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Food Microbiology

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Food Microbiology Definition

MVSAT 2024

Food is very important in part of all living organisms. We get our food from various sources. Microbiology is the study of microbes that are known to affect the animals and human beings around us. Some microbes are also useful in nature and they can be used for the preparation of food products but many of them are harmful in nature and are the main causes of death around the world. The microbes are also the major cause of spoiling the food in our daily lives. So, food microbiology is the mixture of food and microbiology where we learn about the effects of microbes on the food we eat. This is what is food microbiology where we study the microbes and how they cause food spoilage. 

History of Food Microbiology

Before understanding thoroughly what is food microbiology, we will understand the history of food microbiology and how food as a substrate for microorganisms acts.  Although it's extremely difficult to pinpoint the precise beginning of human awareness of the presence and role of microorganisms in foods, the available evidence indicates that this data marks the establishment of food microbiology. The age before the establishment of bacteriology as science could also be designated the pre-scientific era. This era could also be further divided into what has been called the food-gathering period and therefore the food-producing period. During this period, humans were presumably carnivorous, with plant foods coming into their diet later during this period. It is also during this era that foods were first cooked. Around 8000 years ago the process of processing food preparations started. It is presumed that the issues of spoilage and gastrointestinal disorder were encountered early during this period. With the arrival of prepared foods, the issues of disease transmission by foods and of faster spoilage caused by improper storage made their appearance. 

Around 6000 BC years back, the spoilage of prepared food products could be seen. The practice of creating pottery was delivered to Western Europe about 5000 BC from the Middle East. The primary boiler pots are thought to have originated in the Middle East about 8,000 years ago. The humanities of cereal cookery, brewing, and food storage, were either started at about this point or stimulated by this new development. The primary evidence of beer manufacture has been traced to ancient Babylonia as far back as 7000 BC. The Sumerians of about 3000 BC are believed to have been the primary great livestock breeders and dairymen and were among the first to form butter. Salted meats, fish, fat, dried skins, wheat, and barley also are known to have been associated with this culture. Milk, butter, and cheese were employed by the Egyptians as early as 3000 bc. Between 3000 BC and 1200 BC, the Jews used salt from the Dead Sea within the preservation of varied foods. The Chinese and Greeks used salted fish in their diet, and therefore the Greeks are credited with passing this practice on to the Romans, whose diet included pickled meats. Mummification and preservation of foods were related technologies that appear to have influenced each other’s development. Wines are known to have been prepared by the Assyrians by 3500 BC.

Sources of Fungi and Bacteria

There are various types of microorganisms in food. It is food as a substrate for microorganisms that help them to grow. 

  • Soil and Water: The soil and water are the main sources of bacteria and fungi in the food. By the action of wind, the soil organisms can enter the air and later enter water bodies when it rains. They also enter the water when rainwater flows over soils into bodies of water. Aquatic organisms are often deposited onto soils through the actions of cloud formation and subsequent rainfall. This common cycling leads to soil and aquatic organisms being one and therefore the same to an outsized degree. Some aquatic organisms, however, are unable to continue soils, especially those that are indigenous to marine waters. Alteromonas spp. are aquatic forms that need seawater salinity for growth and wouldn't be expected to continue soils. The bacterial biota of seawater is actually Gram-negative.

  • Plants and Plant Products: It is going to be assumed that a lot of or most soil and water organisms contaminate plants. However, only a comparatively small number find the plant environment suitable for their overall well-being. People who persist on plant products do so by virtue of a capacity to stick to plant surfaces so that they're not easily washed away and since they're ready to obtain their nutritional requirements. Notable among these are the carboxylic acid bacteria and a few yeasts. 

  • Food Utensils: When vegetables are harvested in containers and utensils, one would expect to seek out the surface of contaminators to contact.  As more and more vegetables are placed within the same containers, a normalization of the microbiota would be expected to occur. In a similar way, the cutting block during a butcher shop alongside cutting knives and grinders are contaminated from initial samples, and this process results in a buildup of organisms, thus ensuring a fairly constant level of contamination of meat-borne organisms. 

