Effects of different breeding and feeding systems on lipid oxidation of freeze-dried egg yolks

Lipid oxidation of freeze-dried egg yolks produced with two breeding systems (traditional battery and open) and two types of feedings (non-organic and organic), was studied. Nine fresh egg yolks of each treatment were pooled, freeze-dried, packed in aluminum foil bags under vacuum and kept at –18°C until analysis. Several parameters were evaluated: tocopherols, peroxide value, cholesterol and its oxidation products (COPs). The lipid content was slightly higher in the egg yolks produced with an open breeding system (62%) as compared to the traditional battery one (59%). No significant differences were observed in the cholesterol content (3.5%) of the egg yolks, which corresponded to about 99% of total sterols; the remaining 1% were phytosterols (β-sitosterol and campesterol). The amount of campesterol was higher in the sample obtained with open breeding and organic feeding. The level of COPs (17.2-25.8 ppm) and the percentage of oxidized cholesterol (0.02-0.03%) found in the freeze-dried egg yolks, were not significant different, except for 7β-hydroxycholesterol which was significantly higher than the traditional battery sample. The little extent of lipid oxidation in all freeze-dried egg yolks was confirmed by a low, similar peroxide value. Traditional feeding and open breeding resulted in a significantly higher α-tocopherol and β-tocopherol contents, respectively; the total tocopherol content was consequently more elevated in the freeze-dried egg yolk obtained with traditional feeding and open breeding.