Transcript Food: Battleground of the Species!

Professor James Dooley
School of Biomedical Sciences,
University of Ulster,
Coleraine
Space
Exploration
WAR

Main points of today’s lecture
◦ Essential element of modern society
 Not appreciated by most individuals
◦ A changing environment requiring constant
innovation
 Will always be a problem for humans

Hunter-Gatherer society
◦ supported low numbers/ self-sufficient
◦ unreliable food supply
◦ limited specialisation of individuals

Industrial and Agricultural society
◦ supports high numbers/ produce excess
◦ supports specialisation
◦ generally predictable food supply
Vitamins
Proteins
Food
Energy
Carbohydrate
Building materials
Lipids
Human
Growth/Repair
Microbial
Growth

“Organisms that are too small to be seen
with the naked eye”
Bacteria
Viruses
Fungi
Protozoa


Unicellular organisms
Very small!!!!!!!
◦ 1-10 microns

Enormous diversity
◦ Shape
◦ Habitat
◦ Nutrition

Many bacteria require similar growth and
nutrition conditions to humans
◦ very many do not but we do not deal with them when
considering food spoilage and preservation.
Light Microscope
x 1,000

Everywhere!
◦
◦
◦
◦
Soil
Plant roots
Water
Bodies of animals, fish,
birds etc,
◦ E. coli
◦ C. difficile (C diff)
◦ Superbugs
 MRSA
Doublings
1
2
3
4
5
6
7
8
90
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Number of cells
1
2
4
8
16
32
64
128
256
512
1,024
2,048
4,096
8,192
16,384
32,768
65,536
1,310,752
2,621,504
5,243,008
10,486,016
20,972,032
41,944,064
83,888,128
167,776,256
Doubling is a Big Deal
Some bacteria can double
every 30 min. and a few
can double in 20 minutes!!
• Escherichia coli
• 20 minutes
•Mycobacterium tuberculosis
• 15 hours

Source of nutrients
◦ amino acids, sugars, lipids, vitamins
 released by action of enzymes operating outside
the cell
 E.g starch digested by amylase releases glucose

Correct temperature
◦ Bacteria grow within temperature ranges
◦ mesophiles (10-45oC)
◦ psycrophiles (0-20oC)

Suitable pH

Absence of toxic chemicals

Correct atmosphere (N/CO2/O2)
◦ 6-7.5
◦ Aerobic
 Bacillus
◦ Anaerobic
 Clostridium
◦ facultative anaerobes
 Salmonella

some bacteria produce
endospores
◦ response to stress

very resistant to heat

very resistant to harsh conditions


◦ 121oC
◦ chemicals, drying, radiation
can remain dormant for a long
time (years)
endospore - forming bacteria
◦ universal in soil
◦ Bacillus anthracis: anthrax

“Organisms that are too small to be seen
with the naked eye”
Bacteria
Viruses
Fungi
Protozoa





unicellular (yeasts) and multicellular
(moulds)
Non-photosynthetic,plant-like organisms
Multicellular, filamentous organisms
Normally
inhabitants of the soil,
rhizosphere and water
Can tolerate acidic and dry conditions

Fungi are the main organisms involved in
the decay of organic material
◦ recycling of essential elements
◦ C, N, H, O, S etc.

Agents of food production

Agents of disease

Agents of food spoilage

We need to know about how spoilage
organisms live

We need to understand their biology

We need Microbiologists!
Nutrients
Suitable
Environment
Time
More Bacteria!
Food Components: Starch, protein etc.
Sugars, amino acids etc.
Digestive enzymes
Waste products:
Altered
Food
CO2
Alcohol
Lactic acid etc.
Altered
Environment

Microbial growth introduces unwanted
alterations in food
◦
◦
◦
◦

appearance
smell
Taste
Nutritional content
Changes not necessarily harmful!
◦ Hákarl

Each food unique microbial environment
◦ unique spoilage agents

Each food has it’s own unique microbial
population

Uncontrolled growth of the microbes results
in food spoilage

We can predict (and therefore control) food
spoilage

Bacterial growth on milk sugars

Bacterial waste products

Only lactic acid bacteria can grow
and all others inhibited
◦ Lactose
◦ Lactobacillus spp., Lactococcus spp.
◦ lactic acid build up (bitter taste!)
◦ pH reduction
◦ continues until all sugars used up

Yeasts
acidity
and
moulds
tolerate
◦ use lactic acid for growth.
◦ pH rise
◦ allowing different bacterial species to
grow

New bacteria use proteins as
major nutrient
◦ (Primary amines produced- Smelly!!!!!)

