| Dendrobium officinale Kimura et Migo is a precious Chinese herbal,with a long history of medication.It is mainly used for nourishing yin,beautifying,strengthening body,tonifying stomach and promoting fluid,prolong life and so on.With the improvement of people’s living standard,more and more people pay attention to health.Therefore,the demand for Dendrobium officinale increased.The main medicinal part of Dendrobium officinale is stem.Dendrobium officinale is difficult to reproduce due to its special habitat,and coupled with unrestrained picking,wild resources are running out.Although its seedling cultivation and cultivation technology have been broken through,it is still far from meeting the market demand.Dendrobium officinale leaves are rich in flavonoids,polysaccharides and alkaloids,but they are often abandoned,resulting in waste of resources.Therefore,exploiting the value of medicinal parts of Dendrobium officinale leaves,making full use of resources and deep processing can not only meet the market demand for Dendrobium officinale products,but also further explore the potential medical and commercial value of Dendrobium officinale.The specific research results are as follows:1.The correlation of flavonoids in different parts of Dendrobium officinale leaves,stems and flowers were analyzed by high performance liquid chromatography(HPLC),and to compare the antioxidant activities of its extracts in vitro under five antioxidant systems(DPPH radical,hydroxyl radical,ABTS radical method,Fe3+reduction and Fe2+chelation).Comparing the characteristic chromatograms of different parts by HPLC,it was found that the species and content of flavonoids in leaves and flowers were significantly higher than those in stems.The results showed that the crude extract of total flavonoids from Dendrobium officinale leaves showed the strongest ability in hydroxyl radical scavenging,ABTS radical scavenging and metal chelating.The antioxidant capacity was positively correlated with the mass concentration of total flavonoids.The scavenging ability of DPPH radical and chelating ability of iron ion were slightly lower than those of total flavonoids.The crude extract of total flavonoids from Dendrobium officinale stem exhibited strong antioxidant activity.Considering types and contents of flavonoids,the source and price of raw materials,it can be concluded that Dendrobium officinale leaves have more development value.2.Optimization of ultrasonic-assisted enzymatic extraction of total flavonoids from D.officinale leaves using analysis of single factors and response surface methodology.Taking flavonoid extraction rate as a screening standard,by single factor experiment,the results showed that the optimal extraction conditions are 45%ethanol concentration,enzymolysis temperature 55 ℃,enzymolysis time 60min,ultrasonic time 10min.Based on the above single factor conditions,Box-Behnken response surface experiment was carried out to further optimize some conditions,and the optimum extraction process are liquid-solid ratio(v/m)30:1,ratio of compound enzyme 1.5:1,enzyme concentration 1.0%,ultrasonic power 120 w.By Verifying,D.officinale leaves flavonoids extraction yield was 1.81%,compared with the predicted value relative error is 2.71.The optimized extraction process is stable,reasonable and can be used for D.officinale leaves extract of total flavonoids.3.It aims to study the purification process by D101 macroporous resin and antioxidant activity of the purification of total flavonoids in Dendrobium officinale leaves.Analyses were made to the factors influencing the purification effect of macroporous adsorption resin from the aspect of dynamic adsorption ratio,desorption ratio and total flavonoid content as evaluation factors,to determine the optimum purification-desorption process conditions.The antioxidant activity of total flavonoids in Dendrobium officinale leaves and its purified products were compared and analyzed,and the effect of purification process on the antioxidant activity of total flavonoids in leaves was explored.The results indicate that the optimal purification conditions of total flavonoids are:loading buffer of concentration of 2.2 mg/mL,16 bed volume(BV),of 2.4 pH value,80%-ethanol-contained eluent of elution volume of 3.25 BV(desorption rate up to 90.83%),and room temperature,under which the content of total flavonoids can reach 193.95 mg/g.In the three antioxidant systems of DPPH and ABTS+ radicals scavenging and Fe2+ chelating,the antioxidant activity of TFDL depends on concentration,the half inhibitory concentration(IC50)of DPPH,ABTS and Fe2+scavenging were 0.1123,0.7845 and 0.6434 mg·mL-1 respectively;the DPPH radical scavenging capacity was strongest,namely,TFDL has a strong ability to provide hydrogen atoms.D101 macroporous adsorption resin is suitable for separation and purification of TFDL,and the purification obviously improves the antioxidant activity of total flavonoids from Dendrobium officinale leaves in vitro.In this paper,through preliminary analysis of flavonoids in leaves,stems and flowers of Dendrobium officinale,optimization of extraction and purification process of flavonoids from leaves,and in-depth study of antioxidant activity in vitro,the flavonoids in leaves of Dendrobium officinale have been deeply understood.It is considered that leaves are a resource with great potential for development.Its cheap and sufficient sources and excellent antioxidant activity in vitro will have great development in the fields of medicine,food,health care products and cosmetics. |
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