Chilled and frozen foods

Determining shelf life and control test

G. Betts and L. Averis, Satrs1ep Aps1 С1yu1еу \ ¥ 00s [Boos! Izezegs Azeospiop


During storage, the quality of all food products may deteriorate. Chilled products are particularly perishable. The time during which the quality of the product is maintained at a level acceptable to the consumer can be called the shelf life during storage (shelf life). The shelf life is defined by some authors as the time between the production / packaging of a product and the moment when the product becomes unacceptable for consumption under given environmental conditions [11], or the time when the product is considered unacceptable for consumption [23]. The shelf life of a product is determined by undesirable quality changes caused by biological, chemical, biochemical, and physiological causes, or food safety considerations associated with the growth of foodborne pathogens that do not necessarily cause changes in product quality.

There are a number of reference books that list the shelf life of refrigerated products, since each product has its own snoring period, depending on the specific recipe, ingredients, and applied production and storage conditions. If some of the listed factors change, the shelf life is subject to change (see 10.2 section). There are some general recommendations in the literature for refrigerated products [11] and products packaged in CSG [9], but the shelf life of the product should be determined already when it is developed on a scientific basis in accordance with the techniques, the basic principles of which are described below.

The rationale for a specific retention period is based on the concepts of safety, quality and commercial solutions. It is unlikely that all these components will give one result, but the safety of the product should always have the highest priority. There are, however, many commercial and marketing factors that impose limitations that must be considered when determining the acceptability of shelf life, determined on the basis of microbiological evaluation from a commercial point of view. For example, how does the shelf life of a product relate to the shelf life of similar products of competitors? Is this shelf life sufficient to sell a significant portion of the product before the expiration of this period, which minimizes the amount of inventory that must be disposed of after it expires? Is the shelf life long enough to be able to purchase the product weekly, how are most of the refrigerated products [12] purchased? If there is a minimum commercially acceptable shelf life, it must be taken into account when developing a product and the recipe is changed accordingly.

Another limitation for manufacturers of refrigerated products is the rapid expansion of the market. Over the past ten years, the number of products and their types has increased significantly [10]. About 7450 new products appear each year, with approximately 3600 being chilled products [7]. The market for chilled products in 1997 was 5,1 billion pounds [4]. Such a dynamic market requires the rapid development and release of new products and new combinations of ingredients. Traditionally, the safety and quality of new products have been evaluated only on the basis of laboratory tests, which are long and expensive. Currently, there are prognostic mathematical modeling methods that are increasingly used in the development of new products, the use of which in determining the shelf life will be discussed later in the 10.3 section.

Along with commercial considerations, the need for the rapid development of a large number of new products is determined by consumer demand for products with a new taste, lower salt and preservatives and requiring minimal preparation [15]. The implementation of such requirements can potentially enhance the growth of microorganisms that cause food spoilage and pathogens, and consequently, reduce the probable shelf life achievable in cold storage conditions. Such product changes mean the need to use new combinations of ingredients and preservatives to maximize shelf life. This issue will also be discussed below.

The determination of the shelf life of a product is based on a combination of safety, quality, marketing, and customer demand requirements. The correct definition of the shelf life is necessary for the success of the product on the market, and in this chapter we will try to show how this can be achieved.

Factors affecting shelf life


To develop a new product, it is necessary to take into account a number of fundamental issues that affect the likely achievable shelf life.

product features

The first step that needs to be taken is to decide which product characteristics are necessary - for example, is dairy a product or a product based on tomatoes? Should it be a homogeneous sauce or will it contain solids? The type of product will give initial indications as to which microorganisms are likely to influence the product, and therefore, how long the storage time can be reached. For example, non-dairy products are more susceptible to the rapid growth of microorganisms and will likely have a shorter shelf life than fermented milk products.

Pasteurized chilled products may require different heat treatments depending on the basic characteristics of the product [14], and the requirements for it can be determined at this stage.

product Packaging

It is necessary to consider the desired type of packaging. If the product is pasteurized in a package, in the absence of subsequent contamination in the product there will be fewer spoilage vegetative microorganisms or pathogens, and the achievable shelf life will be relatively long. Bacteria spores will be present in the product, but at low temperatures they grow relatively slowly (see chapter 7). If the product is packaged after heat treatment, there is a high risk of contamination by microorganisms even in good sanitary and hygienic conditions, and the shelf life of these products is likely to be shorter than the products pasteurized in the package.

You must also consider the gas environment in the package. If the product is packaged under normal atmospheric conditions, aerobic organisms that cause spoilage (for example, Pseudomonas) can grow and quickly spoil refrigerated products stored at temperatures below 5 ° C. If, however, an adjustable gaseous environment without oxygen is used, anaerobic organisms will cause spoilage and grow more slowly with strong cooling (see chapter 7).


