FRACTIONATION AND COMPOSITIONAL FEATURES OF THE CARBOHYDRATE COMPLEX OF WILD PEAR (Pyrus pyraster L.) FRUITS
Abstract
Mature fruits collected in the Bakhmal district of the Jizzakh region of Uzbekistan were air-dried and ground before analysis. Low-molecular-weight sugars were extracted with aqueous ethanol and analyzed by high-performance liquid chromatography with refractive index detection. The remaining plant material was subjected to successive extraction with water, an oxalic acid–ammonium oxalate solution, and 5% KOH to obtain water-soluble polysaccharides (WSP), pectic substances (PS), and hemicelluloses (HC), respectively. After acid hydrolysis, the monosaccharide composition of the isolated fractions was examined chromatographically. Fructose, glucose, and sucrose were detected in the alcohol-soluble fraction of P. pyraster fruits. Their relative ratio depended on the ethanol concentration used for extraction. The fructose/glucose/sucrose ratios were 2.5:1.5:1.0 and 6.0:3.0:1.0 in the 40% and 70% ethanol extracts, respectively. Thus, fructose was the predominant soluble sugar in both extracts, while its relative contribution increased in the 70% ethanol fraction. Successive extraction of the plant material afforded WSP, PS, and HC in yields of 1.9, 2.1, and 2.8%, respectively, calculated on an air-dried raw material basis. The three fractions differed noticeably in their monosaccharide profiles. The WSP fraction contained mainly arabinose, glucose, and galactose, with smaller amounts of xylose. Pectic substances were distinguished by a relatively high proportion of arabinose and the presence of uronic acids. The hemicellulose fraction showed a different distribution of neutral monosaccharides, with xylose and glucose among its characteristic constituents. These differences indicate that the carbohydrate complex of wild pear fruits is composed of chemically heterogeneous polysaccharide populations rather than a single dominant polymer fraction.
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