History and Scope of Food Microbiology
Dr. Radhika Kapur
Abstract
The main objective of this research paper is to understand the history and scope of
food microbiology. Micro-organisms play an important role in production, storage and
consumption of foods. They are found in water, air, soil and in foods. Micro-organisms also
perform useful functions in some branches of the food industry. One of the major limitations
are, micro-organisms cause contamination of food that may cause spoilage. For instance,
when milk products are not consumed within two to three days, they may get spoiled and
micro-organisms are responsible for this. Similarly when food is exposed to room
temperature and not refrigerated, it may get spoiled, due to the occurrence of microorganisms. Therefore, it is vital to formulate measures in terms of food preservation. The
occurrence of micro-organisms, characteristics used for identification, conditions of growth
and eventual industrial use will be treated as food borne pathogens. The main aspects that
have been taken into account in this research paper include, history of food microbiology,
importance of micro-organisms in food, micro-organisms in food, and primary sources of
micro-organisms to food.
Keywords: Food, Food Microbiology, Food Products, Micro-organisms, Microbes
Food microbiology is the study of the micro-organisms that occupy, produce, or
contaminate food. The factors that is of major significance is the study of micro-organisms
causing food spoilage. Good bacteria, however, such as probiotics, are becoming
progressivelysignificant in food science. In addition, micro-organisms are essential for the
production of foods such as, cheese, yogurt, and other fermented foods such as bread, beer
and wine.Food safety is the primary focus of food microbiology. Pathogenic bacteria, viruses
and toxinsproduced by micro-organisms are all possible contaminants of food. However,
micro-organisms andtheir products can also be used to combat these pathogenic microbes.
Probiotic bacteria, includingthose that produce bacteriocins, can kill and inhibit pathogens.
Alternatively, purified bacteriocinssuch as,nisincan be added directly to food products.
Finally, bacteriophages, viruses that only infect bacteria, can be used to kill bacterial
pathogens. Thorough preparation of food,including utilization of proper methods in
preparation of meals, eliminates most bacteria and viruses. However, toxins produced
bycontaminants may not be heat-labile, and some are not eliminated through cooking (Food
Microbiology, n.d.).
The micro-organisms occurring on and/or in foods are from a practical point of view
divided into three groups, i.e.molds, yeast and bacteria. Molds are generally concerned in
causing spoilage of foods; their use in the food industry is limited e.g. mold ripened cheese.
Yeasts are the broadly used micro-organisms in the food industry due to their ability to
ferment sugars to ethanol and carbon-dioxide. Some types of yeast, such as baker’s yeasts are
grown industrially, and some may be used as protein sources, mainly in animal feed. Bacteria
important in food microbiology may be divided into groups according to the product of
fermentation, e.g. lactic acid bacteria, acetic acid bacteria, and propionic acid bacteria.
Bearing in mind the food constituent attacked, i.e. used as food for micro-organisms,
proteolytic, saccharolytic and lipolytic bacteria may be distinguished. Their methodical
classification is based primarily on morphological and physiological properties e.g. aerobic
and anaerobic bacteria, gas forming bacteria, etc. Lactic acidbacteria are broadly used in the
dairy industry, and acetic acid bacteria in vinegar production. Many bacteria are known as
micro-organisms that cause spoilage and some are pathogens, e.g.salmonellae, staphylococci,
etc. (Lasztity, n.d.).
History of Food Microbiology
Although processes of food spoilage and methods of food preservation and food
fermentation have been recognized since ancient times.It was not until the 1800s that the
relationship between foods and micro-organisms was established. In 1837, Schwann
proposed that the yeast which appeared during alcoholic fermentation was a microscopic
plant, and between 1857 and 1876, Pasteur showed that micro-organisms were responsible
for the chemical changes that take place in foods and beverages. The observations laid the
foundation for the development of food microbiology. Knowledge in terms of the role that
micro-organisms play in food preservation, food spoilage and food preservation, food
spoilage and food poisoning accelerated rapidly until food microbiology gradually emerged
as a discipline. Not all groups of micro-organisms are of equal interest to the food
microbiologist. Bacteria come on top of the list with molds and yeasts also of considerable
importance and viruses (Unit I, n.d.).
