Food tests (Practical)
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31 Terms
What is the benedicts test used for
Sugars
What is the biuret test used for
Proteins
What is the iodine test used for
Starch
What is the Sudan III test used for
Lipids
What is the first step in preparing a food sample
Get the food and break it down using a mortar and pestle
What do you do after crushing the food
Put the crushed food in a beaker with distilled water
Why do you stir the mixture
To dissolve some of the food in the water
How do you separate the solid from the liquid
By using a funnel lined with filter paper
What is the final solution used for
Food sample
What can sugars be split into as
Reducing sugars
Non-reducing sugars
What does the benedict test only test in terms of sugars
Reducing sugars
What is the first step in the Benedict’s test
Prepare the food sample and transfer 5cm³ of it into a test tube
What temperature should the water bath be at
75 degrees celsius
What do you add to the test tube
10 drops of Benedict’s solution
How long should the test tube be heated for
5 minutes in water bath
What colour indicates no reducing sugars
Blue
What colour changes show reducing sugars are present
Green, yellow, or red (depending on concentration)
How much food sample do you need for an iodine test
5cm³
What do you add to the sample
Iodine solution
What is the initial colour of the solution
Brown-Orange
What indicates the presence of starch
Colour changes to blue-black
How much food sample and reagent do you need? (Biuret)
2 cm³ of food sample + 2 cm³ of Biuret solution
What does the biuret solution initially do
Turns blue when added to the sample
How do you detect protein
Shake gently; if protein is present, it changes to purple/pink
What chemicals make biuret solution work
: Potassium hydroxide (KOH) + copper sulfate (CuSO₄)
How much food sample do you need for the Sudan III test
5cm³
Do you need to filter the solution for Sudan III
No
How do you test for lipids with Sudan III
Add three drops of Sudan III stain solution
Shake gently
What indicates lipids are present
A bright red layer forms on top
How do you peform the emulsion test
Add 2 cm³ ethanol to the food, shake vigorously, then add to 2 cm³ distilled water
What indicates lipids in the emulsion test
The solution turns cloudy white
