Chilled and frozen foods

Simulation of the retention period

As noted above, one of the most important factors in determining the shelf life of a product is the possibility of the growth of microorganisms,

and therefore, new chilled products must be tested in order to assess the growth potential of pathogens or spoilage microorganisms, thereby determining the period of time during which the product will be considered suitable for its intended use. Traditionally, the only objective way to do this was expensive laboratory tests during the pilot production of the product (see section 10.4). This method is still the best for final product testing, but in the initial stages of development it is very laborious and expensive. With a huge number of new products on sale, other methods of estimating shelf life are required. A method that is becoming more widespread in the production of chilled products is the use of prognostic models, which can become indispensable tools at all stages of the development and production of food products.

The types of existing models for predicting the growth of microorganisms are described in Chapter 7, and below we will consider them more specifically in relation to the determination of shelf life.

Creating a concept (product development)

For the primary identification of the main problems, we consider the extreme case: it is supposed to create a product with a neutral pH and a shelf life of 20 days, but pathogen growth models show that L. monocytogenes, B. cereus and Salmonella can grow within 2 days, and therefore on the most The inability to create a product is obvious at an early stage.

Development of product formulations

After determining the type of product, which is likely to be safe and stable for the desired shelf life models can help to create the final product formulation. Three different combinations of the amount of salt and pH, giving the same storage period at a predetermined temperature, for example:

pH Salt (wt.%)
6,4 0,8
6,2 0,7
6,0 0,4

From the standpoint of consumer preferences, one of them can have a better taste. The effect of these formulations on three microorganisms in this step can be estimated without laboratory tests.

Setting the technical conditions

Very few materials have been published on the microbiological characteristics of chilled products for the manufacturer, but there are two very useful publications on the characteristics of finished products ([16] and [21]) that can help determine them. These two documents use different approaches. For example, in [21] the content of certain microorganisms is given that is acceptable at the end of the shelf life, that is, when consumed. If the producer of chilled products wants to use these characteristics to ensure an acceptable level of microorganism content at the end of the shelf life, then prognostic models can be used to determine the level of microorganism content at the beginning of product storage. If, for example, the recommended level of TUS or EMBASepaseae at the end of the shelf life is 106 cfu / g (some colony forming unit), then the prognostic model can be used as shown in the examples below.

Example 1

Enterobacteriaceae pH 5,5; salt of 5,25% of the mass. (water. steam), 15 ° С

Original content 1 g The desired shelf life, days Estimated content via 5 days Time to achieve 106 content cfu / g (d)
10 5 X 1,39 104 13,5
100 5 X 2,39 105 9
103 5 X 2,75 106 6
104 5 X 1,5 107 3

As can be seen from these data, to achieve a shelf life 5 day, if at the end of the storage period requires at most 106 cfu / g, the initial level should not exceed EMegoaiepaseae 103 cfu / g.

In [16], the maximum content of microorganisms allowed after the production of a given food product is given. Predictive models in this case can be used to demonstrate the likely increase in their content under various modes of refrigerated storage.

Example 2

Epegoas1epaseae pH 5,5; salt 2% by weight.

Temperature ° C Baseline (characteristics at issue) Time to achieve soderzhaniya106 cfu / g (d) (final data)
3 100 33
5 100 17
8 100 7
10 100 4

As can be seen from the above data, if after the release of the product the microorganism content is 100 cfu / g, then the storage temperature has a great influence on the probable shelf life (for example, at 3 ° C it will be 33 days, and at 8 ° C only 7 days) .

Most prognostic models provide information that can be used to determine the shelf life of a product. The data received contains the following parameters (all or some):

  • phase lag (delay time), i.e. the time before the growth of microorganisms;
  • generation time, ie the time required for each cell division;
  • growth curve that shows the lag phase, the exponential growth phase and stationary phase of growth;
  • time required to achieve the desired cell number, or vice versa, the target number of cells versus time;
  • the number of cells after a given time.