Is the product positioned as “product without preservatives” or “low salt”? If additional preservative factors are not used (for example, adding lemon juice), the removal of preservatives will make possible the rapid growth of microorganisms and thereby reduce the shelf life. The effects of the exclusion of traditional preservatives and alternatives should be considered at the initial stage of the development of a new product.

Restrictions on the expiry date

It may be that there is some minimum shelf life to be achieved in order to make the product commercially viable (for example, to make it possible to store the product at the weekend, such a period could be 10 days). This must be determined from the very beginning of the determination of the shelf life, so that the selected product formulation and packaging characteristics will achieve the desired shelf life. Often, according to consumers, the maximum shelf life of the product is less than that which can actually be achieved. For example, in [13], the average shelf life of a number of refrigerated products was considered (actual and estimated by consumers), and it was found that for the pate (pate) the actual shelf life exceeded 10 days, while according to consumers it was only 4 days

After creating a recipe for a specific product and identifying the characteristics of the package, the intended shelf life will most likely be determined based on past experience. This shelf life must then be scientifically verified in accordance with the principles set out in the 10.4 section. After determining the shelf life, as will be shown below, it will be influenced by a number of factors that also need to be considered at the product development stage to ensure their control during production.


The raw materials used in the production of the product affect the biochemical and microbiological properties of the finished product. To obtain a stable shelf life, the quality of the raw material must be standardized, and the characteristics, whose effect on the shelf life of the product is most likely, must be incorporated into the technical conditions for the raw material. Changes in the quality of raw materials can lead to changes in the finished product that can change its shelf life. Changes in raw materials can occur for a number of reasons, in particular due to natural fluctuations, changes in variety, supplier, seasonal availability of raw materials or their pre-treatment. The production of colesloh lettuce (see above) gives an example of the effect on the shelf life of seasonal availability of freshly harvested cabbage with a low yeast content, while in cabbage after refrigerated storage more yeast. The use of cabbage from the refrigerator results in a salad with a noticeably shorter shelf life due to the higher initial yeast content introduced with the raw materials.

If a certain ingredient of the raw material does not meet the agreed requirements (for example, due to the level of microorganisms contained in it), then this ingredient may be used for another purpose - for example, to add to the product before cooking, provided that it does not affect it. security. The likely consequences of using products with higher levels of microorganisms can be estimated using prognostic models (see section 10.3). The limits of tolerance for those ingredients that give the main preservative effect in the finished product (for example, salt content) must be established during product development or with special (“provocative”) testing (see section 10.6) and are specified in the product specifications and in the recipe. Any fluctuations in the content of these components due to the inaccuracy of their dosing during production will affect the achieved shelf life. Ingredients that are critical to product safety or stability during a given shelf life must be determined using product safety analysis [17], and in its production, the levels of these ingredients must be monitored. For example, for refrigerated products packaged in CSGs, the main determining factor may be the level of salt 3,5% in the aqueous phase, and this level must be monitored in each batch of produced product [5].

To overcome the critical factors in raw material variability, it is possible to use the composition (formulation) of a product, thus reducing changes in the final product. One of the most important factors influencing the degree of heat treatment required to achieve sterilization is the pH level. In tomatoes, for example, variability of acidity is observed from grade to grade. The composition of the product can be used to overcome this variability by mixing varieties with high and low acidity or by adding approved organic acids. It is of fundamental importance here to control the pH of each batch of the product so as to ensure that the preset level is reached when the pH level is used as the main preservative factor.

Drawing product

In complex and multicomponent products, contact of components can lead to the migration of flavorings, dyes, moisture, or oil from one component to another. This may limit the shelf life of, for example, multi-layer cakes, where the appearance deteriorates due to the migration of coloring components from one layer to another, and fruit pies (pies), where the migration of moisture from the filling to dough leads to a violation of the texture. Migration can lead to the combination of substances entering into chemical reactions, and the products of these reactions affect the shelf life of the product. Pizza toppings with unblanched green pepper can give a rancid taste and smell due to the contact of green pepper lipoxygenase in contact with fatty acid containing substances of a pizza crust or cheese.

How multicomponent products combine may significantly affect the microbiological safety of the product. If components that are stable due to low at or low pH come in contact with components that are unstable due to high at or pH, a layer is formed between them in which at and pH allow the microorganisms to grow, and any microorganisms from stable component. To increase the shelf life, migration or contact between components may be limited, and this issue should be considered already during product development. In cases where the migration or contact of components is detrimental to the quality of the product, it is recommended to consider the use of edible films or packaging in separate compartments.

