Fig. 3. The ratio value in the fraction that results from each crystallization process
Overall, the urea crystallization method was known to be able to provide more effective and efficient purification compared to the acetone and n-hexane crystallization methods. Urea crystallization was able to maintain the presence of PUFA n-3 groups, especially EPA and DHA in the fraction so that the levels increased [37]. Based on figures 2 and 3, the UPF fraction was very rich in n-3. UPF was able to increase the PUFA/trans-FA ratio from 0.37 to 1.45 and n-3/trans-FA from 0.3 to 1.36. The urea crystallization method proved to be able to produce fractions very rich in n-3 fatty acids. Even so, this method still needs to be further optimized because there was still an EA which has a higher amount compared to EPA and DHA. As shown in Figure 3, the ratio of EPA/EA and DHA/EA, although increasing, but still below one.
To eliminate EA completely, it is necessary to combine two purification methods such as urea crystallization method with molecular distillation which was able to separate EPA and DHA from sardine oil [38] or with Argentated Silica Gel Column Chromatography which was able to separate PUFA from tuna oil [36].
Conclusion
The urea crystallization method was significantly able to reduce the content of SFA and EA (trans-FA), and be able to maintain n-3 PUFA especially EPA and DHA in the oil fraction. Its seem from the increase of ratio value of PUFA/trans-FA from 0.37 to 1.45 and n-3/trans-FA from 0.3 to 1.36. Even so, the crystallization of Urea has not completely eliminated EA from the oil fraction. The only SFA that survived in the three factions was lauric acid. Overall the Urea crystallization method was able to recycle MAM became n-3 rich fraction.