Enrichment of eggs with n-3 polyunsaturated fatty acids: effects of vitamin E supplementation

Eggs enriched with n−3 polyunsaturated fatty acids (PUFA) could contribute to dietary intake of these healthful fatty acids (FA). Because n−3 PUFA are highly susceptible to peroxidation, a first part of the study with Leghorn laying hens was carried out to investigate the influence of different levels of fish oil (0, 0.7, 1.4, 2.8, or 5.6%, respectively) in the diet on n−3 PUFA, cholesterol, vitamin E, and lipid peroxidation product contents in eggs. Addition of fish oil to a complete diet based on wheat, rye, tapioca, and soybean constituents containing 11 IU vitamin E/kg resulted in increased n−3 PUFA content in egg yolk, mainly due to accumulation of docosahexaenoic acid. Cholesterol was not altered up to 2.8% fish oil in the diet. The vitamin E content of the yolk was insufficient for the protection of PUFA from peroxidation. Addition of up to 2.8% fish oil to laying hen diets increased the n−3 PUFA content of yolks with a concomitant imbalance between vitamin E and PUFA, leading to increased levels of cytotoxic aldehydic lipid peroxidation products such as malondialdehyde (MDA). In a second part of the studies, the balance between vitamin E, PUFA, and lipid peroxidation was analyzed during the period of storage of n−3 PUFA-enriched eggs produced after feeding the laying hens with 1.5% fish oil diets with different concentrations of vitamin E (0, 5, 10, 20, 40, 80, 160 IU/kg). Storage of eggs resulted in a marked loss of vitamin E in yolk. In stored eggs, the cytotoxic lipid peroxidation products MDA, 4-hydroxynonenal, and 4-hydroxyhexenal were reduced in response to vitamin E supplementation. To prevent the increase of cytotoxic aldehydic lipid peroxidation during production and storage of n−3 PUFA-enriched eggs, a high vitamin E supplementation with at least 80 IU vitamin E/kg is needed.