Comparative Analysis of Water-Soluble Polysaccharides from Dendrobium Second Love 'Tokimeki' and Dendrobium nobile in Structure, Antioxidant, and Anti-Tumor Activity In Vitro.

With potential anti-tumor and antioxidant properties, the polysaccharide content of D. nobile is relatively lower than that of the other medicinal Dendrobium. To find high-content polysaccharide resources, the polysaccharide (DHPP-Ⅰs) was prepared from D. Second Love 'Tokimeki' (a D. nobile hybrid) and compared with DNPP-Ⅰs from D. nobile. DHPP-Is (Mn 31.09 kDa) and DNPP-Is (Mn 46.65 kDa) were found to be O-acetylated glucomannans (-Glcp-(1,4) and O-acetylated-D-Manp-(1,4) backbones), analogous to other Dendrobium polysaccharides. DHPP-Ⅰs had higher glucose content (31.1%) and a lower degree (0.16) of acetylation than DNPP-Ⅰs (15.8%, 0.28). Meanwhile, DHPP-Ⅰs and DNPP-Ⅰs had the same ability in the radical scavenging assay, which was milder than the control of Vc. Both DHPP-Is and DNPP-Is inhibited SPC-A-1 cell proliferation in vitro, with obvious differences in dose concentrations (0.5-2.0 mg/mL) and treatment times (24-72 h). Therefore, the antioxidant activity of DHPP-Ⅰs and DNPP-Ⅰs is not associated with distinction in anti-proliferative activity. As a glucomannan derived from non-medicinal Dendrobium, DHPP-Ⅰs has similar bioactivity to other medicinal Dendrobium, and this could serve as a starting point for studying the conformational-bioactivity relationship of Dendrobium polysaccharides.

RID serve as a more appropriate measure than phenol sulfuric acid method for natural water-soluble polysaccharides quantification.

With structural diversity of water-soluble polysaccharides, their precise quantitative analysis by phenol­sulfuric acid method becomes more difficult and challenging. In this study, the quantification analysis of dextran and glucose in phenol sulfuric acid method was compared in this paper. When the concentration is below 90 µg/mL, the quantification of glucose is close to theoretical value, however, glucose derivatives have significantly different absorption. Later, quantitative factors of water-soluble polysaccharide in RID measurement were investigated. The optimum temperature was 40 °C and linear range was 0.3125-10.0 mg/mL in RID for dextrans (1.0-500 kDa) and glucose derivatives. Method validation studies of the RID method were further performed and compared to conventional phenol sulfuric acid method, which demonstrated that RID measurement is more reliable and satisfactory method. The intervention of water-soluble impurity in RID response should be well control below 6% (w/w). By comparison, the RID measurement could well alleviate drawbacks in phenol­sulfuric acid method.