Chilled and frozen foods

Microorganisms cause spoilage

Microbiological spoilage of refrigerated products may take various forms, but usually they are all a result of the growth of microorganisms, manifested in a change in organoleptic properties.

In the simplest case, this may be a result of the growth itself, and often its visible manifestations, which is noticeable in the case of molds that form large, sometimes pigmented colonies. Bacteria and yeast can also form visible (sometimes pigmented) colonies on food. Other types of spoilage are also possible: the formation of gases, mucus (extracellular polysaccharide substances), diffusing pigments and enzymes that cause softening, decay, the appearance of foreign odors and tastes as a result of the decomposition of individual components of food. Such types of damage caused by microorganisms are discussed in [25] and [120].

Damage usually occurs most quickly in protein-cooled foods — red meat (lamb, beef), poultry, fish, shellfish, milk, and some dairy products, which create favorable conditions for the development of microorganisms (they are highly nourishing, contain a lot of moisture, and are relatively close to neutral pH). To reduce the rate of damage to these products often change them, as shown above. In cooled products, these changes can prevent the growth of microorganisms and damage not completely, only limiting its speed and nature. Usually, microorganisms capable of growing in the presence of preservatives cause food spoilage. It is necessary to distinguish between microorganisms present in spoiled products and microorganisms that cause spoilage (sometimes they are called microorganisms that cause specific spoilage organisms (SSO)). The latter can be only part of the microflora [55], and therefore organoleptic spoilage in it and the number of microorganisms of the product are often weakly related.

The benefits of traditional microbiology for controlling spoilage microorganisms are often limited, since the time required to produce results is a significant part of the shelf life. Recently, faster molecular methods [58,113] have become available to identify both microorganisms in general and those causing a certain type of damage. For ease of discussion in this chapter, the microorganisms that cause spoilage are arbitrarily divided into six categories:

  • Gram (oksidazopolozhitelnye) rod-shaped bacteria;
  • koliformы enteroʙakterii;
  • Gram-positive spore-forming bacteria;
  • lactic bacteria;
  • other bacteria;
  • yeasts and molds.

Gram (oksidazopolozhitelnye) rod-shaped bacteria

This group includes the most common microorganisms that cause spoilage of refrigerated products. The minimum temperatures of their growth are usually 0-3 ° С, and they grow relatively quickly at 5-10 ° С. Although these microorganisms can make up only a small fraction of the original microflora, they quickly begin to predominate in fresh protein products stored chilled [23,45,64]. This group includes the most common genus Pseudomonas, as well as various species of the following genera: Acinetobacter, Aeromonas, Alcaligenes, Altermonas, Flavobacterium, Moraxella, Shewenella and Vibrio [116]. These microorganisms are common in the environment, especially in water, and therefore many of them easily contaminate food. They can multiply on insufficiently cleaned surfaces of equipment or technological installations, infecting food products.

Gram-negative (oxido-positive) sticks can spoil the products, forming diffusing pigments, mucus on the surface and enzymes that lead to rotting, the appearance of foreign flavors and odors [23,45,67]. Some enzymes formed by Pseudomonas species that are extremely heat-resistant and in products that have undergone heat treatment, with long shelf life may form deterioration that develops over time (for example, rancidity or gelation).

Microorganisms of this group are well adapted to growth at low temperatures, but are often sensitive to other factors, such as the presence of salt or preservatives, lack of oxygen, low (<5,5) pH and water activity (aw <0,98). If these preservation mechanisms operate in a product, gram-negative (oxidase-positive) rod-shaped bacteria become less competitive and other groups of microorganisms can lead to spoilage. Vibrio species are atypical as they tolerate relatively high levels of salt and can therefore spoil bacon and other salted foods stored refrigerated (Photobacterium phosphorum, a very large marine vibrio, is the main microorganism that causes spoilage of vacuum packed cod) [55] ... This group of bacteria is not heat-resistant and therefore can be easily eliminated with moderate heat treatment. The presence of such microorganisms in cooked foods is usually due to contamination after processing.

