The antioxidant properties of phosphoHpids (PL) in a refined salmon oil model system were measured by deteP mining changes in the 2-thiobarbituric acid number and decreases in the ratio of docosahexaenoic acid (DHA)I palmitic acid (22:6/16:0) of a fish oil system incubated at 180°C for up to 3 h. The more phosphatidylcholine (PC) added to the oil system, the higher the oxidative stability obtained. The order of effectiveness of commercial phospholipids in inhibiting oxidation and the loss of polyunsaturated fatty acids was as follows: sphingomyelin (SPH) = lysophosphatidylcholine (LPC) = phosphatidylcholine (PC) = phosphatidylethanol~mine (PE) > phosphatidylserine (PS) > phosphatidyHnositol (PI) > phosphatidylglycerol (PG) > control s n|mon oil. Nitrogen contaJnlng PL, including PE, PC, LPC and SPH, were equally effective in exerting greater antioxidant properties than PS, PG and PI. The inverse relationship observed between the oxidation index (C22:6/C16:0) and color intensity for treatments following 2 h of heating suggests that Maillard-type reaction products may have contributed to the oxidative stability of PL-supplemented fish oils.

The stability of unsaturated fatty acids to oxidation was monitored by following gas chromatographic (GC) analyses of headspaee volatiles in comparison to changes in polyunsaturated fatty acids (PUFA) and increases in malonaldehyde v/a the 2-thiobarbituric (TBA) assay. Pure standards of linoleic acid (Lo) and n~ fatty acids [eicosapentaenoic (EPA) and docosahexaenoic acid (DHA)] were added to headspace vials, equilibrated in air for 10 mln, followed by heating at 80°C in teflon~apped vials for different time intervals. Headspace analysis showed inc~mses in acetaldehyde, propenal, and propanal, corresponding to the oxidation of n-3 fatty acids, whereas hexanal production corresponded to losses of linoleic acid. The analysis of pro panal by GC-headspace after only five minutes of heating appeared to be the most effective method of monitoring the oxidation of n-3 fatty acids, as indicated by correlations between TBA values and loss of PUFA. The oxidation of I~ EPA and DHA appeared to be a function of the number of double bonds. Correlations between PUFA depletion, TBA values and volatile formation indicate that under the prescribed conditions of this experiment, GCheadspace analysis of propanal and pentane/hexanal is an excellent method for following the oxidation of selected n-3 fatty acids and linoleic acid.

Total lipid (TL), neutral lipid (NL), and phospholipid (PL) fractions were extracted from bluefish (Pomatomus saltatrix) white and dark muscle with skin. The effects of each fraction on the oxidative stability of a refined salmon oil model system was measured by monitoring changes in the 2‐thiobarbituric acid assay and decreases in the ratio of docosahexaenoic acid (DHA) to palmitic acid (C22:6/C16:0) following incubation at 55°C or 180°C. Phospholipid fractions at 2.5% and 5.0% (wt/wt) of oil improved the oxidative stability of oils incubated at both temperatures compared to controls, TL‐ and NL‐supplemented oils at similar concentrations. Phospholipid fractions exhibiting antioxidant properties contained an average of 34% DHA as compared to only 15% in the NL and TL fractions.

Abstract:The antioxidant properties of tert-butylhydroquinone (05 g kg-' + 20 g kg-' ascorbic acid-TBHQ-AS) and an extract of rosemary (2.5 g kg-') alone and in combination were determined by their addition as solutions to cooked fish flakes stored at -20°C. Oxidation was measured by following changes in free fatty acids, thiobarbituric acid number, fatty acid composition and sensory evaluation. The order of effectiveness in inhibiting oxidation was TBHQ-AS > combination > rosemary > untreated control -70°C > untreated control -20°C. Sensory evaluation indicated that green aroma and flavor notes were associated with the rosemary extract, while fish oil notes were associated with untreated samples.

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