Foods are characteristically spoiled by known
organisms
Food
Chicken
Organism
Type of Spoilage
Pseudomonas spp. Sliminess
Green colour
Milk (pasteurised) Lactobacillus
thermophilus
Sour
Bread
Bread mould
Rhizopus nigrans

Food spoilage
has major
economic
impacts
WAR
“An army travels on its stomach”
◦ a Frenchman who invented a
method to preserve perishable
organic materials.
◦ In 1809, Appert received 12,000
francs for his method of
enclosing food in airtight jars
which were then heated.
 boiling products in jars for four to six
hours and then pouring molten wax
over the jars.
◦ By this method, food could be
preserved indefinitely.
◦ Unfortunately, the glass jars often
broke on their journeys with the
army!!!!
Microbes killed

Microbial GROWTH causes food spoilage
◦ Kill microbes: no growth = no spoilage
◦ Stop microbes growing: no growth = no spoilage

Temperature
◦
◦
◦
◦
canning
sterilization by heat
121oC for 15 minutes
all bacteria and
endospores killed


Killing of all microbes from a food will
prevent spoilage!
Killing of all microbes from a food will
drastically alter the food
◦ taste
◦ texture
◦ nutritional content

Temperature
◦ Less extreme than canning
◦ Pasteurization
◦ mild heat treatment
◦ overall microbial population is reduced
◦ disease causing microbes are eliminated since
these tend to be more heat sensitive than other
organisms.


63°C for 30 min. (batch pasteurization)
72°C for 15 sec. (flash pasteurization)

Radiation
◦ use of gamma rays from Co60
◦ microbes killed by free radicals




Food can be packaged!
No recontamination possible
Pasteurization of meat, poultry, cheese
No alteration of food
◦ controversial claim


Irradiation of
various foods
accepted in US and
many other
countries
UK only allows for
irradiation of herbs,
spices or vegetable
seasonings
NASA

highly perishable
◦
◦
◦
◦
◦
meat
fruit
milk
vegetables
eggs
WET

semi perishable

stable
◦ potatoes
◦ nuts
◦ rice
◦ flour
◦ dry beans
Dry
What defines each group?
Amount of water

A number of parameters can be manipulated
to slow down microbial growth
◦ Moisture content {water activity (Aw)}
◦ Perishable foods have a high Aw
 preserve by lowering Aw

drying
◦ sun
◦ heat
◦ freeze - dried
(expensive!)

addition of salt or
sugar
◦ water needed to
keep salt and sugar
in solution

pH
◦ very few bacteria grow below pH
5.0

How to make food acidic?
◦ Add acid e.g. acetic acid
◦ Allow bacteria to make acid from
natural food components
 lactic acid bacteria

Temperature
◦ storage at 4oC degrees
 rate of spoilage decreased
◦ storage at -20oC degrees
 rate of spoilage extremely
slow
◦ need -70oC to eliminate
spoilage

Modified Atmosphere
Packaging
◦
◦
◦
◦

Oxygen
Nitrogen
Carbon Dioxide
Argon
Mix depends on food in
question
◦ Vacuum packing also used

BBC Radio 4 Science

Food Safety Through the Ages

Food Preservation site

Food Standards Agency
◦ “On the shelf”
◦ http://www.bbc.co.uk/radio4/science/connect_20
021030.shtml
◦ Dr. Bill Grierson
◦ http://www.acsh.org/healthissues/newsID.767/he
althissue_detail.asp
◦ Good links to related material
◦ http://www.bookrags.com/sciences/biology/food
-preservation-wmi.html
◦ www.food.gov.uk/
◦ Good site for general information

A good site to visit
◦ http://resources.schoolscience.co.uk/SGM/index.html



EGGS - When something starts pecking its way out of the
shell, the egg is probably past its prime. Especially if the
something is NOT a chicken.
DAIRY PRODUCTS - Milk is spoiled when it starts to look
like yogurt. Yogurt is spoiled when it starts to look like
cottage cheese. Cottage cheese is spoiled when it starts
to look like regular cheese. Regular cheese is nothing but
spoiled milk anyway and can't get any more spoiled than
it is already. Cheddar cheese is spoiled when you think it
is blue cheese but you realize you've never purchased that
kind. Blue cheese, by definition, is never spoiled.
FROZEN FOODS - Frozen foods that have become an
integral part of the defrosting problem in your freezer
compartment will probably be spoiled - (or wrecked
anyway) by the time you pry them out with a kitchen
knife.


MEAT - If opening the fridge door causes stray animals to
congregate outside your house, the meat is spoiled.
BREAD - Sesame seeds and Poppy seeds are the only
officially acceptable "spots" that should be seen on the
surface of any loaf of bread. Fuzzy and hairy looking
white or green growth areas are a good indication that
your bread has turned into a pharmaceutical laboratory
experiment.

FLOUR - Flour is spoiled when it wiggles.

SALT - It never spoils.

LETTUCE - lettuce is spoiled when you can't get it off the
bottom of the fridge without Mr Muscle.
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CANNED GOODS - Any canned goods that have become the
size or shape of a softball should be disposed of. Carefully.
CARROTS - A carrot that you can tie in a clove hitch in is not
fresh.
RAISINS - Raisins should not be harder than your teeth.
POTATOES - Fresh potatoes do not have roots, branches, or
dense, leafy undergrowth.
CHIP DIP - If you can take it out of its container and bounce it
on the floor, it has gone bad.
GENERAL RULE OF THUMB - Most food cannot be kept longer
than the average life span of a hamster. Keep a hamster in or
nearby your fridge to gauge this.