Carbohydrates provides energy to cells in the body. Protein is the major functional and structural component of all the cells of the body. Fats and oils are the highest energy sources contain fatty acids which is essential for health which is not produced by the human body.
To detect the presence of carbohydrates, fats and proteins in the given food stuffs.
The presence of carbohydrates, fats and proteins in any food stuff is detected by performing the tests for proteins, fats and carbohydrates with the extract of the foodstuff. The advantage is these tests do not interfere with each other.
Test for Carbohydrates:
- Molisch’s test – Given sample food + Molisch’s reagent → Purple or violet ring confirms the presence of carbohydrate.
- Fehling’s test – Given sample food + Fehling’s reagent → Red precipitate confirms the presence of carbohydrates
- Benedict’s test – Given sample food + Benedict’s reagent → Red precipitate confirms the presence of carbohydrates.
- Tollen’s test – Given sample food + Tollen’s reagent → Silver mirror confirms the presence of carbohydrates.
- Iodine test – Given sample food + Iodine solution → Blue colour solution confirms the presence of starch.
Test for Proteins:
- Biuret test – Given sample food + Aqueous copper sulfate → Violet colouration confirms the presence of Proteins
- Xanthoproteic test – Given sample food + Nitric acid → Yellow colour solution confirms the presence of proteins.
- Millions test – Given sample food + Mercuric sulfate in the presence of sodium nitrite and sulfuric acid → Brick red colour solution confirms the presence of proteins.
- Ninhydrin test – Given sample food + Pyridine solution of ninhydrin → Violet colour solution confirms the presence of proteins.
Test for Oils and Fats:
- Solubility test – Given sample food + Chloroform or alcohol → Miscible with chloroform and immiscible with water the fat presence is confirmed.
- Translucent spot test – Given sample food + rubbed between the folds of filter paper → presence of translucent spot then the presence of fats is confirmed.
- Acrolein test – Given sample food + Potassium bisulfite KHSO4 → Pungent irritating odor then the presence of fats or oil is confirmed.
- Molisch’s reagent
- Fehling’s reagent
- Benedict’s reagent
- Tollen’s reagent
- Iodine solution
- Copper sulfate solution
- Sodium hydroxide
- Nitric acid
- Mercuric sulfate
- Sodium nitrite
- Filter paper
- Potassium bisulfate
- Concentrated hydrochloric acid
- Furfural solution
- Test tubes
- Test tube holder
- Water bath
- Bunsen burner
To test the presence of carbohydrates, proteins, fats and oils in the given food sample, first the extract of the given foodstuff should be prepared. Dry the given foodstuff in the mortar with a pestle or by boiling with minimum quantity of water extracting with a small quantity of an organic solvent after grinding the foodstuff.
Some of the examples of preparing extract of food stuff is given below.
- For potatoes – cut to slices and boil with water.
- For butter – test directly
- For grapes – Extract the juice.
- For boiled egg – take the white portion grind and shake with water.
Observation and Inference:
|Food stuff||For carbohydrates||For proteins||For oils and fats|
Results and Discussions:
The given food sample contains _________ (carbohydrates/ proteins/ fats).
- Always use minimum quantity of reagents and freshly prepared ones to test the sample food.
- Use droppers to take the reagents from the bottle.
- Use lab aprons and hand gloves during the experiment.
1. Mention the major types of carbohydrates.
Ans: The main types of carbohydrates are monosaccharides, disaccharides and polysaccharides.
2. Name the bond which holds the monomer units of proteins together?
Ans: Peptide bond are the bonds which hold together the monomer units of proteins.
3. What is called denaturation of proteins?
Ans: Denaturation of proteins involves both secondary and tertiary structures being disrupted and potentially destroyed. Because denaturation reactions are not strong enough to break peptide bonds, after a denaturation process, the primary structure (amino acid sequence) remains the same.
4. Name some of the food source rich in carbohydrates?
Ans: Milk, ice cream, yogurt, fruit, whole juice of fruits and grains. Bread, rice, cereal, crackers. Legumes. Beans and other proteins based on plants. Vegetables that are starchy. Maize and potatoes. Sugary candy. Limit it! Soda, sweets, cookies, desserts, etc.
5. What is the colour of precipitate formed if millon’s reagent is added to food solution having proteins?
Ans: Yellow colour precipitate is formed when millon’s reagent is added to food solution having proteins.
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