The development of sound technology, equipment and technology

The production of chilled products is a complex process. From the point of view of microbiology, technological processes must be designed so that it is possible to control the presence, growth and activity of certain types of microorganisms. Some operations, which constitute a typical technological process, allow to destroy bacteria or reduce their number, others allow for repeated infection or growth of microorganisms. The development of the product, its planned shelf life (see Table 11.2), and also, apparently, the sanitary and hygienic conditions at the plant are determined by those bacteria, for the appearance of which it is necessary to follow at each stage of the process. Already at the very beginning of the supply chain, agricultural products and livestock products can act as sources of bacteria that cause food poisoning (for example, Salmonella, Campylobacter and E. coli 0157). Therefore it is important to take this into account when working with raw materials, and when developing the technology, to provide reliable means of destroying microorganisms or preventing contamination of food products. The amount of precautions necessary to ensure the effective prevention of certain risks is proportional to the extent and complexity of the supply chain.

For finished refrigerated products with a short shelf life (less than 10 - 14 day) the main risk is the presence of infectious pathogens, and the technology must be designed to predictably reduce their number. If these types of bacteria tolerate heat treatment or re-contamination occurs after a technological operation intended to destroy them, they can be a danger to the health of consumers. There are two main ways to re-infection: through personnel working with products, or cross-infection from other products. When designing technological routes and operations, it is necessary to proceed from the assumption that raw foods always contain a small amount of bacteria that cause food poisoning, and therefore it is necessary to effectively separate the flows of raw materials. The risks are even greater if the product is ready for use, and the time and storage temperatures make it possible for microorganisms to grow.

The prolongation of the shelf life of the product in a cooled form carries an additional danger arising from the growth of toxicogenic bacteria, and therefore special technological processes must be developed for their destruction. The reason is that in normal cooling conditions (that is, below 10 ° C) in about two weeks the number of microorganisms growing in cold conditions of Clostridium botulinum strain can grow to levels at which toxin formation is possible. The spores of this microorganism can remain viable in foods pasteurized with the use of mild regimens designed to kill infectious pathogens. In the production of products with a long shelf life, it is necessary to use more stringent heat treatment, which should cause a predictable reduction in the number of heat-sensitive spores. If the canning system can prevent the sprouting of these spores, it is necessary to develop a heating process to fight only the microorganisms that cause spoilage. Many chilled products have effective internal canning systems and are therefore safe, despite very weak heat treatment.

Currently, manufacturers and regulatory authorities have not reached a consensus on the seriousness of the danger of botulism as a result of the use of refrigerated unpreserved product. There is sufficient evidence that in model systems based ready meals, infected with spores when used in real-world temperatures the growth and toxin formation [72].

If the heating of the product was not carried out in the original packaging, to prevent its re-infection with spores and infectious pathogens, unpackaged components intended for long-term storage products that have undergone heat treatment must be cooled, processed and collected in an area of ​​increased purity. Even if the risks of re-infection are controlled, there remains the risk of maintaining the viability of heat-resistant spores of bacteria that can grow in individual components of the product at cold storage temperatures. These are mainly varieties of bacillus (Bacillus), which can eventually cause spoilage in the form of mold.


Many of the most important quality properties of refrigerated products and their safety are determined by the technical characteristics of the process unit and equipment. The degree of heat treatment effect on the lethality of microorganisms determines its influence on the probability of survival of microorganisms and the level of their presence in the product, and therefore the correct construction of the equipment and reliable heating are very important. The delay periods and the growth rate of any harmful micro-organisms depend on a number of technological parameters (including the cooling rate and the accuracy with which the storage temperature is maintained). Critical factors also include the uniformity with which preservatives (preservative salt and acidulants) are dosed and mixed, as well as the effectiveness of packaging machines in the production of gas-tight packages (for example, containing the inhibitory gas mixture C02 and N2).

