Chemistry of Cooking Flashcards
What are long chain molecules which can be twisted to form spirals and folded into sheets?
Proteins
How are proteins held in spiral and sheet forms?
Hydrogen bonding within the molecules.
What happens when a protein is heated?
The forces of attraction from the hydrogen bonding are broken and the protein is denatured.
What happens when a protein is denatured?
It loses its shape.
What’s an example of a protein being denatured?
The white of an egg (albumen) - a globular protein and when heated the strands unwind as the hydrogen bonds are broken. New bonds form between the protein strands resulting in the change in colour and texture of the egg.
What chemicals give flavour to food?
Aldehydes and ketones.
What is the functional group in both aldehydes and ketones?
Carbonyl group, C=O
Are carbonyl compounds polar or non-polar? - Why?
Polar - they contain a dipole along the carbon-oxygen double bond creating a permanent dipole - permanent dipole attraction between the molecules.
Describe the boiling points of aldehydes and ketones.
Due to the permanent dipole - permanent dipole interaction, they have higher boiling points than the equivalent alkane (due to weaker London dispersion forces), but lower than the equivalent alcohol (due to stronger hydrogen bonding).
What’s an example of how volatile small aldehydes and ketones are?
Even gently warming them causes them to emit odours often associated with cooking certain foods.
Carbonyl compounds can form hydrogen bonds with water molecules meaning…
they are soluble (miscible) in water.
Out of aldehydes and ketones, which can be oxidised?
Aldehydes
What is formed when an aldehyde is oxidised?
A carboxylic acid
Which three oxidising agents can be used to distinguish aldehydes and ketones?
Acidified potassium dichromate
Fehling’s solution
Tollens’ reagent
What happens when acidified potassium dichromate reacts with an aldehyde?
Orange dichromate ions are reduced to green chromium (III) ions.
