Biochemical Tests Flashcards
test for reducing sugars
Benedict’s reagent
original colour of Benedict’s reagent
blue liquid
what is the name reducing sugar given to
sugars that can reduce Cu2+ ions in Benedict’s reagent to Cu+ ionsin the form of copper (I) oxide
what colour does a positive Benedict’s test turn
brick red
procedure for testing for a reducing sugar
1- add Benedict’s reagent to sample
2-heat
3-if colour change observed then reducing sugar present
4-if solution remains blue, no reducing sugar
why is sucrose a non reducing sugar
-it cannot reduce cu2+
-because the chemical group needed for the reduction is involved in glycosidic bonds between the monosaccharides
how can sucrose be proven to still be a sugar
the glycosidic bond must be hydrolysed to expose the reducing group
procedure for testing for non reducing sugars
-complete Benedict’s test
-mix with HCL and boil
-cool the solution and add sodium hydroxide to make the solution alkaline
-add a few drop of Benedict’s and heat
what are the different colours a Benedict’s test can turn
yellow/green/red
why is the non reducing sugar mixed with hcl and boiled
-to break the glycosidic bond so it has hydrolysed to its monomers
why is the non reducing sugar solution cooled and sodium hydroxide solution added
-benedicts only works in alkaline solutions
-cooling prevents excessive fizzing
why must a few drops of Benedict’s reagent be added and the non reducing sugar solution heated
-to observe a colour change to identify if a non reducing sugar is present
what does the colour indicate in a non reducing sugar test
a rustier red suggests a higher sugar concentration as copper oxide has been formed
how is starch presence tested
-adding a few drops of iodine
original colour of iodine
orange/brown
