2.7 oxidation of food Flashcards
What is oxidation in a carbon compound?
increase on the oxygen to hydrogen ratio
what is reduction in a carbon compound?
decrease in the oxygen to hydrogen ratio
What can hot copper(II) oxide or acidified dichromate(VI) solutions be used to oxidise?
- primary alcohols->aldehydes->carboxylic acids
- secondary alcohols-> ketones
What happens to hot copper(II) oxide and dichromate (VI) solutions when oxidising primary and secondary alcohols?
copper(II)oxide
-black->brown solid
dichromate(VI)solution
-orange->green
explain the use of hot copper(II) oxide and dichromate (VI) solutions on tertiary alcohols
- tertiary alcohols are not readily oxidised
- they cannot be oxidised using these oxidation agents
What is the functional group in aldehydes and keynotes?
carbonyl >C=O
what happens to aldehydes when oxidised?
oxidised to carboxylic acids
what happened to ketones when oxidised?
they can’t be oxidised to carboxylic acids. They are not readily oxidised
What is the reaction of blue Fehling’s solution with an aldehyde?
-brick red precipitate
what is the reaction of Tollens’ solution with an aldehyde?
-colourless/clear–>silver mirror
what is the reaction of acidified dichromate solution when there is an aldehyde present?
-orange->green
What causes the oxidation of food?
oxygen in the air
What happens when edible oils are oxidised
it gives food a rancid flavour
What are antioxidants?
-molecules that prevent unwanted oxidation reactions occurring
-substances that are easily oxidised
-oxidise in place of the compounds they have been added to protect
-they can be identified as the substance being oxidised in a redox equation
(preserving flavour in foods)
How do antioxidants work?
-they are substances that are easily oxidised, they oxidise in place of the compounds they haven been added to protect
What is the difference between and aldehyde and a ketone?
the carbonyl functional group is on an end carbon in an aldehyde and an intermediate carbon in a ketone.
What is an isomer?
compounds with the same molecular formula but different structural formula
What 3 oxidising agents can be used to differentiate between and aldehyde and a ketone?
- acidified potassium dichromate solution
- Fehling’s solution
- Tollens’ reagent
What can aldehydes be used for?
flavour and aroma molecules
What is produced when primary alcohols are oxidised?
aldehydes
What is produced when secondary alcohols are oxidised?
ketones
What is produced when aldehydes are oxidised?
carboxylic acids
What are 3 oxidising agents used to distinguish between aldehydes and ketones?
- acidified potassium dichromate solution
- Fehling’s solution
- Tollens’ reagent
describe the reduction of carboxylic acids
carboxylic acid–>aldehyde–>primary alcohol
Explain how different cooking methods can alter the flavour and nutritional value of foods?
- polar groups are soluble in water
- if the vitamin is polar then cooking the food in water will remove the vitamin value from the food
- non-polar groups do not dissolve in water and therefore by cooking non-polar molecules in water, the molecules do not dissolve
What functional groups are polar?
- OH
- C=O
- COOH
- NH2
- CONH
What happens when aldehydes are oxidised in foods?
they produce carboxylic acids
-the food becomes spoiled and can have a very acidic taste (due to the carboxylic acids)
How do food manufactures prevent oxidation of foods?
- packages in an atmosphere of nitrogen
- addition of antioxidants
What are flavour and aroma molecules in food often?
aldehydes and ketones
What is the volatility of a flavour compound determined by?
its structure
