Chemistry Of Cooking Flashcards
What does a person sense of taste come form?
A combination of sensors on the tongue and also their sense of smell
What do many of the chemical compounds that give foods their flavour contain? And what does this mean?
Weak intermolecular forces. Due to this such chemicals are volatile molecules e.g. Aldehydes
How do different cooking methods alter the flavour of foods?
By affecting the chemical compounds responsible for flavour
What are the sources of flavour and aroma in our food? 2
Aldehydes or ketones
During cooking what happens to volatile molecules?
Leave the food and enter the air
Or
Dissolve in the cooking liquid
Why is the method of cooking important?
To preserve flavour
What is the best of method to cook some foods?
If polar cook in a substance which is non polar such as butter or oil
If non polar cook in a substance which is polar such as water
What makes collagen tough in texture?
The protein chains form a rope-like structure with hydrogen bonds between chains
When meat is cooked what happens?
the hydrogen bonds that holds the protein chains together are broken. This causes the protein chains to unravel and changes the texture of the meat.
As a protein is heated, the intermolecular bonds are broken. As a result what happens to the shape of the protein and what is the protein said to be?
the shape of the protein changes and the protein is said to be denatured.
How is soap made?
By heating fats or oils with an alkali (NaOH). This reaction is called saponification. The fat or oil is hydrolysed to glycerol and ionic salts of fatty acids
What are the ionic salts of these fatty acids?
the actual soap
What are the 2 types of bonding soap molecules have?
an ionic carboxylate head (negatively charged) and a covalent tail
What is the non-polar covalent tail described to be?
hydrophobic
What is the ionic head described to be?
hydrophilic
Describe what happens when a salt is mixed with grease/ oil and what happens when it is mixed with water?
When mixed with grease or oil, the non-polar end dissolves in oil and grease (like dissolves in like).
The ionic end of the molecules dissolves in water (polar).
What does agitation result in?
a ball-like structure forming with the hydrophobic tail on the inside and negative hydrophilic head on the outside
What does repulsion between these negative charges of the soap head result in?
an emulsion being formed and the dirt released
What does ‘hard water’ mean?
the water contains dissolved calcium and magnesium ions
What happens when hard water is mixed with soap?
a precipitate called a ‘‘scum’’ is formed rather than a latter.
The scum that forms reduces the effectiveness of the soap to clean. How could we overcome this problem?
by using soapless detergents which will not form a scum with the hard water
Where are detergents found?
In many household cleaners e.g. washing powders and washing-up liquids
Give an example of a soapless detergent?
dodecylbenzenesulfonate
What does dodecylbenzenesulfonate have that makes it similar to soap?
A non polar tail and an ionic head
What makes dodecylbenzenesulfonate different from soap apart from the benzene ring?
It will not react with calcium or magnesium to form a precipitate I.e. Scum
What is the simplest aromatic compound?
Benzene
Benzene doesn’t react with bromine water. What can this indicate about its structure?
It doesn’t have c=c bonds
What does the circle in the benzene ring indicate?
Delocalised electrons
What is an emulsion?
A liquid which contains small droplets of one liquid dispersed in another liquid (e.g. Oil and water mixture)
Grease and water would normally separate into two layers? How could these substances be brought together?
Soap can be added to act like an emulsifier
What are emulsifiers present in?
A large range of foods such as mayo is an emulsion of olive oil and vinegar. Egg yolk acts as an emulsifier in this instance
How are emulsifiers used in food normally made?
Reacting edible oils with glycerol. This leaves one or two fatty acid molecules linked with a glycerol backbone
What is the long fatty acid chains said to be?
Non polar and hydrophobic
What are the hydroxyl groups said to be?
Polar and hydrophilic
In the case of vinegar and oil describe what would happen if an emulsifier was added?
The nonpolar fatty acid part of the emulsifier is attracted to the oil
The polar hydroxyl part of the emulsifier is attracted to the vinegar
The emulsifier acts like a soap as it is capable of dissolving both nonpolar and polar substances
