2.2 Food Tests Flashcards
Iodine Test for Starch
- Place sample in test tube
- Add iodine
Positive- blue-black
Negative- Orange-yellow
Biuret Test for Proteins
- Place sample in test tube
- Add equal volume of biuret solution (made of sodium hydroxide and copper sulphate solution)
- Mix by swirling
Positive- Lilac (purple)
Negative- no change
Emulsion Test for Lipids
- Crush substance
- Add to test tube with ethanol
- Filter ethanol into test tube with cold water
- Discard the solid residue
Positive- Milky emulsion
Negative- no change
Benedict’s Test for Reducing Sugars
e.g Glucose, fructose, most sugars
- Add substance to a test-tube
- Add same volume of Benedict’s solution
- Heat to 80°C in a water bath
Positive- Blue to green to yellow to orange to red
Negative- no change
Benedict’s Test for Non-Reducing Sugars
- Negative reducing sugar test
- Add hydrochloric acid
- Heat in a water bath
- Cool the test tube and add sodium hydrogencarbonate
- Repeat Benedict’s test
Positive- Positive to Benedict’s
Negative- no change
Colorimeter
- A colorimeter shines light through a sample
- Photoelectric cell picks up light
- Place solution of sample in a chamber between the light and the cell
- More light = less reducing sugar
Colorimeter using Benedict’s reagent
-Do a Benedict’s test on known concentration of sugar
- filter precipitate
- do colorimeter test
- calibration curve
- test on unknown sample
- read off graph to find concentration
Lipid
Positive = white emulsion
Protein
biurets reagent
Starch
positive = blue-black
Reducing sugar
- use heat
- Benedict’s reagent
Non-reducing sugar
- use heat
- Benedict’s reagent
- Boil with acid
Chromatography
used to separate mixtures into their biological molecules
stationary phase
Chromatography paper or TLC plate
what is chromatography paper made out of?
cellulose
