Tests for digestive products

a mind map of various tests that you are often asked to recall in exams in a simple format

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  • Created by: Tiff
  • Created on: 16-12-12 19:24
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  • Tests - digestive products
    • Lipids
      • shake thoroughly
      • 2cm^3 sample + 5cm^3 ethanol --> test tube
      • + 5cm^3 water + shake gently
      • take comp. dry + grease-free test tube
      • cloudy white colour = lipid present
      • as a control, repeat with water instead of sample, final soln. should remain clear.
    • Protiens, "biuret test"
      • add few drops of v. dilute copper (II) sulphate soln.  + mix gently
      • add an equal amount of liquid sample and NaOH soln. --> test tube
      • colour change blue --> purple = protien present
    • Non-Reducing Sugars (disaccharides)
      • place in gently boiling water bath, 5 mins; any dissacharides would be hydrolysed
      • add equal amounts of another sample (l) to dilute HCL
      • slowly add some sodium hydrogencarbonate soln. (neutralises HCL, check with indicator paper)
      • first do test for reducing sugars, if none present:
      • retest the soln, by heating with 2cm^3 Benedicts' reagent  (wouldn't work in acidic conditions) in gently boiling water bath, 5 mins.
      • if a non-reducing sugar was present the colour will turn orange/brown
    • Starch
      • add 2 drops iodine soln. + shake/stir
      • 2cm^3 sample --> test tube if liquid, --> spotting tile if solid
      • colour change brown --> blue-black if starch present
    • Reducing Sugars (monosaccharides). "Benedicts' test"
      • Add equal amounts of sample (liquid) + Benedicts' reagent --> test tube
      • heat in gently boiling water bath, 5 mins
      • if colour change blue -->  red/brown, a reducing sugar is present. (it's a semi-quantitative test because degree of colour change depends on conc. of reducing sugar)
      • Non-Reducing Sugars (disaccharides)
        • place in gently boiling water bath, 5 mins; any dissacharides would be hydrolysed
        • add equal amounts of another sample (l) to dilute HCL
        • slowly add some sodium hydrogencarbonate soln. (neutralises HCL, check with indicator paper)
        • first do test for reducing sugars, if none present:
        • retest the soln, by heating with 2cm^3 Benedicts' reagent  (wouldn't work in acidic conditions) in gently boiling water bath, 5 mins.
        • if a non-reducing sugar was present the colour will turn orange/brown
  • Reducing Sugars (monosaccharides). "Benedicts' test"
    • Add equal amounts of sample (liquid) + Benedicts' reagent --> test tube
    • heat in gently boiling water bath, 5 mins
    • if colour change blue -->  red/brown, a reducing sugar is present. (it's a semi-quantitative test because degree of colour change depends on conc. of reducing sugar)

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