Koliformы enteroʙakterii

This group of bacteria also consists of gram-negative rods, but differs from the previous group by a negative oxidase reaction. Traditionally, microbiologists have sought to define these groups separately, as their sources, significance and factors affecting growth may differ. The presence in food of microorganisms of this group is often used as an indicator of insufficient treatment or contamination after it. Compared with gram-negative (oxidative-positive) rod-shaped bacteria, coliforms and enterobacteria are usually less adapted to grow at temperatures below 5-10 ° С, although many can grow even at 0 ° С [95]. They can dominate the microflora at temperatures 8-15 ° С [23, 64]. Compared with gram-negative (oxido-positive) rod-shaped bacteria, the group of coli and enterobacteria is less sensitive to pH changes, therefore, it requires more attention in weakly acidic products. However, bacteria of this group are usually sensitive to low aw water activity, preservatives, salt, and heat treatment [67].

The group of coliforms and enterobacteria does not necessarily require the presence of oxygen for their growth. In addition, they have an enzymatic metabolism and can therefore destroy carbohydrates, forming acids that lead to the coagulation of milk [23]. The metabolism of gram-negative (oxidizing) bacteria is oxidative, and fermentation does not occur. Other forms of spoilage include pigmentation, gas, mucus, odor and aftertaste. In this case, extraneous odors are grassy, ​​medicinal, unpleasant and fecal [116].

Types that commonly cause spoilage include Citrobacter; Escherichia, Enterobacter, Hafnia, Klebsiella, Proteus and Serratia [67,114], which are widely distributed in the environment, including animals. The appearance of these microorganisms in food can be caused by inappropriate methods of slaughter and cutting of carcasses.

Gram-positive spore-forming bacteria

This very important group of microorganisms can form heat-resistant spores that can withstand different types of heat treatment, which can destroy all vegetative cells, but relatively slowly developing spore-forming bacteria will prevail in the microflora. The minimum growth temperatures are 0-5 ° С, although it often slows down at temperatures below 8 ° С [21,23,64].

In this group, species of microorganisms of the genera Bacillus and Clostridium require special attention. They are common in the environment, and their disputes can exist for a long time. The most common form of spoilage is the formation of large quantities of gas, which can lead to inflation of the package or product [23, 114]. It is believed that the heat resistance of psychrotrophic strains is lower than that of mesophilic [94], but it is they that are of particular concern in cooled pasteurized products.

Lactic acid bacteria

At low temperatures, lactic acid forming bacteria do not grow at all or grow slowly. Therefore, it is they who cause spoilage if the growth of other types of microorganisms is suppressed. Bacteria in this group tolerate a lower pH level better than other bacteria that cause spoilage, and can multiply even at pH 3,6 [67]. In addition, lactic acid bacteria are more resistant than the microorganisms discussed above, to small changes aw, and some species of Pediococcus are salt-resistant. Lactic acid bacteria usually predominate in vacuum-packed products, in some products stored in the CSG, and can even grow in a medium with 100% carbon dioxide [44]. This group of bacteria includes rod-shaped and spherical or sphere-like Gram-positive bacteria belonging to such genera as Camobacterium, Lactobacillus, Leuconostoc, Pediococcus and Streptococcus [16]. Damage usually consists in the formation of an acid, which leads to souring with the accompanying evolution of gases or without such release [116].

Lactic acid forming bacteria are specifically introduced in the production of certain chilled products (for example, cheese, yogurt, some sausages), as they are necessary to obtain the desired characteristics of the product. In addition, there is considerable interest in the potential use of lactic acid bacteria as a new canning system, since many of them produce, in addition to acids, antibacterial compounds [77].

