Microwave-assisted extraction of oleuropein from olive leaves and its antioxidant properties

The operation conditions of microwave-assisted extraction of oleuropein from olive leaves were studied.According to single factor experiment design,the effects of solvent,extraction time,temperature,solid-liquid ratio,ethanol concentration and extraction times on extraction yield of oleuropein were investigated.Based on the results of single factor experiment,three more significant factors, extraction temperature, extraction time and solid-liquid ratio, were selected in L₉(3³) orthogonal experiment.The optimal extraction parameters were determined as follows:ethanol concentration 75%, solid-liquid ratio 1:50 g/mL,extraction temperature 40℃,extraction time 3 min,microwave power 600 W.Under this operational condition,the oleuropein yield was(8.06%±0.06%),the total polyphenols content was(7.85%±0.01%) and the total flavonoids content was(2.20%±0.11%), however, the oleuropein yield was(6.61%±0.16%), the total polyphenols content was(6.99%±0.13%) and the total flavonoids content was(1.25%±0.11%) by thermal circumfluence extraction.The effects of the drying methods on DPPH free radical scavenging ability were discussed.It was observed that the olive leaf extract obtained by oven drying(30℃,IC₅₀=0.65 mg/mL) was found to have more scavenge DPPH capacity than that obtained by freeze vacuum drying (IC₅₀=0.69 mg/mL) and vacuum drying(IC₅₀=0.71 mg/mL).Microwave-assisted extraction of oleuropein and other active components is better than thermal circumfluence extraction.In three drying methods,oven drying(30℃) is better than other drying methods.A method is provided for extraction and preservation of olearopein in this article.