Chemistry Experiment: Tests of Carbohydrates Fats and Proteins in Pure Samples and Detection of Their Presence in Given Food Stuffs
Carbohydrates provide energy to your brain, kidneys, heart muscles, and nervous system. Fibre, for example, is a carbohydrate that aids digestion, makes you feel full, and helps keep blood cholesterol levels in check. Proteins are the building blocks of living tissues and are coded for by our genes. They are also important in biological processes.
Proteins, for example, catalyse reactions in our bodies, transport molecules like oxygen, keep us healthy as part of the immune system, and communicate messages from cell to cell. Fats also aid in the transport of fat-soluble vitamins such as A and D. They cushion and form protective pads around sensitive organs like the heart, liver, and kidneys, and the layer of fat beneath the skin helps insulate the body against excessive heat loss.
Table of Contents
Aim of the Experiment
Apparatus Required
Theory
Procedure
Observations
Result
Precautions
Aim of the Experiment
To test the presence of carbohydrates, proteins and fats in pure samples
Apparatus Required
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
Alcohol
Chloroform
Filter Paper
Potassium Bisulfate
Concentrated Hydrochloric Acid
Furfural Solution
Test Tubes
Test Tube Holder
Water Bath
Dropper
Stirrer
Bunsen Burner
Theory
The presence of protein, carbohydrates and fats in any food is detected by performing protein, fat, and carbohydrate tests on the food extract. The benefit is that these tests do not interfere with one another.
Test for Carbohydrates:
Molisch’s test – Molisch’s reagent + Given sample food → Purple or violet ring confirms the presence of carbohydrates.
Fehling’s test – Fehling’s reagent + Given sample food → Red precipitate confirms the presence of carbohydrates
Benedict’s test – Benedict’s reagent + Given sample food → Red precipitate confirms the presence of carbohydrates.
Tollen’s test – Tollen’s reagent + Given sample food → Silver mirror confirms the presence of carbohydrates.
Iodine test – Iodine solution + Given sample food → Blue colour solution confirms the presence of starch.
Protein Test in Food:
Biuret test – Aqueous copper sulfate + Given sample food → Violet colouration confirms the presence of Proteins
Xanthoproteic test – Nitric acid + Given sample food → Yellow colour solution confirms the presence of proteins.
Millions test – Mercuric sulfate in the presence of sodium nitrite and sulfuric acid + Given sample food → Brick red colour solution confirms the presence of proteins.
Ninhydrin test – Pyridine solution of ninhydrin + Given sample food → Violet colour solution confirms the presence of proteins.
Test for Fats:
Solubility test – Chloroform or alcohol + Given sample food → Miscible with chloroform and immiscible with water the fat presence is confirmed.
Translucent spot test – rubbed between the folds of filter paper + Given sample food → presence of translucent spot then the presence of fats is confirmed.
Acrolein test – Potassium bisulfite $${{K}{H}{S}{O}_{4}}$$ + Given sample food → Pungent irritating odour, then the presence of fats or oil is confirmed.
Procedure
To determine the presence of carbohydrates, proteins, fats, and oils in a given food sample, an extract of the food should be prepared first. After grinding the foodstuff, dry it in a mortar with a pestle or by boiling it with a small amount of water and extracting it with a small amount of an organic solvent.
Some examples of food extract preparation are provided below.
Cut potatoes into slices and boil in water.
For butter, conduct a direct test.
Extract the juice from grapes and test.
Take the white portion of an egg and grind it with water to make boiled eggs.
Observations
Result
The given sample of food may contain carbohydrates, proteins and fats.
Precautions
To test the sample food, always use the smallest amount of reagents that are freshly prepared.
Take the reagents from the bottle with droppers.
During the experiment, wear lab aprons and hand gloves.
Lab Manual Questions
1. How will you distinguish between sucrose and glucose?
Ans. Glucose on heating with Tollens' reagent gives a silver mirror while sucrose does not.
2. Explain why fructose reduces Fehling’s solution and Tollens reagent inspite of the presence of a ketonic group?
Ans. In alkaline medium fructose rearranges to glucose and the two are in equilibrium with each other.
3. What is the role of tartrate and citrate ions in Fehling’s reagent and Benedict’s reagent respectively?
Ans. Using Fehling's solution or Benedict's solution, complexing the copper(II) ions with tartrate ions prevents precipitation of copper(II) hydroxide. Benedict's solution contains copper(II) ions complexed with citrate ions in sodium carbonate solution.
4. What are the reagents used in this experiment?
Ans. Following are the reagents used in this experiment:
Molisch's reagent
Fehling's reagent
Benedict's reagent
Tollen's reagent
Viva Questions
1. Which chemical is used for carbohydrate testing?
Ans. Concentrated sulphuric acid is used in testing carbohydrates.
