Food microbiology

Food microbiology . It is the branch of Microbiology that deals, among other aspects, with the study of microorganisms that can affect the sanitary quality of food and water .

Summary

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  • 1 Microbiology
  • 2 Food Microbiology and its relationship with Other Branches
  • 3 Basic Concepts for the Food Microbiology Discipline
  • 4 Incidence and Types of Microorganisms Present in Food
    • 1 Microbiological examination of food
    • 2 Three large groups of microorganisms carry the scope of sanitary microbiology:
  • 5 Microorganisms Indicators of Health Quality.
    • 1 The most widely used health quality indicators are:
    • 2 Indicator microorganisms
  • 6 Sources

Microbiology

The microorganisms are used for a wide variety of foods, they are due to impairment and can cause disease in humans. Producing, distributing and consuming food of good sanitary quality, raw, prepared for immediate consumption or processed, is part of the interests of any community. This objective is met in direct relation to the social, economic and cultural development of a country. Various circumstances have made the microbiological control of food necessary: ​​the increase in international trade in these products, the possible risk derived from the use of new techniques in their mass production, their rapid and wide distribution, and consumption in certain areas or countries of food from areas where diseases are prevalententeric. The presence of microorganisms in food does not necessarily mean a danger to the consumer or a lower quality of these products. Except for the small number of sterilized products, each bite of food contains harmless yeasts, molds, bacteriaand other microorganisms. Most food becomes potentially pathogenic for the consumer after the principles of hygiene, cleaning and disinfection have been violated during the process of preparation, transport and preservation. If the food has been subjected to conditions that could have allowed the arrival of the food and / or the multiplication of infectious or toxigenic agents, they may constitute a vehicle for the transmission of diseases, such as salmonellosis or staphylococcal poisoning. Poor sanitary quality of food translates into damage of various kinds for the populations involved. Damages include presentation of illnesses, health care expenses, impairment of quality of life, economic losses due to food spoilage, damage to tourism and cause of death. According toWorld Health Organization Foodborne Illness (ETA) is the most widespread public health problem in the world today.

Food Microbiology and its relationship with Other Branches

Food Microbiology is the branch of Microbiology that deals, among other aspects, with the study of microorganisms that can affect the sanitary quality of food and water. The area of ​​food microbiology is coarse and complex, as it also includes the general characteristics of these microorganisms, their ecology, their resistance to the environment, their ability to survive and develop in food, the consequences of this development and the factors that influence this process.

Food Microbiology relates to medical microbiology , the veterinary , the virology , the parasitology , the genetics , the biochemistry , food technology, the epidemiology . It is important in the design and application of the hazard analysis system and critical control points, essential to guarantee food safety, in the study of outbreaks of diseases associated with food consumption, in the design and evaluation of modern techniques of analysis, in the study of the processes that take place during food spoilage and in the manufacture of those that make use of microorganisms.

Basic Concepts for the Food Microbiology Discipline

Some basic concepts are important to know to better understand Food Microbiology and its area of ​​action.
It is very difficult to classify foods because they are very varied. They are classified as follows:
1. According to their origin:

  • Vegetable (potato)
  • Microbial (yeast)
  • Animal (meat)
  1. Your physical condition
  • Liquids (milk)
  • Semisolids (butter)
  • Solids (cheese)
  1. According to how they are ingested
  • Fresh food (milk, grass)
  • Processed foods (cheese and butter or silage material)

4.Main nutritious foods that provide the individual

  • Carbohydrates (sugar, sweets and honey)
  • Protein (meat, egg)
  1. Subject to feed
  • For humans (children, adults and the elderly)
  • For animals (monogastric, ruminants, birds, etc.)

Health: it is the state or complete state of physical, mental and social well-being and not only the absence of disease.

Healthy food or food with good sanitary quality: It involves not only the absence of pathogenic microorganisms and / or their toxins, but also the recording of organoleptic characteristics that provide full satisfaction when consumed. This means that in the process of sanitary control of food, actions must be considered that not only tend to achieve products free of such agents, but also that the food must meet certain requirements so that they can reach the population: fresh, attractive, tasty , digestive and with nutritional capacity at the highest level. Quality: degree of excellence that a product possesses, that is, how good it is to fulfill its purpose.

Health quality: In this sense, the definition of health quality is directly linked to the concept of health.

