Biochemical Tests Flashcards
How do you test for starch?
Add iodine solution to the sample.
What is a positive result from testing for starch?
The solution turns from orange to blue/black.
How do you test for reducing sugars?
Benedict’s reagent is added and the solution is heated.
What is a positive result from testing for reducing sugars?
The solution turns from blue to either green, yellow, orange or brick red depending on the amount present (more red=more present).
What are all monosaccharides?
Reducing sugars.
How do you test for non-reducing sugars?
Use the Benedict test to work out if the sugar is reducing. If it’s not, add acid and boil the solution. Cool it and add an alkali, then retest the Benedict test.
Why do we use the Benedict test in the test for non-reducing sugars?
To see if monosaccharides hydrolysed from a non-reducing sugar are present.
Why do we add acid and boil the solution in the test for non-reducing sugars?
For acid hydrolysis which converts the sugar into its monosaccharides.
Why do we add an alkali to the solution in the test for non-reducing sugars?
To neutralise the solution as Benedict’s reagent won’t work in acidic conditions.
What is an example of a non-reducing sugar?
Sucrose.
How do we test for proteins?
Biuret solution is added to the sample.
What is a positive result from testing for proteins?
The solution turns from blue to lilac/purple.
How do we test for lipids?
We add ethanol to the solution, shake it up to dissolve it, then add distilled water and shake again.
What is a positive result from testing for lipids?
A white cloudy emulsion forms.
