Eggs: nutritional and hygienic aspectsArea Laboratorio
Eggs are a nutritious and versatile, relatively cheap and easy-to-find foodstuff that, either directly or as an ingredient in other preparations, characterises the usual diet of a large part of the world’s population.
Nutritionally, they are a source of protein of high biological value, being complete with all essential amino acids, and are rich in nutrients such as vitamins B12, D and A as well as iron, selenium and zinc. They are also characterised by a significant cholesterol content and, for this reason, their consumption has been questioned for many years due to their potential impact on cardiovascular health, especially in the presence of risk factors such as diabetes or hypertension.
However, several recent scientific studies, based on decades of monitoring hundreds of thousands of people on their daily diet and related medical conditions, have shown that moderate consumption of eggs (one to three a day) is not correlated with these negative effects, if, however, within a varied and balanced diet and an active lifestyle, and may even reduce their occurrence. In fact, cholesterol levels in the blood do not depend so much on the amount taken in through food, but on the relative metabolism that takes place in the liver, which is stimulated more by the introduction of saturated and trans fatty acids.
As far as health and hygiene aspects are concerned, the greatest risk is associated with possible contamination by potentially pathogenic micro-organisms, such as Listeria monocytogenes, Staphylococcus aureus, faecal coliforms but especially Salmonella spp. Indeed, if not properly controlled, domestic birds often harbour several serotypes of Salmonella spp. within their digestive tracts, without, however, showing any signs of infection. Therefore, as the hen’s reproductive tract shares the terminal portion with the digestive tract, the egg may come into contact with it and become contaminated.
The application of Good Breeding Practices, HACCP in packaging centres and Good Transport and Sales Practices guarantees a certain level of management of this risk by the entire supply chain.
Washing the shell could indeed benefit external contamination, however this practice is not carried out as it would remove the thin cuticle released during deposition which has the function of closing the pores naturally present, and would therefore significantly increase the permeability to external agents. For this reason, unlike in other countries, in Europe eggs are only subjected to dry cleaning treatments and regulations recommend maintaining a constant temperature during transport and sale: any changes in temperature would in fact cause condensation to form.
To further mitigate the risks associated with such contamination, proper handling of eggs by the end user is also of paramount importance, paying close attention to hand hygiene, which must be adequately cleaned whenever handling such foodstuffs and their containers and in any case before any further activity, and to avoid any cross-contamination phenomena.
In fact, it is necessary to ensure that the shells do not come into contact with food to be consumed as such (raw or already cooked) and with surfaces and equipment directly involved, and it is advisable to store them under refrigeration, avoiding the transfer of the product into reusable containers and therefore different from the original packaging.
Lastly, the consumption of such food should only take place in the absence of cracks in the shell and in any case always preferably after adequate cooking (reaching 70°C at the core of the product or in any case when the yolk is hard-boiled), as heat treatments are able to reduce the microbial load that may have been transferred from the shell to its interior or in any case already present due to the phenomenon of internal contamination. Further guarantees are the respect of the Minimum Conservation Period indicated on the label (fixed by law at 28 days from the date of laying) and, in general, the assessment of the degree of freshness, which can be conducted empirically by observing the behaviour of the eggs during immersion in water, as this is strongly conditioned by the size of the air chamber, which increases in volume as the days after laying pass.