Sample: portion or item that represents the quality of the whole from which it was taken.

Perishable food: food whose shelf life is short and needs refrigeration for preservation.

Semi-finished food : food that has received heat treatment or not in its preparation and that needs cooking for subsequent consumption.

Preserves: food that is placed in a hermetically closed container and is subjected to a sterilization process that ensures a shelf life of between 6 months and several years depending on the type of food and the intensity of the heat treatment applied.

Semi-preserves: foods partially stabilized by the addition of chemical substances, packaged in unalterable containers, impervious to water, gases and microorganisms and that generally require storage at low temperatures. They are products established for a limited time.

Incidence and Types of Microorganisms Present in Food

There is a great diversity of microorganisms in food. In general, the number and type of microorganisms present in a finished food product are influenced by:

  • The general environment from which the food was obtained
  • The microbiological quality of the food in its fresh state or before being treated
  • The hygienic conditions under which the food was handled and treated
  • The adequacy of subsequent packaging, handling and

storage to keep the microbiota at a low level.
In fresh and cured meats, poultry and seafood, the most frequent are: Achromobacter
bacteria Bacterium Clostridium Corynebacterium Escherichia Lactobacillus Micrococcus Salmonella Streptococcus, etc. Penicillum Mucor Cladosporium fungi When producing good quality commercial food, it is important to keep the microorganisms at a Low level for aesthetic, public health and shelf life reasons.

Microbiological examination of food

It provides information regarding the quality of the raw product and the sanitary conditions in which it has been produced, as well as the effectiveness of the preservation medium. In the case of products, it is possible to identify the causative agent of the alteration and once it is known to investigate: Focus of contamination Conditions that have made it possible Take measures to avoid repetition. Microbiological techniques are not specialized, generally a direct microscopic examination and consecutive culture methods are done. It is always important to detect coliform bacteria.

 

Three large groups of microorganisms carry the scope of sanitary microbiology:

  • Those that affect the organoleptic characteristics of food
  • Those that are grouped outside the taxonomic lines, based on certain morphological, physiological and ecological characteristics.
  • Those that affect consumer health and are closely related to medical microbiology.

Hence, the microbiological control of food, in direct relation to the aforementioned groups, is aimed at the investigation of:

  • disrupting microorganisms
  • indicator microorganisms
  • pathogenic microorganisms and / or their toxins

Microbial activity is the main mechanism that produces alteration in the appearance of a food, in terms of frequency and intensity. Food spoilage is, of course, like the presence of pathogenic microorganisms, an undesirable condition. However, consider that this fact is detectable by the consumer against the food, so that he is in the advantageous situation of deciding whether to accept it or not. The presence of pathogens in contrast is not usually accompanied by objectionable sensory changes. The lower the incidence of active deteriorating microorganisms, the greater the risk that a concurrent colonization by pathogens will go unnoticed, an obvious situation of greater risk. The general rule is that colonization of a food by pathogenic bacteria does not result in adverse sensory changes, that is,

The main groups of disrupting microorganisms are made up of:

  • Psychrophilic germs, which are those microorganisms capable of developing at low temperatures, such as refrigeration temperatures

of food.

  • Thermophilic germs, which are those that grow at elevated temperatures.
  • Halophilic germs, which are those that affect foods with high salt content.
  • Lipolytic germs, which are capable of degrading the compounds of origin

lipid found in food.

  • Acidophilic germs, which are microorganisms that grow in foods with low pH.

Microorganisms Indicators of Health Quality.

