Food and
industrial
microbiology
Khairul Farihan Kasim
CO3:
Ability to define, describe and utilize
microbial growth in fermentation and
biological process
At the end of the chapter, the
student should be able to:

discuss the interaction of intrinsic (food-related) and extrinsic (environmental) factors related to
food spoilage

describe the various physical, chemical, and biological processes used to preserve foods

discuss the various diseases that can be transmitted to humans by foods

differentiate between food infections and food intoxications

discuss the detection of disease-causing organisms in foods

describe the fermentation of dairy products, grains, meats, fruits, and vegetables

discuss the toxins produced by fungi growing in moist corn and grain products

discuss the direct use of microbial cells as food by humans and animals

list foods that are made with the aid of microorganisms and indicate the types of microorganisms
used in their production

describe probiotics

discuss the sources of microorganisms for use in industrial microbiology and
biotechnology

discuss the preservation of microorganisms

describe the design or manipulation of environments in which desired
processes will be carried out

discuss the management of growth characteristics to produce the desired
product

list the major products or uses of industrial microbiology and biotechnology

discuss the use of microorganisms in manufacturing biosensors,
microarrays, and biopesticides
discuss the manipulation of microorganisms in the environment to control
biodegradation

Microorganism Growth in
Foods
Intrinsic and Extrinsic Factors
Intrinsic Factors
composition
 pH
 presence and availability of water
 oxidation-reduction potential

 altered
by cooking
physical structure
 presence of antimicrobial substances


Food composition
 Carbohydrates–do
 Proteins
not result in major odor
and/or fats result in a variety of foul
odors (e.g., putrefactions)

pH
 low
pH allows yeasts and molds to become
dominant; higher pH allows bacteria to
become dominant; higher pH favors
putrefaction (the anaerobic breakdown of
proteins that releases foul-smelling amine
compounds)

Physical structure affects the course and
extent of spoilage
 Grinding
and mixing (e.g., sausage and
hamburger) increases surface area, alters
cellular structure, and distributes
microorganisms throughout the food
 Vegetables
and fruits have outer skins that
protect against spoilage; spoilage
microorganisms have enzymes that weaken
and penetrate such protective coverings

Presence and availability of water

Drying (removal of water) controls or eliminates food
spoilage

Addition of salt or sugar decreases water availability
and reduces microbial spoilage

Even under these conditions spoilage can occur by
certain kinds of microorganisms



Osmophilic–prefer high osmotic pressure
Xerophilic–prefer low water availability
Oxidation-reduction potential can be affected
(lowered) by cooking, making foods more susceptible
to anaerobic spoilage

Many foods contain natural antimicrobial
substances
 coumarins
– fruits and vegetables
 lysozyme – cow’s milk and eggs
 aldehydic and phenolic compounds – herbs
and spices
 allicin – garlic
 polyphenols – green and black teas
Extrinsic Factors

temperature
 lower

temperatures retard microbial growth
relative humidity
 higher

levels promote microbial growth
atmosphere
 oxygen
promotes growth
 modified atmosphere packaging (MAP)
 use
of shrink wrap and vacuum technologies to
package food in controlled atmospheres

Temperature and relative humidity–at higher relative
humidity, microbial growth is initiated more rapidly, even
at lower temperatures

Atmosphere–oxygen usually promotes growth and
spoilage even in shrink-wrapped foods since oxygen can
diffuse through the plastic; high CO2 tends to decrease
pH and reduce spoilage; modified atmosphere packaging
(MAP) involves the use of modern shrink wrap materials
and vacuum technology to package foods in a desired
atmosphere (e.g., high CO2 or high O2)
Microbial Growth and Food
Spoilage

Meats and dairy products are ideal
environments for spoilage by
microorganisms because of their high
nutritional value and the presence of
easily utilizable carbohydrates, fats, and
proteins; proteolysis (aerobic) and
putrefaction (anaerobic) decompose
proteins; in spoilage of unpasteurized
milk, a four-step succession of
microorganisms occurs

Fruits and vegetables have much lower
protein and fat content then meats and
dairy products and undergo different
kind of spoilage; the presence of readily
degradable carbohydrates in vegetables
favors spoilage by bacteria; high
oxidation–reduction potential favors
aerobic and facultative bacteria; molds
usually initiate spoilage in whole fruits

