Food Science 78.100

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Food Science 78.100 Food Safety Today and
Tomorrow Food Spoilage and Preservation Sp
oilage basics Food preservation and microbe
control
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Food is of biological origin!!!!! Food
gradually deteriorates because of a natural aging
process (we all have a shelf life!) Once
food is harvested or slaughtered, its plant or
animal tissue soon starts to decay Most
changes are POST HARVEST or POST-MORTEM Primary
cause of spoilage microorganisms, such as fungi
(molds yeasts), spoilage bacteria, and their
enzymes usually cause the spoilage process.
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First, some terms
Food-borne (or water-borne) illness Any
illness caused by contaminated food or water.
The most common food-borne illness is food
poisoning. But note also BSE (prion - Mad
Cow) Avian Flu (virus)
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Causes of food-borne illness

• Bacteria
• Leading cause
• Viruses
• Parasites
• Fungi
• Food can taste good, look good and smell good but
  still give you food poisoning - bacteria cannot
  be seen with the human eye.
• Bacteria grow and multiply very quickly. After
  two hours, there can be enough bacteria to cause
  food poisoning.

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Some bacteria produce spores or
toxins Spores not killed by normal heating,
so may be present in some cooked foods.
Spores, unlike bacteria, can survive in soil just
resting for many years. Only when they have
enough food, moisture, warmth and time will
they hatch out of their coats into
bacteria. Toxins some bacteria produce toxins
(poisons) while they grow. the toxins from
these bacteria that cause food poisoning.
Normal cooking often does not destroy
toxins. Anaerobic bacteria grow in absence
of air (facultative or obligate) always keep
vacuum-packed food in the refrigerator use by
the "use by" date anaerobic bacteria will not
grow in the refrigerator.
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Salmonella
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Escherichia coli
E. coli O157H7
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Clostridium perfringens (Gram positive)
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Who is at risk for food-borne illness?

• EVERYONE is potentially at risk for food-borne
  illness, but the following groups are at higher
  risk than others
• Children
• Pregnant women
• Seniors
• Individuals with compromised immune systems
• Medications that weaken natural immunity

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Food poisoning This is an illness, which can
start one hour after eating contaminated food,
or it may take as long as 48 hours to develop.
Usually includes either vomiting or diarrhea,
or both. Food poisoning usually occurs when
bacteria have been allowed to grow and multiply
in the food. Due primarily to toxins produced
by microorganisms
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Food spoilage Food is spoiled if it has
changed so much that customers do not want to
buy it and the chef or cook does not want to
cook it. May be due to Bacteria (e.g.
Salmonella, Listeria, Clostridium, etc) Viruses
(e.g. Hepatitis, Norwalk) Fungi / molds (e.g.
Penicillium) Parasites or worms (Giardia,
Ascaris) Prions (BSE)
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Spoilage bacteria cause food to deteriorate and
spoil. Spoiled food generally has an unpleasant
taste, odor, or appearance. For example, fruits
and vegetables can get mushy or slimy, or meat
products may develop a bad smell. Most people
will not become ill from consuming spoiled food,
provided it has not also been contaminated with
pathogenic bacteria. Unlike spoilage bacteria,
pathogenic bacteria do not generally affect the
taste, odor, or appearance of food, so they can
be difficult to detect. They grow very rapidly
between the temperatures of 40 degrees and 140
degrees Fahrenheit.
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Moldy oranges (Penicillium sp)
Potato blight (Phytophthora sp)

Moldy cheese (Penicillium sp)
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Penicillium notatum mold
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Other Types of spoilage in food
Slime Food becomes slimy when there is so many
bacteria they touch one another Souring Foods
may go sour when the micro-organisms produce
acids, e.g. sour milk.  Some meat products become
sour if packaged in certain types of
plastic Discoloration Food may become
discoloured from microbiological growth.   Some
moulds have coloured spores, e.g. black mould on
bread, or blue and green mould on citrus fruit. 
Sometimes meat becomes green due to the growth of
micro-organisms Gas Bacteria often produces
gas as a by-product which affects food, e.g.
-   Meat becomes spongy in texture -  
Packages, cans or vacuum packs will smell
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Food is more likely to spoil if its?
Damp Keep food in well-ventilated places to
avoid build-up of moisture
Warm Do not keep food at warm temperatures
Low acid Make sure pickles or foods preserved in
acid (vinegar, acetic acid) have sufficient
acid added during processing and are used
within a reasonable time.
Low in sugar Adding sugar to food will preserve
them, e.g. jam.  However they should be used
within a reasonable time.
Damaged Check food on delivery and do not accept
damaged stock
Old Rotate food using a first in-first out
policy.
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Good bugs vs Bad bugs Not all these
changes in food are undesirable. Some people like
aged beef and cheeses or very ripe fruit. The
production of wine and beer involves conversion
of sugars to alcohol, while souring of milk is
essential in the production of cheese.
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Intentional spoilage - Good Bugs Sometimes
micro-organisms can be used to produce foods we
like The blue veins in cheese are formed by
mold growth (so store your blue cheeses
separately from your other cheeses). Roquefort
cheese is a particular blue cheese that is made
in the south of France. Some other blue cheeses
are Stilton (England), Gorgonzola (Italy),
Danablu (Denmark) Milk is soured in the
production of yoghurt and cheese by useful
bacteria (e.g. Streptococcus salivarius subsp.
thermophilus (ST) and Lactobacillus delbrueckii
subsp. Bulgaricus) Yeast is used in the making
of bread and alcoholic beverages (Saccharomyces,
sp.)
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Lactobacillus bulgaricus
Lactococcus lactis
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Saccharomyces sp
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Other causes of spoilage (non-microbiological)
- hydration / dehydration (texture,
glass transition, Aw) -
discoloration e.g. meat oxidizes from myoglobin
(dark red) to oxymyoglobin (bright red) to
metmyoblobin (brown) -
oxidative rancidity (lipids / fats)
antioxidants needed - odor -
enzymatic degradation (rancidity,
softening) - others?
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Water Activity Aw
Water in food which is not bound to food
molecules can support the growth of bacteria,
yeasts and moulds (fungi). The term water
activity (aw) refers to this unbound water. The
water activity of a food is NOT the same thing as
its moisture content. Although moist foods are
likely to have greater water activity than are
dry foods, this is not always so in fact a
variety of foods may have exactly the same
moisture content and yet have quite different
water activities.