ORIGINAL PAPER Effect of ionic liquids on enzymatic synthesis of caffeic acid phenethyl ester Sung Ho Ha • Tran Van Anh • Sang Hyun Lee • Yoon-Mo Koo Received: 30 May 2011 / Accepted: 17 July 2011 / Published online: 10 September 2011 Ó Springer-Verlag 2011 Abstract Although caffeic acid phenethyl ester (CAPE), an active flavonoid, plays an important role in the antio- xidant activity of honeybee propolis, the isolation of CAPE from honeybee propolis is time-consuming due to wide variety of impurities present. Therefore, biochemical method to synthesize CAPE was investigated in this study. Since ionic liquids (ILs) possess some unique characteris- tics as appreciated alternatives to conventional solvents for certain biotransformation, the effect of ILs as reaction media for enzymatic synthesis of CAPE was assessed. Several factors including substrate molar ratio, and reaction temperature affecting the conversion yield of lipase-cata- lyzed CAPE synthesis were also investigated. Reaction yields were significantly higher in hydrophobic ILs than in hydrophilic ILs (almost zero). Among nine hydrophobic ILs tested, the highest conversion of synthetic reaction was obtained in 1-ethyl-3-methylimidazolium bis[(trifluoro- methyl)sulfonyl]imide ([Emim][Tf 2 N]). A reaction tem- perature of 70 °C was found to give high conversion. In addition, optimal substrate molar ratio between phenethyl alcohol and caffeic acid (CA) was decreased significantly from 92:1 to 30:1 when ILs were used instead of isooctane. Keywords Ionic liquids Á Caffeic acid phenethyl ester Á Lipase Á Esterification Introduction Propolis, a natural product produced by the honeybee, has been used for centuries as a traditional medicine for several purposes all around the world. It has been reported that caffeic acid phenethyl ester (CAPE), an active flavonoid, plays an important role in the antioxidant activity of propolis [1]. Beside antioxidant effect, CAPE possesses several interesting biological and pharmacological activi- ties including antimicrobial, antiinflammatory, anticancer and immune modulatory activity [2–5]. Since the isolation of CAPE from honeybee propolis is time-consuming due to wide variety of impurities present, many of the studies developed (bio)chemical methods to synthesize CAPE. Some chemical processes proved success of CAPE synthesis from caffeic acid (CA) with basic or acidic catalysts [4, 5]. However, these routes do not meet the requirement for food applications due to the chemical reagents used causing harm to human body. The use of enzymatic synthesis, on the other hand, offers the advantages of specificity, milder reaction conditions and minimization of side effects [6–8]. However, enzy- matic synthesis of CAPE in toxic organic solvents often suffers from low yields and productivity because of the poor solubility of CA in most organic solvents. In regard to environment-friendly processes, it is required to use green alternatives to conventional organic solvents for a broad range of applications. Ionic liquids (ILs) are organic salts composed entirely of ions, with melting points below 100 °C. Interest in ILs stems from their potential as ‘‘green solvents’’ because of S. H. Ha (&) Department of Chemical Engineering and Nano-Bio Technology, Hannam University, Daejeon 305-811, Korea e-mail: shha@hnu.kr T. V. Anh Á Y.-M. Koo (&) Department of Biological Engineering, Inha University, Incheon 402-751, Korea e-mail: ymkoo@inha.ac.kr S. H. Lee Department of Microbial Engineering, Konkuk University, Seoul 143-701, Korea 123 Bioprocess Biosyst Eng (2012) 35:235–240 DOI 10.1007/s00449-011-0601-4