Extraction Process Optimization of Total Flavonoids from Euchresta tubulosa Dunn and its Antioxidant Activity
Microwave-ultrasonic assisted deep eutectic solvent(DES)was used to optimize the extraction conditions of total flavonoids from the leaves of Euchresta tubulosa Dunn and the optimal DES were selected.On the basis of single factor experiment,Plackett-Burman and response surface experiments were used to optimize the extraction process.The scavenging effects of the total flavonoids on DPPH·,·ABTS+and·OH under the optimal extraction process were investigated.The results showed that the optimum solvent system was n(choline chloride)∶n(triethylene glycol)=1∶3.The optimum extraction conditions were as follows:extraction time was 45 min,extraction temperature was 74℃,solid-liquid ratio was 1∶45,microwave power was 300 W,DES water content was 25%and ultrasonic power was 300 W.Under these conditions,the yield of total flavonoids in leaves was 3.460%.Total flavonoids were separated by ethyl acetate,hot ethyl acetate(50±1)℃,AB-8,NKA-9 and D101 macroporous adsorbent resins,with the recovery rates were 23.40%,28.09%,88.66%,71.55%and 41.86%,respectively.The half inhibitory mass concentration(IC50)values of total flavonoids isolated by AB-8 macroporous resin on DPPH·,·ABTS+and·OH were0.017 05,0.018 35 and 0.123 30 g/L,respectively.The scavenging rate of DPPH·and·ABTS+by total flavonoids was significantly higher than that of vitamin C(Vc),while the scavenging rate of·OH was slightly lower than that of Vc.Further analysis showed that under optimized conditions,the yield of total flavonoids from leaves(3.460%)was higher than those of stems and roots(2.059%and 1.875%),higher than those of single microwave extraction and ultrasonic extraction(3.377%and 3.390%),lower than that of heating reflux extraction(3.635%),while the time was only 1/4 of that of refluxing extraction.
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