Physicochemical Characteristics of Polygonatum sibiricum Root and Evolution of Its Polysaccharide Components during the Nine-steam-nine-bask Process
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Abstract:
Sensory evaluation combined with colorimeter, gas chromatography-mass spectrometry, electronic tongue and scanning electron microscope were used to describe the "color, aroma, taste and shape" of Polygonatum sibiricum root. The molecular weight distribution, monosaccharide composition and structure of the polysaccharides were analyzed by size exclusion gel chromatography, ion chromatography and Fourier transform infrared spectroscopy. The results showed that during the steaming process, the Polygonatum sibiricum root changed from yellowish white to dark brown. The bitterness score and sweetness score decreased, and the bitterness appeared after being steamed five times. Internal pores appeared during the second steaming, with the tissue structure changing from dense to loose and porous. The molecular weight of polysaccharide in the raw Polygonatum sibiricum root was about 12.8 ku. The molecular weight distribution of the Polygonatum sibiricum root polysaccharides increased after the nine-steam-nine-dry-bask process, leading to the presence of fractions containing components with molecular weights greater than 670 ku and around 2 000 u. D-ribose and galacturonic acid were found in the monosaccharides from the Polygonatum root steamed once, whilst the glucuronic acid and fucose disappeared after the third and fourth steaming, respectively. The IR spectra showed relatively strong characteristic absorption at 3 410 cm-1 and 2 930 cm-1 for the polysaccharides from the Polygonatum root steamed for 0~9 times, and the absorption peaks at 1 200~1 000 cm-1 and 880 cm-1 indicated the occurrence of pyranose and β-glycosidic bonds in the polysaccharides. Investigations on the development of the physicochemical quality of Polygonatum root and the changing trend of its polysaccharide during the nine-steam-nine-bask process allow us to provide a reference for the standardization of nine-steam-nine-bask process and the establishment of quality standards.