The main cause of infection with microorganisms is food products that remain for some time in the plant or in the production area after treatment, and if these residues are not regularly removed, they pose a risk for finished products, which is much less associated with infection from the air or From the staff. Many norms and rules indicate that "technological equipment for processing food products must be designed so that it can be cleaned or disinfected". However, these instructions conceal real issues of design, operation and maintenance of process equipment for the production of food products, which often boil down to finding an acceptable balance between costs, production efficiency and hygienic design (see chapter 15).

heating processes. The use of heat for disinfection products

heating methods

In the production of chilled products heat - it is the most widespread means of inactivation of microorganisms and cause of favorable texture and color changes in products. Depending on the type of product is used for heating various equipment, some examples of which are given below.

  • Direct heating of mixtures or particles suspended in sauces steam or hot water in open vessels.
  • The individual pieces of meat, fish or vegetable can be subjected to heat treatment in trays, molds or packaging in air heating. If the products are tightly packed, they can be heated in water baths. Open containers or furnace can be heated indirectly through shirts, direct injection, circulating steam, air or mixtures thereof. Substances in direct contact with the product must be of corresponding quality.
  • Liquid or pumpable ingredients can be heated indirectly via equipment with shirts or via heat exchangers. Conventional processing equipment can be used at temperatures up product 100 ° C; if used or planned higher temperatures, it should select and use equipment such as autoclave.
  • Solids (e.g., pieces of meat or vegetables) may be heated by contact heating or frying to produce temperatures exceeding 100 ° C at the surface and lower temperatures at the center. These temperatures depend on the initial temperature and the thermal conductivity and heat transfer characteristics of the product.

Packed products or ingredients may be heated in autoclaves or other pressure vessels by means of coolants, with temperatures above 100 ° C; often for their heating using water bath. It is important that for good heat transfer from the thus treated packaging has been removed to air or heating processes were developed with the insulating properties of the packaged product space and its expansion upon heating.

heating control

The heating process must be designed to provide the defined minimum heat treatment described above. Since this is very important, critical control parameters and tolerances should be defined in the requirements that are available to the process leading operators. The preparation of these operators should allow them to reliably perform heating, monitor and record the progress of the process. This is most effectively accomplished by monitoring the time and temperature conditions in the vessel, chamber, or sometimes in the product itself. For each batch of the product, it is necessary to confirm the performance of the given treatment, and consequently, the achievement of the specified lethality of the microorganisms.

To ensure reliable destruction of microorganisms by means of heat treatment, food and equipment manufacturers should take into account some important points, namely:

equipment, its use and maintenance should provide accurate and reliable supply of heat to the surface of the product so as to achieve a given rate of heat transfer, and therefore the autoclave should always be loaded in batches, placed in the same way, and the contents of the vessel with the jacket to provide uniform coolant impacts on each product or packaging should be mixed;

heat penetration rate of the product should also be known and controlled to safely reach the required total time-temperature exposure at the points of the weakest and slowest heat; the achievement of such a regime is determined by formulation of the product (eg, particle size, viscosity and other physical characteristics), package size, shape and thermal conductivity of the packaging material;

hardware design, control systems and supply of steam, cooling water or air should provide a constant supply of the same quantity of heat.

The suitability of the equipment is not the only factor determining how successfully or reliably the desired product temperatures are reached. Process control can affect the characteristics of the material being processed. For example, the temperature of the component at the beginning of the treatment, regardless of whether it is frozen, thawed or warm, determines the heating rate, and such parameters should be reflected in the process maps. To obtain safe products it is necessary that irrespective of the heating method used, it can supply a certain amount of heat to all parts of the product or package.

equipment Jobs

When delivered, many types of industrial heating equipment (for example, furnaces) are not supplied with information on the distribution of heat in them. In addition, the heating of the product depends on the type of heat input to the product surface, the unit of product or packaging, and the penetration of heat into the package. The study of these characteristics is an essential part of the development of the technological process or product. For example, the uniformity of heating in a jacketed vessel depends on the degree of mixing that can be performed by an additional device or operator. In an oven or autoclave, the distribution of heat may depend on the density of the package or the location of the product that forms or blocks the channels between the production units, which disrupts the uniformity of the coolant circulation. Measurement of temperatures in the center of the product and (at a more complex level) the heat flow in the product depends on the type of equipment [32,33], and therefore the user must create a heat distribution scheme for his own conditions, so that the technological processes can be calculated with units Product located in the coldest part of the equipment. [86] proposed an optimization process procedure based on the use of a two- or three-component temperature-time sensor to evaluate thermal processes. The proposed procedure for assessing the effect of specific temperature-time characteristics can take into account the different values ​​of z associated with the destruction of microorganisms and loss of quality.

