Food tests / PAG 9 Flashcards
(21 cards)
what food test tests for starch?
Iodine
what colour does iodine turn if starch is present?
turns blue/black
what colour is iodine when starch is not present?
orange/brown
what food test tests for protein?
biuret test
what colour does biuret test turn when protein is present?
lilac/purple
what colour is biuret originally?
blue
what food test tests for reducing sugars?
benedict’s reagent
what is the difference between reducing and non-reducing sugars?
reducing sugars: can reduce copper sulphate into copper oxide.
non-reducing sugars: can not reduce copper sulphate into copper oxide.
what are the reducing sugars?
glucose, fructose, galactose, lactose, and maltose
what are the non-reducing sugars?
sucrose
what food test tests for non-reducing sugars?
Acid
how does acid test of non-reducing sugars?
acid hydrolysis
what colour will the acid turn if non-reducing sugars are present?
turns from blue, to red/orange
what food test tests for lipids?
ethanol emulsion test
how does the emulsion test work?
it is mixed with alcohol which dissolves the lipid. the solution is then mixed with water
when a lipid is present, what happens?
a white emulsion forms (Not precipitate) and lipids form droplets in the water
how do you use iodine to test for starch?
- add iodine solution to sample and look for a colour change
how do you use biuret to test for proteins?
- add biurets to the solution and look for a colour change
how do you use ethanol to test for lipids?
- add ethanol to the solution and shake thoroughly
- add water and look for a colour change
how do you use benedict’s solution to test for reducing sugars?
- add benedict’s to the solution
- heat for 2 minutes in a water bath at boiling temperatures.