Other bacteria

Problems in chilled products can be caused by other microorganisms, and the situation depends on the type of product and the preservation system used. For example, Brochothrix thermosphacta, a gram-positive rod-shaped bacterium that is sometimes present in raw meat, usually does not cause spoilage, but can develop in products stored with sulfites (for example, in fresh sausages, british sausage) [38]. In addition, this bacterium can grow with a low oxygen content and / or a high carbon dioxide content, and therefore can cause problems in the case of meat products in vacuum packaging or in packaging with CGS. In vacuum-packed meat, this microorganism gives an unpleasant sharp cheesy smell.

The genus Micrococcus is gram-positive cocci that can grow at high salt concentrations. They grow poorly at low temperatures, but if they are disturbed, they can cause souring and mucus formation in salted / dried meat and in brines [39]. Microorganisms that can cause spoilage in salted meat and / or meat products in vacuum packaging include Corynebacterium, Kurthia and Arthobacter [39, 53].

Yeast and mold

Compared to bacteria, yeasts and molds grow more slowly in products with good growth conditions and usually lose out in competition. Therefore, this group is rarely responsible for spoiling fresh protein products. If, however, conditions in products change due to attempts to limit bacterial growth, the role of yeast and molds may increase. Many yeasts can grow at temperatures below 0 ° C [84]. In addition, yeasts and molds are usually more resistant to low pH values, lower aw values ​​and the presence of preservatives [67] compared to bacteria. Molds often need oxygen for their growth, while many yeasts can grow with or without the presence of oxygen. Most yeasts and molds are not heat-resistant and are easily destroyed by heat treatment. The genus of mold Byssochlamys, however, can form relatively heat-resistant ascospores [10].

Fresh meat, poultry, fish, and dairy products rarely contain yeast or mold that enters them from the environment. The most important factor in their transfer may be air movement (especially ascospores of molds). The most common yeast causing spoilage include such species as Candida, Debaryomyces, Hansenula, Kluveromyces, Rhodotorula, Saccharomyces, Torula and Zygosaccharomyces [91,116]. Molds that can be isolated from spoiled chilled products include Aspergillus, Cladosporium, Geotrichum, Mucor, Pénicillium, Rhizopus and Thamnidium [36, 91]. Fungal spoilage can be accompanied by the formation of well-marked, often pigmented spots of growth, mucus, fermentation of sugars with the formation of acid, gas or alcohol, as well as the appearance of extraneous odors and flavors. These smells and tastes are described as yeast-like, fruity, stale / moldy, rancid and ammoniac.

Like lactic acid bacteria, yeast and molds are sometimes specially introduced into food products. For example, the development of Pénicillium camembertii on the surface of Brie and Camembert cheeses is necessary to obtain the desired taste, smell and texture, and the growth of this mold on other types of cheese is considered as spoiling them.

The pathogenic (disease-causing) microorganisms

A food product can be considered microbiologically dangerous due to the presence of microorganisms in it that can be ingested (for example, Salmonella, Listeria monocytogenes, E. coli 0157: Я7 and Campylobacter) or that form toxins that enter the body through food (for example, Clostridium botulinum, Staphylococcus aureus and Bacillus cereus). The growth of pathogenic microorganisms in a food product does not necessarily lead to its deterioration, and therefore the absence of unwanted organoleptic changes cannot serve as an indicator of the microbiological safety of the product. In addition, some toxins are resistant to heat and can therefore remain in food after the elimination of viable microorganisms. In this regard, it is necessary to use an effective food safety program at all stages from production to consumption, including processing, storage and marketing. A detailed review of the current state and various aspects of the food poisoning problem in the UK is given in [17].

As was shown above, storage at low temperature cannot completely eliminate the growth of microorganisms, but it can prevent the growth of some of their species and slow the growth of others. Back in 1936, it was recommended in [92] to store products that allow the growth of microorganisms at temperatures below 10 ° C, and to prevent the growth of pathogenic microorganisms or the formation of toxins, preferably at a temperature around 4 ° C. It was sensible advice on food pathogens known at the time. The risk of growth of such microorganisms depends on the combination of minimum growth temperatures, growth rate at cold storage temperature, time and storage temperatures. Minimum growth temperatures of pathogenic bacteria are discussed in [116].

