Extraction and structural identification of alkali-soluble polysaccharides of longan (Dimocarpus longan Lour.) fruit pericarp

Two alkali-soluble polysaccharide fractions (ASPS I and II) were extracted from longan fruit pericarp in this work. The results of chemical composition indicated that ASP I and II fractions comprised mainly of polysaccharides. proteins and lignins. Four monosaccharides, namely Xyl. Ara, Glc and Gal, were identified for both ASPS I and II. Xyl was the dominant monosaccharide in the two alkali-soluble polysaccharides with relative molar percentages of > 60%. It constructed the backbone in combination with Ara for both ASPS I and II. The analysis of glycosidic linkage indicated that Xyl had two linkages, -> 3)-Xyl-(1 -> and -> 3, 4)-Xyl-(1 ->. The substitution at C-4 position indicated that Xyl was of pyranose structure. The infrared spectra of ASPS I and II showed the characteristic bands at approximate 897 cm(-1) which indicated the beta-linkage configuration of Xyl. Industrial relevance: Hemicellulose has been suggested as an important polysaccharide with good pharmaceutical properties, including immune modulation and anti-cardiovascular diseases. In this work, alkali-soluble polysaccharides were extracted from longan fruit pericarp and fractionated. The structural characteristics were identified by gas chromatography/mass spectrometry and infrared spectrophotometry. The results will be helpful for application of hemicellulose in functional food industry. (C) 2009 Elsevier Ltd. All rights reserved.