The history and scope of food microbiology has been classified during various time
periods and these have been stated as follows: (Oberg, 2012).
7000 BC – Evidence that the Babylonians manufactured beer (fermentation). Wine
appeared in about 3500 BC. In early civilizations and even in the present world in
underdeveloped countries, where modern sanitation is lacking, alcoholic beverages like beer
and wine were much safe to consume than the local water supply.The reason being, the water
was often contaminated with intestinal micro-organisms that caused cholera, dysentery and
other serious diseases.
6000 BC – The first apparent reference to food spoilage in recorded history.
3000 BC – Egyptians manufactured cheese (fermentation) and butter (fermentation,
low aw). Fermented foods, such as cheese and sour milk (yogurt) were safe to consume and
repelleddamage better as compared to their raw agricultural counterparts. Several cultures
also learned to use salt (low aw) to preserve meat and other foods around this time.
1000 BC – Romans made use of snow to preserve shrimp. As it has to be preserved in
low temperature, records of smoked and fermented meats also appeared. Even though early
human cultures revealed effective ways to preserve food, i.e. fermentation, salt, ice, drying
and smoking, they did not understood how these practices, inhibited food spoilage or food
borne disease. Their unawareness was compounded by a confidence that living things formed
spontaneously from non-living matter.
1665 – An Italian physician, FrancesoRediestablished that maggots on putrefying
meat did not arise unexpectedly but were instead the larval stages of flies. This was the first
step away from the doctrine of spontaneous generation.
1683 – Anton van Leeuwenhoek from the Netherlands scrutinized and researched
upon bacteria through a microscope. At about the same time, the Royal Society was
established in England to communicate and publish scientific work. They invited
Leeuwenhoek to impart informationregarding his observations. He did so for nearly 50 years
until his death in 1723. As a result, Leeuwenhoek’s reports were comprehensively
disseminated and he is justly regarded as the person, who discovered the microbial world.
1765 – Italian named Spallanzani tried to disprove the theory of spontaneous
generation of life by demonstrating that beef broth, which was boiled and then sealed
remained sterile. His work was criticized because they believed O2 was excluded, which they
thought was vital forgeneration that was unstructured.
1795 – The French government offered 12,000 francs to anyone who could develop a
practical way to preserve food. A French confectioner, named Nicholas Appert was issued
the patent after showing that meat could be preserved when it was placed in glass bottles and
boiled. This was the beginning of food preservation by canning.
1837 – Schwann validates that healed infusions remain sterile in the presence of air,
which he passed in through heated coils, again to invalidate spontaneous generation. Critics
suggest heating somehow changed the effect of air as it was needed for spontaneous
generation.
The first person to actuallyacknowledge and understand the causal relationship
between micro-organisms in infusions and the chemical changes that took place in those
infusions was Louis Pasteur. Through his experiments, Pasteur convinced the scientific world
that all fermentative processes were caused by micro-organisms and that explicit types of
fermentations e.g. alcoholic, lactic or butyric were the result of precise types of microorganisms (Oberg, 2012).
In 1857, he showed that souring milk was caused by microbes and in 1860, he
demonstrated that heat destroyed unwanted microbes in wine and beer. The latter process is
now used for a variety of foods and is called pasteurization. Because of the importance of his
work, Pasteur is known as the founder of food microbiology and microbiological science. He
demonstrated that air doesn’t have to be heated to remain sterile using his famous swannecked flasks that finally invalidated spontaneous generation (Oberg, 2012).