 Performing the shaping

A wide range of methods is used for processing products — from simple cutting or washing (for example, ready-to-eat chilled salads) to heat treatment, acidification, adding preservatives, fermentation, or pickling. The type of processing significantly affects the microflora, chemical, biochemical and organoleptic properties of food products. In some cases, their processing can be aimed at achieving the desired characteristics of the product (for example, in the case of fermented salads) and by reducing the pH can lead to changes that increase the shelf life. In other cases, a treatment specifically chosen to influence the factors that affect the shelf life may be used — for example, heat treatment of a food product to inactivate microorganisms and harmful enzymes. When using one or another type of processing to achieve the desired shelf life, it should be understood that even small changes in processing conditions can significantly affect the shelf life. Any stages of production of a product that are necessary for safe storage during the shelf life must be identified during the risk analysis and be monitored accordingly during production.

Sanitary-hygienic control

Lack of hygienic control during the preparation, processing and packaging of food products can lead to a high level of microorganisms introduced into the product (for example, poor cleaning of meat cutting equipment leads to an increase in the number of microorganisms in the product). This may adversely affect the safety and quality of the product, which in turn will affect the shelf life. The shelf life of a specific product may reflect only the range of variables included in the testing procedures. To produce a product with a specified shelf life, constant sanitary and hygienic control is required during production (see chapters 13 and 14).


Packaging prevents contamination of the product by microorganisms, protects against physical damage and can be used to isolate the product from the effects of negative environmental factors (light, atmospheric oxygen or humidity). To prevent or reduce photocatalytic reactions leading to oxidation or degradation of nutrients, special packaging materials can be used to filter light with a specific wavelength. Products that are sensitive to oxidation by atmospheric oxygen can be protected by packaging materials that prevent access to oxygen, and the choice of moisture-proof materials can prevent the product from drying out or retain moisture in the package.

Packaging in a controlled gaseous environment increases the shelf life of meat and vegetables, directly affecting a factor critical to their quality (as in the case of fresh red meat (lamb, beef). At the same time, bright red color is maintained by a gaseous environment with a high oxygen content, affecting speed, which leads to reactions leading to negative quality changes. In addition, the shelf life may be extended by “active packaging” (for example, absorbing 02/ С02/ N20 or secretes ethanol) (see. 6 chapter).

When the gaseous environment in the package is regulated, that is, differs in composition from the normal atmosphere, its effect on microorganisms should be taken into account. Removing oxygen from the package will prevent the natural growth of microorganisms (for example, Pseudomonas species) that cause spoilage of refrigerated products that contain air in their packaging. At the same time, such products can become dangerous due to a hundred hundred anaerobic pathogens (for example, C. botulinum [2], but to be organoleptically stable [5].

Storage and Distribution

The conditions in which the product is located during storage and marketing can significantly affect the shelf life. Temperature, light and humidity affect the growth of microorganisms, as well as the types and speed of biochemical reactions and physical changes that occur. To estimate the shelf life of the finished product, it is necessary to know or determine the conditions in which the product is likely to be located and the impact they will have on it. The number of papers devoted to the study of the time-temperature dependencies of refrigerated products during storage, transportation, in retail and at the consumer is very limited, and some of them are reviewed in the [6] review.

Currently, food safety regulations (Food Control (Temperature Control) Regulations 1995 SI No. 2200) adopted in the UK for refrigerated products allow the maximum temperature 8 ° С for refrigerated products to be sold and sold in retail. This is important to consider when determining the shelf life of products, since any estimates made at lower temperatures will be incorrect (see section 10.4).

Use of the product by the consumer

Consumer handling of the chilled product can also affect quality and safety. When setting the time and temperature conditions used in tests for determining the shelf life, it is necessary to take into account such factors as the time spent on delivery of the product to the home, the perception of the cooled products by the consumer and the storage conditions at home. This is, in all likelihood, the most volatile part of the cold chain, on which the manufacturer can have only a minimal impact. A review of how consumer products with refrigerated products in the UK [13] showed that most consumers bought a large amount of refrigerated products at least once a week. In most cases, food was delivered home by car or on foot (83%), and on average, food delivery from the store to the home refrigerator took 43 minutes. The product temperature was usually in the range of 4-20 ° C. It turned out that the temperature in domestic refrigerators ranged from -1 to + 11 ° С with an average value of 6 ° С. On average, only 30% of refrigerators operated at temperatures below 5 ° C. Of the refrigerators included in the review, 7,3% worked at an average temperature above 9 ° C, although differences in temperature depending on the position of the product show that this value is higher if the product is stored in the upper part of such refrigerators.

Although such information indicates temperature and time, which are likely to be necessary for testing to determine the shelf life, simulating the consumer's handling of products, it is necessary to reasonably choose which strategies to take as the worst. If in such tests the temperatures were used under the worst conditions and the storage time was fixed, then few of the products currently on sale would have survived to the intended shelf life. The manufacturer must assess where the “reasonable” violation of the storage mode ends and the “unreasonable” begins.

