Effective means of verifying free-range eggs developed
eggs labelled as free-range or barn have in fact been laid under
battery conditions, suggesting eggs could be tested without the
need to visit farms.
This could speed up the process of verifying free-range eggs because the technique can be applied at any stage of the supply chain, and could also boost consumer confidence in what is a growing market.
The procedure, published in Journal of the Science of Food & Agriculture this month, targets the dust that the eggs pick up from the surface on which they are laid.
Because the eggs are wet when freshly-laid, the dust attaches to the shell surfaces. The pattern this creates varies according to whether the eggs were laid on cage floors, barn nestboxes or outside. These distinctive patterns can easily be distinguished under ultraviolet light, as the dust fluoresces.
The UK is still recovering from wide outbreaks of Salmonella enteritidis in the 1980s that knocked the local egg industry. However figures now show that the number of cases in England and Wales has decreased significantly, from 16,047 cases in 1998 to 9757 cases in 2003 mainly due to industry control programmes, including the vaccination of chicken flocks.
In addition, research on the UK egg market by analysts Mintel found that while volume sales have risen by 10 per cent between 1999 and 2003, value sales have increased by double this amount, some 23 per cent, due to consumers trading up to premium egg varieties.
The trade up to higher-priced eggs - free range and organic - suggests overall health concerns are driving the market. In 2003 free-range eggs accounted for 30 per cent of egg sales by volume compared to just 24 per cent in 1998, representing a 38 per cent rise in sales since 1998.
The effective and efficient verification of free-range eggs could therefore become an important factor in the future.
Professor Neville Gregory of the Royal Veterinary College, UK and colleagues in Australia used ultraviolet light to examine the surface patterns on 11520 eggs from cage, barn and free-range production systems. 360 eggs from each of 20 cage, seven barn and five free range units were examined, and categorised according to their dust patterns when exposed to UV light.
The type of floor material onto which each egg was laid was known for each farm. The authors found that the prevalence of white double parallel lines with 2-2.5cm spacing was a distinguishing feature for eggs laid on wire floors in cages.
They conclude that if five or more eggs in a sample of 90 eggs have double fluorescent lines that there is a greater than 999 in 1000 probability that the batch contains some cage-laid eggs.
"The method is effective in distinguishing between free-range eggs and those laid on a wire floor cage," said professor Gregory. "It does not damage the eggs, and can be applied at any stage in the egg marketing chain."
However, washing the eggs removed or obscured the double lines, so the authors recommend that in countries where egg washing is common, it is best to perform the test before washing. Distinguishing features in egg shell fluorescence can be used to identify when eggs have been washed, and they can also be used in preliminary screening tests for sun exposure, which in some countries is a cause of runniness of the egg white.
