Tag: simple test for nutrients

Iodine test is used to distinguish between the presence of starch and glycogen and other saccharides.
When starch solution is treated with iodine, it gives a blue color. The blue color develops because of the trapping of iodine in the helical coils of amylose. When this test solution is heated, the color disappears due to disruption of the helical coils of amylose and the color reappears upon cooling, due to the reformation of helical coils. Glycogen however gives red color with iodine.
Therefore, the correct answer is option B.

• Raw potato contains approximately 17% starch. when iodine solution added to the raw potato sample, it turns blue-black. Iodine reacts with the starch present in the raw potato which results in the formation of blue-black colored complex. 

When two drops of copper sulphate and ten drops of caustic soda or NaOH is added to egg, it turns violet. This indicates the presence of proteins.
This is Biuret's test and the principle is simple as follows:
In the presence of alkaline medium (caustic soda or NaOH), the Cu2+ ions get reduced to Cu+ and binds to the egg proteins, thereby giving a violet color.
Therefore, the correct answer is option B.

Shake or crush the food to make it dissolve. Filter or dilute the food and ethanol mix so that you get a clear liquid (a solution of fat in ethanol). Add this to a test tube of water. A white (milk-like) emulsion indicates the presence of fats or oils.

The iodine test is used to test for the presence of starch. Iodine dissolved in an aqueous solution of potassium iodide reacts with the starch, producing a purple-black colour. The intensity of the colour decreases with increasing temperature and with the presence of water-soluble organic solvents, such as ethanol.

A chemical test for starch is to add iodine solution (red) and see if it turns blue/black in colour. It is possible to distinguish starch from other carbohydrates using this iodine solution test. For example, if iodine is added to an peeled potato then it will turn black. 

The Biuret test is a chemical test used for detecting the presence of peptide bonds. In the presence of peptides, a copper (II) ion forms violet-coloured coordination complexes in an alkaline solution. The Biuret reaction can be used to assess the concentration of proteins because peptide bonds occur with the same frequency per amino acid in the peptide. 

If an animal needed to store energy for long-term use, but not be encumbered with the weight of extra tissue, then high-calorie fat molecules are the best molecules for storage. So, the correct answer is "high-calorie fat molecules".