While most foodborne diseases are caused by a relatively small number of bacterial types (mainly Salmonella and Campylobacter [17]), the number of bacterial species is constantly increasing, for which it is known that they can cause foodborne diseases. This may partly reflect the actual expansion of the field of action of microorganisms, but may also be due to increased awareness of these microorganisms and improved analysis techniques. For the convenience of discussion in this chapter, pathogenic bacteria that can affect the storage conditions of chilled products can be divided into the following groups.

Microorganisms capable of growing at temperatures below 5 ° C

These microorganisms are the biggest concern because they continue to multiply even at low cooling temperatures. Here, temperature control is fundamentally important, and although the growth of microorganisms can continue, its rate decreases with decreasing temperature (see fig. 7.1). In addition, to prevent or significantly limit the growth of microorganisms, temperature control can be effective in combination with other factors.

Listeria monocytogenes

In 1926, it was first discovered that this bacterium, which is currently defined as L. monocytogenes, can cause human disease [87], but its role in diseases of the gastrointestinal tract was unclear until the end of the 1970's. The number of cases detected in the UK increased dramatically in the 1980s. and declined in subsequent years. Symptoms of the disease are diverse and range from mild influenza to meningitis, sepsis (septicemia), miscarriages and dead fetus [93]. Usually severe symptoms of the disease are observed only in pregnant women, the elderly and those with impaired immunity. In the last three groups, the mortality rate can be high [79]. The epidemiology of L. monocytogenes is reviewed in [100].

It has been reported that a very wide range of products, including meat, poultry, dairy products, seafood, and vegetables, is infected with L. monocytogenes (see [12]). The complete absence of L. monocytogenes in raw meat, poultry and vegetables is rather difficult to provide, and the bacteria were isolated even from products subjected to special listericidal heat treatment [78]. This is worrying, since many of these refrigerated products can be eaten without additional heat treatment. The presence of L. monocytogenes in cooked products suggests that infection could occur after treatment. A number of studies have shown that this bacterium is secreted in many places in different plants [24] and may spread as a result of some cleaning operations [63]. Places of particular concern are places where water is present. To prevent contamination of the product, control of environmental contamination with Listeria bacteria is particularly important, especially in key production areas (for example, after heat treatment). The number of registered cases of listeriosis in England and Wales increased dramatically in 1986-1988, which was caused by contaminated imported pate. Subsequent consumer warnings led to a decrease in the number of cases to the normal annual level (100-150 cases per year) [17].

The main problem is the ability of L. monocytogenes to grow at low temperatures. A minimum growth temperature of -0,4 ° C [118] has been reported. Temperature regulation, however, slows the growth (see fig. 7.2), and, conversely, a violation of the temperature regime during storage of the product can exacerbate existing problems. L. monocytogenes, more than many other vegetative bacteria, is resistant to some of the preservation mechanisms used in food production (for example, to cool and reduce water activity) (see the review [117]). If we study separately the effects of these preservation systems, we can note the resistance of bacteria to them, but the products are complex systems, and interactions are possible, leading to effective growth prevention. An effective method for identifying such interactions is the use of prognostic models in microbiology (see the 7.9 section).The effect of temperature on the generation of L. monocytogenes and Y. enterocolitica

Fig. 7.2. The effect of temperature on the generation of L. monocytogenes and Y. enterocolitica

L. monocytogenes is not considered a classic heat-resistant bacterium. It is believed that the traditional pasteurization of milk at high temperature and short time (HTST '71,7 ° C, 15 с) destroys this microorganism, which is in the milk in its free form [18]. It has been reported to decrease its population by 10 times when processed for 8-16 with at 70 ° С [41]. In order to ensure the effective destruction of this bacterium, it is recommended that products subjected to heat treatment with subsequent cooling be heated to at least 70 ° C for 2 minutes (or subjected to equivalent heat treatment) [6]. It should be noted that the fight against L. monocytogenes in food products and their environment is very important for enterprises engaged in the production of food [62].

