food tests Flashcards
What is iodine used for and what is the colour change
To see if starch is present, it will change from orange to blue-black
What is benedict’s solution used to test for and what will be the colour change
To test for sugars, it will change from blue to green/yellow
but if the amount of sugar is high it will turn red/orange
What is biruets reagent used to test for and what is the colour change
To test for proteins it will go from blue to purple
What do we use to test for lipids
Ethanol, it will go from clear to cloudy/milky white
What is the test for sugars (whole explanation)
Get food sample by breaking up the food with mortar and pestle and put it in a beaker with distilled water and stir it with a glass rod until it dissolves.
Add a few drops of benedict’s solution into the sample and place it in a 75 degree water bath for 5 minutes
If sugars are present it will change to green, yellow or even brick red. If sugars aren’t present it will stay blue.
What is the test for starch
Add 5cmcubed of your food sample and add a few drops of iodine.
This will turn it orange.
Then shake the test tube, if it turns from orange to blue-black, it contains starch
How do we test for proteins (full explanation)
Add two cm cubed of your sample to a test tube.
Add 2cm cubed of buirent solution to your sample, turning it blue.
Add potassium hydroxide and copper sulphate.
If the food sample did contain protein it would change from blue to purple.
How do we test for lipids (full explanation)
add 2cm cubed of ethanol to the food sample and shake it vigorously then add 2cm cubed of distilled water
If it goes a cloudy white colour lipid is present, if it stays the same it means lipid isn’t present.