The more variable and non-uniform the heat supply to achieve the required minimum, the higher the intensity of the thermal process. An essential part of the development of thermal processes is the study of the ranges of heat treatment achieved on this equipment in the predicted range of conditions. The criteria for the lethality of microorganisms for the development of technological parameters are given below, taking into account the species and the number of microorganisms that must be destroyed. It is important that the number of these microorganisms is also controlled at the entrance; If the input is higher than the technologies provided by the developer, then microorganisms that have retained their viability will later be detected (possibly by the consumer).


Although heat is efficient for the destruction of microorganisms, the efficiency of the cooling processes [90] and the sanitizing state of the cooling equipment [51] must also be carefully determined. Even in equipment designed specifically to achieve high cooling rates, the risk of re-contamination of the product remains either from microorganisms endemic to the coolant or introduced into it, and then spread by forced air circulation, often associated with rapid cooling. Cooling speed is also important, since it determines the resting degree of any spores that survive in the product, which affects their willingness to grow when storing the food. This resting degree is especially important for determining the storage period when using heating in combination with the use of preservatives such as salt and nitrites.

Microbiology of heat treatment

Heat treatment of packaged products is usually performed by hot water, steam, autoclave or (more rarely) by microwave or electric heating. The degree of heating is chosen to meet the intended marketing conditions and shelf life of the product, as well as specific ("target") microorganisms, taking into account the type of raw material and product (see below the minimum treatment regimes offered for products with short or long shelf life). Target microorganisms include pathogenic non-spore microorganisms (Salmonella), enteropathogenic (E. coli, Campylobacter, Listeria monocytogenes and Yersinia enterocolitica), as well as sporeforming non-proteolytic strains (Clostridium botulinum type E and some types B and F). It is possible that some strains of Bacillus cereus that can slowly grow at temperatures up to 4 ° C [91] may be dangerous, but epidemiological data on this issue are not enough. Since raw materials are supplied from all over the world, it is possible that other pathogens are admitted and, in order to ensure the use of proper heat treatment, it should be analyzed in terms of HACCP.

While heat treatment at 70 ° C for 2 min in the coldest part of the package will ensure reduction of L. monocytogenes (most of the heat-resistant vegetative microorganisms mentioned above) at least 106 times, such treatment is not expected to have any impact on the debate psihrotrofnyh strains C /, botulinum. Therefore, heat treatment in the UK with low heating temperature 70 ° C for 2 minutes only recommended for products with a short shelf life or public food service products to be accurately kept at 3 ° C [38]. In the Netherlands, the heat treatment at 72 ° C for 2 minutes also recommended for inactivation of L. monocytogenes more than 108 time [70].

Although prolonged mild heating (as in the heat treatment of products in the package) can sometimes be desirable for organoleptic reasons, it is important to remember that slow heating can cause a so-called thermal shock, in which the resistance of vegetative microorganisms to subsequent heating increases [62]. Therefore, for reasons of microbiological safety, the duration of warming up or keeping in warm form during processing should be small, since otherwise it is possible to increase the heat resistance of microorganisms.

Although psihrotrofnye strain Ci botulinum can not grow at 3 ° C and below, the possibility of slow growth in products with a long shelf life at somewhat higher temperatures require more stringent heat treatment regime. This process should be designed so as to substantially (more than 106 Time) to reduce the probability of surviving a dispute, but there is still a debate about the minimum necessary heating. For example, in [72] it is concluded that there is currently insufficient data on the thermal stability of spores of non-proteolytic C / botulinum in order to provide the necessary lethal effect for traditional processing in the package (see below). It was found that surviving spores can grow and form a toxin at 8 ° C over a period of about three weeks. Pre-incubation at 3 ° C shortened the subsequent time to toxin formation at 8 ° C. It was concluded that if storage can not be guaranteed (as is often the case in retail and at home) storage below 3,3 ° C, then the storage period should be limited. At the same time, it should be noted that these products are already present on the market for many years and so far there have not been recorded problems related to their microbiological safety.

