| Lotus (Nelumbo nucifera Gaertn.), one of the most well known ornamental and economic perennial aquatic plants, has been cultivated for more than 3,000 years in China and now widely cultivated and consumed all over the world. Almost all parts of the plant may be eaten as a vegetable and it is also used in traditional medicine, especially lotus seed, nelumbinis plumula, lotus seedpod, lotus stamen and lotus leaf have listed in the Chinese Pharmacopoeia and have remarkable physiological activity. The study of lotus flower is relatively less, which restricted the development and utilization of this material, in this study, by investigating the chemical constitution and antioxidant activity of lotus flower to provide scientific basis for its development and utilization.(1) Determination of essential oil from Nelumbo nucifera Gaertn flower by GC-MSThe essential oil of Nelumbo nucifera Gaertn flower was extracted by steam distillation, its constituents and the relative contents were analyzed by gas chromatography-mass spectrometry (GC-MS) and determined by area normalization. 79 compounds were identified and among them Acetic ether (6.61%), 1, 4-dimethoxy benzene (9.06%), Cinnamic aldehyde (6.60%), Cinnamic alcohol (10.20%) and Jasmone (4.75%) were the main compounds. The constituents of essential oil of Nelumbo nucifera Gaertn flower were determined, which provided a scientific basis for the further exploitation and utilization of the resource of Nelumbo nucifera Gaertn flower.(2) Extraction, separation and identification of flavonoids from the petals of Nelumbo nuciferaFollowing an initial clear-up step on polyamide, four main flavonoids were isolated and purified from the petals of Nelumbo nucifera for the first time by high-speed counter-current chromatography (HSCCC). The separation was performed in one step with a two-phase solvent system composed of ethyl acetate-methanol-water-acetic acid (4:1:5:0.1, v/v/v/v), in which the lower phase was used as the mobile phase at flow-rate of 1.0 mL/min in the head-to-tail elution mode. Ultimately, 5.0 mg syringetin-3-O-β-D-glucoside, 6.5 mg quercetin-3-O-β-D-glucoside, 12.8 mg isorhamnetin-3-O-β-D-glucoside and 32.5 mg kaempferol-3-O-β-D-glucoside could be obtain from 125 mg crude sample and their purities were 98.6%, 98.2%, 97.3% and 99.2%, respectively. Their structures were identified by ESI-MS, 1H-NMR and 13C-NMR. (3) Determination of antioxidant activity and chemical compositions of Nelumbo nuciferaTo study the effect of different drying methods (room drying, sunny drying, hot-air drying, microwave drying and freeze drying) on antioxidant activity and chemical compositions of Nelumbo nucifera. Compared with ascorbic acid, antioxidant activity of Nelumbo nucifera, which were dried by different methods, has been measured and evaluated by three in vitro models, e.g. reducing power, DPPH radical scavenging and hydroxyl radical scavenging. The content of flavonoid, total phenolic and anthocyanin were also determined. The results indicated that the extract of Nelumbo nucifera has remarkable abilities in reducing power, scavenging DPPH radical and hydroxyl radical; Antioxidant activity and the contents of active components showed significant differences among different drying methods, the sample by freeze drying showed the best antioxidant activity and the contents of flavonoid, total phenolic and anthocyanin in which were 60.20 mg/g, 85.35 mg/g and 15.03μg/100g, respectively, while the sample dried by sunny drying showed the worst antioxidant activity and the content of flavonoid, total phenolic and anthocyanin in which were 0.39 mg/g, 19.08 mg/g and 0.28μg/100g, respectively. The methods effectively evaluated the effect of different drying methods on antioxidant activity and chemical compositions of Nelumbo nucifera.
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