Food Tests Flashcards
What does iodine test for?
Tests for starch, turning blue-black if present
What does ethanol test for?
With water it tests for lipids, giving a white emulsion if present
What does Benedict’s test for?
Test for both reducing and non-reducing sugars, giving a brick-red precipitate
Benedict’s for reducing sugars examples
Glucose, galactose, lactose, maltose and fructose
Benedict’s testing for sugars
Sucrose
Benedict’s test for reducing sugars method
Add equal volumes of Benedict’s solution to your samples, heat to 95°C, if reducing sugars are present a brick-red precipitate should form. If not then it remains the same colour, blue.
Benedict’s test for non-reducing sugars
Boil with hydrochloride acid to break the glycosidic bonds for 5 minutes, neutralise it using an alkali (sodium hydrogen carbonate), add equal volumes of Benedict’s to sample, heat to 95°C, if present a brick-red precipitate.
Why are they called reducing sugars?
Reducing sugars give an electron from a specific part of the molecule to the benedicts
What’s a colorimeter?
A device that is able to measure the amount of light absorbable and transmission from a substance, gives statistical data to make it a quantitive experiment.
What does a low concentrated substance give in a colorimeter?
Low concentration -> More light passes through means a high absorption but a low transmission
What result does a high concentrated substance give in a colorimeter?
High concentration -> Less light passes through means low absorbance but a high transmission
What does quantitative data mean?
Numerical data
What does qualitative data mean?
Non-numerical data
Method to make benedicts test quantitive
Filter the solution, the dry/evaporate to get a powder. Find the mass by weighing it
Precautions in the practical
Using safety google and washing hands often as Benedict’s is an irritant