Since Schardinger determined sanitary quality in 1882 based on the presence of what we now know as Escherichia coli , instead of according to Salmonella typhiindicator microorganisms have been very useful to us. A wide use is made of groups or species of microorganisms whose enumeration or counting is carried out more easily and whose presence in food in a certain number indicates that these products were exposed to conditions that could have introduced dangerous organisms and / or allowed the multiplication of infectious and / or toxigenic species. The groups or species used for these purposes are called “Indicator Microorganisms”, and serve to assess both the safety of food in terms of microorganisms and their toxins and their microbiological quality. Indicator microorganisms usually do not meet criteria for taxonomic grouping. Rather, they are defined based on certain ecological and physiological characteristics that support or justify the application value that they are trying to confer. The main objective of using microorganisms as indicators of non-sanitary practices is to reveal treatment defects that carry with them a potential hazard that is not necessarily present in the particular sample examined, but is likely to be found in parallel samples. The food examination methodology to detect indicator microorganisms and enteropathogenic bacteria has been revised by several researchers in order to help the different organizations that are dedicated to developing the procedures for the microbiological study of food. The main objective of using microorganisms as indicators of non-sanitary practices is to reveal treatment defects that carry with them a potential hazard that is not necessarily present in the particular sample examined, but is likely to be found in parallel samples. The food examination methodology to detect indicator microorganisms and enteropathogenic bacteria has been reviewed by several researchers in order to help the different organizations that are dedicated to developing the procedures for the microbiological study of food. The main objective of using microorganisms as indicators of non-sanitary practices is to reveal treatment defects that carry with them a potential hazard that is not necessarily present in the particular sample examined, but is likely to be found in parallel samples. The food examination methodology to detect indicator microorganisms and enteropathogenic bacteria has been revised by several researchers in order to help the different organizations that are dedicated to developing the procedures for the microbiological study of food.

The most used health quality indicators are:

  • Determination of microorganisms at 30 ºC
  • Coliform determination
  • Determination of fecal coliforms (currently better known as thermotolerant)
  • Determination of Escherichia coli
  • Determination of filamentous fungi
  • Determination of viable yeasts
  • Determination of total enterobacteria
  • Determination of fetal enterococci or streptococci
  • Sterility test

Indicator microorganisms

* Microorganisms at 30ºC This indicator is commonly known as mesophilic aerobic microorganisms, this term is still used by some authors, but taking into account the criteria of the ISO (International Standard Operation) Standards, by which the food microbiologists of our country, this new denomination of microorganisms at 30º C is the one used in the text. The microorganisms that are part of this group are very heterogeneous. This quality is derived from the definition of the group itself. It includes all bacteria, molds and yeasts that are aerobicallythey show the capacity to form visible colonies, under the conditions in which the test with growth at optimum temperature for mesophiles is carried out. It is clear that pathogenic microorganisms could be included in a particular situation. Most industrialized and / or ready-to-eat foods (except for example fermented products) should be considered as undesirable for consumption, when they have a large number of microorganisms, even when these microorganisms are not known as pathogens and have not appreciably altered the organoleptic characteristics of the food. There may be several reasons that justify this behavior.

Interpretation of high counts by type of food:

In stable products: indicates contaminated raw material. Treatments not satisfactory from the health point of view. In perishable products: it also indicates inadequate conditions of time and temperature during storage. It means that there may have been favorable conditions for the multiplication of pathogenic microorganisms of human or animal origin. Some common mesophilic strains of bacteria , not generally considered to be agents of foodborne illness ( Proteus sp ., Enterococci, and mesophyll Pseudomonas) have been identified as a cause of disease when there were a high number of viable cells. All known pathogenic bacteria in food are mesophilic and in some cases contribute to the plate counts found with their presence. The detection method commonly used for the determination of this indicator is the standard counted plate count. In general, a culture medium rich in nutrients without inhibiting substances or indicators is used; the most widely used medium worldwide is plate count agar or tryptone-glucose-yeast extract agar. C for 72 hours. °Colonies obtained in the solid medium are counted after incubation aerobically at 30

* Coliform organisms For practical reasons, species of the genera Escherichia, Klebsiella, Enterobacter and Citrobacter and other species of enterobacteriaceae that are capable of fermenting lactose with gas production are grouped together under the name of coliform group. C, some ferment lactose slowly.°They are defined as non-spore-forming, aerobic, or facultatively anaerobic Gram negative bacilli, which ferment lactose with gas formation within 48 hours at 35 Coliform organisms are the indicator group with the longest tradition in sanitary microbiology. It is a totally conventional definition without taxonomic validity, which aims to involve bacteria from typically intestinal habitats, although there are microorganisms that satisfy the definition and that are frequently located in extra-intestinal environments. Its natural habitat is the intestinal content of man and higher animals. In the stool they reach figures of 106 to 109 cfu / g. Due to their survival capacity and their potential to develop in organic matter, they can recover from a variety of extra-intestinal substrates. Food is no exception and the finding of coliforms may be determined by contamination, followed or not by active development. they can recover from a variety of extra-intestinal substrates. Food is no exception and the finding of coliforms may be determined by contamination, followed or not by active development. they can recover from a variety of extra-intestinal substrates. Food is no exception and the finding of coliforms may be determined by contamination, followed or not by active development.