  • Gastrointestinal Tract: This biota becomes a water source when polluted water is employed to scrub raw food products. The intestinal biota consists of the many organisms that don't persist as long in waters as do others, and notable among these are pathogens like salmonellae. Any or all of the Enterobacteriaceae could also be expected in fecal wastes, alongside intestinal pathogens, including the five protozoal species already listed.

  • Food Handlers: The microorganisms that are present in the hands of handlers generally reflect the environment and habits of people, and therefore the organisms in question could also be those from the soil, water, dust, and other environmental sources. Additional important sources are people who are common in nasal cavities, the mouth, and on the skin, and people from the alimentary canal who will enter foods through poor personal hygiene practices.

  • Animal Feeds: This is often a source of salmonellae to poultry and other livestock. Within the case of some silage, it's a known source of Listeria monocytogenes to dairy and meat animals. The organisms in dry animal feed are spread throughout the animal environment and should be expected to occur on animal hides.

  • Animal Hides: Within the case of milk cows, the kinds of organisms found in milk are often a mirrored image of the biota of the udder when proper procedures aren't followed in milking and of the overall environment of such animals. From the udder and also from the hide the organisms can contaminate the sources. They can also do so at the hands of the handlers. 

  • Air and mud: They may sometimes be found in air and dust during a food-processing operation, those which will persist include most of the Gram-positive organisms listed. Among fungi, a variety of molds could also be expected to occur in air and mud, along with some yeasts. Generally, the kinds of organisms in air and mud would be people who are constantly reseeded to the environment. 

These all factors help us to understand what is food microbiology and how food as a substrate for microorganisms works. 

Molds Found in Food

Molds are also studied in food microbiology as they are also able to cause spoilage of food. Molds are filamentous fungi and are formed in the form of entangled structures. They spread rapidly and can cover several inches of area in two to three days. the entire of the mass or any large portion of it's mentioned as mycelium. Mycelium consists of branches or filaments mentioned as hyphae. The molds by the formation or multiplication by ascospores, zygospores, or conidia. The ascospores of some genera are notable for his or her extreme degrees of warmth resistance. One group forms pycnidia or acervuli. They are small, flask-shaped, fruiting bodies that are lined with conidiophores. Arthrospores result from the fragmentation of hyphae in some groups.

There were no radical changes within the systematics of foodborne fungi during the 1980s. The most notable changes involve the invention of the sexual or perfect states of some well-known genera and species. The ascomycete stage is the most important reproductive state of the organism. Holomorph indicates that both states are known, but the teleomorph name is employed.

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Yeasts Found in Food

Yeast finds their role in the importance of food microbiology. But they can also play a role in spoiling the food products. Yeasts could also be viewed as being unicellular fungi in contrast to the molds, which are multicellular. However, this is often not a particular definition, as many of what are commonly considered yeasts actually produce mycelia to varying degrees. They are present in oval, elongate, elliptical, or spherical cell shapes. Typical yeast cells range from 5 to eight µm in diameter, with some being even larger. Older yeast cultures tend to possess smaller cells. Most of these of importance in foods divide by budding or fission. Yeasts can grow over wide ranges of acid pH and in up to 18% ethanol. Many grow within the presence of 55–60% sucrose. Many colours are produced by yeasts, starting from creamy, to pink, to red. Regarding the taxonomy of yeasts, newer methods are employed within the past decade approximately consisting of 5S rRNA, DNA base composition, and ubiquinone profiles. Due to the larger genome size of yeasts, 5S rRNA sequence analyses are employed for larger RNA fractions. Many changes have occurred in yeast systematics, due in part to the utilization of newer methods but also to what appears to be a philosophy toward grouping instead of splitting taxa.