The above remarks refer to pasteurized products packed in vacuum, in which only the heating, vacuum packing and maintaining the temperature in the sales chain are the preserving factors determining the shelf life and safety. Such products usually have high water activity, close to neutral pH and do not contain preservatives. Many other pasteurized products in vacuum packaging have additional developmental preserving factors, which further increase shelf life and safety [18]. Examples of this are, for example, products containing salt and nitrites (ham and other canned meat products), acidified pasteurized meat sausages and a wide range of traditional products with reduced water activity, some of which are stable in a cooled form, and some So-called SSP (shelf -stable products), products stable at room temperature) are stable even at ambient temperatures [59]. The handling, safety and stability requirements of these products differ from those of traditional pasteurized refrigerated products.

Pasteurization of products with short shelf life (1 and 2 classes)

Products with a short shelf life are designed so that they are suitable for 10-14 days. Thermal treatment of such products during production should reduce the number of infectious pathogens (Salmonella and Listeria) by at least 106 times, and handling of products after heating and packaging should prevent re-contamination. With neutral pH in antiseptic-free products with high water activity, the combination of temperatures and treatment times equivalent to 70 ° C for 2 min is more than sufficient for this reduction in the number of pathogens. Experience has shown that a longer holding time in this temperature range is required to effectively control some bacteria that do not form spores, causing damage (eg, lactic acid). This combination of time and temperature can also be used by the consumer for destruction in the products of these infectious pathogens.

Pasteurization of products with a long shelf life (3 and 4 classes)

Products with a long shelf life in a refrigerated state persist long enough to allow any surviving psychotropic spores to germinate. To ensure the safety of such products and exclude their spoilage during the specified shelf life, thermal processes should be used to destroy any spores capable of growing. This means that technologies developed to ensure food safety should lead to a decrease in the number of cold-growing strains of Clostridium botulinum at least 106 times. It is generally considered that to ensure safety, it is sufficient to use heating at 90 ° C for 10 min or equivalent technology, but this regime is not sufficient to destroy the spores of all psychotropic Bacillus species to the same extent. In non-preserved foods, some species are able to grow and reach spoilage levels for about three weeks at temperatures of 7-10 ° C, which are known to be used in a chilled product distribution system in many countries [14]. These sporadically growing spores often have D values ​​at 90 ° C to 11 min [66].

Microwave processing

Cooking or warming up with microwave heating, especially at home, has become very common in recent years. At the same time, in response to consumer demand, the variety and volume of sales of products intended for subsequent microwave heating and stored at ambient temperature in a chilled or frozen form has increased. In addition, it is very likely that the use of microwave ovens for the preparation and pasteurization of food will continue to grow. The key issues here are the development and preparation of products with predicted absorption in the microwave range. It is known that heating is determined by the dielectric properties, location and thickness of the product in the furnace chamber [92]. The problem in practice is a fairly accurate dosing on an industrial scale to ensure a homogeneous and predictable product heating taking into account absorption in the microwave range.

There is no fundamental difference in the effect on microorganisms of heating by means of microwaves or other forms of energy, although there is no reliable data on the additional bactericidal nonthermal effects of industrial or household microwave equipment. At the same time, the microbiological safety of products heated in household microwave ovens raises some concerns; Thus, the inconstancy of heating and its effect on the survival of microorganisms are considered in [45, 80, 87]. Of particular concern are cases where the products are not completely cooked, can be contaminated after cooking or contain raw ingredients. Anxiety was mainly expressed after the presence of Listeria monocytogenes in a wide range of products, including some suitable for microwave heating, was demonstrated in retail. For example, a survey in the UK showed that this microorganism can be detected in 25-gram samples in 18% of the tested refrigerated products manufactured commercially and commercially [36]. The concern was that the UK Ministry of Agriculture conducted a thorough study of the problem with the involvement of furnace manufacturers, various food industries, retailers and consumers, and then disseminated recommendations on the proper use of microwave ovens to achieve effective pasteurization when the products were heated.

