Transcript NATURE OF MICROBES

NATURE OF MICROBES
What are microbes and are there different types?
How are they seen?
How can they be grown?
How were their effects first proved?
Learning outcomes
• Know that microbes include bacteria,
viruses and fungi.
• know that viruses are smaller than
bacteria.
• know that yeasts are fungi.
Bacteria
• A bacterial cell consists of cytoplasm,
cell membrane and a cell wall.
• There is no distinct nucleus.
• Bacteria reproduce by dividing into two.
Viruses
• Viruses are smaller than bacteria
• they consist of a protein coat
surrounding a small number of genes and
can only reproduce inside a host cell.
• The production of new viruses results in
the destruction of the host cell and the
release of new viruses which can then
attack new cells.
Fungi
• Yeast are a type of fungi
• Yeast cells are larger than bacteria
• They have a nucleus, cytoplasm and a
membrane surrounded by a cell wall.
• Yeasts reproduce by budding.
Pupil Activity
• Read through the hand out and make a
labelled diagram of
– A bacterial cell
– A virus
Learning outcomes
• understand the safe use of basic
aseptic techniques
• investigate the presence of bacteria in
milk using agar plates.
Aseptic Techniques
• Aseptic techniques are used to safely
inoculate, plate and incubate microbes.
Culturing micro organisms
• Micro organisms can be grown in a
culture medium containing
carbohydrates as an energy source,
mineral ions, and in some cases
supplementary protein and vitamins.
• These nutrients are often contained in
an agar medium which can be poured
into a petri dish.
Aseptic Techniques
• For this:
– petri dishes and culture media must be sterilised
before use to kill unwanted micro organisms;
– inoculating loops used to transfer micro organisms
to the media must be sterilised by passing them
through a flame;
– the lid of the petri dish should be sealed with
adhesive tape to prevent micro organisms from the
air contaminating the culture.
Risk assessment
• cultures should be incubated at a
maximum temperature of 25°C to
prevent the growth of pathogens that
might be harmful to humans.
• In industrial conditions higher
temperatures can produce more rapid
growth.
Learning outcomes
• understand how Pasteur used scientific
method to devise experiments and make
deductions.
Spontaneous Generation
• Read through the worksheet
– Spallanzani’ experiment
• What did Spallanzani's experiment show?
• Was his hypothesis correct or incorrect?
– Proponents of spontaneous generation
argued that Spallanzani had only proven
that spontaneous generation could not
occur without air.
Louis Pasteur
• Pasteur's Experiment Results
– What did Pasteur's experiment show?
– Was his hypothesis correct or incorrect?
• The theory of spontaneous generation was
finally laid to rest in 1859 by Louis Pasteur.
• Pasteur's experiment was a variation of
earlier methods
• He boiled meat broth in a flask, heated the
neck of the flask in a flame until it became
pliable, and bent it into the shape of an S.
– Air could enter the flask, but airborne
microorganisms could not - they would settle by
gravity in the neck.
• As Pasteur had expected, no microorganisms
grew.
• When Pasteur tilted the flask so that
the broth reached the lowest point in
the neck, where any airborne particles
would have settled, the broth rapidly
became cloudy with life.
More Louis Pasteur
Learning outcomes
• explore information about the effect of
temperature on the growth of bacteria
and understand its application in food
storage
Stages of Growth
• In micro-organisms, such as bacteria
and yeast, growth leads to cell division
and consequently an increase in
population size.
• The growth of a population of singlecelled microorganisms grown in a closed
environment typically shows four stages:
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lag phase;
exponential phase;
stationary phase;
death phase.
Growth Curve
• The lengths and characteristics of
these phases will depend upon factors
such as the nature of the growth
medium and temperature of incubation.
• In industry, it is important to
understand the factors which affect
the growth rate of a given microorganism in order to generate maximum
product by the most economic means.
Example
• If the product is produced when the
organism has stopped growing the
manufacturer will want to provide
optimum conditions for the culture to:
– reach maximum numbers in stationary
phase
– in the shortest time possible
Food Storage
• food preservation
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by canning,
freezing,
drying,
ultra heat treatment,
high solute concentrations)
Temperature and food storage
• Freezing
• UHT
Micro-organisms in the food
industry
• Micro-organisms are heterotrophic – they
take in ready made foods molecules from
their environment.
• Examples of Microbes useful in food
production
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Acetobacter – vinegar production
Lactobacillus - yoghurt and cheese production
“ripening” bacteria in cheese production
Fusarium and mycoprotein
Use of micro-organism
process
Use of microorganism
Baking
Yeast is mixed with flour, sugar and water to make dough. The yeast
respire the sugar and produce pockets of carbon dioxide that makes
the dough rise.
When the bread is baked the yeast is killed.
Brewing
Yeast respires sugar to form ethanol and carbon dioxide. The ethanol
makes the drink alcoholic and the carbon dioxide gives the drink its
fizz. The process is called fermentation.
Yoghurt
making
Bacteria are used to ferment milk at 46oC. As a result lactic acid is
produced which makes the milk lumpy (coagulate). The temperature is
then reduced to 5oC to prevent further bacterial action. The whole
process is carried out in sterile conditions
Single-cell
protein
This is a protein produced by microorgansism such as bacteria. Fungi
or unicellular algae in a fermentation vessel. While the product
contains 72% protein it does not taste very nice and is expensive to
produce. An alternative is quorn – this is a mycoprotein made from a
filamentous FUNGUS, which has 12.2% protein, low fat content and
6% fibre.
Food Additives
• Food Additives are substances with no
nutritional value
• They are added to improve the
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Appearance
Flavour
Texture
Storage properties of food
antioxidants
• Stop food reacting with oxygen, which
may spoil the taste of the food or
change it’s colour
Colourings
• Improve the appearance of food
• Some colourings can be hazardous
– Sunset yellow
• Hyperactivity
• Allergic reactions and asthma
Flavourings
• Enhance the taste of the food
– MSG – monosodium glutamate in processed
food
– Sugar
– Artificial sweetners e.g. aspartame
Preservatives
• Give processed foods a longer shelf life
by preventing the growth of microorganisms
• Disadvantages of preservatives
– Sulphur dioxide - destroys vitamin B1
– Sodium nitrite - carcinogen