Analysis of eggshell mineral composition for tracing the origin of table eggs

In Australia and many other countries, free-range eggs can be sold at significantly higher prices than cage eggs. The mislabeling of cage eggs as free-range eggs and vice versa has been documented, and has a significant impact on consumer confidence and therefore egg consumption. The development of methods to distinguish eggs produced from different production systems is necessary to satisfy consumer demand. The objective of this study was to determine if eggshell mineral composition could be used as a way to differentiate eggs originating from each production system. Our hypothesis was that hens having access to soil would have higher levels of trace minerals in their egg shells than would caged hens. Egg samples were randomly collected from six commercial caged and six commercial free-range flocks in Australia. Twelve eggshell samples from each flock were analysed for mineral composition ( calcium, phosphorus, magnesiwn, sodium, aluminium, boron, copper, 1nanganese, iron, potassium, sulfur and zinc) using inductively coupled plasma optical emission spectro,netry (ICP-OES). The results showed that eggshells from free-range hens contained significantly higher macro-minerals (P, Mg and Na) but lower micro-minerals (Cu, Fe, K, S and Mn) than eggshells from caged hens (P < 0.05). Mean differences in mineral content of eggshells were observed between the two production syste1ns with 1025 μg Na /g eggshell for free range versus 917 μg/g for cage and 3.38 μg Fe /g eggshell for free range versus 4.64 μg/g for cage. However, variable levels of eggshell minerals (including Na and Fe) were noted within and between production systems. Thus, it is concluded that analysis of eggshell mineral co1nposition is not effective to differentiate the origin of eggs.