Differentiation of Pigment in Eggs Using Carbon (13C/12C) and Nitrogen (15N/14N) Stable Isotopes

Consumers prefer natural and healthy food, but artificial pigments are often abused in egg products. The study aimed at differentiating the origin of pigments in eggs by applying the technique of carbon (C-13/C-12) and nitrogen (N-15/N-14) stable isotope analysis. Five hundred sixty laying hens were randomly distributed into 14 treatments, which were divided into four groups: maize, carophyll red pigment, carophyll yellow pigment, and a mixture of carophyll red and yellow pigments. Eggs were collected and pretreated to determe the values of the Roche Yolk Color Fan (RCF), delta C-13, and delta N-15. With increasing maize content, the RCF and delta C-13 values of yolks increased. Moreover, the RCF values in the three pigment groups were significantly influenced by the artificial colors, but delta C-13 values were not significantly different, regardless of the existence of pigment. The delta N-15 values in all treatments did not vary as regularly as the carbon stable isotope. A strong positive correlation was found between RCF and delta C-13 in the maize group, but no such correlation was be observed in the pigment groups. It is concluded that carbon stable isotope ratio analysis (delta C-13) of the yolk can be used to differentiate the origin of the pigment added to eggs.