2. Why is testing for carbohydrates important?
Ans. To characterise carbohydrates present in an unknown solution based on various chemical assays.
3. What is the purpose of testing known samples for lipids, carbohydrates, and proteins?
Ans. To detect the presence of carbohydrates, fats and proteins in the samples of the given food.
4. What colour does protein go?
Ans. Proteins are detected using Biuret reagent. This turns a mauve or purple colour when mixed with protein.
5. Why are carbohydrates polar?
Ans. Carbohydrates are more polar than lipids due to the presence of many -OH groups in carbohydrates.
6. What organism makes carbohydrates?
Ans. Green plants form carbohydrates from carbon dioxide and water during the process of photosynthesis.
7. What are proteins made of?
Ans. Proteins are made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains.
8. What is the protein factor?
Ans. The protein factor is the numeric factor (6.25) by which the nitrogen content of a protein is multiplied to approximate the amount of protein.
9. What is the chemical formula of protein?
Ans. Proteins general chemical formula is $${{R}{C}{H}{(}{N}{H}_{2}{)}{C}{O}{O}{H}}$$.
10. How is protein measured?
Ans. The most frequently used methods for measuring protein content in foods include the Kjeldahl method, Dumas method, direct measurement methods using UV-spectroscopy and refractive index measurement.
Practical Based Questions
Which of the following Biomolecules simply refers to as “Staff of life”?
(a) Lipids
(b) Proteins
(c) Vitamins
(d) Carbohydrates
Answer: (d)
Which of the following is the simplest form of carbohydrates?
(a) Carboxyl groups
(b) Aldehyde and Ketone groups
(c) Alcohol and Carboxyl groups
(d) Hydroxyl groups and Hydrogen groups
Answer: (b)
Protein, carbohydrates and fat are examples of macronutrients.
(a)True
(b)False
Answer: (a)
Which of the following monosaccharides is the majority found in the human body?
(a) D-type
(b) L-type
(c) LD-types
(d) None of the above
Answer: (a)
Which of the following is the most abundant biomolecule on the earth?
(a) Lipids
(b) Proteins
(c) Carbohydrates
(d) Nucleic acids.
Answer: (c)
Which of the following are the major functions of carbohydrates?
(a) Storage
(b) Structural framework
(c) Transport Materials
(d) Both Storage and structural framework
Answer: (d)
Which of the following is the smallest carbohydrate – triose?
(a) Ribose
(b) Glucose
(c) Glyceraldehyde
(d) Dihydroxyacetone
Answer: (c)
Which of the following is the simplest carbohydrate?
(a) Gulose
(b) Glucose
(c) Dihydroxyacetone
(d) Glyceraldehyde
Answer: (d)
Which of the following factors is not responsible for the denaturation of proteins?
(a) Heat
(b) Charge
(c) pH change
(d) Organic solvents
Answer: (b)
Carbohydrates and fats are called energy food
(a)False
(b)True
Answer: (b)
Conclusion
Carbohydrates provide energy to the body's cells. Protein is the most important functional and structural component of all body cells. Fats and oils are the most abundant fatty acid-containing energy sources. Carbohydrates provide energy to your brain, kidneys, heart muscles, and nervous system. Proteins are the building blocks of living tissues and are coded for by our genes. They are also important in biological processes. Fats also aid in transporting fat-soluble vitamins such as A and D.
FAQs on Tests of Carbohydrates Fats and Proteins in Pure Samples and Detection of Their Presence in Given Food Stuffs
1. Justify the presence of carbohydrates in glucose solution.
The Fehling Test can detect the presence of carbohydrates in a glucose solution. This test can only be performed by lowering sugar levels (like glucose). The presence of carbohydrates is confirmed by the formation of a red-coloured precipitate of $${{Cu}_{2}{O}}$$ after the addition of Fehling's solution.
2. What are protein standards?
Protein standards are well-characterized natural or recombinant protein mixtures that are loaded in a gel alongside protein samples. They aid in the monitoring of electrophoretic separation as well as the estimation of the size and concentration of proteins separated in a gel.
3. How many types of proteins are there?
Proteins are classified into two types: complete proteins and incomplete proteins. Proteins are composed of smaller units known as amino acids. Complete proteins, including meat, fish, poultry, dairy, and soy products, contain all the amino acids your body requires.
4. What is the main element of protein?
Proteins contain the elements carbon, hydrogen, and oxygen, just as carbohydrates and lipids do, but proteins are the only macronutrient that contains nitrogen. In each amino acid, the elements are arranged in a specific manner around a carbon centre.
5.List the carbohydrates, proteins and fats percentage in a food item.
Protein, fat, and carbohydrates are all found in dairy products. All dairy products begin with whole milk containing approximately 20% protein, 30% carbohydrate, and 50% fat.