Frozen citrus products are minimally
processed and can be spoiled by
lactobacilli and yeasts

Grains, corn, and nuts can spoil when held under moist
conditions; this can lead to production of toxic
substances



Ergotism is caused by hallucinogenic alkaloids produced by fungi
in corn and grains
Aflatoxins—planar molecules that intercalate into DNA and act as
frameshift mutagens and carcinogens; if consumed by dairy
cows, aflatoxins can appear in milk; have also been observed in
beer, cocoa, raisins, and soybean meal; aflatoxin sensitivity can
be influenced by prior disease exposure (e.g., hepatitis B
infection increases sensitivity)
Fumonisins—contaminants of corn; cause disease in animals and
esophageal cancer in humans; disrupt synthesis and metabolism
of sphingolipids

Shellfish and finfish can be contaminated
by algal toxins, which cause a variety of
illnesses in humans
Controlling Food Spoilage


Removal of microorganisms—filtration of
water, wine, beer, juices, soft drinks and
other liquids can keep bacterial
populations low or eliminate them
entirely
Low temperature—refrigeration and/or
freezing retards microbial growth but
does not prevent spoilage

High temperature
 Canning
 Canned
food is heated in special containers called
retorts to 115°C for 25-100 minutes to kill spoilage
microorganisms
 Canned foods can undergo spoilage despite safety
precautions; spoilage can be due to spoilage prior
to canning, underprocessing during canning, or
leakage of contaminated water through can seams
during cooling

PasteurizationCkills pathogens and substantially
reduces the number of spoilage organisms
Low-temperature holding (LTH)—62.8°C for 30
minutes
 High-temperature short-time (HTST)—71°C for 15
seconds
 Ultra-high temperature (UHT)—141°C for 2 seconds
 Shorter times result in improved flavor and extended
shelf life


Heat treatments are based on a
statistical process involving the
probability that the number of remaining
viable microorganisms will be below a
certain level after a specified time at a
specified temperature

Water availability—dehydration
procedures (e.g., freeze-drying) remove
water and increase solute concentration

Chemical–based preservation
 Regulated
by the U.S. Food and Drug
Administration (FDA); preservatives are listed as
“generally recognized as safe” (GRAS); include
simple organic acids, sulfite, ethylene oxide as a
gaseous sterilant, sodium nitrite, and ethyl formate
 Effectiveness depends on pH; nitrites protect
against Clostridium botulinum, but are of some
concern because of their potential to form
carcinogenic nitrosamines when meats preserved
with them are cooked

Radiation—nonionizing (ultraviolet or UV)
radiation is used for surfaces of foodhandling utensils, but does not penetrate
foods; ionizing (gamma radiation)
penetrates well but must be used with
moist foods to produce peroxides, which
oxidize sensitive cellular constituents
(radappertization); ionizing radiation is
used for seafoods, fruits, vegetables, and
meats

Microbial product-based inhibition
 Bacteriocins—bactericidal
proteins produced by
bacteria; active against only closely related
bacteria (e.g., nisin)
 Bacteriocins function by several mechanisms,
including dissipation of proton motive force,
formation of hydrophobic pores in membranes, or
inhibition of protein and RNA synthesis
Food-borne Diseases

Food-borne illnesses impact the entire
world;
are either infections or intoxications;
 are associated with poor hygiene practices

Food-borne infections
Due to ingestion of microorganisms,
followed by growth, tissue invasion
and/or release of toxins

Salmonellosis




caused by a variety of Salmonella serovars;
commonly transmitted by meats, poultry, and eggs;
can arise from contamination of food by workers in
food-processing plants and restaurants
Campylobacter jejuni
transmitted by uncooked or poorly cooked poultry
products,
 raw milk and red meats;
 thorough cooking prevents transmission


Listeriosis
 transmitted

by dairy products
Enteropathogenic, enteroinvasive, and
enterotoxigenic Escherichia coli
 Spread
by fecal-oral route; found in meat
products, in unpasteurized fruit drinks, and on
fruits and vegetables
 Prevention requires prevention of food
contamination throughout all stages of
production, handling, and cooking

