oxidation of food Flashcards
What alcohols types can be oxidised?
primary and secondary alcohols can be oxidised by oxidising agents but tertiary alcohols can not oxidise.
Name examples of oxidising agents and there colour changes…
hot copper (II) oxide = black -> brown
acidified potassium dichromate = orange -> green
Tollen’s reagent = colourless -> silver
Fehling’s solution = blue -> brick red
What do primary alcohols form when oxidised?
Aldehydes
What do secondary alcohols form when oxidised?
Ketones
What is the functional group of aldehydes and ketones?
carbonyl (=O)
What is the positioning of the carbonyl group on an aldehyde?
At the end of the carbon chain.
What is the positioning of the carbonyl group on a ketone?
the carbonyl is in the middle of the carbon chain (carbon number must be specified when naming ketones), minimum 3 carbons.
Is it aldehydes or ketones which can oxidise?
Aldehydes
What do aldehydes form when oxidised?
Carboxylic acids
what is oxygen to hydrogen ratio change when an oxidation has occured?
oxidation occurs when there is an increase in oxygen to hydrogen ratio.
what is oxygen to hydrogen ratio change when a reduction has occured?
reduction occurs when there is a decrease in oxygen to hydrogen ratio.
What do carboxylic acids form when reduced?
Aldehydes and when reduced further, primary alcohols.
how do certain cooking methods affect flavour?
if molecules in food are polar then they are water soluble and can be lost from the food if cooked in water.
the same can be said about non-polar molecules in food that are cooked in oil.
What are many flavour/aroma molecules?
aldehydes and ketones
what happens when aldehydes oxidise to carboxylic acids in food?
The flavour and aroma can change resulting in food going spoiled as the carboxylic acids can give a very acidic taste.
What is a common method of preventing food oxidation?
antioxidants
What does the addition of antioxidants in food do?
it prevents oxidation and preserves the flavour in food.
What is another common problem in food spoilage?
the oxidation of edible oils
How is oil oxidation prevented?
Food will often be packaged in nitrogen atmospheres to minimise oxygen exposure.
Also antioxidants can be added to help prevent oils going rancid.
How do antioxidants work?
they prevent unwanted oxidation occurring; they will oxidise in place of the compounds they have been added to protect.
