2.2 Food Tests Flashcards
What are the two types of sugar?
Reducing and non reducing
What is the process of the test for reducing sugars?
- Add Benedicts reagent
- heat in water bath that has been brought to boil
What colour is Benedicts reagent?
Blue
If the test is positive what will happen?
A coloured precipitate will form
What is the colour change of the precipitate?
Blue > green > yellow > orange > brick red
What happens the higher the concentration of the precipitate?
The further the colour change
What does the colour change indicate?
The presence of a reducing sugar
How can you compare the amount of reducing sugar in different solutions?
Compare the colour changes in both
What is a more accurate way of comparing the amount of reducing sugar in solutions?
Weighing the precipitate
If the test for reducing sugars is negative what could there still be?
A non reducing sugar present
What do you have to do to test for non reducing sugars?
Break them down to monosaccharides
How do you break them down to monosaccharides?
By getting a new sample of solution
Adding dilute hydrochloric acid
Heat in water bath
What do you neutralise the solution with?
Sodium hydrogen carbonate
What is the test for sugars?
Benedicts test
What do you do after neutralising in the test for non reducing sugars?
Carry out the Benedicts test again
If the test is positive why will happen?
A colours precipitate will form
If the test is negative what will happen?
The solution will stay blue meaning it doesn’t contain any sugar
What do you use to test for glucose?
Test strips dipped in reagent
What happens to the colour strips?
They change colour of glucose is present
What is the test for starch?
Iodine test
What does the iodine test involve?
Adding dissolved potassium iodide solution to the test sample
If starch is present what happens to the sample?
It changes from browny orange to blue black
What does the biruet test test for?
Proteins
What is the first stage of the biuret test?
Add a few drops of sodium hydroxide to make the solution alkaline
What is the second stage of the biuret test?
Add some copper sulfate solution
If a protein is present what will happen?
Solution turns purple
What does emulsion test test for?
Lipids
What do you do in the emulsion test?
Shake the test substance with ethanol for a minute then pour the solution in water
If a lipid is present-
Solution turns milky
