biochemical tests Flashcards

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1
Q

name of test for reducing sugars

A

benedicts ONLY

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2
Q

name of test for non-reducing sugars

A

benedicts test + with other steps

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3
Q

name of test for starch

A

iodine

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4
Q

name of test for proteins

A

biurets

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5
Q

name of test for lipids

A

emulsion test

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6
Q

colour change with benedicts (reducing sugars)

A

blue -> brick red

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7
Q

colour change with biurets

A

blue -> purple

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8
Q

colour change benedicts AT THE END of non-reducing sugars

A

blue -> brown/orange

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9
Q

colour change with emulsion test

A

cloudy - white layer

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10
Q

method for iodine test

A
  1. Add 2cm3 of sample
  2. Add 2 drops of iodine
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11
Q

method for reducing sugars

A
  1. Ground sample into water
  2. Add benedicts solution
  3. Heat in water bath
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12
Q

colour change with iodine

A

orange -> blue/black

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13
Q

method for biurets

A
  1. Ground sample into water and place in test tube
  2. Add equal volume of NaOH at room temp
  3. Add a few drops of CuSO4 (very very dilute!!!) and mix gently
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14
Q

method for emulsion test

A
  1. Add 2cms of sample and 5cm3 of ethanol
  2. Shake thoroughly to dissolve lipid
  3. Add 5cm3 of water and shake
  4. Milky/white emulsion should be seen
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15
Q

method for non-reducing sugars

A
  1. Ground sample to water and add 2cm3 of sample to 2cms of benedicts
  2. heat in water bath for 5 minutes
  3. Add 2cms food sample to 2cm3 of dilute HCl, place in water bath for 5 mins
  4. add sodium hydrogencarbonate to neutralise pH (test with pH paper)
  5. Re-test with 2cms benedicts in boiling water bath
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16
Q

why do you add dilute HCl if there is no colour change with biurets

A

dilute HCl contains water, therefore it will hydrolyse disaccharides back into monosaccarides

17
Q

why should you add sodium hydrogen carbonate to solution before benedicts again

A

sodium hydrogen carbonate is alkaline therefore will neutralise the solution as benedicts doesn’t work in acidic conditions

18
Q

exam q
A biochemical test for reducing sugar produces a negative result with
raffinose solution.
Describe a biochemical test to show that raffinose solution contains a
non-reducing sugar. (3)

A

Heat with acid and neutralise;
Heat with Benedict’s (solution);
Red precipitate/colour;
Accept other colours eg orange/ brown/green

19
Q

exam q
there is a solid precipitate produced after benedicts
Suggest a method, other than
using a colorimeter, that this student could use to measure the quantity of
reducing sugar in a solution. (2)

A

Filter and dry (the precipitate);
2. Find mass/weight;