In the United States (U.S.), many food industries hesitated to adopt industry wide
microbiological standards until they were economically endangered by the publicity which
surrounded outbreaks of food borne disease. Several unpleasantoccurrences of botulism in the
early 1920s finally prompted the U.S. canning industry to adopt a conservative heat
treatment, known as the 12D process, that causes a reduction in the probability of survival of
the most heat resistant C. botulinumspores to one in a billion (10-12). This practice continues
in the present existence, and since 1925, the canning industry has produced more than a
trillion containers with only five to six known incidents of botulism. Most of these incidents
involved faulty containers, which are not under processing (Oberg, 2012).
Importance of Micro-Organisms in Food
The importance of micro-organisms in food has been recognized in terms of areas,
which have been stated as follows: (Unit I, n.d.).
Food-Borne Diseases
Many pathogenic micro-organisms (bacteria, molds and viruses) can contaminate
foods during various stages of their management, between production and consumption.
Consumption of these foods can cause food-borne diseases. Food-borne diseases can be fatal
and may also cause economic losses to a large extent. Foods of animal origin are associated,
more with food-borne diseases than foods of plant origin. Mass production of food,
introduction of new technologies in the processing, storage of food, changes in food
consumption patterns, and increased import of food from other countries have increased the
chances of large outbreaks as well as the introduction of new pathogens. Effective
intervention technologies are being developed and implemented to ensure the safety of
consumers against food-borne diseases. New methods are also being developed to efficiently
and rapidly identify the pathogens in contaminated foods.
Food Spoilage
Except for sterile foods, all foods harbour micro-organisms. Food spoilage stems from
the growth of these micro-organisms in food or is due to the action of microbial enzymes.
New marketing trends, the desire for foods on the part of consumers that are not overly
processed and preserved, extended shelf life, and chances of temperature abuse between
production and consumption of foods have significantly increased the chances of food
spoilage and, in some instances, with new types of micro-organisms. The major concerns are
the economic loss and wastage of food. New concepts are being studied to reduce
contamination as well as control the growth of spoilage microbes in foods.
Food Bioprocessing
Many food-grade micro-organisms are used to produce different types of fermented
foods, using raw materials from animal and plant sources. Consumption of these foods has
increased to a large extent over the last 15 to 20 years and is expected to increase further in
future. There have been immense changes in the production and availability of these microorganisms to meet the large demand. In addition, new and superior techniques are being
developed by using genetic engineering techniques.
Food Additives
Microbial enzymes are also being used to produce food and food additives. By
adopting genetic recombination techniques, and making use of different microbial sources,
enzymes of higher purity and activity are obtained. Many types of additives from microbial
sources are being developed and utilized in food. Some of these include, single-cell proteins,
essential amino acids, colour compounds, flavour compounds, stabilizers and organic acids.
Food Bio-preservation
Anti-microbial metabolites e.g. bacteriocins and organic acids like acetic, propionic
and lactic acids of neededmicro-organisms are being developed and used in foods in place of
preservatives of non-food, i.e. chemical origin to control pathogenic and spoilage microorganisms in food. Economic production of these anti-microbial compounds and their
efficacy in food systems have generated wide interest.
Probiotics
Consumption of foods containing live cells of bacteria and that have apparent health
benefits has generated interest among consumers. The role of these bacteria for health and
bacterial efficacy benefits is being researched upon.
Micro-Organisms in Food
The micro-organisms that are most common in food are bacteria and fungi. The fungi,
which are less common than bacteria, consists of two major types of micro-organisms, i.e.
molds and yeasts. Apart from these, food may contain viruses and other parasites such as
protozoans, worms etc. (Unit I, n.d.).
Bacteria
Bacteria are a large sphere of prokaryotic micro-organisms. Bacteria are present in
most habitats on Earth, growing in soil, acidic hot springs, radioactive waste water, organic
matter and live bodies of plants and animals. Bacteria have different types of shapes and
sizes. Bacterial cells are about one tenth the size of eukaryotic cells and 0.5–5.0 micrometres
in length. Most bacterial species are either spherical, called cocci or rod-shaped, called
bacilli. Some rod-shaped bacteria are slightly curved called vibrio or comma-shaped. Many
bacterial species exist as single cells and associate in characteristic patterns such as, form
pairs called diploids, form chains, and group together in clusters. Bacteria can also be
elongated to form filaments (Module 1, n.d.).
