Study on Stable Carbon and Nitrogen Isotope Characteristics of Cage-Free Eggs and Caged Eggs

A method of elemental analysis-stable isotope ratio mass spectrometry (EA-IRMS) was established for determination of the components of carbon and nitrogen stable isotope of EW （egg white）, EY (egg yolks) and EM (eggshell membrane). And carbon and nitrogen stable isotope distribution characteristics of free-range eggs and caged eggs were explored preliminary. The results show that the method has good repeatability in determination of carbon and nitrogen isotopic composition of EW, EY and EM, and SD values are less than 0.2‰ (n=6). Carbon and nitrogen isotopic compositions are different in egg white, egg yolks and eggshell membrane (δ¹³C: EM >EY>EW, δ¹⁵N: EW>EY>EM). But δ¹³C values of each components are linearly related (R² are 0.768, 0.768, 0.761 for EW, EY and EM, respectively), and δ¹⁵N values for each components also have linear relationship (R² are 0.862, 0.862, 0.875). δ¹³C and δ¹⁵N values of free-range eggs (EW) are from -18.00‰ to -14.97‰ and from 3.02‰ to 4.37‰, respectively, and that of caged eggs(EW) are from -18.96‰ to -15.98‰ and from 1.66‰ to 2.68‰, respectively. Combined with δ¹³C and δ¹⁵N values can better distinguish caged eggs and free-range eggs.