With the exception of E. coli, none of them necessarily indicate faecal contamination since they can be found in the soil and vegetables and from there have access to food. Coliforms are found everywhere in plants (leaves, roots, flowers). The Klebsiella genus predominates in samples obtained from forest media and fresh farm products. Most of the fresh vegetables examined have coliform levels of 106 to 107 / g; They can also be found in freshly laid eggshells and can penetrate through the pores if the surface of the eggshell is damaged. These microorganisms can be found in fresh milk by contamination of the lactophoric ducts by feed or manure, they can be present in the feathers of poultry and on the skin of hooves and hairs of other animals.

The shellfish that grow in contaminated areas concentrate the microorganisms in such a way that they are contaminated with higher levels than those present in the water.

They can indicate in processed products lack of hygiene in manufacturing, inadequate processing, post-process contamination, etc. Furthermore, a high number can indicate the possible presence of certain pathogens.

Coliforms are quite resistant under natural conditions and withstand desiccation; On the other hand, they do not resist the rigors of the refrigerator or cryopreservation well, they are inactivated by relatively moderate heat treatments, such as pasteurization. Ultraviolet light, under the conditions used to disinfect water, inactivates coliforms. Germicides such as iodophors and chlorinated compounds are also lethal at the usual concentrations in food plants. Many methods have been used to detect coliforms, with lactose fermentation being the first step in identifying a microorganism as coliforms. There is a method that consists of using the Most Probable Number (NMP). This is a laborious, slow technique and requires a larger volume of laboratory material, but it is much more sensitive, it is widely used in the study of drinking water and food, such as seafood and fish. It is also very suitable for detecting physiologically damaged cells that are frequently found in processed foods. Most of the food research on coliforms is carried out using the plate method poured into red-violet bile agar. This method is faster, cheaper, and more reproducible than NMP; but it does not allow the direct recovery of physiologically damaged bacteria, nor the detection of low concentrations of the product. Another method used for the determination of coliforms is that of membrane filtration, mainly used in water analysis. It is also very suitable for detecting physiologically damaged cells that are frequently found in processed foods. Most of the food research on coliforms is carried out using the plate method poured into red-violet bile agar. This method is faster, cheaper, and more reproducible than NMP; but it does not allow the direct recovery of physiologically damaged bacteria, nor the detection of low concentrations of the product. Another method used for the determination of coliforms is that of membrane filtration, mainly used in water analysis. It is also very suitable for detecting physiologically damaged cells that are frequently found in processed foods. Most of the food research on coliforms is carried out using the plate method poured into red-violet bile agar. This method is faster, cheaper, and more reproducible than NMP; but it does not allow the direct recovery of physiologically damaged bacteria, nor the detection of low concentrations of the product. Another method used for the determination of coliforms is that of membrane filtration, mainly used in water analysis. Most of the food research on coliforms is carried out using the plate method poured into red-violet bile agar. This method is faster, cheaper, and more reproducible than NMP; but it does not allow the direct recovery of physiologically damaged bacteria, nor the detection of low concentrations of the product. Another method used for the determination of coliforms is that of membrane filtration, mainly used in water analysis. Most of the food research on coliforms is carried out using the plate method poured into red-violet bile agar. This method is faster, cheaper, and more reproducible than NMP; but it does not allow the direct recovery of physiologically damaged bacteria, nor the detection of low concentrations of the product. Another method used for the determination of coliforms is that of membrane filtration, mainly used in water analysis.

* Fecal coliforms (thermotolerant).

C, while non-faecal ones do not. °In 1904 Eijkman discovered that presumptive coliforms from faecal contamination produce gas in a glucose medium incubated at 46

The term emerged as an attempt to find fast and reliable methods to demonstrate the presence of E. coli and closely related variants without the need to purify the cultures obtained in the coliform tests or to apply the relatively expensive confirmatory tests2. This group refers to those coliforms that have the capacity to ferment lactose with gas production at temperatures of 44 – 45 ºC. Except for this point, faecal coliforms are identified with the rest of coliforms in terms of their resistance to the environment, chemical agents and factors that favor or impede their development.

