Abstract: Objective: To investigate the effect of extraction temperature on the yield, physicochemical properties and intestinal mucosal immunomodulating activity of polysaccharides extracted from Dendrobium huoshanense. Methods: Four different extraction temperatures including 40, 60, 80 and 100 ℃ were used to investigate the changes in the yield and intrinsic viscosity of Dendrobium huoshanense polysaccharides (DHP) extracted by the water extraction-ethanol precipitation method. High performance liquid chromatography (HPLC), gas chromatography (GC) and Fourier transform infrared spectrometry (FTIR) were used to analyze the molecular weight distribution, monosaccharide compositions and characteristic groups of DHP and its fractions eluted with water and salt solution from DEAE-cellulose anion exchange column. The conditioned medium from Peyer’s patch cells from the small intestine of mice was used to determine the intestinal mucosal immunomodulating activity of DHP and its fractions by observing the proliferation of bone marrow cells of mice. Results: With increasing extraction temperature, the yield of DHP rose and its intrinsic viscosity dropped. HPLC analysis showed that DHP extracted at different temperatures were mainly composed of higher molecular weight fraction (HMW) and lower molecular weight fraction (LMW). LMW, which had better thermal stability, mainly existed in the water-eluted fraction (DHPW) from DEAE-cellulose anion exchange column and HMW, which had weaker thermal stability, mainly existed in the salt-eluted fraction (DHPS). GC and FTIR analysis displayed that DHPW mainly consisted of Glc in α-configuration and DHPS mainly consisted of Glc, Gal, Ara and Man in β-configuration with some uronic acids. All DHPs from different extraction temperatures and the corresponding DHPW and DHPS fractions possessed intestinal mucosal immunomodulating activity and the activity of DHPS was higher than that of DHPW, but their activities decreased significantly with increasing extraction temperature. Conclusion: Extraction temperatures not only influenced the yield of DHP, but also markedly changed its intrinsic viscosity, molecular weight distribution, monosaccharide compositions and immunomodulating activity. Although higher temperature increased the extraction yield of DHP, it significantly decreased the intestinal mucosal immunomodulating activity of DHP because of the reduction in the proportion of HMW in DHP.

Key words: Dendrobium huoshanense, extraction temperature, polysaccharides, physicochemical properties, intestinal mucosa, immunomodulating activities