Original Article Concentration of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) of Asian catfish oil by urea complexation: optimization of reaction conditions Pornpisanu Thammapat 1 , Sirithon Siriamornpun 2 , and Patcharin Raviyan 1 * 1 Division of Food Science and Technology, Faculty of Agro-Industry, Chiang Mai University, Chiang Mai, 50100 Thailand. 2 Department of Food Technology and Nutrition, Faculty of Technology, Mahasarakham University, Mahasarakham, 44100 Thailand. Received: 7 May 2015; Accepted: 1 October 2015 Abstract Optimization of the concentrating conditions of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) ex- tracted from Asian catfish oil was studied to obtain a maximum concentration. The crude fish oil was extracted from the belly flap and adipose tissue of Asian catfish, and the extracted oil was used as fresh crude oil. The EPA and DHA were concentrated by the urea complexation method. A hexagonal rotatable design was applied to examine the effects of crystallization temperature and urea-to-fatty acid ratio on the total content of EPA and DHA (Y 1 ) and the liquid recovery yield (Y 2 ). The second order polynomial regression models for Y 1 and Y 2 were employed to generate the response surfaces. Under the optimum conditions of -20 °C and a urea-to-fatty acid ratio of 4 (w/w), the total concentration of EPA and DHA could be increased by up to 88%, while a liquid recovery yield of 26% was obtained. Keywords: Asian catfish, omega-3 fatty acid, optimization, Pangasius bocourti, response surface Songklanakarin J. Sci. Technol. 38 (2), 163-170, Mar. - Apr. 2016 1. Introduction The Asian catfish (Pangasius bocourti) is a catfish species of the Pangasiidae family (Orban et al., 2008). This fish is being widely cultured in floating cages in the Mekong River in Northeastern provinces of Thailand. The Asian catfish is popular in Thai dishes and is often farmed for food. Among other farm fishes, it has provided local Thai people with fish protein and fish oil. Recently, it has become a highly demanded fish in the European market and has been exported as frozen fillets to European countries (Cacot et al., 2002; Anonymous, 2005). However, many of the Asian catfish by-products are still not utilized, and there are issues associated with acquir- ing and processing them (Wu and Bechtel, 2008). The ability to process Asian catfish by-products or refrigerate large vol- umes of by-product remains low, especially at small, remote processing plants. This problem often results in as much as 60-70% of the by-products being discarded. The major by- products from the processing line of Asian catfish in Thailand are the heads, tails, skin, belly flaps, adipose tissue and viscera (Anonymous, 2005; Silva and Dean, 2001). Fish has been known as a source of high-quality protein and lipid (Weber et al., 2008), with fish oil being an important source of omega-3 polyunsaturated fatty acids (PUFA) (Navarro-García et al., 2004). PUFA takes part in the vascular retina formation and brain development of the child during pregnancy (Gould et al., 2013; San Giovanni and * Corresponding author. Email address: patraviyan@gmail.com http://www.sjst.psu.ac.th