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Food Tests for Nutrients, Study notes of Biology

Biology

The importance of nutrients in food and how to detect the presence of sugars, starch, proteins, and fats in animal and plant materials. It describes the tests for sucrose, starch, and proteins, and the materials required for each test. The document also provides observations for each test and explains the significance of the results. useful for students studying nutrition, biology, or chemistry.

Typology: Study notes

2022/2023

Available from 01/07/2024

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Food Tests for sugars, starch, proteins & lipids - methods and
observations:
Aim
To detect the presence of sugar(sucrose), starch, proteins, and fats in suitable animal and plant
materials.
Nutrition is a source through which living entities obtain food for the body to get fueled with
energy. Therefore the food we eat must be well-balanced with all the substances that are
required by our body to perform daily activities, these substances are known as nutrients.
Nutrients nourish the body by releasing the energy required for the body’s growth. Some of the
nutrients found in food are:
Proteins
Carbohydrates
Fats
Vitamins
Minerals
Dietary fibres
What are proteins?
They are body-building nutrients which aid in the repair of damaged body parts and also in the
growth of the body.
What are vitamins and minerals?
These nutrients are reflected to be protective food. They protect us from diseases by providing
resistance against germs that are known to cause diseases.
What are carbohydrates?
Carbohydrates are nutrients that provide energy to the body instantly. Fats are also energy-
giving foods and store energy.
Carbohydrates contain starch, sugars, and fibres which consist of sugar molecules containing
hydrogen, carbon, and oxygen. Carbohydrates can be categorized into:
Simple carbohydrates – They are composed of 1 or 2 units of sugar, hence can be
broken down and absorbed easily. Simple carbohydrates are further divided into:
Monosaccharides – Composed of one sugar unit
Disaccharides – Consists of 2 chemically-associated monosaccharide units. Example –
Lactose, Maltose, Sucrose, etc.
Complex carbohydrates – These carbohydrates consist of long chains of simple
carbohydrate units. Since they are large in size they can be broken down into simple
carbohydrates. They are further subdivided into:
Oligosaccharides – Composed of less than 10 monosaccharides parts
Polysaccharides – composed of a large number of polysaccharides. Example –
Glycogen, starch, and cellulose
Test for Sucrose
The presence of sucrose can be tested in a sample using Benedict’s test.
Material Required
Benedict’s Reagent
Sugar cane extract
Concentrated HCl
NaOH solution
Burner
Dropper
Test tube
Test tube holder
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Food Tests for sugars, starch, proteins & lipids - methods and

observations:

Aim To detect the presence of sugar(sucrose), starch, proteins, and fats in suitable animal and plant materials. Nutrition is a source through which living entities obtain food for the body to get fueled with energy. Therefore the food we eat must be well-balanced with all the substances that are required by our body to perform daily activities, these substances are known as nutrients. Nutrients nourish the body by releasing the energy required for the body’s growth. Some of the nutrients found in food are:  Proteins  Carbohydrates  Fats  Vitamins  Minerals  Dietary fibres What are proteins? They are body-building nutrients which aid in the repair of damaged body parts and also in the growth of the body. What are vitamins and minerals? These nutrients are reflected to be protective food. They protect us from diseases by providing resistance against germs that are known to cause diseases. What are carbohydrates? Carbohydrates are nutrients that provide energy to the body instantly. Fats are also energy- giving foods and store energy. Carbohydrates contain starch, sugars, and fibres which consist of sugar molecules containing hydrogen, carbon, and oxygen. Carbohydrates can be categorized into:  Simple carbohydrates – They are composed of 1 or 2 units of sugar, hence can be broken down and absorbed easily. Simple carbohydrates are further divided into:  Monosaccharides – Composed of one sugar unit  Disaccharides – Consists of 2 chemically-associated monosaccharide units. Example – Lactose, Maltose, Sucrose, etc.  Complex carbohydrates – These carbohydrates consist of long chains of simple carbohydrate units. Since they are large in size they can be broken down into simple carbohydrates. They are further subdivided into:  Oligosaccharides – Composed of less than 10 monosaccharides parts  Polysaccharides – composed of a large number of polysaccharides. Example – Glycogen, starch, and cellulose Test for Sucrose The presence of sucrose can be tested in a sample using Benedict’s test. Material Required  Benedict’s Reagent  Sugar cane extract  Concentrated HCl  NaOH solution  Burner  Dropper  Test tube  Test tube holder