Yersinia enterocolitica

Like L. monocytogenes, 7. enterocolitica was first described about 50 years ago [98], but before the 1970s. almost completely ignored as a causative agent of disease. Outbreaks of the disease have been associated with the consumption of refrigerated products such as pasteurized milk [107], tofu (bean curd) [108] and chocolate milk [15]. Recorded cases of the presence of Y. enterocolitica in the gastrointestinal microflora are usually rare, but their number increases. As noted above, this may be due not only to the actual increase in infection, but also to increased awareness of this bacterium, awareness of symptoms, and improved analysis techniques. In some countries (for example, in Belgium and Holland) in the number of 7 diseases caused. enterocolitica has already surpassed Shigella and even competes with Salmonella [30]. The symptoms of yersiniosis in humans are varied, and the most common symptom is acute gastroenteritis (especially in children), manifested in the form of diarrhea, abdominal pain, fever and (less commonly) vomiting. In adolescents, abdominal pain can be localized in the area of ​​the right iliac cavity and sometimes misdiagnosed as appendicitis. During an outbreak of chocolate-related disease in 17, an appendix was removed from 257 (in 6,6%) of cases [15]. The mortality rate from yersiniosis is low and, except for cases involving the removal of the appendix, the symptoms go away after a while, rarely requiring treatment [97]. In adults, secondary symptoms (most often it is post-infectious polyarthritis and erythema nodosum) can occur for several weeks after typical gastrointestinal symptoms disappear [97].

7 infection has been reported. enterocolitica of many products, including many chilled, that is, raw and processed meat, poultry, seafood, milk, dairy products and vegetables [56]. Caution is necessary here because the isolates that cause the disease usually belong to several specific bioserotypes, whereas the isolates from the products and the environment belong to their wider range [46,75]. Therefore, before a product is deemed to pose a health risk, it is necessary to establish the pathogenicity of the isolates from the products. Serotypes responsible for human disease are often isolated from pigs and sometimes from pork-based products [97].

The minimum published growth temperature for 7. enterocolitica was -1,3 ° C; this bacterium grows relatively well at low temperatures [119]. As in the case of L. monocytogenes, a decrease in storage temperature significantly affects the growth of Y. enterocolitica (see fig. 7.2). In addition, the growth of this bacterium is prevented by storing the product chilled in combination with other preserving factors. Factors affecting the growth of U. enterocolitica were considered in [116]. U. enterocolitica is a heat-sensitive bacterium that is easily destroyed when heated [76], but, however, it was found in cooked meat, seafood and pasteurized dairy products, and this indicates that the infection occurred after the heat treatment. Careful monitoring of the presence of Y. enterocolitica in the environment of food-producing enterprises is necessary, but this issue is still relatively poorly lit in the literature.

Aeromonas hydrophila

On the issue of the role of A. hydrophila as a causative agent of foodborne diseases, there is still no consensus, since there is no information about fully documented outbreaks of the disease. These bacteria, however, do not possess many of the characteristics of other pathogenic bacteria [20]. As with Y. enterocolitica, the number of cases of gastroenteritis caused by L. hydrophila in England and Wales increased in the 1980-s. [7], and the reasons for this are described above. Cases of foodborne illnesses caused by L. hydrophila are associated with the consumption of oysters and shrimps [110] - both of which are related to chilled foods. In the genus Aeromonas, some major varieties, such as L. hydrophila, L. sobria, and L. caviae, can be considered pathogenic [105]. All three of these species were isolated from many refrigerated foods [1, 37].

