omega-3 çoklu doymamış yağ asitleri (ÇDYA), özellikle eikosapentaerıoik asit (EPA) ve dokosahekzaerıoik asit (DHA) insan sağlığı açısından önemlerinden dolayı artan bir ilgi görmektedir. EPA ve DHA antiinflamatuar, antitrombotik, antiaritmik, antimitojenik, hipolipemik ve vazodilatör özellikler gösterirler. Bu özellikleri ile başta kor oner kalp hastalıkları olmak üzere, hipertansiyon, tip 2 diyabet, ülseratif kolit, romatoid artrit, depresyon ve kanser gibi birçok hastalığın önlenmesinde ve tedavisinde potansiyel etkiye sahiptir. Bu çalışmada balık yağından gıda ve farmasötik kullanımlar için ÇDYA 'ince zenginleştirilmiş ürünlerin eldesi amaçlanmıştır. Bu amaçla, alabalık (Oncorhynchus mykiss) yağından üre fraksiyonlama yöntemine göre ÇDYA (EPA, DHA, 18:3 omega-3, 20:4 omega-3 ve 22:5 omega-3) içeriği yüksek konsantratlar üretilmiştir. Üre fraksiyonlama deneyleri 4 °C' de üç değişkenli ve üç seviye değerli yüzey merkezli küp tasarım noktalarında yapılmıştır. Bağımsız değişkenler olan üre:yağ asitleri oranı (ağ/ağ), etanol:üre oranı (hac/ağ) ve kristalizasyon zamanının (saat) elde edilen ürünlerin ÇDYA içeriğine (tepki değerine) olan etkileri incelenmiş ve reaksiyon koşulları Tepki Yüzey Metodolojisi 'ne göre optimize edilmiştir. Optimum reaksiyon koşulları 3.5 üre.yağ asitleri oranı (ağ/ağ), 5.6 etanol:üre oranı (hac/ağ) ve 4.8 saat kristalizasyon zamanı olarak bulunmuştur. Bu koşullarda, alabalık yağından % 88.1 ÇDYA içeren ürün elde edilmiştir. Ayrıca değişkenlerin tepki değerine olan etkisini gösteren kuadratik polinomiyal model denklem oluşturulmuştur. Elde edilen model denklemin regresyon katsayısı 0.99 olarak bulunmuştur. Bu da model denklemin güvenilir olduğunu göstermektedir.

The omega-3 polyunsaturated fatty acids (PUFA), especially eicosapentaenoic acid (EPA), docosahex-aenoic acid (DHA), alpha-linolenic acid (ALA) are attracting increasing attention because of their importance to human health. EPA is the precursor of prostaglandins, tromboxanes and leukotrienes, which are effective anti aggregatory substances. DHA is a main component of membrane phospholipids of brain and retina cells. Clinical studies show that DHA is essential for the growth and development of the. brain in infants and for maintenance of normal brain functions in adults. Recently it has been shown that EPA and DHA supplementation has positive health effects including attenuation of coronary heart disease risk factors (hypertension, hyper-lipidemia, platelet aggregation, glucose tolerance); modulation of eicoscmoid synthesis (cellular immune system, dermal integrity) and tumoricidal activity. Some studies indicated that the PUFA concentrates, devoid of more saturated fatty acid, are much better than oils themselves since they allow the daily intake of total lipid to be kept as low as possible. The PUFA concentrates can be produced by several methods, including fractional crystallization, urea fractionation, molecular distillation, supercritical fluid extraction, silver ion complexation and enzymatic hydrolysis and esterification reactions. However, the simplest and the most efficient technique for obtaining PUFA concentrates in the form of free fatty acids is urea fractionation. Initially the triacylglyc-erols of the oil are split into their constituent fatty acids by using alcoholic KOH and these fatty acids are then mixed with an ethanol solution of urea for complex formation. The saturated and the monoun-saturated fatty acids easily complex with urea and crystallize out on cooling. The liquid or non-urea complexedfraction (extract) is enriched with PUFA.In this study, urea fractionation of rainbow trout (Oncorhynchus mykiss) fatty acids was carried out to produce PUFA. Urea fractionation experiments were carried out at 4 °C according to a three-factor and three-level fcice-centered cube design points. The effects of independent variables such as urea-to-fatty acid ratio (w/w), ethanol-to-ureci ratio (v/w) and crystallization time (h) on the PUFA content of the obtained products (responce) were investigated and reaction conditions were optimized by Responce Surface Methodology (RSM). Free fatty acids (4 g) were mixed with urea in 95 % aqueous ethanol and heated at 60°C with stirring until the mixture was turned into a clear homogenous solution. The ratio of urea-to-fatty acids was changed by using different amounts of urea, and the ratio of ethanol-to-urea was changed by using different amounts of ethanol. The homogenous solution was cooled to room temperature, placed in refrigerator kept at 4 °C for different periods for further crystallization. The crystals formed (urea-fatty acid adducts, also referred to as the urea complexing fraction) were separated from the liquid (non-urea complexing fraction) by fast filtration. The liquid was diluted with an equal volume of water and acidified to pH 2-3 with 6 N HCl; an equal volume of hexane and 10 mL of saturated salt solution were subsequently added and the mixture was stirred thoroughly for 1 h, and then transferred to a separatory funnel. The hexane layer containing the liberated extract fatty acids was separated from the aqueous layer. The solvent was removed using a rotary evaporator. The obtained fatty acids were weighted and designated as 'extract' throughout this study. The fatty acid composition of the extract was determined by GC.Before RSM was applied, an appropriate range (lower, middle, and upper points, levels) for each independent variable was determined by varying one independent variable at a time while keeping the others constant. A total of 17 experiments were carried out according to a three factor, three level face-centered cubic design points. In the urea fractionation of rainbow trout fatty acids, the range of each variable was selected as follows: urea-to-fatty acids ratio, 2-4; ethanol-to-urea ratio, 5-9; time, 1-15 h. Optimal conditions were determined to be a urea-to-fatty acids ratio of 3.5, ethanol-to-urea ratio of 5.6 and a time of 4.8 h. Experiments conducted under these optimized conditions will be yielded an product containing 88.1 % PUFA. A good quadratic model was obtained as highly significant with a satisfactory regression coefficient (R2) found as 0.99. In conclusion, the PUFA enriched product was obtained from rainbow trout fatty acids by urea fractionation in this study. This concentrate could be used as valuable supplement for food and pharmaceutical purposes.