Nutrient Content in Microorganisms

In order to grow and perform normally, the microorganisms of importance in foods require the


  • Water

  • Source of energy

  • Source of nitrogen

  • Vitamins and related growth factors

  • Minerals

As sources of energy, foodborne microorganisms may utilize sugars, alcohol, and amino acids.

Some microorganisms are ready to utilize complex carbohydrates like starches and cellulose as sources of energy by first degrading these compounds to simple sugars. Fats also are employed by microorganisms as sources of energy, but these compounds are attacked by a comparatively small number of microbes in foods. The primary nitrogen sources utilized by heterotrophic microorganisms are amino acids. A large number of other nitrogenous compounds may serve this function for various sorts of organisms. Some microbes, for instance, are ready to utilize nucleotides and free amino acids, whereas others are ready to utilize peptides and proteins

Generally, simple compounds like amino acids are going to be utilized by most organisms before any attack is formed on the more complex compounds like high-molecular-weight proteins. An equivalent is true of polysaccharides and fats. Microorganisms may require B vitamins in low quantities, and most natural foods have an abundant quantity for those organisms that are unable to synthesize their essential requirements. In general, Gram-positive bacteria are the smallest amount synthetic and must therefore be furnished with one or more of those compounds before they're going to grow. The Gram-negative bacteria and molds are ready to synthesize most or all of their requirements. The content above can be used to form concise food microbiology notes.

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FAQs on Food Microbiology

1. What are Endolysins?

Answer: The newly formed bacteriophages affect their own release by the consecutive use of two small hydrophobic proteins. Holins disrupt the cell membrane and form holes through which endolysins can pass. The endotoxins target the peptidoglycans and then they start destructing the cell barrier which helps the progeny to release. The assembly and use of phage endolysins to regulate some foodborne bacterial pathogens are demonstrated. An examination of the cell membrane lysis system of eubacteria phage 3626 revealed that it produces a holin and an endolysin. 

Holin function was demonstrated by its ability to substitute for the deleted holin of phage lambda during a modified phage vector cloned and expressed in Escherichia coli. Endolysins from monocytogenes phages are introduced into a lactic starter culture, enabling the phage enzyme to scale back or eliminate the pathogen during cheese ripening. This is done so that the optimization of the release of endolysin from the bacteria and on the cheese surface can take place. The endolysin encoding gene was modified to hold a sign peptide. When this construct was introduced into a dairy starter culture of Lactococcus lactis, a clone was identified, which expressed a robust lytic activity that was quantitatively exported from the lactococcal cells into the encompassing medium where it caused rapid lysis of monocytogenes cells. 

In Lactose lactis, the vectors were also introduced where a functional enzyme was produced, and therefore the vector was shown to be compatible with native lactococcal plasmids. These recombinants were also utilized in preliminary dairy fermentation experiments to regulate monocytogenes, and a 95% reduction of the pathogen at the top of a Camembert cheese ripening period was demonstrated by M.J. Loessner. A broad-spectrum endolysin from a Lactobacillus helveticus phage was shown to lyse different species of lactobacilli and also some lactococci, pneumococci-bacteriophages.

2. What are Biocontrol Agents?

Answer: The Lytic phages that are known to be specific for some bacterial strains are known to be effective in destroying their host cells, and this is often the idea of phage typing. Phages were shown within the late 1960s to lyse their host cells recovered from fish, meats, and skim milk but these early studies employed phages and their host bacteria in broth and meat extract cultures. It appears that the primary study of phages directly added to meat to regulate meat spoilage bacteria was that of Greer. During this study, rib-eye steaks, a Pseudomonas previously isolated from spoiled beef, and a homologous phage at A level of 108 pfu/ml were used. Four days after adding the phage to the steaks that were surface inoculated with the host bacterium, a 1–2-log reduction of the bacterium and a 2-log increase in phage numbers were noted. Adding 108 pfu/ml of phage caused steak case-life to extend from 1.6 to 2.9 days. Overall, surface discolouration and retail acceptance were improved by the phage treatments. 

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