Unit 4 - Lesson 11: Bacteria & Yoghurt Flashcards
What is yoghurt made from? (I.E. Yoghurt is made from the fermentation of (?) by (?).)
Yoghurt is made from the fermentation of milk by bacteria.
What three shapes can bacteria be?
Rod, spiral, or spherical shaped.
What structure can be found in bacteria that lets them swim?
Some bacteria even have FLAGELLA (singular: flagellum) that let them swim.
What species of bacteria are used to make yoghurt?
Lactobacillus & Streptococcus.
What are lactobacillus and streptococcus often referred to as?
Lactic acid bacteria.
What do lactobacillus and streptococcus turn the simple sugar in milk (lactose) into? How do they do this?
They turn lactose into lactic acid. They do this by anaerobic respiration.
What is the simple sugar in milk actually called?
Lactose
Write the word equation for lactobacillus and streptococcus turning lactose into lactic acid.
Lactose –> Lactic Acid + Energy
What is lactic acid sometimes referred to as?
Lactate
What process do we (humans and animals) use to get rid of the lactic acid (as it is not a good thing)?
We need to get rid of the lactic acid that has built up by oxidising it (adding oxygen to it).
What do we call the amount of oxygen needed to remove the lactic acid?
The oxygen debt.
What is the oxygen debt?
The oxygen debt is the amount of oxygen needed to remove the lactic acid. It’s the reason you continue to breathe so heavy immediately after intensive exercise.
What is respiration often called due to the fact that oxygen is used?
Respiration is often called an oxidation reaction because oxygen is used.
How is yoghurt made in 6 steps?
- Sterilise the equipment with hot, high pressure steam to prevent/kill unwanted microbes. If other microbes grew, unwanted products could be made which could contaminate the yoghurt.
- Pasteurise the milk. This kills any unwanted bacteria that occurs naturally in the milk. To do this, the temperature is increased to 90 degrees Celsius for 15-30 minutes.
- Homogenise and cool the milk. Homogenising forces the milk through small holes, dispersing the large fat globules into smaller.
- Add the bacteria (lactobacillus) to milk. We sometimes say we ‘inoculate with the starter culture’.
- Incubate in a fermenter at 40 degrees Celsius for 6 hours. The pH drops to 4.4 as the lactic acid is produced. This thickens (coagulates) the milk because the milk proteins denature and become slightly solid. Nutrients in the yoghurt are retained because the low pH prevents the growth of other microorganisms.
- Flavours and fruit can be added.
What are methods to sterilise called?
Aseptic methods.
What is a fermenter?
A fermenter is any object that can be used for fermentation (anaerobic respiration).
Give an example of an antibiotic that can be made using a fermenter.
Penicillin.
What is the industrial fermenter made of and why?
The industrial fermenter is made of steel to reduce corrosion by the potentially acidic conditions.
How is pH controlled in a fermenter?
By adding acids or alkali
What does an optimum pH do to the rate of the reaction?
An optimum pH increases the rate of the reaction.
What do air inlets do for a fermenter? What do air inlets prevent?
Air inlets let in filtered air to prevent contamination. We’re making yoghurt by anaerobic respiration.
Draw & label a diagram of a fermenter.
https://i.pinimg.com/736x/b7/c2/b8/b7c2b80ea4ad26a580cc48a9319b3d1c.jpg
To produce a product that requires oxygen (to grow a microorganism that respires aerobically), how could we add oxygen to the fermenter? What would the “fermenter” technically be if we were to add oxygen to it?
We could add oxygen via the air inlets. If we were to add oxygen via the air inlets, it would technically be called a bioreactor, not a fermenter. However, the syllabus doesn’t differentiate between the two.
What does sterilisation kill?
Sterilisation kills other microorganisms that could provide competition for the one we want.
