This study explored the structural characteristics and in vitro hypoglycemic activity of polysaccharides from the stems of Dendrobium nobile Lindl.. Two homogeneous polysaccharides, DNP-6 and DNP-7, were obtained by water extraction followed by alcohol precipitation and subsequent successive anion exchange and gel column chromatography. Their structures were analyzed by high performance liquid chromatography (HPLC), ultraviolet-visible (UV-vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). The results showed that DNP-6 and DNP-7 were neutral polysaccharides with molecular mass of 2.70 × 10³ and 1.23 × 10³ Da, containing 90.45% and 93.49% total sugar and 2.28% and 1.29% protein, respectively. They were mainly composed of glucose and mannose, with molar ratios of 6.76:1 and 6.63:1, respectively. The glycosidic bonds were mainly of α-configuration, with a small amount of β-pyranose. One-dimensional and two-dimensional NMR results showed that the main chain composition of DNP-6 and DNP-7 was: →4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-β-D-Manp-(1→4)-α-D-Glcp/β-D-Glcp. In addition, the results of in vitro glucose consumption and insulin resistance tests showed that both polysaccharides had good hypoglycemic activity, and DNP-6 possessed stronger activity than DNP-7.

In order to study the effect of chemical degradation on the physicochemical properties and anti-aging activity of Dendrobium officinale polysaccharide (DOP), four degraded polysaccharides were prepared by vitamin C (VC), H₂O₂, H₂O₂-VC and citric acid methods. The results showed that DOP was primarily composed of component I (t_R = 4.5 min), with relative molecular mass of 1.168 × 10⁷ Da. The molecular mass distribution of DOP did not change after treatment with H₂O₂ and citric acid, showing that neither treatment with H₂O₂ nor citric acid degraded DOP. VC-degraded DOP was composed of two components with relative molecular masses of 9.24 × 10⁵ and 1.49 × 10⁴ Da (t_R = 5.923 and 8.239 min), demonstrating that VC alone and combined with H₂O₂ could partially degrade DOP. All treatments resulted in no significant change in the content of total sugar in DOP but increased the protein content. The results of Fourier transform infrared spectroscopy (FTIR) showed that none of these four chemical degradation methods destroyed the primary functional groups of DOP. Monosaccharide composition analysis showed that DOP and VC-degraded DOP were mainly composed of mannose and glucose. The results of particle size and zeta potential measurements showed that the particle size and zeta potential absolute value decreased after the degradation of VC; the results of electron microscope scanning observations showed that the polysaccharide structure became loose after degradation. The results of in vitro anti-aging activity test showed that both DOP and VC-degraded DOP promoted collagen secretion and inhibited elastase, and the elastase inhibitory effect of VC-degraded DOP at a concentration of 200 μg/mL was more pronounced than that of DOP. In general, VC-degraded DOP showed better elastase inhibitory effect. Both DOP and VC-degraded DOP had collagenase inhibitory effects. This study provides a theoretical reference for the application of DOP in various important areas such as anti-aging foods, pharmaceuticals and health products.