Most models predicting the number of microorganisms are based on the growth of a single species or genus of organisms, or (in some cases) on a group of related organisms (for example, lactic acid bacteria or Epigensaceae). In cases where problems can be caused by several microorganisms, the forecasts should be obtained using appropriate models and interpreted by qualified personnel.

Example 3

This example shows how different spoilage models can be used to assess the likely shelf life of refrigerated meat products.

 The microorganisms that cause problems:

lactic bacteria;


 End of shelf life:

Lactic acid bacteria - at level 106/ G;

Eptobasteriasee - at level 106/ G.

♦ Product TU:

pH = 5,5;

аφ = 0,983;

% Salt = 3.

Microorganism, CFU / g Baseline (cfu / g) Time to definition 106cfu / g (d) Shelf life day
Lactic acid bacteria 100 9 9
Eptegoasteriaseae 100 7 7

As can be seen from the table, Epilobiaceae will limit the shelf life, since they reach a level of 106 cfu / g within 7 days, and lactic acid bacteria in 9 days.

Definition of the product shelf life

To assess the shelf life of a new or already known product, microbiological analyzes of the finished product are usually carried out on typical microorganisms that cause spoilage and on pathogens during storage for a certain time at specified temperatures. Since such work may require the use of third-party organizations, it can be quite expensive, and therefore it is important to test the shelf life at the right stage of product development. A useful three-stage approach to determining the shelf life is described in [7]:

  • Phase I Pilot production.
  • Stage II Preparations for mass production.
  • Mass production of Stage III.

Estimation of shelf life at the pilot production stage

It is very likely that at this stage the product exists only in the form of a new idea or marketing concept and to assess the likelihood of its success in terms of taste / aroma, color, texture and nutritional properties, it should be produced on a small scale. It is likely that many product data at this stage are still unknown, and therefore it is possible to estimate the shelf life of the product only previously (Fig. 10.1).

First, a product can be described theoretically by listing the likely ingredients, process and packaging characteristics, and storage requirements. To highlight potential quality changes, the potential for microbiological spoilage, and any potential safety problems, this list of characteristics can be used to evaluate product properties that are important for assessing shelf life. Ingredients in which microorganisms may be present that cause product spoilage and food poisoning are desirably controlled at all stages of the manufacture of the product. Changes in the number of microorganisms as a result of each specific operation can be recorded and used.10.1.1

Fig. 10.1. Determination of the retention period at the experimental production of the product (for [7])

in assessing the risks associated with the product, and can also suggest or help assess the most significant changes that should be monitored during storage shelf life testing. For example, heat treatment can reduce the number of microorganisms, and the holding period or the introduction of a certain ingredient can increase their number. Even during pilot production, it is important to consider the risks associated with this product using the HACCP method (see, for example, [17]).

Using the collected documentary data on the ingredients, process and packaging, the possibility of contamination of the product with foodborne microorganisms and their growth during storage should be assessed. If the product is likely to contain infectious pathogens (e.g., Listeria or Salmonella) or toxic microorganisms (e.g., Staphylococcus aureus, Bacillus cereus or Clostridia), their potential harm should be assessed. Initial indications of the likely growth of pathogens or microorganisms causing spoilage can be obtained using predictive models (see section 10.3).

Estimates of the shelf life obtained on products manufactured at the pilot production stage are somewhat limited, since with the further development of the chilled product, he and the technology for producing it will still change several times. Moreover, it is unlikely that the experimental conditions coincide with the conditions of real production.

The quality of raw materials, as well as processing and hygiene standards, will be different than with full-scale production, and the batch size will be significantly smaller, which will lead to less variability of the finished product. Given these limitations, data characterizing the shelf life of at least the intended or shorter time (if changes in the product become unacceptable to the consumer) can be obtained by observing the product, which was produced on a pilot scale, divided into real portions , packed and stored at 8 ° C (if there is no data on other storage conditions).

