biological tests Flashcards
lipids
Crush the food sample and place in a dry test tube.
- Add ethanol to about 2 cm3 above the level of the sample and shake thoroughly.
- Allow the solid to settle (about 3 min) to allow the lipid to be extracted.
- Decant the ethanol into another test tube.
- Add 2 cm3 of deionized water to the second test tube
- Make observations.
Solution remains colourless. No emulsion is formed=Lipids are not present
A layer of cloudy white suspension=Lipids are present
proteins
Used to determine the presence of peptide bonds.
Biuret reagent contains
Hydrated Copper sulphate, Potassium hydroxide solution, Potassium sodium tartrate.
If it is purple. Then there is a protein.
starch (reducing sugar)
benedict’s reagent (copper(II) sulphate, sodium carbonate, sodium citrate)
Add 2 cm3 of the sample solution to a test tube.
• Add an equal volume of Benedict’s solution to the test tube and swirl or vortex the mixture.
• Leave the test tube in a boiling water bath for about 5 minutes, or until the colour of the mixture does not change.
• Observe the colour changes during that time as well as the final colour.
• To prepare a control, repeat the steps above using 2 cm3 of distilled water instead of sample solution
Brick-red= high trace of reducing sugars
starch (non-reducing sugar)
don’t contain aldehyde group.
•Add 2 cm3 of the sample solution to a test tube.
•Add 1 cm3 of dilute hydrochloric acid and boil for one minute.
•Allow the tube to cool and then neutralize the acid with sodium hydrogen carbonate. Exercise caution due to ‘fizzing’ or effervescence.
then do reducing sugar test
•Leave the test tube in a boiling water bath for about 5 minutes, or until the colour of the mixture does not change.
•Observe the colour changes during that time as well as the final colour.
•To prepare a control, repeat the steps using 2 cm3 of distilled water instead of sample solution
carbohydrate
add iodine, check for colour change.
