Study On The Composition And Bioactivity Of Volatile Oil And Polysaccharide From Two Rhododendron Species Of Tibet In China

As one of the largest genera of vascular plants,Rhododendron L.?Ericaceae?comprises 8subgenera with more than 850 species.The majority of the species grow in the Himalayan region,Southeast Asia and Malesia,with others distributed in North America,Europe and North-East Australia.The phytochemistry and bioactivity of this genus have been investigated,and many plants and their active compounds presented the significant biological activities,including anti-inflammatory,analgesic,anti-microbial,antidiabetic,antioxidant,insecticidal and cytotoxic activity.However,Rhododendron aganniphum and Rhododendron nivale,the dominant species of the genus Rhododendron in the Tibet region,have not been studied.The paper studied the volatile oils and polysaccharides from Rhododendron aganniphum and Rhododendron nivale.The volatile oils were extracted by steam distillation and analyzed by GC-MS,and the acaricidal activity of volatile oils was evaluated.Subsequently,the ultrasound-assisted extraction conditions of polysaccharides were optimized and the antioxidant activity and rheological properties of crude polysaccharides were investigated.Finally,the polysaccharides of Rhododendron were isolated and purified,and the structures of the polysaccharide constituents were analyzed.The main contents and conclusions are as follows:1.Analysis of the volatile oils The volatile oils of R.aganniphum and R.nivale were extracted by steam distillation,and the yields were 0.05±0.006%and 2.45±0.08%,respectively.71 volatile components from R.aganniphum,accounting for 80.51%of total volatile oils,were identified by GC-MS analysis.The main components were linalool,calarene,epimanoyl oxide,?-terpineol and?-cadinol,et al..51 chemical constituents were identified from R.nivale,accounting for 87.33%of total volatile oils.The main components were?-cadinene,T-muurolol,?-eudesmol,?-eudesmol,T-cadinol,longifolenaldehyde,?-cadinene,et al..2.Acaricidal activity against Psoroptes cuniculi of Rhododendron extracts After screening and investigating the acaricidal activities of different extracts from R.aganniphum and R.nivale,the results showed that as the active ingredient of R.nivale,volatile oil presented the best acaricidal activity against P.cuniculi in vivo and in vitro,and at the concentration of 33.33 mg/mL the median lethal time(LT₅₀)was 1.476 h.This bioactivity maybe relate to the strong acaricidal activity of?-cadinene whose LT₅₀ was 1.836 h at 6.25?l/ml.3.Ultrasound-assisted extraction of Rhododendron polysaccharides The extraction conditions of crude polysaccharides from R.aganniphum and R.nivale were optimized by the ultrasonic-assisted method.The optimal extraction conditions were as follows:for R.aganniphum,ultrasonic temperature,55?;ultrasonic extraction time,2.2 h;ultrasonic treatment power,200 W;the ratio of material to liquid,1:25;polysaccharide yield up to 9.43±0.021%;for R.nivale,ultrasonic temperature,63?;ultrasonic extraction time,1.4 h;ultrasonic treatment power,200W;the ratio of material to liquid,1:25;polysaccharide yield up to 6.11±0.085%.Compared conventional hot water extraction with the corresponding conditions,the ultrasonic extraction could obtain a higher polysaccharide yield in a short period of time,indicating that the application of ultrasonic extraction technology has a positive impact on the extraction of polysaccharides from two kinds of Rhododendron.4.Structures of purified polysaccharides The polysaccharides by the ultrasonic extraction were isolated and purified by decolorization,deproteinization and cellulosic chromatography,and the single constituents were obtained.By SEC-LLS determination,the molecular weights of RAP-?and RNP-?were 50660Da and 11184Da,respectively.The structures of RAP-?and RNP-?were characterized by chromogenic reaction,periodic acid oxidation,Simth degradation,GC-MS,FT-IR and NMR.The result of chromogenic reaction and FT-IR showed that RAP-?and RNP-?had characteristic absorption peaks of polysaccharide,but did not contain protein and starch.GC-MS analysis indicated that RAP-?was composed of glucose,galactose and glucuronic acid in a molar ratio of 6.27:1.10:1,and RNP-II was composed of arabinose,mannose,glucose,galactose and glucuronic acid in a molar ratio of1:2:7.93:7.08:2.23.The effects of periodic acid oxidation and Simth degradation showed that RAP-?and RNP-?may contain?1?2?,?1?4?and?1?6?glycosidic bonds.NMR analysis showed that the main chain of RAP-?may be composed of?3)-?-D-Glu-?1?6?-?-D-Glu-?1?6?-?-D-Gal-?1?,RNP-?may be composed of?6?-?-D-Glu-?1?6?-?-D-Gal-?1?3?-?-D-Man?1?2?-?-D-Glu-?1?6?-?-D-Gal(1?,and?-D-Gal-?6?3?-?-D-Glu?1?2?as the branched chain and?-D-Man of the main chain connected.5.Antioxidant activity of Rhododendron polysaccharides The antioxidant activity of polysaccharides was evaluated by determining the clearance of superoxide anion,hydroxyl radical and DPPH radical,and the iron ion chelating ability and reducing power of polysaccharides.The results showed that the antioxidant activity of polysaccharides by ultrasonic assisted extraction was higher than that of polysaccharides by heated extraction.We thought that the ultrasonic cavitation effect may accelerate the dissolution of some substances,which played a synergistic role with polysaccharides in enhancing antioxidant activity.6.The rheological properties of Rhododendron polysaccharides The rheological properties were evaluated by steady-state shear and dynamic shear scanning.Steady-state shear scanning indicated that all polysaccharide solutions showed shear thinning in a concentration-dependent manner and belonged to non-Newtonian fluid.The ultrasonic extraction method reduced the apparent viscosity and dynamic viscoelasticity of polysaccharides,but has little effect on its microstructure.The flow curves of two kinds of polysaccharides by the ultrasonic extraction in different concentrations have a good fitting degree with Carreau model,and R² was greater than 0.991.