Positional distribution of fatty acids in hoki and tuna oils was carried out in the present study via pancreatic lipase hydrolysis and 13Carbon nuclear magnetic resonance (13C NMR) spectroscopy. The two methods gave consistent results for hoki but conflicting values for tuna oil. Saturated fatty acids (SFA) were generally enriched at sn-2 while MUFA were preferentially located at sn-1,3 for hoki by pancreatic lipase treatment. Of the PUFA, DHA in hoki oil was significantly located at sn-2 position, whereas eicosapentaenoic acid (EPA) was randomly distributed via both methods. DHA and EPA in tuna oil were both preferentially located at sn-2 position by NMR spectroscopy. The NMR results for n-3 PUFA were in general agreement with other fish oils studied where DHA showed preference for sn-2 but EPA displayed preferential differences among species. The ratio of DHA in hoki oil at sn-2 position was higher than tuna oil, thus enhancing its bioavailability. The opposite was the case for EPA. For pancreatic lipase hydrolysis of tuna oil, results showed that both DHA and EPA were incompletely recovered along with other PUFA confirming that pancreatic lipase hydrolysis is an unreliable method for positional distribution determination in tuna oil compared to 13C NMR analysis. The ratio of long chain PUFA to triglycerides exceeds 1:1 in tuna oil, causing steric hindrance for hydrolysis of the long chain PUFA residue at sn-1,3 position.
Practical applications: Fish oil contains bioactive omega-3 fatty acids (DHA and EPA), however bioavailability and oxidative stability of these omega-3 fatty acids depends on their positional distribution. Pancreatic lipase has been used in determination of positional distribution of fatty acids in fish oil, but this method involves heat and is time consuming and not suitable for fish oil with more than one molecule of PUFA in a single triglyceride. NMR has gained popularity in positional distribution determination of n-3 fatty acids in fish oil as it is a rapid and non-destructive method compared to the conventional chemical and enzymatic methods.