Marine Phospholipids: Methods to Measure Oxidation Status and Stability
MetadataShow full item record
Marine phospholipids (MPL) have a higher content of the omega-3 fatty acids EPA and DHA than triacylglycerols from the same source. In addition they have been shown to have a better bioavailability, and a better resistance towards oxidation. However, marine phospholipids are highly susceptible to oxidation because of the high amount of polyunsaturated fatty acids. This makes it challenging to incorporate phospholipids in food products. Knowledge of the oxidative status and stability of marine phospholipids is extremely important and methods to measure quality of phospholipids are needed. The aim of this master thesis was to screen methods used to measure the oxidation status and stability of marine oils and their applicability to measure oxidation status and stability of marine phospholipids. Phospholipids were isolated in three different ways. The phospholipids were called PL1, PL2, and PL3. PL1 was isolated with the Bligh and Dyer method with subsequent acetone precipitation. PL2 and PL3 were extracted by ethanol extraction, where PL2 was obtained after acetone precipitation of the ethanol extract. Soy lecithin, 18/12 oil, and cod liver oil were used as controls.The content of lipid classes in the phospholipids was analysed by TLC-FID analysis. The content of phospholipids in PL1 and PL2 was 98,7 ± 0,3 % and 97,7 ± 0,5 % respectively. PL3 was composed of 79,6 ± 0,7 % phospholipids and 20,4 ± 1,0 % neutral lipids. The oxidation status in the samples was measured by iodometric titration, the ferric thiocyanate method, and measurement of p-anisidine values, conjugated dienes, and TBARS. Iodometric titration according to ISO 3960 and NFT 60-220 resulted in negative peroxide values for phospholipids isolated by ethanol extraction (PL3). The ferric thiocyanate method and the measurement of TBARS resulted in a low PV-value and TBA-value respectively.The iodometric titration according to ISO 3960, the ferric thiocyanate method, and the measurement of TBARS resulted in positive and consistent results for PL1 and PL2, strengthening these methods as methods that work on these phospholipids. The iodometric titration according to NFT 60-220 resulted in variable results for PL1 and PL2, indicating that this method is not a good method for the determination of peroxide values in phospholipids. The amount of conjugated dienes in the samples was positive and consistent for PL1, PL2, and PL3 both in isooctane and chloroform. However, the results indicated that the measured degree of oxidation depended on the solvent used. The p-anisidine values were not measurable in PL2 and PL3 dissolved neither in isooctane nor in chloroform. This was most probably due to the presence of insoluble particles. A weight gain method (Schaal oven test) was performed to determine the oxidative stability of the samples. This determination resulted in clearly different curve paths for the marine oils and the phospholipids.