How can carotenoids impact cholesterol oxidation in egg yolks?

The oxidative stability of egg yolks from brown hen eggs, previously subjected to a 6-week storage at room temperature, was evaluated as related to the dietary supplementation. Three groups of eggs yolks were obtained according to the carotenoid supplementation: no addition of apo-ester and canthaxanthin (CON); 2.5 ppm of apo-ester and 2.5 ppm of canthaxanthin (MED); 3.5 ppm of apo-ester and 5.5 ppm of canthaxanthin (HIGH). The lipid content of the egg yolks varied from 28.3% to 29.3%, and no significant differences were found among the different dietary treatments (p≥0.05). Peroxide value (PV) ranged from 0.92 (CON) to 1.48 (HIGH) meq O2/kg lipids, which were quite low despite the 6-week egg storage at room temperature. The most common cholesterol oxidation products (COPs) in foods were detected in the stored eggs. The total COPs content varied from 28.2 (CON) to 39.2 (HIGH) µg/g lipids, which corresponded to 8.32 and 10.97 µg/g egg yolk, respectively; however, no significant differences (p≥0.05) on the total COPs level were observed among the different dietary treatments. Regarding the single COPs, the most abundant was 7α-hydroxycholesterol (50-53% of total COPs), followed by 7-ketocholesterol (22-26%), 5,6β-epoxycholesterol (7-9%), 7β-hydroxycholesterol (6-9%), 5,6α-epoxycholesterol (3-4%), and cholestanetriol (2-4%). In conclusion, PV and total COP content of egg yolks confirm that the use of dietary supplementation with carotenoids is not a useful strategy to control and delay the lipid autoxidation in brown hen eggs stored for 6 weeks at room temperature.