food tests Flashcards
(12 cards)
What reagent is used to test for reducing sugars?
Benedict’s solution.
How do you perform the Benedict’s test for reducing sugars?
Add Benedict’s reagent and heat in a water bath at 80–90°C.
What is a positive result for reducing sugars in the Benedict’s test?
Colour change from blue to green then yellow then orange and finally brick red precipitate.
What reagent is used to test for starch?
Iodine solution (iodine in potassium iodide).
What is a positive result for starch with iodine?
Colour change from brown/orange to blue-black.
What reagent is used to test for proteins?
Biuret reagent.
How do you perform the Biuret test?
Add Biuret reagent (NaOH and CuSO₄) to the sample.
What is a positive result in the Biuret test?
Colour change to purple/lilac.
What reagent is used to test for lipids?
ethanol
How do you perform the emulsion test for lipids?
Mix sample with ethanol, then add water and shake.
What is a positive result in the test for lipids?
A white, cloudy emulsion forms.
How do you test for non-reducing sugars?
First, hydrolyse the sugar by adding dilute hydrochloric acid and heating it in a water bath before neutralising with sodium hydrogen carbonate and then perform the benedict’s test
