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J. Cosmet. Sci., 65, 245–252 (July/August 2014) 245 Nanoemulsion of D -limonene in water system prepared by ultrasonic emulsifi cation WEN-CHIEN LU, TING-JIE ZHANG, DA-WEI HUANG, and PO-HSIEN LI, Department of Medicinal Botanical and Health Applications, Da-Yeh University, Dacun, Changhua 51591 (W.-C.L., T.-J.Z., P.-H.L.), and Department of Food & Beverage Management, China University of Science and Technology, Nangang District, Taipei City 115 (D.-W.H.), Taiwan, Republic of China. Accepted for publication May 23, 2014. Synopsis D -Limonene is a component of essential oil extracted from citrus fruits. This component has shown chemo- preventive and therapeutic activity against a wide variety of experimental tumors, but D -limonene is unstable and lose its lemon-like fl avor under normal storage condition, and it is almost insoluble in water. Therefore, studying the formation of nanoemulsion in D -limonene in water system is probably a good method to prevent the oxidation degradation of D -limonene. For the purpose of our study, we used mixed surfactant to form D - limonene-in-water emulsion, and found the best formula for forming nanoemulsion droplets with specifi ed hydrophilic–lipophilic balance (HLB) value and droplet size. The results demonstrated that nanoemulsion droplets formed at So ratio of 0.4 and applied power of 18 W for 120 s under mixed surfactant at HLB values 12 and had droplet size of 20–50 nm. INTRODUCTION Nanoemulsions are emulsions with droplet size between 20 and 100 nm (1). Because of the small droplet size, nanoemulsions appear transparent or translucent and possess more stability against sedimentation, coalescence, fl occulation, and Ostwald ripening com- pared with convention emulsions (2,3). The physicochemical properties of nanoemulsions are interesting for practical applications because of the small droplet size and longtime stability. Nanoemulsions are used in agrochemicals for pesticide delivery (4), in cosmetics as a vehicle for personal care or skincare products (5), in fragrance as a matrix to encapsu- late the volatile compounds and controlled release which are desirable to be formulated alcohol free (6), and in beverages, to give the products an opaque appearance and suitable aroma (7). Address all correspondence to Po-Hsien Li at pohsien@mail.dyu.edu.tw.