The minimum known growth temperature for L. hydrophila is from -0,1 to 1,2 ° C (four strains tested), so the growth will occur at low storage temperatures [115]. As in the case of the above-described psychrotrophic pathogens, it is important to regulate the temperature of products, and the violation of the temperature regime greatly increases the growth rate. There are relatively few publications on the heat resistance of L. hydrophila, but these bacteria are considered to be heat-sensitive and can be easily removed from products. The influence of other factors (for example, pH, salt, preservatives, etc.) on the growth of L. hydrophila is discussed in [89]. Little data has been published on the presence of L. hydrophila in the production environment, but it is likely that they will be highlighted in it (especially in humid areas).

Bacillus cereus

The role of B. cereus as bacteria causing spoilage of refrigerated products is generally recognized [57]. Many of their strains can grow even at 1 ° C [21]. These bacteria can also cause food poisoning, but the number of cases described is usually small [17]. The known minimum growth temperatures for these strains are usually 10-15 ° C [48,68], although some isolates obtained during disease outbreaks caused by the consumption of vegetable pies, pasteurized milk and cod could grow and form toxins at 4 ° C [66,112]. In addition, psychrotrophic strains suspected of causing the formation of enterotoxins were isolated from pasteurized milk and some types of cooked and cooled meat [112]. In case of violation of the temperature storage conditions of the product (when the temperature rises from 4 to 7 ° C), the time to detect toxin was reduced by 50%.

Bacillus cereus can play a large role in products subjected to heat or pasteurization, as heat treatment can eliminate competing microorganisms. During subsequent refrigerated storage, spores that have undergone heat treatment are able to develop and grow. Although currently there is little published information, the heat resistance of psychrotrophic B. cereus (and other related species) is usually lower than that of mesophilic strains [94]. Other Bacillus species (eg, B. subtilis and B. licheniformis) can also cause human disease [73]. Although psychrotrophic strains of these bacteria have been isolated from milk, their relationship to human diseases is currently unclear.

Clostridium botulinum

Human botulism is caused by the ingestion of neurotoxin in food, seven types of which (denoted by letters from L to G) can be isolated on the basis of antigen analysis [60]. Traditionally, food poisoning has been caused by species A and B. At present, it is generally accepted that types E and F, after ingestion of a previously formed toxin, can also cause disease. Pathogenic strains can be divided into two main groups. First, types A and some strains B are proteolytic and therefore often, if there is a significant increase in them, they cause rotting of the products [60]. Secondly, species E and other strains of species B and F are non-proteolytic, and therefore the consequences of their growth in food will be less pronounced [60].

It is believed that the minimum temperature of growth of mesophilic proteolytic strains is equal to 10 ° С, therefore their role in chilled products is limited. In 1961, it was reported [99] that the species is E CI. botulinum could grow and form toxins in beef stew after seasoning at 3,3 ° C for 32 days. It is now recognized that non-proteolytic strains of species В and ^ are also capable of growing and forming toxins at temperatures of 5 ° С or lower [31,102]. Therefore, these non-proteolytic strains can grow in chilled products.

The growth of non-proteolytic CI botulinum is especially dangerous when pasteurized in vacuum packaging. This treatment consists of packing the products under vacuum in sealed airtight containers, which are then cooked and stored refrigerated for a long time. The time and temperature of heat treatment are determined by the type of product, contribute to the destruction of vegetative cells of microorganisms, but may be insufficient to destroy the spores of bacteria that can later develop and grow anaerobically during refrigerated storage [13].

It should be noted that the thermostability of psychrotrophic non-proteolytic strains is significantly lower than that of mesophilic proteolytic strains (Table 7.3). The risk of botulism in products after pasteurization in packaging under vacuum can be minimized by applying, when heated, an appropriate time-temperature regime, good temperature control during storage in a cooled form and / or making changes in the composition of the product to prevent the growth of microorganisms [13,14]. The minimum pH and Au values ​​for growth are also different for proteolytic and non-proteolytic strains (see Table 7.3). In general, non-proteolytic strains are less resistant to low pH values ​​and in. [60].

