Study On The Enzymatic Assisted Extraction, Isolation, Purification And Antioxidant Activity Of Flavonoids In Onion Skin

Onion peels belong to liliaceae plant, which mainly located in the Province of Shandong, Sichuan, Xinjiang, Gansu et al. Flavonoids from onion peel has strong antioxidant activities, antivirus, anticancer, preventing and curing cardiovascular diseases. Onion is one of the important export vegetables in our country, and has a lot of useless materials during processing, which couses resource waste and environmental pollution. The technologies of the cellulase-assist extraction of the total flavonoids from onion peel were studied in this thesis. The chemical, spectral and chromatographic analysis were also used to research the structure and antioxidant activities of flavonoids in onion peel. Main results are as follows:1. Based on the single factor, we use central composite design to extract the onion-skin flavonoids with cellulase enzyme, the results showed that the optimum extraction conditions were obtained as follows:the added ratio of cellulose 0.52%,pH value 5.0,the temperature48℃,the extraction time 105min,solid-liquid ratio 1:40.2. The characteristic of absorption and desorption of six kinds of macroporous resins for onion peel flavonoids was studied. The dynamic absorbing and desorption behavior of X-5 resin was observed. The result showed the optimum absorption and desorption conditions of resin X-5 were: feeding rate 2.0 mL/min , pH value 5, concentration of feed 0.5 mg/mL, 80 % Ethanol was taken as desorption solution, elution rate 1.0 mL/min, elute volume 50ml.3. The purity of onion peel flavonoids can reach to 94.5% if they are separated by recrystallization for three times.The experiment aimed to analyze the main components of flavonoids from onion peel by using color reaction, thin-layer chromatography(TLC) and high performance liquid chromatography(HPLC) respectively. Color reactions proved the extract from onion peel be to flavonoids, According to TLC results, the flavonoids from onion peel are mainly composed of quercetin, and the results of HPLC showed that the flavonoids of onion peel are mainly quercetin and kaempferol.4. Antioxidation experiments showed that flavoniods from onion peel have very strong scavenging capabilities for DPPH free radical and hydroxyl radical. IC50 values of the onion peel crude flavoniods are 3.751,4.267μg/mL respectively, however, IC50 values of the flavones after purification are 5.633μg/mL,5.675μg/mL. Meanwhile, onion peel flavones has the ability of scavenging NO₂^-. The order of DPPH free radical scavenging: Tea polyphenol > The onion peel crude flavoniods > The flavones after purification > Vc; The order of·OH scavenging: Tea polyphenol > The onion peel crude flavoniods> The flavones after purification > Vc; The order of NO₂^-scavenging: The onion peel crude flavoniods > Tea polyphenols > Vc > The flavones after purification; The order of reducing Power: The onion peel crude flavoniods > Tea polyphenols > Vc > The flavones after purification. Flavonoid from onion peel has strong antioxidant activities, which can be used in health food and pharmaceutical.