Procedure  Take a clean and dried test tube and add sugar cane extract into it.  Now carefully add a few drops of concentrated HCl using a dropper to the test tube.  Hold the test tube securely with the help of a test tube holder.  Place the test tube near the Bunsen burner and allow the solution to boil for two minutes.  While boiling, the hydrolysis of sucrose occurs and the fructose converts to glucose.  With the help of a dropper, add a few drops of NaOH solution to the test tube so that the solution turns alkaline.  Now add a few drops of Benedict’s reagent with the help of a dropper into the test tube.  With the help of a test tube holder, place the test tube near the Bunsen burner and allow the solution to boil for a few minutes.  Observe the changes. Observation The colour of the solution colour from blue colour to green colour. From green colour, it finally changes to brick red or orange colour. This indicates that the solution contains glucose. Test for Starch Material Required  Potato extract  Iodine solution  Test tube  Dropper Procedure  Take a clean and dried test tube and add potato extract into it.  Add five to six drops of iodine solution with the help of a dropper into the test tube.  Keep the test tube undisturbed and allow the mixtures to stand for a few seconds.  Observe the changes. Observation The presence of starch in the potato extract is indicated when the colour changes to a blue- black colour. Test for Proteins The presence of proteins in a sample can be detected by the following tests:  Biuret Test  Xanthoproteic Test  Million’s Test

1. Biuret Test Material Required  1% CuSO  40% NaOH solution  Dropper  Egg Albumin  Test tube  Test tube holder

Procedure  Take a clean and dried test tube and add egg albumin into it.  With the help of a dropper, add a few drops of Million’s reagent into the test tube containing the egg albumin.  Keep the test tube undisturbed and allow the mixtures to stand for 5 minutes.  After a few minutes, observe the changes. Observation The sample indicates the presence of proteins when the colour changes to pink. Test for Fats The presence of fats in a sample can be detected by the following tests:  Sudan III Test  Paper Spot Test

1. Sudan III Test Materials Required  Sudan III Solution  Oil  Test tube  Dropper  Egg Albumin Procedure  Take a clean and dried test tube and add a few drops of oil into it.  Now into the same test tube, add five to six drops of the Sudan III reagent with the help of a dropper.  Stir the test tube continuously and allow the solution to stand for a while.  After a few seconds, observe the changes.  Observation The presence of fat in the sample is indicated when pink colour droplets appear on the test tube. 2. Paper Spot Test Materials Required  A piece of white paper  Peanut seeds  Watch glass Procedure  On the piece of white paper, place the fresh peanut seeds.  Crush and rub the peanut seeds on the white paper.  Remove the peanut seed remaining on the watch glass.  Observe the changes on the piece of white paper. Observation The spot where the peanut seeds are rubbed turns translucent. This indicates the presence of fats in the sample. Detection of Vitamin C Measure the vitamin C content of a sample of fruit juice by measuring the volume of the sample required to decolourise a solution of DCPIP. Calibrate the results by comparison with a known concentration of vitamin C. Apparatus and Chemicals Vitamin C solution, 1% ( Note 1 ) DCPIP solution, 1% ( Note 2 ) For each group of students: Burette Pipette, graduated Pipette filler Fruit juice samples Procedure SAFETY: Take care with fragile glassware such as burettes. Preparation a Make up a 1% solution of vitamin C with 1 g of vitamin C in 100 cm^3 ; this is 10 mg cm –^3. b Make up a 1% solution of DCPIP. Investigation c Pipette 2 cm^3 of vitamin C solution into a test tube.

d Using a graduated pipette or a burette, add 1% DCPIP drop by drop to the vitamin C solution. Shake the tube gently after adding each drop. Add DCPIP solution until the blue colour of the final drop does not disappear. e Record the exact amount of DCPIP solution that was added. f Repeat the procedure and calculate an average result. g Repeat with the fruit juices to be tested. If more than 5 cm^3 of DCPIP are completely decolourised, dilute the fruit juice and repeat the test. If the fruit juice has a strong colour that will interfere with determining the end point, dilute the juice before testing. h Calculate the amount of vitamin C in the standard solution in mg cm –^3. Calculate how much vitamin C there is in each of the fruit juices in mg cm –^3. Teaching notes In acidic conditions, DCPIP does not decolourise completely, but remains pink. With strongly acidic juices such as lemon juice this could confuse determination of the endpoint. If you are testing lots of different solutions, it is easier to put the DCPIP in a burette and titrate it into measured samples of fruit juice, rather than cleaning a burette several times in one lesson. If you have plenty of graduated pipettes, you could measure each juice into a measured sample of DCPIP and observe the point at which the DCPIP loses its colour. Hypotheses to test could include…  fresh juices have more vitamin C than long-life  juice ‘not from concentrate’ is best in terms of vitamin content  fruit squashes have less vitamin C than fruit juices  if heat destroys vitamin C, then heat-treated long-life juices will have lower concentrations  if heat destroys vitamin C, then boiled fruit juice will have lower concentrations than unboiled  manufacturers generally provide reliable information about their products answers.  vitamin C degrades in vitamin tablets, and old tablets will have less than fresh ones