biochemical tests

Question 1

reducing sugar test + positive result + explain colour changes

Answer 1

-reducing sugars = monosaccharides (glucose), also, maltose and lactose

METHOD

-add benedict’s reagent (blue) to a sample
-heat it in a boiling water bath for 5 minutes
-positive result: solution changes from blue, green, yellow, orange to brick red

-the further the colour change goes (the more red) the higher the concentration of reducing sugar - compare amounts of reducing sugar in different solution

Question 2

non reducing sugar method + positive result

Answer 2

on reducing sugars = sucrose

METHOD
-do benedicts test and if it stays blue (negative result) then carry out this test:
-add hydrochloric acid (to break them down into monosaccharides) and heat it in a boiling water bath for 5 minutes, in order to hydrolyse into reducing sugars
-neautralise it with an alkali (e.g. sodium carbonate)
-carry out the benedict’s test for a reducing sugar: (adding benedict’s solution and heating it in a boiling water bath for 5 minutes)

POSITIVE RESULT: solution changes from blue to brick red

-NEGATIVE RESULT: the solution will stay blue which means it doesn’t contain any sugar (either reducing or non reducing)

Question 3

test for starch + positive result

Answer 3

METHOD
-add iodine in a potassium iodide solution to the test sample

POSITIVE RESULT
-the solution will change from orange to blue/black

Question 4

test for lipid + positive result

Answer 4

-using emulsion test
-add ethanol, then add water
-POSITIVE RESULT: clear to white/milky

Question 5

test for proteins + positive + negative result

Answer 5

-use the biuret test
-(test solution must be alkaline) add biuret reagent sodium hydroxide
-then add copper (II) sulfate solution

-POSITIVE RESULT: blue to purple/ lilac
-NEGATIVE RESULT: no colour change, stays blue