Food testing is routinely carried out in senior biology classes. Students test a variety of food samples for carbohydrates, such as sugar and starch; lipids; proteins and vitamin C. In response to this question we have developed an information sheet. See Laboratory Notes: Food Tests
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?
Positive Test Results for
Test 1: Glucose
When you add Bendeict’s solution, the solution turns blue.
As it heats the colour changes from
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.
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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