In addition, the consumer may not treat the products in the manner planned or intended by the manufacturer. Many chilled products are bought based on a “fresh product image,” but then they are frozen at home. After the sealed vacuum package or the CGS package is opened and the product is partially used, the information on the shelf life for the remaining products becomes invalid. An analysis of consumer perceptions about the shelf life of chilled products showed that although consumers thought that most chilled products should be stored for two days or less, in fact, the same consumers stored some chilled products for much longer [12].

legal requirements

For more information on the legal responsibility of the manufacturer of refrigerated products, see chapter 2. The main regulatory restrictions for chilled products in connection with their shelf life relate to the temperatures used during marketing and storage. In the UK, chilled products can be stored at temperatures up to 8 ° C, and this should be taken into account when determining the shelf life during product development. It is possible that the product will be stored at lower temperatures for most of its storage period in retail and in stock, however, since the permissible maximum temperature is 8 ° C, the product batch can sometimes be stored at 8 ° C for the entire storage period. This means that the product can withstand such time and temperature conditions, while maintaining its quality and safety.

In addition, if the cooled product must be exported to the EU countries apply other restrictions on the cooling temperature, which must be considered when developing the product. The EU has a number of different requirements, and is currently considering a draft agreed requirements for the temperature in the EU [3].

For chilled products packaged in the CGS, there are guidelines limiting the shelf life of such products to ten days or less at temperatures <8 ° C, unless specific regulatory factors are used to minimize the growth potential of psychrotrophic C. botulinum [2, 5]. Any deviation from these guidelines will only be possible after scientifically proven evidence that additional preservatives will prevent increased production of C. botulinum toxins in foods.

 The influence of internal and external factors

The factors described above, namely the type and source of ingredients, as well as the subsequent processing and packaging, affect the types and quantities of microorganisms present, as well as the chemical and biochemical reactions that can occur in the finished product. The ability of microorganisms to grow or create problems, the possibility of chemical reactions in the final product depends on the properties of the final product, that is, pH, am (internal factors) and external factors affecting the finished product - in particular, temperature. Internal factors include:

  • water activity (am) (available water);
  • pH (total acidity);
  • kind of acid;
  • preservatives including salt and spices;
  • nutrients;
  • estestvennaya microflora;
  • redox potential (£ / *);
  • available oxygen;
  • natural biochemical factors (enzymes, chemical reagents).
  • The external factors include:
  • the type of heat treatment (frying, cooking or heating food before consumption);
  • the gas composition in the headspace in the container;
  • temperature during storage and distribution;
  • Relative Humidity (Yak);
  • Council (UF i IK).

Examples of minimum growth conditions for pathogens and microorganisms that cause spoilage and play an important role in refrigerated products are given in Table. 10.1. It should be emphasized that the values ​​given are typical and depend on the specific strain of the microorganism and the storage conditions used in the studies. Such data only tentatively indicate microorganisms, the probability of growth of which in the product is high, and should be confirmed by thorough scientific research.

10.1 Table. Minimum conditions for the growth of microorganisms in refrigerated foods

type of micro-organism The minimum pH for growth The maximum aω for growth * Anaérobnıy Rost Maximum temperature**
1 2 3 4 5
Pathogens *
Salmonella 4,0 0,94 Yes 7
Staphylococcus aureus 4,0 0,83 Yes 6
(4,5 for toxins) (0,90 for toxins) (10 for toxins)
Bacillus cereus (психротрофный) 4,4 0,91 Yes <4
Clostridium botulinum
протеолитический A, В ,F 4,6 0,93 Yes 10
neproteoliticheskiy B, E, F 5,0 0,97 Yes 3,3
1 2 3 4 5
Listeria monocytogenes 4,3 0,92 Yes 0
Escherichia coli 4,4 0,95 Yes 7,0
Vibrio parahaemolyticus 4,8 0,94 Yes 5
Yersinia enterocolitica 4,2 0,96 Yes -2
E. coli 0157 4,5 0,95 Yes -6,5
The microorganisms that cause spoilage * * * *
Pseudomonas 5,5 0,97 No <0
Enterobacter aerogenes 4,4 0,94 Yes 2
Lactic acid bacteria 3,8 0,94 Yes 4
Micrococcus 5,6 0,9 No 4
Yeast 1 – 5 0,8 Yes -5
Mould <2,0 0,6 No <0

Notes. The following table lists various species and indicates approximate growth and survival limits with the independent action of various factors. It is very likely that the interaction between the factors will lead to a significant change in these values.

* For example, in a vacuum (sealed) package.

** Minimum growth temperature for typical neutral pH, high water activity in refrigerated foods.

*** Data for pathogens - according to [3].

**** Data for spoilage microorganisms - according to [7].

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