Chilled and frozen foods

Shelf life at full-scale production

The aim is to provide full-scale production of the product for sale.

Shelf life test at this stage serve to confirm the results obtained in the pre-production stages (Fig. 10.3).

In tests of the shelf life of products manufactured during their full-scale production, the same key parameters should be controlled as in the preparation of production, but special attention should be paid to determining the full range of changes during production, especially if it is greater than at the preparatory stage. If the storage period differs from that determined during preparationDetermination of retention periods when full-scale production

Fig. 10.3. Determination of retention periods when full-scale production ([7])

production, to identify the reasons to analyze issues of party in the preparation of production.

Ideally, shelf life tests should be performed on the first three batches of products. With the accumulation of product manufacturing experience and the receipt of feedback signals in the form of possible consumer complaints, the storage period may be adjusted accordingly. In this case, changes in ingredients, in production technology or in the organization of a marketing system are inevitable. Although each individual change in itself may not seem to affect the shelf life of the product, together they can have a noticeable effect on it. It is very important that the personnel responsible for conducting shelf life tests are even informed of minor changes, and the process as a whole is periodically analyzed (if necessary, tests for compliance with technical conditions should be performed).

 Maximizing shelf life

To increase shelf life while maintaining the safety of the product can be taken a number of steps, described below.

Changes in the product formulation

To prevent or delay the growth of microorganisms that cause product spoilage, small changes in the composition of the product may be sufficient to increase its shelf life. This is especially true if a variable factor (e.g., salt content) limits the growth of microorganisms. Currently, quite often they reduce the amount of salt in ready-to-eat foods. At the same time, a slight change in the acidity of the product can, like salt, increase the shelf life. This position is illustrated by the example below. In the absence of salt, the shelf life of the product is only 5 days, but with 2% salt, the shelf life of the product can be increased.


EXTRA, pH 5.5, temperature 8 ° С

Salt (wt.%) Number of days after 5
5 X 1,1 102
4 X 2,89 102
3 X 5,78 103
2 X 6,8 105
1 X 3,1 107
0,5 X 8,8 107

Application of new technologies

The most effective way to inactivate pathogens that cause damage to microorganisms and enzymes is through heat treatment. However, it can cause various changes in the taste / aroma of the product and reduce the feeling of “fresh taste”. There is the possibility of using alternative cold processing systems for products that inactivate microorganisms and, in some cases, enzymes without causing damage to the product. Examples of such technologies include the use of high pressure and ultrasound (see section 10.7) ([18]).

storage temperatures

Storage temperature control is one of the most effective ways to maximize product shelf life. If you store finished products and raw materials at 2 ° C instead of 5 ° C, and in retail at 5 ° C instead of 8 ° C, you can significantly increase the shelf life (see table 10.2 for ready-to-use products stored at different temperatures at the place of manufacture and in retail).

10.2 Table. Levels Pseudomonas (Ps) after each storage period

(At an initial level 10koe / g)

Storage at the place of manufacture, 2 days A display in the retail trade, 6 days The probable shelf life, days
t, ° С Level Ps through 2 days, cfu / g t, ° С The final level Ps, cfu / g
2 16 3 X 7,8 105 9,0
8 7,3 × 108 5,5
3 21 3 X 1,0 106 9,0
8 X 7,5 108 5,5
5 54 3 2,3 х106 8,5
8 X 8,7 108 5,0

Product Features: chilled, ready to eat; salt - 0,8% of the mass .; pH - 6,2; intended shelf life - 8 days; at the end of the storage period, the contents of Pseudomonas at the 10 level7 cfu / g (baseline - 10 / g).

The use of packaging with controlled atmosphere

Possible packaging options for chilled products are discussed in chapter 7. An increase in the carbon dioxide content in the package and the exclusion of oxygen packaging from the gaseous medium can significantly increase the shelf life determined by microbiological factors [5]. It should be emphasized, however, that the use of SRGS packaging for chilled products may limit the shelf life to 10 days if it is not shown that such packaging can prevent the growth of C. botulinum (see section 10.2).