Material obtained in the laboratory or in pilot production should not be subjected to extensive organoleptic or microbiological studies, but each quality change should be identified and described. Before a product can be tasted, it must be shown that it is microbiologically safe. The main objective of the research is to identify and describe the acceptability of the product and the degree of its organoleptic changes during storage. Such studies are needed that allow us to describe the characteristics of the product, making it unacceptable to the consumer. In many cases, a certain change in quality is likely to occur, that is, a critical quality parameter appears that limits the shelf life. The combination of information collected earlier and obtained as a result of real product testing should give a general idea of ​​whether the product will withstand the intended shelf life.

At this stage of testing, developers usually have already made significant progress in product development. If the product does not reach the desired level of quality, they should be able to decide whether, by changing the process, packaging or formulation, it is possible to achieve the desired quality, and whether repeated tests are necessary at the pilot production stage or whether these changes should be made at the preparatory production stage. If changes in product quality are unacceptable to the consumer, then the whole concept of the product or its processing needs to be reviewed. In this case, prognostic models can help decide whether changes in the composition of the product will affect its shelf life, determined by the growth of microorganisms.

Evaluation of the shelf life of the preparation of production

The goals of production preparation are to ensure an increase in production volumes, to ensure and confirm the characteristics of the product, the process and formulation, as well as to ensure the competitiveness of the product (compliance with marketing requirements, including the intended shelf life). The production output in the preparation of mass production is carried out on a pilot plant or, more preferably, by the release of batches on production equipment. When product development is complete, its characteristics should be documented in accordance with the requirements of any existing quality control system, such as HACCP. Product characteristics (specifications) cover the raw materials, composition (recipe) of the product, principles of product compilation, its processing, packaging and sanitary and hygienic conditions of production. Deviation from these characteristics (TU) can affect the shelf life of the product, and therefore it applies only to the product that is produced under certain given conditions. Any changes to any aspect of production should be recorded. At the stage of preparation for production, the verification of the shelf life should be the most thorough, and for the organization of its testing, storage conditions, a sampling system and the analyzes performed must be determined.

Storage conditions must be real or carefully selected - so as to meet the actual conditions in which the product will be during storage. The main condition for storing chilled food is a temporary temperature regime. Both time and temperature should be set so that, taking into account the given time periods, cover the entire temperature range in which the product will be during transportation - as part of the sales system, in refrigerators or display cabinets in the retail system, as well as at home for consumers, including transportation from a retail outlet to a home and storage in home refrigerators.

The sequence of temperatures and the corresponding time intervals require careful analysis. A product purchased at the beginning of its shelf life can spend most of its shelf life in a home refrigerator at temperatures that are usually higher than those allowed by regulations for retail outlets [22]. In the same way, the influence of conditions when transporting a product from a retail outlet to a home can be different depending on at what point in the shelf life it occurs.

In connection with the foregoing, it is rather difficult to determine all possible combinations of time and temperatures affecting the product, and it should be decided which options will be most typical for normal conditions. In [7], it was suggested that the storage mode of the product at a temperature not lower than 8 ° С with holding at 22 ° С for 4 hours at the earliest possible sale moment can be taken as the basis. As experience is gained with the product and data on its behavior, the standard conditions for testing shelf life can be subsequently revised.

It is important to remember that the shelf life of the product will be valid only for a given batch of product and tested temperatures. If the product reaches the specified storage period when tested at 8 ° C, then it is undoubted that at lower temperatures (for example, at 5 ° C) it will withstand a longer shelf life. Conversely, if the shelf life tests are performed at 5 ° C and the product is stored at a higher temperature, it is likely that the shelf life will be less than expected.

