Study on Extraction and Antioxidant Activity of Oleuropein from Olive Leaves by Synergistic Ultrasonic/Microwave Assisted
The optimum process for ultrasonic-microwave synergistic extraction(UMAE)of oleuropein was investigated using olive leaves as raw material.Ethanol was selected as the extraction solvent,and the content of oleuropein was determined using differential subtraction method of UV-Vis spectroscopy.The effects of the independent variables time,microwave power,solid-liquid ratio,temperature and ethanol concentration on the content of oleuropein were investigated through one-way experiments.The Plackett-Burman(PB)test was performed to obtain the key process parameters in the ultrasound-microwave synergistic extraction method,and finally,response surface analysis(RSA)was performed.On this basis,the effect of oleuropein on the scavenging rate of DPPH,ABTS+andhydroxyl radicals was examined by in vitro antioxidant test.The results showed that the extraction time of 18 min,microwave power of 475 W,solid-liquid ratio of 1∶45 g/mL,temperature of 40 ℃,and ethanol concentration of 60% were the optimal condition for the ultrasound-microwave synergistic extraction,at which the content of oleuropein was 68.91±0.64 mg/g.The semi-inhibitory concentration(IC50)for the scavenging rate of the DPPH radicals was 0.035±0.001 mg/mL,the semi-inhibitory concentration(IC50)for ABTS radical scavenging was 0.058±0.003 mg/mL,and the semi-inhibitory concentration(IC50)for hydroxyl radical scavenging was 0.004±0.010 mg/mL.The study showed that olive extract obtained from olive leaves had strong antioxidant effect.
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