Viral pathogens
usually transmitted by water or by direct
contamination by food processors and handlers;
 recently Norwalk-like viruses have been involved in
major outbreaks on several large cruise ships


Variant Creutzfeld-Jakob disease



transmitted by ingestion of beef from infected cattle;
transmission between animals is due to the use of
mammalian tissue in ruminant animal feeds;
prevention and control is difficult

Foods transported and consumed in
uncooked state are increasingly important
sources of food-borne infection, especially
as there is increasingly rapid movement of
people and products around the world
 Sprouts
can be a problem if germinated in
contaminated water
 Shellfish and finfish can be contaminated by
pathogens (e.g., Vibrio and viruses) found in
raw sewage
 Raspberries are often transported by air to
far-away markets; if contaminated, outbreak
occurs far from source of pathogen
Food intoxications

Ingestion of microbial toxins in foods

Staphylococcal food poisoning is caused by exotoxins
released by Staphylococcus aureus, which is frequently
transmitted from its normal habitat (nasal cavity) to food
by person’s hands; improper refrigeration leads to
growth of bacterium and toxin production

Clostridium botulinum, C. perfringens, and B. subtilis
also cause food intoxication



Botulism, caused by C. botulinum
C. perfringens is a common inhabitant of food, soil, water,
spices and intestinal tract; upon ingestion, endospores
germinate and produce enterotoxins within the intestine; this
causes food poisoning; often occurs when meats are cooked
slowly
Bacillus cereus food poisoning is associated with starchy foods
Detection of Food-borne Pathogens

Methods need to be rapid; therefore, traditional
culture methods that might take days to weeks
to complete are too slow

identification is also complicated by low numbers
of pathogens compared to normal microflora

chemical and physical properties of food can
make isolation of food-borne pathogens difficult

Molecular methods are valuable for three
reasons
 They
can detect the presence of a single,
specific pathogen
 They can detect viruses that cannot be
conveniently cultured
 They can identify slow-growing or
nonculturable pathogens
Some examples

DNA probes can be linked to enzymatic,
isotopic, chromogenic, or luminescent/
fluorescent markers; are very rapid

PCR can detect small numbers of
pathogens (e.g., as few as 10 toxinproducing E. coli cells in a population of
100,000 cells isolated from soft cheese
samples; as few as two colony- forming
units of Salmonella); PCR systems are
being developed for Campylobacter jejuni
and Arcobacter butzleri

Food-borne pathogen fingerprinting is an
integral part of an initiative by the Centers
for Disease Control (CDC) to control foodborne pathogens; The CDC has
established a procedure (PulseNet) in
which pulse-field gel electrophoresis is
used under carefully controlled and
standardized conditions to detect the
distinctive DNA patterns of nine major
food pathogens; these pathogens are
being followed in an surveillance network
(FoodNet)
Microbiology of Fermented
Foods

Fermented milks
 at
least 400 different fermented milks are
produced throughout the world;
 fermentations are carried out by mesophilic,
thermophilic, and therapeutic lactic acid
bacteria,
 as well as by yeasts and molds

Mesophilic
 acid
produced from microbial activity at
temperatures lower than 45°C causes protein
denaturation (e.g., cultured buttermilk and
sour cream)

Thermophilic
 fermentations
yogurt)
carried out at about 45°C (e.g.,

Therapeutic
 fermented
milks may have beneficial
therapeutic effects

Acidophilus milk contains L. acidophilus; improves
general health by altering intestinal microflora; may help
control colon cancer

Bifid-amended fermented milk products (containing
Bifidobacterium spp.) improve lactose tolerance, possess
anticancer activity, help reduce serum cholesterol levels,
assist calcium absorption, and promote the synthesis of
B-complex vitamins; may also reduce or prevent the
excretion of rotaviruses, a cause of diarrhea among
children

Yeast lactic
 these
fermentations include kefir, which is
made by the action of yeasts, lactic acid
bacteria, and acetic acid bacteria

Mold lactic
 this
fermentation is used to make viili, a
Finnish beverage;
 carried out by the mold Geotrichium
candidum and lactic acid bacteria

CheesesCproduced by coagulation of curd,
expression of whey, and ripening by
microbial fermentation; cheese can be
internally inoculated or surface ripened

