# Production and Refinement of Omega-3 Rich Oils from Processing By-Products of Farmed Fish Species
## 3 Results and Discussion
### Fatty Acid Profile of Oils  
The results of the fatty acid profile of the crude oils and their changes after oil refinement are presented in Table 2 and in Figure 2A-D. The most dominant SFA contributing approximately 52-55% of total SFA, in all investigate oils was palmitic FA (C16:0). Its content was significantly higher in tuna oils in comparison to seabream/seabass oil and the control. Palmitic FA occurs naturally in fish, being a source of metabolic energy for their growth. The oleic acid (C18:1_n-9 cis_) was the major compound among MUFAs and in the studied oils amounted to approximately 14% in tuna oils, to 40% in seabass and gilthead seabream by-product refined oil. Among PUFAs, high concentrations of EPA (C20:5_n-3_) and even higher those of DHA (C22:6_n-3_) were found in all studied oils. The relative contents of EPA and DHA were expected to increase during the refining process [14; 33], but in this study the minimal increase was observed after refinement only for DHA in tuna liver oil. However, in both crude and refined tuna by-product oils amounts of EPA and DHA were found to be extremely high. In tuna oils and the control oil, especially in tuna liver oil dihomo-\(\gamma\)-linolenic acid (20:3_n-6_), was found in higher amounts (7.32-9.89%), while in seabream/seabass oil its precursor, linoleic acid (C18:2_n-6_) was found  
Figure 1: The oxidative stability (_n_ = 18) of crude and deodorized (refined) oils from tuna by-products, tuna liver, seabass and gilthead seabream by-products, and cod liver oil (control). significantly higher compared to other oils (17.32%). Erucic acid (22:1_n_-9) was found in small amounts in studied oils, with the highest content (1%) found in the control oil. The crude oils from tuna by-products and liver contained significantly higher total amounts of saturated fatty acids (32.7 and 35.6%, Figure 2) in comparison to seabass and gilthead seabream by-product oil (23.6%). The SFA profile of the oils did not statistically change with the refining process and tuna oils had significantly higher SFA content than the control. The MUFAs content was the highest in seabass and gilthead seabream by-product oil (46%) and did not change after refining. Tuna by-product oil had slightly higher MUFA content then tuna liver oil. The PUFAs were significantly higher in tuna by-product and tuna liver crude oils (37.7 and 35.2%) and they increased to 40.2 and 39.6% in refined oils, respectively. The content of PUFA-3, in the studied oils, ranged from 11.6-32.3% and was higher than that of PUFA-6 for 8.9-18.7% (Figure 2). A high percentage of PUFA indicates good nutritional values of the studied fish oils. The PUFA/SFA ratio of 0.4-0.5 is considered beneficial for human health [34], and it was significantly higher in the crude oils, while in refined oils it ranged from 1.1 to 1.2, significantly lower than in the control oil (Figure 2). In general, it is accepted that compared to wild caught fish, modern aquaculture products have lower _n_-3 FAs, and higher levels of terrestrial plant-originating C18:2_n_-6 as a result of feed composition [35]. Very high intake of _n_-6 was recognized as undesirable and it reduces the nutritional quality of fish oil. The sum of n-6 was 18-19% higher in seabass and gilthead seabream by-product oils and along with the lowest sum of _n_-3 and EPA+DHA. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Fatty Acid**} & \multirow{2}{*}{**Tuna By-Product Oil**} & \multicolumn{3}{c}{**Tuna Liver Oil**} & \multicolumn{3}{c}{**Seabass and Seabream**} & \multicolumn{1}{c}{**Cod Liver**} \\  & & & & & & **By-Product Oil** & **Oil** \\ \hline  & _Crude Oil_ & _Refined_ & _Crude Oil_ & _Refined_ & _Crude Oil_ & _Refined_ & _Control_ \\ \hline
**C12:0** & n.d. 1 & \(0.06\pm 0.00\) & \(0.07\pm 0.00\) & \(0.06\pm 0.01\) & \(0.02\pm 0.01\) & \(0.03\pm 0.00\) & \(0.02\pm 0.02\) \\
**C13:0** & n.d. & \(0.06\pm 0  
In tuna by-product oils the refining process resulted with a decrease share of MUFAs and the increase of PUFAs.