And finally, before determining the time and temperature of storage, it is necessary to determine whether they correspond to the needs of customers. Many chilled-food retailers have developed specific shelf life test requirements based on knowledge of their sales and storage systems. Before starting a shelf life study, it is recommended that you verify that the intended tests will meet these requirements.

sampling time

After selecting the time and temperature parameters, this mode should be applied to a sufficient amount of the product to make it possible to evaluate several units of the product several times. The sampling frequency and volume significantly depends on the experience with this or a similar product, as well as on its stability. It is undesirable to use less than three parallel samples for each time period (preferably five), as this will expand the possibilities of statistical data analysis. The number of samples and the frequency of sampling depends on the intended shelf life of the product.

It is recommended to take samples at the beginning of the storage period (“day 0”), at the end of the storage period, and at least three times between these time points. For products with a short shelf life (2-5 days), this can be expressed in daily sampling, and with a longer shelf life of the product, sampling can be performed less frequently. To control the “margin” of safety and / or quality after the expiration of the storage period, it is recommended to take additional samples. The main parameters for control when checking the shelf life should be determined on the basis of observations made at the stages of pilot production, as well as on the basis of estimates by the HACCP method. Organoleptic evaluations (see chapter 12), as well as microbiological and chemical analyzes (see chapters 8 and 9) are needed to determine the extent to which a product changes over time.

Under normal production, most of the basic parameters have some variability. It is important that the appropriate limits for these key parameters are provided for during shelf life testing so that the shelf life is applicable to all possible product manufacturing extreme cases. In order for such a product to be available, it may be necessary, in preparation for production, to specially manufacture for the shelf life tests a batch of product characteristic of the extreme case. In some cases, it is not possible to guarantee the presence of a microorganism that is potentially important for checking the shelf life of the product, or it may be highly likely that the level of content of the microorganism changes significantly. In such cases, the best solution may be the intentional introduction of the microorganism into the product for the so-called "provocative" (control) testing. When using this approach to interpret test results, it is necessary to clearly understand its limitations (see section 10.5). Tests of the shelf life before serial production should ideally be repeated for several batches of the product, which will help to identify differences in batches produced on different days, and determine the level of reliability of the data obtained and the development of technology. The data obtained in the first tests may allow further sampling less frequently.

Information collected during shelf life tests is interpreted according to fig. 10.2. First, the most important characteristic should always be the safety of the product, and therefore the first limit that must be set is the maximum safe shelf life of the product. The main reasons that food becomes dangerous are the growth of pathogenic microorganisms or an increase in the content of toxins produced by microorganisms (in the case ofDetermination of shelf life with the release of batches during production preparation

Fig. 10.2. Determination of shelf life with the release of batches during the pre-production (by [7])

their presence). The control and monitoring procedures used in the HACCP technique should minimize the likelihood of the presence of pathogenic microorganisms.

Secondly, shelf life tests should allow determining the maximum shelf life while maintaining good quality. Establishing criteria and determining the minimum acceptable level is a matter of strategy for a particular manufacturer. Many companies use a comprehensive criterion based on the “product image”, price, market share, and consumer complaints to select and confirm a standard shelf life based on good quality. Changes in the appearance, texture and taste / aroma occur as a result of chemical or biochemical reactions, changes in the physical structure and growth of certain microorganisms. These changes can be assessed by counting the number of microorganisms, the value of specific factors related to quality (for example, the peroxide value for oxidized fats) or by organoleptic evaluation. When a product ceases to meet standards or marketing requirements, quality changes reach a certain level. The time interval up to this point determines the shelf life (by product quality).

After determining the storage periods for safety and product quality, they should be compared with the indicated (planned) shelf life, which ideally should exceed both of these periods. The shelf life should be set as a limit on safety or quality - depending on which one is shorter, but it is always preferable to limit the shelf life on quality rather than safety, since most often quality changes can be determined by smell, taste or external mind, and the achievement of safety limits but these characteristics can not be determined. To evaluate product safety, the results of “provocative” tests should be considered. Since an increase in production volumes from pilot to full-scale production can lead to some changes, it is recommended to reduce the maximum storage period to provide an additional "safety margin". If the shelf life is shorter than planned, you must either change the product or evaluate the promising marketing of a product with a shorter shelf life.

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