The bacterial cell is encircled by cell membrane, which encompasses the contents of
the cell and acts as a barrier to hold nutrients, proteins and other crucial components of the
cytoplasm within the cell. They lack a true nucleus, mitochondria, chloroplasts, Golgi
apparatus and endoplasmic reticulum. Most bacteria do not have a membrane-bound nucleus,
and their genetic material is normally a single circular chromosome located in the cytoplasm
in an irregularly shaped body called the nucleoid. The nucleoid contains the chromosome
with associated proteins and RNA. The bacteria contain ribosomes for the production of
proteinsbut different from those of eukaryotes and Archaea. Some bacteria produce
intracellular nutrient storage granules, such as glycogen, polyphosphate, sulfur or
polyhydroxyalkanoates.These granules enable bacteria to store compounds for later use
(Module 1, n.d.).
Molds
Molds are multicellular micro-organisms with mycelial (filamentous) morphology.
These microbes are also characterized by their exhibition of a variety of colours and are
generally recognized by their mild or incoherent, cotton like appearance. Molds can develop
numerous tiny spores that are found in the air and can be spread by air currents. These spores
can produce new mold growth, if they are transferred to a location that has conditions
conducive to germination. Molds normally withstand greater fluctuation in pH than bacteria
and yeasts and can frequently tolerate more temperature fluctuation (Unit I, n.d.).
Although molds thrive best at or near a pH of 7.0, a pH range of 2.0 to 8.0 can be
tolerated, even though an acid to neutral pH is preferred. Molds flourish better at ambient
temperature than in a colder environment, even though growth can occur below 0°C.
Although mold growth is optimal at a water activity (Aw) of approximately 0.85, and growth
can take place below 0.80. At an Aw of 0.90 or higher, bacteria and yeasts grow more
effectively and normally utilize available nutrients for growth at the expense of molds. When
the Aw goes below 0.90, molds grow more effectively. That is why foodstuffs, such as
pastries, cheese, and nuts, that are low in moisture content are more likely to spoil from mold
growth (Unit I, n.d.).
Yeasts
Yeasts are generally unicellular and differ from bacteria in their large cell size
and morphology, and because they produce buds during the process of reproduction by
division. Like molds, yeasts can spread through the air, or other means, and alight on the
surface of foodstuffs. Yeast colonies are normally moist or slimy in appearance and creamy
white coloured. Yeasts prefer an Aw of 0.90 - 0.94, but can grow below 0.90. These microorganisms grow best in the intermediate acid range, pH from 4.0 to 4.5. Food that is
contaminated with yeasts will have a slightly fruity odour on a frequent basis (Unit I, n.d.).
Viruses
Viruses are 10-450 nm in size, cannot reproduce without a living host, attack
only susceptible host cell lines, infect plants, animals, and bacteria, and have the ability to
produce specific diseases in explicit hosts. Transmission occurs in foods, water and air.
Viruses that infect bacteria are called bacteriophages. Viruses are included in the order
Virales. Viruses are too small to be visualized with an ordinary compound microscope.Only
after the electron microscope was developed, the direct observation ofviruses was possible.
Viruses consist of a DNA or RNA core surrounded bya protein coat. Because they lack all the
apparatus for normal cellular metabolism, they must utilize the cellular machinery of the host
cell in order to grow and divide. Once they invade a host cell, however, viruses can multiply
rapidly (Unit I, n.d.).
Protozoa
Protozoa are parasitic and animal-like protists because of their motility. Their sizes
range from 10 to 52 micro-meters. They move by flagella, hair-like structures called
ciliaandand foot-like structures called pseudopodia. Protozoa absorb food through theircell
membranes e.g., amoebas, surround food and consume it. All protozoa digest their food in
stomach-like compartments called vacuoles. Protozoa can reproduce by binary fission or
multiple fission. Some protozoa reproduce sexually, some asexually, while some use a
combination. They cause many diseases in humans such as, malaria, amoebiasis and
leishmaniasis (Module 1, n.d.).
