The deposition profile of oxy-carotenoids, fat and PCBs in egg yolks

A layer trial consisting of a preliminary period and 2 subsequent fortnight main periods was performed to establish if the metabolism, in terms of deposition of both oxy-carotenoids, fat and PCBs (based on the 7 marker congeners) into eggs shows a parallel profile in the light of the sequential and gradual maturation of the growing follicles. Therefore, two diets were formulated with a constant set of nutrient specifications with exception for the components under study: diet 1 was based on rendered animal fat without any supplement of oxy-carotenoids and PCBs (during the preliminary period and the last main period) while diet 2 was based on crude soybean oil but supplemented with yellow and red oxy-carotenoids and PCBs (during the first main period) as well. The change. in yolk colour was curvilineary related to time during the transition phase to both the repletion (main period 1) and depletion (main period 2); during these periods, responses were plateauing for most spectro-parameters. The fatty acid profile of the yolk fat is relatively because the unsaturated fatty acids amounted up to about 68% of the total fatty acids. The major changes were within the "C18:1 + C18:2"-unsaturates; changes in C18:2 acid were balanced by proportional changes in C18:1. The plateauing in response for both yolk colour, C18:1, and C18:2 indicate clearly that a period of about 9-11 days is needed for an entire shift in fatty acid profile throughout the yolk. Correlations between the dietary PCB-profile and the corresponding profiles in liver fat, abdominal fat, excreta, and eggs were variable. In relation to the 14 day cumulative PCB-intake, the PCB-deposition in liver. abdominal fat, and excreta was <1%, about 10%, and 5%, respectively. On the other hand, PCB-secretion periods into the egg yolk during the 2 main periodsamounted up to 43% of the 14 day cumulative PCB-intake; the response in egg yolk PCB was not plateauing within the 14 days. The PCB-excretion curve could be modelled very well using a tanks-in-series model. Extrapolation of the present response demonstrates that a period of 40 days is needed to reduce the daily PCB excretion to 1 mug, which corresponds 245 ng per g yolk fat