Experiments on digestion and food tests

Nutrients are important elements present in food for proper development and growth of the body.

There are specific tests for each kind of nutrient. These tests help to identify the presence of enzymes or nutrients in a food substrate.

Salivary amylase present in saliva converts starch into maltose.

Pepsin digests protein only when it is acidic. Pepsin does not act in alkaline medium. Boiled pepsin fails to digest protein, as it is destroyed by heat.

The change in colour of Fehling’s solution from blue-green colour to deep brick red with a precipitate confirms the presence of glucose in food stuff.

When the sucrose is boiled with dilute HCl and neutralized with sodium bicarbonate, it responds to sugar test and gives positive result.

Starch can be detected by iodine solution. The starch solution turns blue-black on the addition of a few drops of iodine solution.

The change in color of ammonium hydroxide from yellow to orange confirms the presence of protein.

Food material such as ground nut, walnut, etc. contain oil. Whenever food containing fat and oil is rubbed against paper, it leaves patches on it. The paper is able to pass light through the patch, therefore, making it translucent. It indicates the presence of fats and oils in the food stuff.

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  • Q1

    On adding a few drops of concentrated nitric acid on crushed food and then heating, colour of food turns yellow, it indicates the presence of

    Marks:1
    Answer:

    proteins.

    Explanation:
    It is a test for detecting the presence of proteins in the food.
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  • Q2

    Starch is a kind of

    Marks:1
    Answer:

    carbohydrate.

    Explanation:
    Starch is made by repeated units of glucose and is a carbohydrate.
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  • Q3

    Starch is tested with the solution of

    Marks:1
    Answer:

    iodine.

    Explanation:
    In the presence of iodine, starch gives a blue black colour.
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  • Q4

    White portion of an egg turns orange after the addition of ammonium hydroxide. This indicates the presence of___.

    Marks:1
    Answer:

    proteins.

    Explanation:

    Initially, a change in colour from white to yellow takes place due to the addition of dilute nitric acid. After addition of ammonium hydroxide, the colour changes from yellow to orange.
    .

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  • Q5

    The food item that turns blue-black with iodine solution is

    Marks:1
    Answer:

    raw potato.

    Explanation:
    Iodine turns the starch color to black, which is carbohydrate. Raw potato will turn to blue-black in color as it is a rich source of starch.
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