Abstract: The selective enzyme was screened from the 10 enzymes with high degradation rate of oleuropein (OE).The process of single factor (pH,temperature,time,the ratio of enzyme quantity and substrate) and a Box-Behnken Design on enzymatic hydrolysis of 81.04% OE olive leaf extract were studied.It was suggested that preparation of hydroxytyrosol from enzymatic hydrolysis of OE in the olive leaves was feasible.The result showed that the performance of hydrolysis treatments was best using hemicellulase as a bio-catalyst,and the high purity of OE in olive extract was beneficial to biotransform OE into hydroxytyrosol (HT).The optimal enzymatic conditions for achieving maximal yield of HT content obtained by the regression were as follows:pH 5,temperature 55 ℃ and the ratio of enzyme quantity and substrate 1:9.1.The experimental result was (11.31±0.15)%,and the degradation rate of OE was 98.54%.The presented results will provide effective foundation for hydroxytyrosol preparation from oleurpein in olive leaf extract.

Key words: Olea europea Leaf, hydroxytyrosol, oleuropein, enzymatic hydrolysis, hemicellulase