2.5 Food spoilage

• Biologie
• Middelbare school
• havo, vwo
• Leerjaar 2

What causes your food to spoil?

Today

Learning objectives

Instruction

Assignments

End of class

Learning objectives

You will learn how food can spoil and how to prevent this.

Fungi (schimmels) and bacteria on food are..

1. harmfull
2. normal

What causes your food to spoil?

Micro organisms (molds and bacteria)

The decomposers break down natural waste (chapter 6). 

They secrete toxins (which are harmfull to humans)

Fungi (or moulds)

They contain thin threads with which they suck up food. 

They also contain small balls, containing spores.  A new fungus can grow from each spore.

Bacteria

Replicate by cell division (celdeling)

Replication speed depends on the conditions:

- temperature

- moisture

Food poisoning

Food spoilage (voedselbederf) = when unwanted fungi or bacteria grow on your food. 

Food poisoning (voedselvergiftiging) = When you fall ill by toxic substances in your food. 

How do you prevent food spoilage?

Preserving (conserveren)= keeping food fresh for a longer period of time

1. Heating 
2. Cooling and freezing 
3. Adding substances (stoffen toevoegen)
4. Vacuüm or special gas packaging
5. Drying

How do you prevent food spoilage?

1. Heating (pasteurizing and sterilizing): fungi and bacteria die at high temperatures.
   
2. Cooling and freezing: fungi and bacteria grow slower at low temperatures. Growth completely stops at a temperature below 0°C.
   
3. Adding substances: by adding a lot of salt, sugar, or acid to food, fungi and bacteria are not able to grow anymore. There are also special preservatives to prevent growth.
   
4. Vacuum or special gas packaging (figure 13): most of the fungi and bacteria cannot live without oxygen. By replacing all the air in the package by a gas mixture without oxygen, food decay is prevented.
   
5. Drying: fungi and bacteria cannot grow without water

Heating

Sterilize (steriliseren) = Heat at least to 100°C for a while. 

E.g. long-life milk and jam.

Pasteurize (pasteuriseren) = Heat at a lower temperature of around 60°C. Not all micro-organisms die, but the taste of the food does not change very much either. E.g. milk, yoghurt and custard.

Which statement is false?

1. Food spoilage is caused by fungi and bacteria.
2. Fungi cannot be seen with the naked eye, bacteria can.
3. Food can be infected by other people and animals.
4. Food spoilage can cause diarrhoea.

What cannot be a symptom of a salmonella infection?

1. abdominal pain
2. diarrhoea
3. feeling sick
4. dripping nose

Wat?	Make: 8, 9-11, 17-20
Hoe?	In your (online) book. Choose: whispering or listening to music on your laptop.
Hulp?	Raise your hand. If he/she is not listening to music, you may ask your neighbour first.
Tijd?	10 minutes
Klaar?	Make a summary of 7.1.
Opbrengst	You have finished your homework! Well done!