Studies On Extraction, Separation, Identification And Antioxidant Ablity Of Mulberry (Morus Alba L.) Leaf Flavonoids

With the aim of extraction, separation and purification flavonoids frommulberry leaf, extraction experiments of flavonoids using variousmethods, including ultra high pressure extraction and microwave-assistedextraction. Based on a large number of resources investigation, literaturesystematization and experiments, optimum extraction, separation andpurification conditions were found. The structures of flavonoids wereconfirmed withUV, IR, ESI-MS, ¹H-NMR, ¹³C-NMR.1. Determination of mulberry leaf flavonoids.The contents of flavonoids in mulberry leaf were determined bydeveloped reversed phase high performance liquid chromatography(RP-HPLC). Mulberry leaf flavonoids could be separated on HypersilODS2 (4.6×250 mm, 5μm) with methanol-0.5% phosphoric acid asmobile phase gradient elution with UV detector (358 nm). At the flowrate of 0.8 mL/min, analysis could be finished in 30 min. This method isnot only simple and fast, but also the accuracy, precision and stability ofthe method are very good. The content of mulberry leaf flavonoids was 25.30 mg/g2. Extraction of mulberry leaf flavonoids.Ultra high pressure extraction of mulberry leaf flavonoids indicatedthat the order of influence ultra high pressure extraction factors was asfollows: the pressure, the time, the solvent/solid ratio, respectively. Theoptimal plan was as follows: solvent 70% ethanol, sample to solvent 1:20, ultra high pressure 500 MPa extracting for 6.0 min. The optimalextraction yield of flavonoids from mulberry leaf was up to 24.0 mg/g.Microwave-assisted extraction of mulberry leaf flavonoids indicatedthat the order of influence microwave-assisted factors was as follows: thepower, the time, the temperature, respectively. The optimal plan was asfollows: solvent 70% ethanol, sample to solvent 1:20,microwave-assisted power 600W, microwave-assisted time 15.0 min,microwave-assisted temperature 70℃,The optimal extraction yield offlavonoids from mulberry leaf was up to 22.8 mg/g.Ultra high pressure extraction or microwave-assisted extraction ofmulberry leaf sample surface pore changed a lot and the fill-out obviously;its superficial organization also had become looser and specific surfacearea had increased. The ultra high pressure extraction, themicrowave-assisted extraction mulberry leaf flavonoids extraction ratecan achieve 94.9% and 90.1%, respectively, much higher than the roomtemperature extraction (62.5%) by far; And that the extraction time is only 6.0 min and 15.0 min, which is much faster than the roomtemperature extraction (24h).3. Separation and identification of mulberry leaf flavonoids.Five flavonoids were obtained and identificated as Rutin,Isoquercitrin, Astragalin, Morin and Kaempferol. Morin exists in root,stem and leaf of Morus nigra L or root skin of Morus alba L, but only intrace leave. This is the first isolation of Morin from the leaf of Morusalba L.4. Antioxidant activity of mulberry leaf flavonoids.The research discovered the mulberry leaf flavonoids have strongantioxidant activity. Their antioxidant activity is stronger than BHT's, asynthesized commonly used food antioxidant. DPPH radical-scavengingappraisal indicated that the order of antioxidant activity of differentmulberry leaf flavonoids was as follows:Kaempferol≈Morin＞Isoquercitrin＞Astragalin＞Rutin...