Biochemical Food Tests Flashcards
What biochemical test do you carry out for reducing sugars (all monosaccharides)
Benedict’s test
How do you carry out Benedict’s test for reducing sugars
Add benedict’s solution to each test tube containing unknown solution
heat all solutions in test tubes in water bath
positive result = red, negative = blue
What biochemical test do you carry out for non-reducing sugars (all disaccharides except maltose and lactose)
Benedict’s test
How do you carry out Benedict’s test for non-reducing sugars
first carry out the test for reducing sugars: add benedict’s solution to each test tube, and heat in water bath
add HCl to test tubes that tested negative (blue) for reducing sugars
heat test tube containing solution
add sodium hydrogencarbonate
add benedict’s solution
heat
positive = red
negative = blue
explain why a non-reducing sugar test can only be carried out on a solution that tests negative for a reducing sugar
If the test is positive for reducing sugar, the solution would turn red. If it is positive for a non-reducing sugar, the solution would also turn red. So you would not be able to tell if the solution contains a reducing or non-reducing sugar
What biochemical test do you carry out for starch
iodine test
How do you carry out an iodine test for starch
add iodine to each test tube containing unknown solution
NO HEAT
positive = blue/black
negative = iodine colour
What biochemical test do you carry out for protein
biuret’s test
how do you carry out a biuret’s test for protein
add 3 drops of biuret reagent to each test tube
NO HEAT
positive = purple
negative = blue
What biochemical test do you carry out for lipids
emulsion test
how do you carry out an emulsion test for lipids
add ethanol to the test tube containing unknown solution
plug the test tube and shake well
pour solution into test tube containing water
positive = cloudy white emulsion forms
negative = no emulsion forms
