Transcript Food and industrial microbiology

Industrial microbiology
Part 1
Applied to food and beverages
Compiled by Dr. Harbant
CO3:
Ability to define, describe and utilize
microbial growth in fermentation and
biological process
Topics for discussion
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discuss the interaction of intrinsic (food-related) and extrinsic
(environmental) factors related to food spoilage
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describe the various physical, chemical, and biological
processes used to preserve foods
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discuss the various diseases that can be transmitted to
humans by foods
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differentiate between food infections and food intoxications
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discuss the detection of disease-causing organisms in foods
Contd.
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describe the fermentation of dairy products, grains, meats,
fruits, and vegetables
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discuss the toxins produced by fungi growing in moist corn
and grain products
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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
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describe probiotics
Intrinsic and Extrinsic
Factors
Intrinsic Factors
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composition
pH
presence and availability of water
oxidation-reduction potential
– altered by cooking
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physical structure
presence of antimicrobial substances
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Food composition
– Carbohydrates–do not result in major odor
– Proteins and/or fats result in a variety of foul
odors (e.g., putrefactions)
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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)
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
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Physical structure affects the course and
extent of spoilage
– Grinding and mixing (e.g., sausage and meat
burger) 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
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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
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temperature
– lower temperatures retard microbial growth
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relative humidity
– higher levels promote microbial growth
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atmosphere
– oxygen promotes growth
– modified atmosphere packaging (MAP)
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use of shrink wrap and vacuum technologies to
package food in controlled atmospheres
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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
Spoilage in meat and diary products
Meats and dairy products are ideal
environments for spoilage by microorganisms
because:
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of their high nutritional value and the
presence of easily utilizable carbohydrates,
fats, and proteins;
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proteolysis (aerobic) and putrefaction
(anaerobic) decompose proteins;
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unpasteurized milk, favors
microorganisms growth
Spoilage in plant material
Fruits and vegetables have much lower
protein and fat content then meats and dairy
products and undergo different kind of
spoilage:
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the presence of readily degradable
carbohydrates in vegetables favors
spoilage by bacteria;
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high oxidation–reduction potential favors
aerobic and facultative bacteria;
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molds usually initiate spoilage in fruits.
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Frozen citrus products are minimally
processed and can be spoiled by
lactobacilli and yeasts
Spoilage in cereals and nuts
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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
– Fumonisins—contaminants of corn; cause
disease in animals and esophageal cancer
in humans; disrupt synthesis and
metabolism of sphingolipids
Aflatoxins in food
1. Aflatoxins—planar molecules that
intercalate into DNA and act as frame
shift mutagens and carcinogens;
2. Aflatoxins can appear in milk if
consumed by dairy cows,
3. Have also been observed in beer, cocoa,
raisins, and soybean meal;
4. Aflatoxin sensitivity can be influenced by
prior disease exposure (e.g., hepatitis B
infection increases sensitivity)
Spoilage in sea food
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Shellfish and finfish can be
contaminated by algal toxins, which
cause a variety of illnesses in
humans
Controlling Food
Spoilage
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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
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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
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Pasteurization kills 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
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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
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Water availability—dehydration
procedures (e.g., freeze-drying)
remove water and increase solute
concentration
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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
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Radiation—non-ionizing (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 sea foods,
fruits, vegetables, and meats
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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
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Food-borne Diseases
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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
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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
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Campylobacter jejuni
– transmitted by uncooked or poorly cooked poultry
products,
– raw milk and red meats;
– thorough cooking prevents transmission
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Listeriosis
– transmitted by dairy products
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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
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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
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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
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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
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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
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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
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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
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DNA probes can be linked to enzymatic, isotopic,
chromogenic, or luminescent/ fluorescent
markers; are very rapid
PCR (Polymerase Chain Reaction) can detect
small numbers of pathogens (e.g., as few as 10
toxin-producing 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
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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
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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
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Mesophilic
– acid produced from microbial activity at
temperatures lower than 45°C causes protein
denaturation (e.g., cultured buttermilk and
sour cream)
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Thermophilic
– fermentations carried out at about 45°C (e.g.,
yogurt)
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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
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Yeast lactic
– these fermentations include kefir, which is
made by the action of yeasts, lactic acid
bacteria, and acetic acid bacteria
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Mold lactic
– this fermentation is used to make viili, a
Finnish beverage;
– carried out by the mold Geotrichium
candidum and lactic acid bacteria
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Cheeses produced by coagulation of curd,
expression of whey, and ripening by
microbial fermentation; cheese can be
internally inoculated or surface ripened
Meat and Fish
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Meat products include sausages, country-cured
hams, bologna, and salami; these fermentations
frequently involve Pediococcus cerevisiae and
Lactobacillus plantarum
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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
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Grapes are crushed and liquids that contain
fermentable substrates (musts)
Musts are separated and 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)
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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
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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
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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)
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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
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Distilled spirits beerlike 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
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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
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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
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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
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Microbes that are eaten include a
variety of bacteria, yeasts, and other
fungi (e.g., mushrooms, Spirulina)
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Probiotics
– the addition of microorganisms to the diet in
order to provide health benefits beyond basic
nutritive value
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also called microbial dietary adjuvants
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Prebiotics
– oligosaccharide polymers that are not
processed until reaching the large intestine;
– often combined with probiotics to create a
symbiotic system
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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