Lesson Notes By Weeks and Term - Senior Secondary 2

Scientific study of food nutrients

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  4. Scientific study of food nutrients

Term: 2nd Term

Week: 4

Class: Senior Secondary School 2

Age: 16 years

Duration: 40 minutes of 2 periods each

Date:       

Subject:      Home management

Topic:-       Scientific study of food nutrients

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to:            

  1. Perform the various tests food nutrients.
  2. Interpret the result of the test for food
  3. Discover the effects of heat on food nutrients.

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S ACTIVITY

STEP 1

INTRODUCTION

The teacher reviews the previous lesson on family planning

Students pay attention

STEP 2

EXPLANATION

She performs the various tests on food nutrients and interprets the results

Students pay attention and participates

STEP 3

DEMONSTRATION

She highlights the effect of heat on foods                                             

Students pay attention and participate

STEP 4

NOTE TAKING

The teacher writes a summarized note on the board

The students copy the note in their books

 

NOTE

SCIENTIFIC STUDY OF FOOD NUTRIENTS

SIMPLE FOOD TEST
Simple tests to identify the presence of nutrients in foodstuffs.

  1. Test for Protein
    Millions Test:- The presence of protein in food can be tested by the use of a chemical called million reagents.

PROCEDURE
a. Place 1-3g of egg white or other ground protein in a test tube.
b. Add about 4ml of water and shake.
c. Add about 2.5ml of Millions reagent.
d. Observe a white precipitate that will be formed.
e. Place the test tube in a beaker that is half-filled with water.
f. Heat the water gently.

Observation: The precipitate will turn red, indicating the presence of protein.

Burette Test:

PROCEDURE
a. Obtain a small quantity of ground meat or egg white.
b. Place in a test tube and mix with a few drops of water.
c. Add about one cube centimeter (1cm3) of dilute caustic soda (NaOH) and mix well.

  1. Add, drop by drop, 1% copper (ii) sulphate solution. Shake thoroughly after each drop.

Observation: A purple or violet colour indicates the presence of protein.

  1. Test for Carbohydrates
    Test for starch (yam, potatoes, rice, maize etc)
    Iodine Test

PROCEDURE
a. Get a slice of yam.
b. Place it on a clean glass slide or flat plate.
c. Add 1-2 drop of iodine solution to the cut slice of yam.

Observation: The yam turns blue-black in colour. This shows the presence of starch.

Fehling’s test
Test for simple sugars. (table sugar, honey, fruits e.g. ripe bananas)

PROCEDURE
a. Place about 5ml of 5% sugar solution in a test tube.
b. Prepare the Fehling’s solution by adding equal amounts of Fehling’s solution. A (copper (II) sulphate in water) and B (sodium potassium tartrate and sodium hydroxide in water).
c. Add 5ml of Fehling’s solution to sugar solution.
d. Place the tube in beaker that has been half-filled with water.
e. Heat the beaker gently to boiling point.

Observation: An orange or brick-red precipitate will be formed. This shows the presence of sugar.

  1. Test for Oils
    The Grease Spot Test

PROCEDURE
a. Rub or mark a little piece of butter of groundnut oil on a sheet of light, white paper.
b. Hold up the paper.

Observation: A translucent patch is formed by the oil mark.

Sudan III Test

PROCEDURE
a. Place a small quantity of groundnut paste (or any other chopped or mashed food substance that contains fat) in a test tube.
b. Add a few drops of Sudan (III) solution or osmic acid.

Observation: A distinct red colouration is produced

EFFECTS OF HEAT ON NUTRIENTS

Effects of heat on carbohydrates

  1. They are dextrinized i.e. broken down into simpler units and therefore easier to digest.
  2. In moist heat, carbohydrates gelatinize i.e. they expand and burst and thereby making them more digestible.
  3. They caramelize i.e. turn brownish. This is usually produced with dry heat.

 

Effects of heat on proteins

  1. Heat denature protein i.e. it alters the primary structure and state of the native protein e.g. egg, beans.
  2. The protein contracts and the food shrinks e.g. meat.
  3. If the protein is overcooked it becomes tough and indigestible e.g. fried fish.

 

Effects of heat on fats and oil

  1. Fat changes from solid state to liquid state when heated.
  2. When oil is heated to a temperature of between 2000 -2100 F, the oil produces a blue haze which signifies the smoke point, at the “smoke point”, the oil may catch fire.
  3. When the oil is heated beyond smoke point, it decomposes to produce a poisonous substance known as 

 

EVALUATION:    1. Describe and perform a test for the presence of

       a. carbohydrates

       b. proteins

       c. fats and oils

         (write out the result of the tests)

  1. State three effects each of heat on

       a. carbohydrates

       b. proteins

       c. fats and oils

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively