inositol and disaccharide sucrose. Among the monosaccharides in the studied raw material, xylose, which was formed after acid hydrolysis, dominated; its highest content was observed in the underground organs of couch grass (39.03 mg/g). Also, the predominant glucose content was observed after acid hydrolysis (27.30 mg/g), and in the free state its content in the rhizomes and roots of the plant was 3.42 mg/g. The content of sucrose in the studied object was 2.14 mg/g. In addition to glucose, the presence of inositol was observed in the composition of free sugars and sugars after acid hydrolysis - 0.37 mg/g and 1.47 mg/g, respectively. Conclusions. The analysis of the results of the conducted research indicates a high content of water-soluble polysaccharides and pectin substances in the rhizomes and roots of couch grass. The composition of sugars of the subterranean organs of the plant is characterized by the predominance in the quantitative ratio of the monosugar xylose and the disugar sucrose. The studied species is promising for use in medical practice and requires extensive phytochemical and pharmacological analysis.

 Keywords: Agropyron repens L., carbohydrates, subterranean organs, GC/MS-chromatography.