Subject: Food and nutrition
Topic: Scientific study of foods.
(a) Measurement, units and accuracy
(b) Protein tests; (i) action of heat on complex protein (ii) foam test of alcohol on complex protein (iii) millions test.
Sub topic 1: Measurement, units and accuracy
Man at different stages in life requires different amounts of nutrients to get to the desired effects in the body. Different food nutrients need to be identified by carrying out some scientific tests in order to ascertain the different quantities in different foods.
This is the act or process of discovering exact size or amount of something.
This is the standard measure which is used to express amounts. For example gram me is a unit of weight.
This is the means to be correct, exact and avoid mistakes. Measurement in foods and nutrition requires accuracy. This is the very essential so as to get good results.
Energy measurement in food nutrients
Energy value of foods or energy needs of the body are measured in calories or joules. A larger unit known as kilocalories can be used. The most common unit of measuring energy is known as the kilocalories.
1 gm of carbohydrate (glucose) =4 kcal of energy
1gm of protein (amino acids) =4 kcal of energy
1 gm of fat (fatty acids) =9 kcal of energy
1kcal is equivalent to 3.142kilojoules.
Define measurement, accuracy and unit.
Sub Topic 2: Protein tests; (i) action of heat on complex protein (ii) foam test of alcohol on complex protein (iii) millions test.
Test for protein
Action of heat on complex protein
The chemical reaction that occurs when heat is applied to protein is called Coagulation e.g. when an egg is boiled it coagulates.
Effects of heat on protein:
- It denatures protein
- It impairs the physical function of the protein e.g. hormonal and enzymic functions are stopped.
- It may toughen the protein and makes it indigestible especially if over cooked
- It shrinks the protein e.g meat.
- Coagulation :when heat is applied to protein it coagulates.
(ii.) Foam test on complex protein
Dissolve the protein in pure and clean water shake vigorously. If foam is produced, then it shows the presence of protein.
(iii) Million’s test
Dissolve the protein in clean water. Then to a little portion of the solution, add a few drops of million’s reagent and warm in boiling water. If a red color of precipitate is obtained, it indicates the presence of protein.
(iv) Alcohol test: Immerse food substance into alcohol. If it coagulates, shrinks or curdles, it indicates the presence of protein.
- Explain the following terms:
- Describe the foam test on complex protein.
- Enumerate five effects of heat on protein.
- The act of discovering the exact size or amount of something is…..
- What is the unit for measuring energy value of foods….
- A kilogram is equivalent to ………. Kilojoules
- Which of these is used to ascertain the presence of protein in foods?
- Biuret test
- Sudan III test
- Benedict test
- Shrinkage test
- In million test the presence of red precipitate denotes …………….
- Explain two ways of confirming the presence of protein in food stuff.
- Explain foam test and list 4 effects of heat on complex protein.
Read Evans food and nutrition for senior secondary school 1 by F.A. Bakare et el; (pages 41-44)
Pre- reading assignment:
Read about tests of fat and carbohydrates.
- Evans food and nutrition for SSS book 1 by F.A et al; Evans brothers Nigeria limited.
- Exam focus foods and nutrition for WASSCE and SSCE by J.O Olusanya et al. University press.