Fungi
Fungi are eukaryotic organisms that include yeasts, molds and mushrooms. They are
non-photosynthetic and do not contain chlorophyll pigments. Most of them are multi-cellular
and some are uni-cellular e.g. yeast. They are non-motile and lack true leaves, roots and
stems. Fungi need warm and moist places to grow. They are found mainly in moist foods,
damp tree barks, and wet bathroom tiles. Fungi are heterotrophs that feed by absorption.They
absorb small organic molecules from the surrounding medium. The enzymes and hydrolytic
enzymes secreted by the fungus break down food outside its body into simpler compounds
that the fungus can absorb and use. The absorptive mode of nutrition is associated with the
ecological roles of fungi as decomposers, parasites, and mutualistic symbionts (Module 1,
n.d.).
Saprobic fungi absorb nutrients from non-living organisms. Parasitic fungi absorb
nutrients from the cells of living hosts. The fungal cells contain membrane-bound nuclei with
chromosomes that contain DNA with non-coding regions called introns and coding regions
called exons. They also possess membrane-bound cytoplasmic organelles, such as
mitochondria, sterol-containing membranes, and ribosomes of 80S type. They have soluble
carbohydrates and storage compounds, including sugar alcohols, disaccharides, and
polysaccharides. Fungi lack chloroplasts and are heterotrophic organisms, requiring
preformed organic compounds as energy sources (Module 1, n.d.).
Fungi possess a cell wall and vacuoles. They reproduce by both sexual and asexual
means and produce spores. They have haploid nuclei. The cells of most fungi grow as
tubular, elongated, and thread-like structures are called hyphae which may contain numerous
nuclei. Some species grow as single-celled yeasts that reproduce by budding or binary
fission. The fungal cell wall is composed of glucans and chitin. Most fungi grow as hyphae,
which are cylindrical, thread-like structures 2–10 μm in diameter and up to several
centimeters in length. Hyphae grow at their tips; new hyphae are typically formed by a
process called branching, or growing hyphal tips bifurcate giving rise to two parallel-growing
hyphae. Hyphae can be either septate or coenocytic, septate hyphae are divided into
compartments separated by cross walls, with each compartment containing one or more
nuclei; coenocytic hyphae are not compartmentalized. Fungal reproduction is multifaceted.
They reproduced by both sexually and asexually. Asexual reproduction via vegetative spores
(conidia) or through mycelial fragmentation. Sexual reproduction involves joining of hyphae
is called conjugation, two mating strains with different nuclei form continuous membrane is
known as plasmogamy and sometimes the nuclei are fused is called karyogamy (Module 1,
n.d.).
Primary Sources of Micro-organisms to Food
The primary sources of micro-organisms to food have been stated as follows: (Osho,
n.d.).
Soil and Water - In soil and water, organisms are generally encountered which are
often food-borne bacteria, i.e. Alcaligenes, Bacillus, Citrobacter, Clostridium,
Corynebacterium, Enterobacter, Micrococcus, Proteus, Pseudomonas, Serratiaand
Streptomyces among others. For molds, some of the most commonly encountered in soils are
Aspergillus, Rhizopus, Penicillium, Trichothecium, Botrytis, Fusarium, and others. In the
case of yeast, a large number of yeast genera are found in the soil, but their number are
generally low in water.
Plants and Plant Products - Bacteria often found to be associated with plants and
plant products are,Acetobacter, Erwinia, Flavobacterium, Kurthia, Lactobacillus,
Leuconostoc, Pediococcus and Streptococcus. As for molds, the most important plant-borne
genera are those that cause the damage of vegetables and fruits and these include,Fusarium,
Aspergillus, Botrytis, Alternariaetc. The commonly encountered genera of yeast in plant
products are the genus Saccharomyces, Rhodotorulaand Torulas.
