Low-temperature Drying of Dendrobium officinale Inhibit Polymerization of Water-soluble Polysaccharides
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Abstract:
The present study was carried out to investigate the effects of drying temperature on the molecular structure and antioxidant activity of the polysaccharides in Dendrobium officinale. Four types of water-soluble polysaccharides from D. officinale, i.e., FDOP, 60 DOP, 100 DOP and 140 DOP, were prepared through extraction and purification after hot air drying of fresh D. officinale, and D. officinale at 60 ℃, 100 ℃, 140 ℃, respectively. Molecular structure and antioxidant activity of the polysaccharides from D. officinale were analyzed. It was found that the contents of the reducing end were 1.82% and 1.70% for FDOP and 60 DOP, respectively, but decreased to 1.42% for 100 DOP and 1.10% for 140 DOP. Each D. officinale polysaccharide was composed mainly of mannose and glucose. No obvious correlation was found between drying temperature and the molar ratio of monosaccharides. As the drying temperature increased, the molecular weight distribution curve of D. officinale polysaccharides shifted towards high molecular weight. The mass ratios of the polysaccharide fractions within the molecular weight range of 103~106 u were 70.68%, 67.70%, 62.24% and 58.11%, respectively, for FDOP, 60 DOP, 100 DOP and 140 DOP. At 280 nm of the UV spectra, 140 DOP had an absorption peak whilst FDOP, 60 DOP and 100 DOP hadn't. The polysaccharide constituents with the molecular weights in the range of 103~106 u and containing more reducing ends showed higher free radical scavenging ability and reducing power. During the drying of Dendrobium officinale, the drying temperature set at 60 ℃ facilitated the suppression of polymerization reaction while retaining the antioxidant activity of its polysaccharides. The present study provides technical data and theoretical basis for the production and utilization of D. officinale-containing functional foods.