Meat and Fish
 Meat
products include sausages, country-cured
hams, bologna, and salami; these fermentations
frequently involve Pediococcus cerevisiae and
Lactobacillus plantarum
 Fish
products include izushi (fresh fish, rice, and
vegetables incubated with Lactobacillus spp.) and
katsuobushi (tuna incubated with Aspergillus
glaucus)
Production of Alcoholic
Beverages
Wines and champagnes

Grapes are crushed and liquids that contain
fermentable substrates (musts) are separated;
musts can be fermented immediately, but the
results can be unpredictable; usually must is
sterilized by pasteurization or with sulfur dioxide
fumigant; to make a red wine, the skins of a red
grape are left in contact with the must before
the fermentation process; if must was sterilized,
the desired strain of Saccharomyces cerevisiae
or S. ellipsoideus is added, and the mixture
fermented (10 to 18% alcohol)

Another important fermentative process that
occurs is the malo-lactic fermentation carried out
by Leuoconostoc spp.; this fermentation reduces
the amount of organic acids (e.g., malic acid) in
the wine, improving its flavor, stability, and
“mouth feel”

For dry wine (no free sugar), the amount of
sugar is limited so that all sugar is fermented
before fermentation stops; for sweet wine (free
sugar present), the fermentation is inhibited by
alcohol accumulation before all sugar is used up;
in the aging process flavoring compounds
accumulate

RackingCremoval of sediments accumulated
during the fermentation process

Brandy (burned wine) is made by distilling wine
to increase alcohol concentration; wine vinegar
is made by controlled microbial oxidation (by
Acetobacter or Gluconobacter) to produce acetic
acid from ethanol

For champagnes, fermentation is continued in
bottles to produce a naturally sparkling wine
Beers and ales
Malt is produced by germination of the
barley grains and the activation of their
enzymes;
 mash is produced from malt by enzymatic
starch hydrolysis to accumulate utilizable
carbohydrates;
 mash is heated with hops (dried flowers of
the female vine Humulus lupulis) to
provide flavor and clarify the wort;
 hops inactivate hydrolytic enzymes so that
wort can be pitched (inoculated with
yeast)

Beer is produced with a bottom yeast,
such as Saccharomyces carlsbergensis and
ale is produced with a top yeast, such as
S. cerevisiae; freshly fermented (green)
beers are lagered (aged),
 bottled, and carbonated;
 beer can be pasteurized or filtered to
remove microorganisms and minimize
flavor changes





Distilled spiritsCbeerlike fermented liquid
is distilled to concentrate alcohol;
type of liquor depends on composition of
starting mash;
flavorings can also be added;
a sour mash involving Lactobacillus
delbrueckii mediated fermentation is
often used
Production of breads

Aerobic yeast fermentation is used to
increase carbon dioxide production and
decrease alcohol production; other
metabolic products add flavors

Other microorganisms make special
breads, such as sourdough

Bread products can be spoiled by Bacillus
species that produce ropiness
Other fermented foods

Sufu, fermented tofu (a chemically
coagulated soybean milk product) and
tempeh, made from soybean mash, are
made by the action of molds

SauerkrautCfermented cabbage; involves
a microbial succession mediated by
Leuconostoc mesenteroides, Lactobacillus
plantarum, and Lactobacillus brevis

Pickles are cucumbers fermented in brine
by a variety of bacteria; fermentation
process involves a complex microbial
succession

Silages–animal feeds produced by
anaerobic, lactic-type mixed
fermentation of grass, corn, and other
fresh animal feeds
Microorganisms as Foods
and Food Amendments

Microbes that are eaten include a variety
of bacteria, yeasts, and other fungi (e.g.,
mushrooms, Spirulina)

Probiotics
 the
addition of microorganisms to the diet in
order to provide health benefits beyond basic
nutritive value

also called microbial dietary adjuvants

Prebiotics
 oligosaccharide
polymers that are not
processed until reaching the large intestine;
 often combined with probiotics to create a
synbiotic system

Probiotics
 are
being used with poultry to increase body
weight and feed conversion;
 also reduce coliforms and Campylobacter; may
be useful in preventing Salmonella from
colonizing gut due to competitive exclusion