Extended shelf life (ESL) egg products continue to grow in popularity, with requests from processors seeking ways to better control and plan their production. With ESL, it is possible to optimize daily production and to provide long lasting products for customers.

End users want a product that is of good quality, that is able to last longer, at a reasonable price and that complies with food regulations.

What is shelf life?

When defining shelf life, there are two main parameters to consider:

a) obligatory aspects

b) optional aspects

Obligatory aspects are parameters that the product must fulfil in accordance with local regulations.

Optional aspects refer to rules that companies set themselves to ensure production of a safe and good product.

The methodology with which the obligatory aspects and optional aspects are measured is highly important. It needs to be as objective as possible, and the shelf life must be defined mainly by experimental measurements where the difference between the obligatory aspects and optional aspects must be kept at an acceptable level.

Another aspect to be considered are the degradation phenomena, manifested through bad smell and coagulation. These phenomena, are mainly due to non-pathogen bacteria that survive pasteurization. These non-pathogens need to be considered in the shelf life of the products and the producer needs to reduce them to the absolute minimum, in order to achieve ESL.

As an example, figure 1 shows some Microbiological Criteria generally followed to achieve a good product:

Mesophilic Aerobic Bacteria                      100.000 UFC/g

Enterobacteriaceae                                   100 UFC/g

Staphylococcus Aureus                             absence/g

Salmonella                                                 absence/25g

Listeria Monocytogenes                             absence/25g

Based on this, the first quality aspect in egg products depends on the microbiological status in terms of Quality-Quantity, i.e. zero tolerance of pathogenic elements (obligatory aspects ) with a bacterial residual charge at the lowest level (optional aspects ), in order to reduce the degenerative aspects to the minimum.

Other optional aspects are related to the residual functionality of the egg product in terms of “performance aspects” , such as heat setting properties, whipping, binding, and emulsifying, among many others.

In Europe, the responsibility of the Producer for disclosing the safety of the product has increased aollowing fter the application of the “Hygiene Packet” law. 

The Hygiene Packet includes 4 community regulations:

  • Regulation EC 852/04 - Alimentary Hygiene Products;
  • Regulation EC 853/04 - Defines Hygiene Specifications and Rules for Animal Foods;
  • Regulation EC 854/04 - Defines Specification Rules and establishes an Official Agency for the Control of Animal Foods for Human Consumption;
  • Regulation EC 882/04 - Establishes Official Verification Rules for Conformity of Food and Feeds for the Health and Wellbeing of Animals.

The definition of the parameters for a product labeled “edible” is not completely regulated by law. There are only some guidelines that every producer, in the most objective way possible, must use to define their limits of acceptance.

Furthermore, methods to measure, verify and certify these limits are extremely important. So, it is crucial to define procedures in order to obtain the bacteriological data and decide which types of analysis to conduct.

When looking at “bacterial counting” it is necessary to specify the guidelines taken as reference to define the measurement methods, admitted precision and repetitiveness. For example, in Europe, a regulation that thoroughly describes the analysis methodology is ISO 4833 (Microbiology of food and animal feeding stuffs — Horizontal method for the enumeration of microorganisms — Colony-count technique at 30 °C).

In this regulation, one of the well described parameters is the incubation period. To compare different products, the incubation period must be respected, otherwise the results would be incomparable. In fact, an incubation time of 48 hours would show a much better product compared with 72 hours because the bacteria growth is exponential. In addition, the use of preservatives must be considered, with regards to shelf life, as the addition of preservatives can significantly extend shelf life.

Once the limits and procedures followed to analyze products have been defined, it is also necessary to define the percentage of admissibility, i.e. the Probability of Microbilogical Failure. For instance, a product for which there is a probability of 0.1% to be expired after “x” days might be considered good, or it could be acceptable with a probability of 0.5%. These two values, even if close to each other have a big influence on the declared “shelf life”.

To give an example:

After several samples and analysis, suppose that a product, statistically, has shelf life of:
- 15 days with a expiring probability of 0,000%         
- 30 days with a expiring probability of 0,001%         
- 45 days with a expiring probability of 0,020%         
- 60 days with a expiring probability of 0,150%

It is then possible to consider that, after 45 days, the probability that the product is unexpired is 99,98%, while after 60 days the probability is 99,85%.

Minute differences (only 0,13%) in the admissibility result in substantial differences in the lasting of the product.

All of this proves, that there are several parameters to be considered, while differing analysis methods, or parameters evaluated differently, will provide differing shelf life results.

To obtain good shelf life

Generally, the efficiency of an egg products plant is evaluated based on the starting total plate count (TPC) of the raw product and the final TPC of the packaged product.

It should be pointed out that with the TPC, bacterial charge of the sample is estimated by means of small selective growth conditions with mesophile temperatures (32°C). However, we know that the micro organisms responsible for the degeneration during refrigeration time are the psicrofili which remain active at temperatures equal to or below 5°C.

With a small selective analysis like the TPC, we can estimate the content of the bacteria in the product but we cannot identify their characteristics. It is only known that they are thermal resistant, but their metabolism and their degenerative aspects during the preservation time are not known. Therefore, under the same TPC we can have different performances in the packaged product.

It is also very important to underline that the shelf life of an egg product is not only the result of a pasteurization process but depends also on many other factors:

Type of product

The production of long shelf life products (ESL) is first determined by a fresh, and high quality shell egg, that has not suffered stress during storage. Consider, for example, micro-cracks created during transport and handling, or sudden temperature changes (thermal shock), all of which can result in pre-contamination of the product before breaking.

Treatment during breaking operations

This is a very critical concern, as this is the first contact the product will have with the external environment and it is extremely important that the breaking machine is designed with regard to the maximum level of hygiene, ensuring a thorough cleaning cycle. For example, one processor decided to exchange their old breakers with new OptiBreakers, to handle a total daily production of 150 tons of egg products. Previously, the UHST pasteurised egg had a bacteria count at an average of 950.ufc/g . After the installation of the new Optibreakers, the bacteria count was reduced to an average of 60.UFC/g. This is the equivalent of one log reduction of the bacteria.

In order to confirm how difficult it is to define the meaning of shelf life, it is important to underline that the bacteriological result has been obtained from the final product (pasteurized), so it is clear that the effect of the pasteurizer (in terms of killing rate) is strongly connected to the quality of raw product used and the production equipment and hygiene in between the breakers and the pasteurizer

Furthermore, it is important that the product is filtered (to eliminate possible shell parts) and cooled down as soon as possible after breaking, in order to inactivate bacteria growth.

As an example, figure 1, illustrates the generation time of some bacteria in relation to time and temperature:

This clearly illustrates how important it is to keep the products below 4°C in order to avoid bacteria growth.