Properties and Stability of Catfish Oil-in-water Emulsions as Affected by Oil and Emulsifier Concentrations Nor Hayati Ibrahim + and Nurul Najwa Md Yusof Department of Food Science, Faculty of Agrotechnology and Food Science, Universiti Malaysia Terengganu, Kuala Terengganu, Terengganu, Malaysia Abstract. This study was conducted to investigate the effect of oil and emulsifier concentrations on the properties and stability of catfish oil-in-water emulsions. Beverage-type emulsions were prepared with 5 and 10% catfish oil as dispersed phases and the emulsions were stabilized by sodium caseinate (emulsifier) at 0.10, 0.25 and 0.5% concentrations. Almost all emulsions exhibited a monomodal type of droplet size distribution with average sizes of 9 – 17 and 16 – 33 μm for surface-weighted (d 3,2 ) and volume-weighted (d 4,3 ) mean diameters, respectively. All emulsions demonstrated a thixotropic flow behavior with apparent viscosities ranging from 87 – 166 mPa.s. The interaction of oil and emulsifier concentrations was found to give significant (p < 0.05) effects on the droplet size distribution and viscosity of the emulsions. The physical stability of the emulsions was found to be significantly (p < 0.05) affected by the oil concentration alone whereby the phase separation was high in the emulsion containing 5% oil. Inversely, the peroxide value was significantly (p < 0.05) affected by the emulsifier concentration alone in which the highest concentration (0.5%) exhibited a high lipid oxidation. Keywords: Catfish oil, emulsion, oil-emulsifier interaction, droplet size, viscosity, stability. 1. Introduction African catfish (Clarias gariepinus) is a main species used for aquaculture industry mainly in Africa, and has also been introduced in Europe and southern Asia. The fish contains the highest amount of oil (10.9%) compared to the other types of catfish such as Clarias batrachus (9.73%) and Clarias macrocephalus (8.99%). Fish oil is one of major fishery products with pharmaceutically importance. Fish oil is known to have docosahexanoic acid (DHA) and ecosapentanoic acid (EPA) or omega-3 fatty acids in various amounts depends on the type of fish itself and other factors. EPA and DHA are crucial for growth and development especially for the infants [1] and also for preventing treatment of coronary artery disease (arteriosclerosis), hypertension, arthritis and autoimmune disorders [2]. African catfish oil contains about 25% polyunsaturated fatty acid (PUFA) with a significant amount of EPA and DHA [3]. Recently, consumption of fish oil in the form of emulsion seems to become increasingly popular. Moreover, a number of scientific studies on fish oil emulsions are available such as on salmon, tuna and menhaden oil-in-water emulsions [4, 5]. In short, these studies found that properties and stability of fish oil emulsions are much affected by the level of oil itself as well as other minor ingredients especially emulsifier. However, being a complex system, interaction effect between oil and emulsifier at an interfacial phase of the emulsion should also be of concern. Despite catfish oil is known to have important health benefits due to its omega-3 fatty acid content, yet no research has been done on its potential as functional foods like fish oil emulsion. Therefore, the objective of the present study was to investigate the interaction effects between catfish oil and sodium caseinate at different concentrations and the interaction effect between both factors on the stability and properties of catfish oil-in-water emulsion. + Corresponding author. Tel.: +6096683644; fax: +6096683434; Email: yati@umt.edu.my 248 2012 International Conference on Environment, Energy and Biotechnology IPCBEE vol.33 (2012) © (2012) IACSIT Press, Singapore