Abstract:

Crude pumpkin polysaccharide was obtained by hot water extraction, and then the pumpkin polysaccharide AP1 was separated from the precipitate by cetyltrim-ethlammonium bromide (CTAB) method. The content of uronic acid in pumpkin AP1 polysaccharide was determined by spectrophotometric method with galacturonic acid as reference susbtance, its relative molecular weight was determined by high performance gel permeation chromatography (HPGPC), and its chemical structure was analyzed by the techniques of ultraviolet-visible spectrometry, infrared spectrometry, gas chromatography and atomic force microscopy (AFM). The determination results of spectrophotometer and HPGPC respectively showed that the content of uronic acid is 38.87%, and the molecular weight is 2.0×105 D. The ultraviolet-visible spectrum indicated that there are no protein and no nucleic acid in pumpkin polysaccharide AP1. The gas chromatogram indicated that it is composed of arabinose, rhamnose, ribose, fructose, galactose and glucose. The infrared spectrum suggested that there are characteristic absorption bands of polysaccharide in pumpkin polysaccharide AP1, and its monosaccharide residues exist in the forms of pyran and furan rings. AFM revealed that it has a multi-branched structure and various small rings or helical structures in linkages of adjacent monosaccharides.

Key words: pumpkin polysaccharide, structure analysis, infrared spectrum, atomic force microscopy (AFM)