There’s more to shelf life than pasteurization
Roberto COLAVITTI and Christoffer ERNST, Sanovo Technology Group
Extended shelf life (ESL) egg products continue to grow in popularity, with requests from processors seeking ways to better control and planning of their production. With ESL, it is possible to optimize the daily production and to provide long lasting products to customers.
End users want a product of good quality which is able to last longer, at a reasonable price and in accordance with food regulations.
What is Shelf Life
When defining shelf life, there are two main parameters to consider:
- “obligatory aspects”
- “optional aspects”
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 very 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 is the degradation phenomena, such as bad smell and coagulation. These phenomena, are mainly due to Non-pathogen bacteria that survive the 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, table 1 shows some Microbiological Criteria generally followed to get a good product:
Based on this, the first quality aspect in the egg products depends on the microbiological status in terms of Quality-Quantity. A 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, emulsifying, among many others.
The Quality Manager should create a list of thermal resistant bacteria to be tested during analysis. In the last few years, stocks of Salmonella pathogen for humans have become interesting. For example, S. Typhimurium has shown a very good thermal resistance threshold.
In Europe, the responsibility of the Producer, in disclosing the safety of the product, has increased after the application of the “Hygiene Packet (*)” law.
(*)The Hygiene Packet includes 4 community regulations:
- Regulation (CE) n. 852/04 - Alimentary Hygiene Products;
- Regulation (CE) n. 853/04 - Defines Hygiene Specifications and Rules for Animal Foods;
- Regulation (CE) n. 854/04 - Defines Specification Rules and establishes an Official Agency for the Control of Animal Foods for Human Consumption;
- Regulation (CE) n. 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 being labeled “edible” is not completely regulated by laws. There are only some guide lines that every producer, in the most objective way possible, must define their limits of acceptance.
Further, 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 which types of analysis to do.
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 can be completely 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 the shelf life.
Once the limits and procedures followed to analyze the products are 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 %
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 a good shelf life
On average, 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:
1. 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), can cause pre-contamination of the product before breaking.
2. Treatment of the product 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 in respect of the maximum level of hygiene and ensures 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, table 2, 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.
Case study
During tests in order to study the efficiency of the killing rate of our pasteurizers we faced a very strange result: The pasteurizer was not operating well (low killing rate) even though the hygienic conditions, temperatures and holding times were strictly respected.
Pasteurization temperature and holding times were increased dramatically, without regards to functional properties, nevertheless the killing rate remained unsatisfactory.
Focus was then put on the equipment used before pasteurization, locating finally a contamination point in the treatment of raw egg. The section was contaminated due to insufficient cleaning. After this had been resolved, the pasteurizer started giving the expected results.
It is interesting to note that a contamination point had generated the presence of a thermally resistant bacteria, that not even the highest temperatures were able to destroy.
Finally packaging and filling are equally important areas to considerwhen producing ESL products. In short, packaging is one of the most critical points in a processing facility, because the product exits from the pipes and is exposed to outside elements providing a high contamination risk.
We can conclude that every pasteurization facility is unique because every plant generates bacteria for differing reasons. The definition of shelf life is not solely related to the pasteurization plant, but also to the whole production system, the quality and kind of raw product used. Every plant should create its own data base of cases and analyze the production process form a general point of view and not only from a single machine point of view.
High temperature pasteurizers
Therefore, it can be unfortunate to choose a system based on promises of extended shelf life. Any pasteurizer can claim to produce ESL, but there are losses that need to be considered within the final functional properties. A company may claim to be able to guarantee ESL production on their pasteurizer, but the egg processor needs to consider all the peripheral factors that play a role in the end product. If the pasteurizer turns out to be incapable of generating the promised results, the manufacturer can always claim that this is due to outside factors not within the scope of the pasteurizer, such as raw shell egg quality or handling of the finished products.
Until now, there are no miracle pasteurizers available, that can guarantee to produce extended shelf life while also maintaining the important functional products, but this is changing.
Wave technology 
Sanovo is now launching the first real revolutionary pasteurization technology that can claim to produce extended shelf life products while maintaining the functional properties. Sanovo’s new Wave Technology, is a technology that exposes the liquid to electromagnetic waves producing an electric field. Under this process, the water molecules point in the same direction as the electric field. The continuous reversion of the electric field polarity generates kinetic energy which in turn creates a heating effect. The heat is created by intermolecular friction, stressing bacteria but not the functional properties.
The Sanovo Wave Technology instantaneously transfers a tremendous quantity of energy in a fraction of a second. The energy is transferred to the entire product mass allowing a uniform heating as the product is heated indirectly by the kinetic energy, making it possible to heat the product to just below the coagulation point.
With Sanovo Wave Technology a processor can achieve 10 times more bacterial inactivation compared to traditional pasteurizers, without influencing the functional properties.
The Sanovo Wave Technology has undergone extensive testing at a commercial processing plant in Europe for over two years. During this real time testing and operation, data has been collected and monitored and the process has been fully refined and optimized.
The Sanovo Wave Technology has achieved >17 weeks shelf life where the TPC after 17 weeks was <10 plate count per gram, while retaining the functional properties as found in raw eggs. Compared to traditional pasteurized products the functional properties are improved 20 % compared to any other pasteurization solution.
