| Sweet potato (Ipomoea batatas LAM.), is one of the four primary crops in China. As a vegetable, its leaves have abundant nutritional value and have enjoyed the " vegetable empress " reputation in the world. Studies have shown that the content of flavonoids, which have antioxidant, antibacterial and other anti-tumor effect was higher in sweet potato leaves than ordinary vegetables. But the leaves after sweet potato harvest have not been paid attention to. In this thesis, the sweet potato leaves after sweet potato harvest were chosen as the raw material. The influence of dynamic high pressure microfluidization(DHPM) on the yield, structure and antioxidant activities of the flavonoids were investigated.The main contents and conclusions were as follows:1. The content of total flavonoids was determined using rutin as control by the Aluminum nitrate chromogenic method. The results showed that, their maximum absorption wavelength were basically consistent, and the linear regression curve had good linearity and precision. So it can be used for the determination of flavonoids. 2. Total flavonoids contents of leaves, stalk and stem were contrasted, the result indicated total flavonoids extracted from leaves was the highest, and thus taking it as the raw material of follow-up tests3. Total flavonoids were extracted from sweet potato leaves by DHPM and optimum extraction conditions were obtained by the orthogonal test. Results showed that temperature is the most significant factor impacting on the yield of total flavonoids. The optimum conditions were as follows:solid-liquid 1:40, pressure of DHPM 100MPa, extraction temperature 75℃, aqueous ethanol(v/v) 70%, extraction time 120 min, treatment times of DHPM twice, and extraction three times. The yield of total flavonoids was up to 5.75% under those conditions.4. The micro structure of sweet potato leaves was observed by scanning electron microscopy, magnification of 300 times and 5,000 times. The results showed that:the particle size of sweet potato leaves pretreated by DHPM were smaller than by Homogenizer, and with the increment of DHPM pressure, the particle size was decreased.It achieved the best result under the pressure of 120MPa, while under the pressure of 140MPa, the particle of sweet potato leaves might produce condensation effects, making some small particles condense into larger ones. The effect of DHPM on cell disruption had positive correlation to the pressure.5. Total flavonoids from sweet potato leaves were purificated by macroporous resin. Through the comparison of static adsorption capacity and desorption capacity of nine macroporous resin, such as LK001, AB-8, HPD-722, HPD-720, and static adsorption kinetics experiment was investigated by choosing five of them. Results showed that LK001 resin had the best adsorption-desorption capacity, and the optimal feed concentration was 2-3mg/mL, the optimal feed flow rate was 2 mL/min, the optimal elution reagent was 70% ethanol, the optimal flow of desorption was 1.5 mL/min.6. HPLC-MS/MS was employed to analyse the flavonoids structure and determining the quercetin concentraction of sweet potato leaves treated by different methods. Results showed that:sweet potato leaves contained quercetin, myricetin, quercetin-3-O-glucoside, rhamnocitrin, Ombuin, Astragalin, 4',7-dimethoxykaempferol, including chlorogenic acid and its derivatives.The flavonoids sample from sweet potato leaves by conventional extraction, conventional extraction treated by DHPM and pretreated by DHPM before extraction were compared. Results showed that there was no significantly effect of DHPM processing on the flavonoid structure. The quercetin component was reduced, while rhamnocitrin content was increased in the flavonoids sample pretreated by DHPM before extraction.7. Antioxidant abilities of crude and purified samples from sweet potato leaves by conventional extraction, conventional extraction treated by 100MPa of DHPM and pretreated by 100 MPa of DHPM before extraction were measured by DPPH scavenging activity, scavenging superoxide anion activity, scavenging hydroxyl radical activity.Results showed that:the extracts obtained by different methods possessed the free radical scavenging activity, and the effect was enhanced with increasing flavonoids concentration, but the scavenging capabilities were weaker than VC. The order of scavenging capability on different free radicals was:DPPH free radical> Superoxide radical>Hydroxyl. Free radical scavenging activity of purified samples was better than the crude ones. There were no differences in free radical scavenging of the three crude samples, and among the purified samples, the one pretreated before extraction possessed the best free radical scavenging capacity. |
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