 "Provocative" (control) testing

Sometimes there is confusion about the difference between shelf life tests and “provocative” testing. When developing new chilled products, there are two different aspects that need to be considered:

  • Is the product safe and stable under normal conditions of production and storage, and for how long will it remain stable and safe, that is, what is its shelf life?
  • Is the product expected to be safe and stable during storage if it is contaminated with foodborne pathogens and microorganisms causing spoilage, is the product formulation and storage conditions safe if microorganisms enter the product?

In the first case, only microorganisms that are initially present in the batch of the product will be present and will be able to grow during storage. Ideally, under good production conditions and when using the HACCP method, the probability of the presence of foodborne pathogens (for example, Salmonella) in the product will be minimal. Therefore, when determining the shelf life, pathogenic microorganisms may be absent, and the product may be considered safe for the specified shelf life. However, it is possible that during the production of the product it will be contaminated with pathogenic microorganisms or organisms causing spoilage, which were absent in the batch used to determine the shelf life. If this happens, the manufacturer must know how likely it is that the product will remain safe and stable during storage. The need to know, “what happens if ...” is the reason for the use of the so-called “provocative” (control) testing. Since UK food safety rules for food require a “proper care”, many manufacturers conduct special “provocative” tests with inoculation of new and existing products with microorganisms.

Microbiological “provocative” testing is a laboratory simulation of what can happen to a product during its production, marketing and storage. Such testing involves inoculating the product with appropriate microorganisms and maintaining it under various controlled environmental conditions to assess the risk of food poisoning or to determine the stability of the product against microorganisms causing spoilage. [19] described four stages of “provocative” testing:

  • design of experiments;
  • inokulyatsii procedure;
  • test procedure (test);
  • interpretation of the results.

 Planning for provocative testing

Such testing of a new or existing product can be made to:

  • determine the safety of the product;
  • determine the possible damage to the product;
  • estimating the stability of the product with new or modified recipe [1].

Safety is the main problem in the production of food products, so it is necessary that the product for the consumer is characterized by minimal risk.

Microbiological “provocative” testing should be performed if there is a suspicion that some microorganism is present in a small amount [20], that it may be in the raw material or be introduced into the product at any stage during production or marketing.

From the point of view of assessing the safety of a chilled product with respect to pathogenic microorganisms, those that may be dangerous and require “provocative” testing should be determined during a risk analysis (for example, within the framework of the HACCP methodology). Using this approach to identify microorganisms that can cause problems is described in [20].

Having determined which microorganisms should be tested, it is necessary to analyze what specific characteristics of the product and storage conditions should be monitored. Storage of products as a whole depends on many factors - these are the same “internal” and “external” factors that were taken into account when determining the shelf life. In “provocative” testing, a sequential change in each of these factors allows us to determine those that are essential for maintaining product quality. In this regard, such tests can be performed to evaluate various product formulations, as well as the effects of various regulated storage conditions. Test conditions should be changed in such a way as to simulate violations that may occur during sales and after the consumer purchases a product - the key factors for the shelf life of refrigerated products may be processing and storage conditions, which also need to be checked during provocative testing.

Another important aspect that should be considered when planning “provocative” trials is the number of samples that must be evaluated at each sampling point in order to get enough data for statistical analysis. You must also determine how many times a sample is taken. As the initial one, you can use the mode that was used to determine the shelf life, that is, the minimum sampling should be carried out five times: one at the beginning, one at the end and three during the entire storage time. To be sure of the reproducibility of the results, in each case a minimum of three should be analyzed, and ideally five or even ten samples. Often, for several hours, days or weeks before starting to increase, the level of microorganisms remains constant and even decreases [8]. During the tests, it is necessary to carry out sampling a sufficient number of times so that any initial decrease in the level of presence of microorganisms is not taken for the end of the tests, and because of this, their subsequent growth did not go unnoticed.

Each experiment should be appropriately monitored to ensure meaningful results. Control experiments should be performed under conditions in which the microorganisms being tested grow in a laboratory environment (“positive control”), and “negative control” in conditions when growth is not expected. As control samples, a standard product with a known shelf life, uninoculated samples, and also products stored under standard conditions can serve. Control samples provide a measure by which changes can be judged and serve to ensure reproducibility of experiments.

