E: Food Engineering & Physical Properties JFS E: Food Engineering and Physical Properties Comparisons of Chemical and Physical Properties of Catfish Oils Prepared from Different Extracting Processes S. SATHIVEL, H. YIN, W. PRINYAWIWATKUL, AND J.M. KING ABSTRACT: Four different catfish oil extraction processes were used to extract oil from catfish viscera: process CF1 involved a mixture of ground catfish viscera and water, no heat treatment, and centrifugation; process CF2 involved ground catfish viscera (no added water), heat treatment, and centrifugation; process CF3 involved a mix- ture of ground catfish viscera and water, heat treatment, and centrifugation; process CF4 involved ground catfish viscera, enzymatic hydrolysis, and centrifugation. Chemical and physical properties of the resulting of catfish oils were evaluated. The CF4 process recovered significantly higher amounts of crude oil from catfish viscera than the other 3 extraction methods. The CF4 oil contained a higher percent of free fatty acid and peroxide values than CF1, CF2, and CF3 oils. Oleic acid in catfish oil was the predominant fatty acid accounting for about 50% of total fatty acids. Weight loss of oils increased with increasing temperatures between 250 and 500 ◦ C. All the catfish oil sam- ples melted around −32 ◦ C regardless of the extraction methods. The flow behavior index of all the oil samples was less than 1, which indicated that the catfish oils exhibited non-Newtonian fluid behavior. The apparent viscosity at −5 and 0 ◦ C was significantly higher (P < 0.05) than those at 5, 10, 15, 20, 25, and 30 ◦ C. The average magnitude of activation energy for apparent viscosity of the oil was higher for CF2 than CF1, CF3, and CF4. Keywords: catfish oil, extraction methods, rheological properties, thermal properties Introduction V iscera from Channel catfish (Ictalurus punctatus) is an abun- dant and underutilized by-product that can be used as a unique lipid source. Channel catfish is the 4th-most popular fish product consumed in the United States. The 4 major commercial catfish producing states in the United States are Alabama, Arkansas, Louisiana, and Mississippi. In 2005, these states produced over 272000 metric tons of catfish with a stable monthly production of about 22700 tons (NASS 2006). The by-products of catfish process- ing consists of heads, frames, skin, and viscera, which often ends up in landfills or rendering plants. The yield of catfish when processed as whole fillets is around 45%, generating about 55% waste. The av- erage weight of viscera is about 265 g, which is about 10% by weight of a live whole catfish. Much of the oil in the catfish is found in the viscera, which contains approximately 33% lipid (Sathivel 2001). The viscera can be used for recovering of catfish oil that could be converted into edible oil or biodiesel products. Extracting oil from viscera may add value to catfish viscera, which is currently a processing waste. For the last 2 decades, inter- est in dietary effects of marine omega-3 fatty acids has increased because they play a major role in human health (Kronhout and others 1985). Natural fish oils have been claimed to help main- tain heart and vascular health in humans (Haglund and others 1998). Producing and purifying catfish oil from catfish viscera for the growing fish oil market can benefit the catfish industry. Small fish oil processors and entrepreneurs are interested in establishing small scale, cost effective oil extraction, clarification, and stabiliza- MS 20080545 Submitted 6/21/2008, Accepted 11/14/2008. Authors are with the Dept. of Food Science, Louisiana State Univ. Agricultural Center, Baton Rouge, LA 70803-4300, U.S.A. Direct inquiries to author Sathivel (E-mail: ssathivel@agcenter.lsu.edu). tion methods for catfish oil destined for human consumption. Fish oil can be extracted using a number of methods including render- ing, enzymatic hydrolysis, chemical extraction, mechanical press- ing, and use of centrifugal force. However, information related to quality of fish oil prepared from the different extraction methods is not readily available. The unpurified catfish oil contains free fatty acids, primary oxidation products, minerals, pigments, moisture, phospholipids, and insoluble impurities that reduce the oil qual- ity. The amount of these impurities present in the oil may depend on the fish oil extraction methods. The longer these components remain in the oil, the greater their negative effects on oil quality. Finding a suitable method to extract oil from catfish viscera may reduce some of the impurities in the oil and thus may cut down the multiple fish oil purification steps to 1 or 2 steps. The amount of impurities present in the oil influences the rheological and ther- mal properties of fish oil (Sathivel and others 2008a, 2008b). Knowl- edge of thermal, rheological, and oxidation properties of the catfish oil is essential for the design of purifying processes, the analysis of production cost, and the final quality evaluation. The objective of study was to evaluate the effects of different extraction processes on chemical and physical properties of catfish oils. Materials and Methods Catfish oil production Catfish viscera was obtained from a local seafood store in Baton Rouge (La., U.S.A.), and stored at −40 ◦ C until further pro- cessed. The viscera was thawed overnight at 4 ◦ C and ground using a Hobart grinder (K5SS, Hobart Corp., Troy, Ohio, U.S.A.) through a 7-cm diameter plate having 12-mm diameter openings, and subsequently ground through a plate with 6-mm diameter openings. The ground viscera was used to produce catfish oil by the E70 JOURNAL OF FOOD SCIENCE—Vol. 74, Nr. 2, 2009 C  2009 Institute of Food Technologists R  doi: 10.1111/j.1750-3841.2009.01050.x Further reproduction without permission is prohibited