In recent years, it is considered that the term fecal coliforms should be replaced by that of thermotolerant coliforms, since the qualification fecal underlines an origin and therefore implications that are far from being supported in reality. For the counting of this group, a very rigorous control of the incubation temperature is required, generally a precision water bath with limits of variation not greater than 0.2º C. The technique for its counting is generally the MPN at an incubation temperature of 44.5 ± 0.2 º C. The NMP is computed in the corresponding tables as indicated for the total coliforms. Membrane filtration methods can also be used in this case.

* Escherichia coli is the genuine representative of fecal origin making it the most reliable indicator of faecal contamination in food.

  1. coli is a germ whose natural habitat is the enteric tract of man and warm-blooded animals. Therefore, the presence of this microorganism in a food generally indicates direct or indirect fecal contamination.

It is the classic indicator of the possible presence of enteric pathogens in water, molluscs, dairy products, and other foods. High numbers of E. coli in a food suggest a lack of cleanliness in handling it and inadequate storage.

The detection methods are very similar to those used in the determination of fecal coliforms and sometimes the same (MPN, poured plate, membrane filtration), at the moment chromogenic and fluorogenic methods are being widely used in developed countries. Recoveries of E. coli from conventional methods require biochemical confirmation of the isolates.

* Total Enterobacteriaceae.

Many countries have introduced the analysis of foods that have been treated to ensure their safety by a test that determines the entire family of Enterobacteriacea (that is, lactose positive and lactose negative types). It is capable of identifying microorganisms that are not included in the coliform group. This indicator is mainly used in Europe, it is not widely used in Latin America and the Caribbean, the reasons why some laboratories prefer this indicator are the following:

The “coliform” or coli-aerogenic group bacteria constitute a poorly defined taxonomically group.

A test only for lactose positive bacteria can lead to falsely safe results in the case where lactose negative (Salmonella, Shigella, E. coli enterinvasiva, etc.) predominate.

C for 24 hours. , the presumptive colonies will be confirmed by means of the oxidase test and the oxy-fermentation of glucose (use of glucose under aerobic and anaerobic conditions). °For its detection, the poured plate method is generally used using red-violet bile agar medium plus glucose since the basis for the isolation of Enterobacteriaceae is given by the fermentation of glucose in the culture medium at 37

In our country, it has been proven by research carried out that the total coliform indicator meets expectations to assess the sanitary quality of the most consumed foods, making it the indicator currently used in national surveillance programs instead of the Enterobacteriaceae indicator. ´

* Enterococci Designations such as fecal streptococci and group D streptococci from Lancenfield were used synonymously with enterococci. Bacteria in this group consist of spherical or ovoid cells noticeably more robust than micrococci and staphylococci, arranged in pairs or short chains. The quantitative determination of enterococci is quite controversial, as it has currently lost its validity as an indicator of faecal contamination, since in addition to being found in the faeces of mammals, they are also widely distributed in nature; They are highly resistant to heat, drying at low temperatures, and detergents and disinfectants. Its use as an indicator should be limited to situations where it is known that they are manifestations of faecal pollution, for example in swimming pool waters.

Culture media for the detection of enterococci are based on relative tolerance to adverse conditions using chemical compounds such as sodium azide to inhibit other bacterial genera, generally using probable count methods or MPN; The poured plate method can also be applied using means specifically designed for this group.

* Molds and yeasts

Yeasts and molds grow more slowly than bacteria in non-acidic foods that retain moisture and therefore rarely cause problems in such foods. However, in acidic foods and foods with low water activity, they grow faster than bacteria . In general this indicator is used in non-perishable products, which undergo long storage, in dehydrated products whose storage is carried out under inadequate conditions. In addition there is the potential danger of mold mycotoxin production.

Some molds show a special resistance to heat, due to the spores they produce. The expression of yeast development in food differs from that observed by molds. While the former can proliferate in the internal mass of the food (solid like cheeses, or liquids like fruit juices), molds are usually limited to the surfaces, visibly distinctive without the need for any increase. For its determination the poured plate method is generally used, acidified media can be used to inhibit microbial growth or the addition of an antibiotic to the culture medium, the incubation temperature is 25 ºC for 5 days.

* Sterility Test

This test is performed on those foods that are considered commercially sterile, such as preserves. Commercial sterility of a heat-treated food is understood to be the condition reached by the application of heat that leaves the food free of microorganisms capable of reproducing under normal conditions of distribution and storage that are not refrigerated and of viable microorganisms of importance to public health, including spores.

 

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