Effects of dietary fats and vitamin E on the fatty acid composition of egg yolk of fresh and refrigerated table eggs

The aim of the present experiment was to investigate how different types of dietary fats and levels of vitamin E affect the fatty acid profile of egg yolk during refrigerated storage of table eggs. ISA Brown hens (n=90; 28 weeks old) were randomly assigned to five experimental diets. The dietary treatments included: (1) control diet without fat supplementation and added vitamin E (2) 5% Alifet supplement (rich in saturated fatty acids) and 20 IU/kg vitamin E (3) 5% Alifet and 40 IU/kg vitamin E (4) 5% pumpkin seed oil (rich in n-6 polyunsaturated fatty acids) and 20 IU/kg vitamin E (5) 5% pumpkin seed oil and 40 IU/kg vitamin E. The diets were fed for two weeks. After two weeks, 20 eggs per dietary group were collected Fatty acid composition of egg yolk was analyzed by means of gas chromatography from fresh samples (n=10 per treatment) and eggs stored for 4 weeks at 5 °C (n=10 per treatment). Feeding of diets supplemented with Alifet increased the proportion of total monounsaturated fatty acids (MUFA), whereas decreased the content of n-6 and total polyunsaturated fatty acids (PUFA) in the fresh egg yolk in comparison to the other groups (P<0.05). In the pumpkin seed oil groups, the contents of MUFA and n-3 PUFA were lower and the content of n-6 and total PUFA and the ratio of n-6 to n-3 fatty acids were higher than in the other groups (P<0.05). The effect of dietary vitamin E on the fatty acid composition of fresh egg yolk was influenced by the type of dietary fat. In the two Alifet treatments, significantly higher saturated fatty acid and MUFA content, and lower n-3, n6 and total PUFA were measured in the egg yolks from hens fed 40 IU/kg vitamin E compared to 20 IU/kg vitamin E. In contrast, different levels of vitamin E supplementation did not influence these parameters in the pumpkin seed oil groups (P>0.05). In comparison to fresh samples, refrigerated storage of eggs for 4 weeks decreased the the proportion of n-3, n-6 and total PUFA and increased the ratio of n-6 to n-3 PUFA in the egg yolk regardless of dietary fat type when 20 IU/kg vitamin E was fed. Although vitamin E at the level of 40 IU/kg was able to prevent the significant changes of these parameters in the pumpkin seed oil group, the proportion of n-3 PUFA decreased, whereas the ratio of n-6 to n-3 increased during storage in the egg yolk of hens fed 5% Alifet and 40 IU/kg vitamin E (P<0.05).