It has been suggested that the unforeseen survival of microorganisms in foods heated by microwave radiation may be due to an increase in the heat resistance of microorganisms (for example, Listeria monocytogenes, see [57]). It is now generally accepted that the survival of microorganisms occurs solely as a result of non-uniform heating leading in certain parts of the product to the appearance of unheated places [23,61]. This is a consequence of heating with the energy of microwaves and the fact that its absorption (and hence the heating rate) depends on the composition and quantity of the ingredients, the geometry of the product and its packaging to a much greater extent than when using conventional heating means. Measurement of the rates of inactivation of Listeria monocytogenes by heating in various food substrates showed that a tenfold decrease in the number of microorganisms is achieved by heating at 70 ° C for 0,14-0,27 min (D70 = 0,14-27 min) [35]. Therefore, recommendations that products in which Listeria can develop should receive a minimum of microwave heating at 70 ° C for 2 min (as indicated in the UK Ministry of Health guidelines for ready-made and chilled products) aim to reduce the number of these Microorganisms more than 106 times [8]. If microwave treatment is used in the production of chilled products with a short shelf life, it must reliably ensure that the minimum allowable amount of heat is supplied to all parts of the product or its ingredient. This is necessary to ensure the necessary reduction in the amount of Listeria and other less heat-resistant vegetative bacteria causing food poisoning, that is, treatment at 70 ° C for 2 min or another combination of time and temperature, providing similar lethality of microorganisms, based on D values ​​at 70 ° C for 0,14-0,27 min and the value of z from 6 to 7,4 ° C [35].

Food cooked in the primary original packaging (food «sous-vide» and REPFED)

Although the term "sous-vide" (processing in packaging), strictly speaking, refers to a vacuum package without any indication of heat treatment, it is used for pasteurized ingredients or products that are hermetically packed before heat treatment, often in their primary packaging ( Risk class 4). Products treated in this way include ready-made dinners and their components, soups and sauces; All of them have a long shelf life in a refrigerated state and are intended for use in the catering industry, and more recently for retail sale. Sous-vide products are usually processed at relatively low temperatures (55 ° C or more). The heat treatment should be sufficient to maintain the safety and microbiological stability of the products at storage temperatures below 3 ° C (the minimum theoretical growth temperature of the cold growing Clostridium botulinum species). Depending on the severity of the thermal process and the microflora of the ingredients, the products can have storage times of up to about six weeks [22]. The plan for the HACCP methodology for these products was published in [2].

The most complete of the early treatment of sous-vide research was carried out in the hospital Nacka in Stockholm. Finished product was packed in vacuo, quenched, and then stored in a well-controlled cooling conditions for one or two months before reheating for consumption [60]. The scope of application of the method is then extended to a more or less centralized public catering in several European countries, and recently (mainly in France) and spread on to the retail products.

Concerns about possible microbiological safety issues are due not to doubts about the principles underlying the sous-vide process, but because of the difficulty of ensuring a reliable maintenance of the required low temperature (max 3 ° C) when transporting for long distances and especially at home (in [13, 55, 76] discuss the risks of botulism, and [10,44] discusses the effectiveness of sous-vide processes with respect to Listeria monocytogenes). [88] considers the effectiveness of this process with respect to Bacillus cereus and bacteria that cause spoilage of chicken breasts, and [11] proposes some rules and regulations.

Other treatment options

Technological operations for the production of products processed in the package {sous-vide and REPFED) basically follow the original concept and the traditional canning procedure in cans, packaging of products, sealing and subsequent heating. Another option - heating with subsequent filling and sealing - if these operations are not performed aseptically, is associated with the risk of entering microorganisms after heating and before sealing, and therefore it is mainly used for products with a short shelf life. If the products are hot when filling the container (> 80 ° C), you can achieve an increase in shelf life at 3 ° C. For such processing, special packaging designs, filling and closing equipment are used.

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