Table 7.3. Comparison proteoliticheskih and neproteoliticheskih shtammov MEDŽIOTOJŲ botulism Clostridium botulinum [13, 60]

Parameters CI. botulinum
Proteolytic Neproteoliticheskie
Minimum temperature 10-12 ° С 3,3 - 5,0 ° C
The minimum pH 4,6 5,0
The maximum salt content 10% 5 - 6,5%
Minimum and t 0,93 0,95 - 0,97
O value at 100 ° C for disputes 25 minutes <0,1 min

Microorganisms capable of growing at temperatures 5-10 ° С

There are pathogenic bacteria that cannot grow at temperatures below 5 ° C, but are capable of growing when the temperature is disturbed. These include Salmonella, Escherichia coli and Staphylococcus aureus, the minimum development temperatures of which are considered equal to 5,1; 7,1 and 7,7 ° C, respectively [4,5]. At temperatures up to 10 ° C, the growth rate of these bacteria is usually low [82], but they can cause food poisoning, sometimes associated with the consumption of chilled foods. Reports of psychrotrophic Salmonella strains are very rare. The role of these strains is particularly important in connection with the role of chilled foods in public opinion [28]. Several species of E. coli are recognized pathogens of foodborne diseases. Currently, E. coli 0157: Я7 and other verocytotoxigenic E. coli (VTEC), which can cause severe hemorrhagic colitis [71], are of particular concern. Limited growth of some strains may occur at 5-10 ° C [3,72]. This microorganism is considered in [I]. Although I am Staph, aureus can grow at temperatures up to 7,7 ° C, the disease is caused by the ingestion of a pre-formed toxin. In [4], the minimum temperature for the formation of a toxin (14,3 ° C) is given, which is higher than the temperature necessary for the growth of a microorganism.

The above types of bacteria do not develop at temperatures below 5 ° C, but they can survive in such conditions. Sometimes pathogenic bacteria that cause food spoilage can withstand adverse conditions better (for example, low pH and high salt content) at cold storage temperatures than at higher temperatures [34]. Therefore, if the dose of bacteria causing the infection is small and / or the growth of the pathogen has already occurred (for example, during slow cooling), its development during refrigerated storage may not cause the disease.

Microorganisms capable of growing at temperatures above 10 ° C

Such species include mesophilic C /, botulinum, mesophilic B. cereus and other Bacillus species, Cl species. perfringens and Campylobacter. Usually they do not develop at temperatures below 10 ° С, and in the interval 10-15 ° С their growth is limited [116]. Campylobacter spp., The most common cause of gastrointestinal diseases in the UK [17], is of particular concern to this group of bacteria. Although many cases are sporadic, outbreaks of the disease are often associated with the consumption of raw milk and chicken that has undergone insufficient heat treatment [103]. Bacteria of this group are rare, since the minimum temperature for their growth is 25-30 ° С, and therefore they do not develop on most products, but the infectious dose of these microorganisms is very small and therefore their growth may not be necessary [ 19].

If diseases caused by mesophilic spore-forming bacteria are associated with chilled products, this is usually the result of a temperature-related disturbance during cooling after heat treatment [53,101]. These bacteria can grow extremely quickly during slow long-term cooling after heat treatment, and then persist during cold storage.

 temperature controls

Good temperature control is necessary for chilled foods, not only to maintain microbiological safety and product quality, but also to minimize changes in their biochemical and physical properties. The storage temperature of chilled products during production, sales, retail and at home can vary greatly, and therefore, when storing a chilled product, there are many possibilities for breaking the temperature regime. The greater the temperature disturbance, the greater the possibilities for the growth of microorganisms. This may cause the product to become dangerous and / or its quality will deteriorate. Maintaining the right temperature is the main problem of chilled foods and an integral part of the canning system. For many stages of the chain of passage of the product after primary cooling, special refrigeration equipment has been designed to maintain the desired temperature, which may not be able to quickly lower the temperature of products exposed to high temperatures.

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