“Provocative" testing is not a quick or easy procedure. It is commonly used if other methods to ensure the safety or stability of a particular product are to be supplemented or considered inappropriate. At first, it is important to clearly identify the reasons for the implementation of the “provocative” testing and the purpose of the experiments, and then determine whether it meets the goals. Once a decision has been made to conduct “provocative” testing, it is necessary to determine the most effective way to achieve your goals. For this, it is necessary to analyze the type of product being tested, the factors affecting its stability and the conditions in which the product may be. Experiments should then be carefully planned to identify the preservative mechanisms in the product and their tolerances that do not impair the stability of the product or its safety.

 inoculation procedures

The choice of microorganisms for use in "provocative" testing is very important, since they must really affect the product. If the selected microorganisms were especially resistant to the preservatives used in the product, they can grow despite the fact that other resistant microorganisms cannot grow. Conversely, if the microorganisms used are very sensitive to the antimicrobials used, they will not be able to grow and the product will appear safe or stable, whereas in fact it might not pass the tests if other microorganisms that could be encountered in real life were selected.

Ideally, selected cultures should be isolated from a food source similar to the test product, or prepared by growing them in a product sample or laboratory medium with similar characteristics [20]. It is preferable to use cultures from recognized culture collections, for example, from the National Collection of Industrial and Marine Bacteria, since they allow to achieve uniformity of measurements and compare different tests. To ensure that they behave the same way as freshly isolated strains, these cultures must be checked. To provide more serious tests, it is preferable to use a mixture of two or more strains of each microorganism.

Other important factors are the sample volume (e.g. 0,1 ml) and the inoculation method used. As for the volume of the inoculum, its minimum quantity should be used so that the product characteristics (for example, aw) are not changed. [1] described inoculation procedures for liquid, dry and medium moisture products in detail. The number of microorganisms in 1 ml should be realistic - their levels should be high enough to be easily determined (for example, the minimum level of 100 cells per 1 g of product), but they should not be so high that microorganisms easily overcome the preservative ability of the product. Carrying out a “provocative” test containing 106 cell inoculum on 1 g is unrealistic and is likely to result in spoilage of the product.

Interpretation of results

Before starting an experiment, it is important to determine product acceptance criteria. The criteria used will vary depending on whether the system in question is internally stable or unstable, as well as what is assessed - safety or the degree of damage to the product. For internally stable systems, the endpoint of a provocation test is determined by the growth of microorganisms or undesirable organoleptic changes after a given time. Various endpoints are possible for internally unstable systems, including the growth of microorganisms per unit mass of the product to a certain amount, a change in the lag phase, a change in the lifetime of one generation, or organoleptic spoilage of the product. In the case of safety tests, the end point may be the beginning of the growth of pathogenic microorganisms, their growth to a predetermined level, the number of microorganisms per unit mass of the product or the production of toxins.

If the specified end point is reached earlier than expected, you must change the product formulation or processing / storage conditions.

If the product withstands “provocative” tests, that is, during the desired shelf life test criteria have not been achieved, it can be considered acceptable for the relevant conditions.

With arbitrarily small changes in the product formulation, processing, storage, marketing or retail conditions, the results of “provocative” tests can no longer be considered reliable. An example application of test procedures for chilled pasta is discussed in [1].


We have considered the modern views on the definition of the storage period, with particular emphasis on the microbiological safety and quality.

One of the main directions in determining the shelf life is prognostic microbiological modeling. In particular, in the future, the development of special models for the food industry will continue. Models for fish products can be obtained at the Ministry of Fisheries of Great Britain, at the Danish Technical University (Seafood Spoilage Predictor program), models are currently being developed for smoked meat products. Such models will allow us to evaluate the effects of the joint effects on spoilage of products usually found mixed microflora in them.In the future, to improve the quality and / or shelf life of chilled products, there will be an increase in the use of alternative technologies.

For chilled pastes / pies, orange juice and national dishes (eg salsa), high pressure is already in use [18]. With the expansion of the use of such technology, the cost of equipment will decrease, which in turn can lead to a further expansion of its application. The chilled food market is showing an upward trend in sales, and one of the keys to success will be the accurate and efficient determination of shelf life.


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