Food tests: glucose, starch and gelatine solutions

Food tests: glucose, starch and gelatine solutions: I have to make up solutions for a prac where students are working out if select foods are a protein, carbohydrate or sugar. I have a couple of questions. I have made a 1% glucose mix, will that be enough or does it have to be stronger? Also can someone give me a good recipe for making up a starch solution? Again not sure how concentrated it needs to be? 

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Publication Date: 03 August 2018
Asked By: Anonymous
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Food tests: glucose, starch and gelatine solutions

Positive Test Results for

Test 1:  Glucose

When you add Bendeict’s solution, the solution turns blue.

As it heats the colour changes from

Blue
Green
Yellow
Tomato Red at the end

NOTE: When starch is heated it also breaks down to a simple sugar and so shows a  positive result.

Test 2:  Fat/Oils

When the oil has been rubbed into the brown paper, if you hold it up to the light it should be translucent.

Test 3:  Starch

After the Iodine - I2/KI has been added the starch solution should be coloured anywhere from purple through to black.

Test 4:  Protein

No colour change should occur when the sodium hydroxide – NaOH is added.

After the copper sulfate – CuSO4 is added it should change from light blue to dark blue to purple.

Foods:

To avoid contamination make sure the students cut each piece of        

food up in a different area on the cutting board.     Also make sure they wash the knife after each food.

Preparations of Solutions:

Keep in fridge until required for use. Then return when finished.

Glucose: Dissolve 1 teaspoon of glucose in 200ml of water. (Do not use sugar)

Protein: Dissolve ¼ teaspoon of gelatine in 200ml of water. Heat to nearly boiling to dissolve.

Starch:   Dissolve 1 teaspoon of powdered starch in 200ml of water. Heat to boiling to dissolve. 

                    If you do not heat, the solution will remain cloudy.

 

Egg White: Use raw. Beat egg white with 100ml water. Store in small dropping bottles.

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