Food Utensils - The types of food borne microbes that are found in food utensils
depend on types of food to a large extent.The care of these utensils, storage and other factors
need to be taken into consideration. For example, utensils used in handling vegetables would
be expected to have organisms that are associated with vegetables. Also utensils which have
been cleaned with hot or boiling water will only as its micro-flora those organisms that are
able to withstand the management. Utensils stored in open place, where dust might gather
should be expected to have air-borne bacteria, yeast and molds.
Intestinal Tract of Man and Animals- Organisms usually found in the intestinal tract
of man are,Bacteroides, Escherichia, Lactobacillus, Proteus, Salmonella, Shigella,
Staphylococcus, and Streptococcus. Others include,Clostridium, Nitrobacteria, Enterobacter,
and Pseudomonas. These organisms, through fecal dissemination in man found their way
directly into soil and water. From soil they may find their way to food utensils. The most
encountered yeast in this case is the Candida.
Food Handlers - The organisms usually found on the hands and outer garments of
food handlers are a function of the environment and the habit of food handlers. Apart from
these, there are some bacteria that are explicitly associated with hands,nasal cavities and
mouth. These include Micrococcus and Staphylococcus. The genera Salmonella and
Shigellaare basically found in the intestine of man.They may be deposited into foods and
utensils by food handlers. If sanitary practices are not followed by each individual. Yeast and
Molds may be found on the hands and garments of individuals depending upon theirdirect
history.
Animal Feeds – The types of organisms to be found in animal feed would depend on
the source of the feeds, the treatment given to them damage micro-organisms, the container in
which they are stored and the like. Any one of the above mentioned genera of bacteria, yeast,
and mold may be found in animal feeds. The micro-organism, which is of particular
importance is Salmonella sp. which causes food poisoning.
Animal Hides - Generally organisms in soils, water, animal feeds, dust and faecal
matter are often found on the hides of animals. From the animal hides, the microbes may find
their ways into the air, hands of workers and directly into foods. Some members of the hide
flora find their way into the lymphatic system of slaughtered animals from which they
migrate into the muscle tissue of the slaughtered animals.
Air and Dust - Majority of genera of bacteria mentioned above except for some
pathogens are found in air and dust. Also, many genera of molds and yeast are found.
Bacillus and Micrococcus spp are some of the notable bacteria often found in air and dust
because of their ability to sustain aridity to changing degrees.
Conclusion
In addition to the natural micro-flora determined by type of plant or animal and
environmental conditions, every food may be contaminated from outside sources on the way
from the field to the processing plant, or during storage, transportation and distribution. There
are thousands of different types of micro-organisms everywhere in air, soil and water, and
consequently on foods, and in the digestive tract of animals and human beings. Fortunately,
the majority of micro-organisms perform useful functions in the environment and also in
some branches of food industry, such as production of wine, beer, bakery products, dairy
products etc. On the other hand, unwanted spoilage of foods is generally caused by microorganisms and contamination of food with pathogens causes food safety problems. Hence, it
is vital for the individuals to make sure that food is cleaned, before they are made use of.
When fruits and vegetables are purchased, they are washed, before they are cooked or
consumed.
Both foods of plant and animal origin normally carry a micro-flora on the surface of
their parts. Animals also have an intestinal micro-flora. Both animals and plants may
alsobecome contaminated from outside sources. The inner and healthy tissues of plants and
animals, however, have been reported to contain a few living micro-organisms, or none.
The fruitsand vegetablesare harvested, milk is drawn, fish and other products are obtained
from natural waters, and animals are collected and slaughtered. All these carry their usual
micro-flora. After initial handling, further contamination initiates and it continues while the
product is being processed and prepared. Therefore, it can be stated that when individuals are
consuming various types of food items, they need to ensure, they are not spoiled or rotten, are
cleaned and proper ingredients and methods need to be made use of in their preparation. This
is essential to maintain good health, and the individuals are able toadequately manage food
items.
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