2.7 Oxidation of Food Flashcards
What are the 3 types of oxidation
- Loss of electrons
- Gain of oxygen
- Loss of hydrogen
What does oxidation always result in
An increase in the oxygen to hydrogen ratio
When oxidation is occurring what is also occurring
Reduction
Name 3 oxidising agents
Acidified sodium dichromate
Potassium permanganate
Copper (II) oxide
What are the only types of alcohols that can oxidise
Primary and Secondary
What happens when potassium permanganate is reduced
Purple permanganate ion turns to colourless Mn2+ ions
What happens when sodium dichromate is reduced
Orange dichromate ion turns to green Cr3+ ions
What happens when hot copper oxide is reduced
Black oxide turns to reddish copper metal
What happens when primary alcohols are oxidised
It forms an aldehyde
What happens when you oxidise a secondary alcohol
It forms a ketone
What is the functional group for aldehydes and ketones
Carbonyl group
Where is the carbonyl group in an aldehyde
At the end of the carbon chain
Where is the carbonyl group in a ketone
It is attached` to other carbon atoms
What is the general formula for aldehydes and ketones
CnH2nO
What compounds can Acidified potassium dichromate oxidise
Primary and Secondary alcohols
What is the colour change for acidified potassium dichromate
Orange > blue/green
What compounds will Fehling’s solution oxidise
Only aldehydes
What is the colour change for Fehling’s solution
Blue > orange/red
What compounds will Tollens reagent oxidise
Only aldehydes
What is the colour change for Tollens reagent
Colourless > silver mirror
What is a useful way of determining weather oxidation has occurred
Calculating the oxygen to hydrogen ratio (It decreases when oxidation has occurred)
When cooking vegetables how is flavour released
Flavour is usually trapped inside the cell wall, cooking damages the cell wall letting it out
Give two examples of aldehydes of ketones used in food
Limonene and Vanillin
What can happen when vitamin C is cooked in water
Since vitamin C is polar, it may dissolve in the water
Why should something be cooked in a solvent that is the opposite of its polarity
So the flavour molecules do not dissolve
What happens when proteins are heated during cooking
They denature, allowing them to change shape
Give an example of a protein that denatures when cooking meat
Collagen
When can oxidation of food occur
When food is exposed to oxygen in the air
What kind of foods are at the greatest risk of oxidisation
Foods containing fats or oils
How can oxidation of food be avoided
Packing it with nitrogen, an inert gas that will not react with the food
Name effects of oxidisation on food
Loss of colour
Deterioration of flavour
Loss of nutritional value
What is an antioxidant
A substance that slows down or prevents the oxidation of another chemical
What type of agent are antioxidant molecules
Reducing agents
What can oxidation reactions produce
Free radicals
How can free radicals damage food
By removing electrons
How does an antioxidant cancel a free radical
The antioxidant donates an electron and stabilises the free radical as a stable electron pair is formed. The antioxidant itself is then oxidised
Give an example of an antioxidant
Vitamin C
