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Dendrobium devonianum Paxt (D. devonianum) is widely used as a healthy food and traditional Chinese medicine. It is rich in bioactive polysaccharides, but the acidic polysaccharide have not been reported. In this research, the enzyme-assisted extraction and structure characterizations of an acid polysaccharide (DDPp2) and its antioxidant activities were studied. The results showed the optimum extraction conditions were at enzyme concentration of 0.94% at 51.06 °C and pH 4.94. The molecular weight of DDPp2 was 306 kDa and composed of four monosaccharides in the molar ratio of mannose:glucose:galactose:glucuronic acid = 6.37:4.99:1.71:2.39 with α-configuration sugar. SEM and TEM analysis showed that the surface of the polysaccharide was smooth and holes in the sheet and multiple molecular chains were intertwined with each other. Free radical scavenging tests in vitro showed DDPp2 had very strong scavenging abilities for hydroxyl radical, ABTS radical and superoxide anion free radicals. Cell experiment showed DDPp2 had no cytotoxicity and could significantly increase the activities of CAT, SOD and GPX, reduce the content of MDA in RAW264.7 cells. The investigation showed that DDPp2 is a potential antioxidant.

The aim of the present study is to investigate the antitumor activity and immunostimulatory effect of the water-soluble polysaccharides (DDP) from stem of Dendrobium devonianum in S180 tumor-bearing mice. The mice were divided into 3 groups, and then DDP or Ganoderma lucidum polysaccharides (GLP) dissolved in deionized water were given to the mice at a dose of 200 mg kg−1 for 30 days. DDP, as well as GLP, significantly inhibited the growth of mouse transplantable tumors and promoted spleen indexes, delayed-type hypersensitivity reaction, natural killer cell activity, macrophage phagocytosis and lymphocyte proliferation. Moreover, DDP and GLP increased the colonic acetate, butyrate and total short-chain fatty acid (SCFA) concentrations. These results indicated that oral administration of DDP significantly inhibited the growth of transplanted tumors in S180 tumor-bearing mice by improving specific and non-specific immune responses, as well as increasing colonic SCFAs.

Response surface methodology (RSM) was employed to optimize the conditions for the ultrasonic-assisted extraction (UAE) of polysaccharides from the flowers of Dendrobium devonianum. The optimal conditions for the maximum yields of DDFPs are as follows: an extraction temperature of 63.13°C, an extraction time of 53.10 min, and a water-to-raw material ratio of 22.11 mL/g. Furthermore, three fractions (DDFPs30, DDFPs50, and DDFPs70) were prepared from Dendrobium devonianum flowers polysaccharides (DDFPs) by the stepwise ethanol precipitation method. The DDFPs50 exhibited the highest antioxidant activity compared to the other fractions. The molecular weight, polydispersity, and conformation of these fractions were also characterized. In particular, the monosaccharide composition analysis of the DDFPs indicates that mannose and glucose are the primary components, similar to those of the D. officinale plant. This study provides a rapid extraction technology and essential information for the production of DDFPs, which could be potentially used as healthcare food.

The chain conformation, chemical characters and immunomodulatory activity of polysaccharide from Dendrobium devonianum (DDP) were investigated. Results showed that molecular weights, polydispersity index, radius of gyrations of DDP were 3.99 × 10 5 Da 1.27, 74.1 nm, respectively. By applying the polymer solution theory, the exponent (v) values of 2 > z 1/2 = kM w v was calculated as 0.38, which revealed that DDP existed as a globular shape in aqueous solution, and further confirmed by AFM analysis. Furthermore, the main monosaccharide compositions were Man and Glc with the ratio of 29.61:1.00. Indeed, the main glycosidic linkages were β-1,4-Manp, and substituted with acetyl groups at O-2 and O-3 position. Notably, DDP could promote the immune functions of macrophages including NO release and phagocytosis. Thus, DDP could be explored as a natural immune-stimulating agent in the health and functional food area as well as pharmaceutical industries.

In this study, microwave assisted puffing technology was developed to increase the extraction efficiency of polysaccharides from D. devonianum. Fresh stems of Dendrobium devonianum were processed using microwave puffing technology and the processing conditions were explored and optimized to increase the extraction yield of polysaccharides. The effects of sample length (SL), initial moisture content (IMC), microwave power (MP), and processing time (PT) on quality attributes of the products, in terms of expansion ratio and sensory evaluation, were analyzed using response surface methodology. The optimal SL, IMC, MP, and PT were 3.5 cm, 22%, 702 W, and 31 s, respectively, which resulted in optimal expansion ratio and sensory score of 326.1% and 8.63, respectively. Furthermore, the extraction yield of polysaccharides from the microwave-puffed products was increased by 18.9% compared with that from nonpuffed samples. Antioxidant and anti-hyperglycemic activities of polysaccharides from puffed and nonpuffed D. devonianum were also evaluated and compared. Practical applications We developed a novel microwave assisted puffing technology to increase the extraction efficiency of polysaccharides from D. devonianum. Polysaccharides, the major active components of Dendrobium species, exhibit the potential as an inhibitor, including immunomodulator, antioxidant, anti-tumor and anti-hyperglycemic agent.