Lesson Notes By Weeks and Term - Senior Secondary 1

Effects of heat on food

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  4. Effects of heat on food

Term: 2nd Term

Week: 3

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes

Date:       

Subject:      Food and nutrition

Topic:-       Effects of heat on food

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

  1. Highlight the effects of heat on food

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

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S ACTIVITY

STEP 1

INTRODUCTION

The teacher reviews the previous lesson on the units of measurement

Students pay attention

STEP 2

EXPLANATION

She highlights the effects of moist heat on food

Students pay attention and participates

STEP 3

DEMONSTRATION

She highlights the effects of dry heat on food

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

EFFECTS OF HEAT ON FOOD
The application of heat is very essential in food preparation. Cooking food has some advantages as well as disadvantages.


Advantages:

  1. We cook foods to make them palatable.
  2. To improve their texture.
  3. For the body to be able to digest.
  4. To improve the flavor.
  5. To destroy bacteria (harmful organisms) that may be present in the food.

Disadvantages:

  1. Generally heat destroys some food nutrients.
  2. Food can also develop some unfavourable colour changes especially when an inappropriate method of cooking is used.

Dry and moist Heat
There are about four different media by which heat is used to cook the food we eat. They are water, air steam and fat/oil.

Effects of Heat on Protein
Dry Heat

  1. Obtain a small piece of beef.
  2. Trim off excess fat.
  3. Wash and allow to drain.
  4. Place in a pan.
  5. Place in the centre of a pre-heated oven.
  6. Turn meat over half way through cooking.

Observation:
When it is cooked, it will be observed that it has become smaller. This shows that protein shrinks when heated. Dry heat hardens the outside of the meat.

Moist Heat

  1. Place an egg gently into a saucepan or a poacher.
  2. Boil or poach the egg for 10 minutes.
  3. Remove the egg.
  4. Let it cool down, shell and cut it into two.

Observation:

The white of the egg has a solidified or set during boiling or poaching. This effect of the heat on protein is known as coagulation. The same changes takes place when milk, meat or fish are cooked.

Effects of Heat on carbohydrates
Dry Heat on starch

  1. Obtain a slice of bread (a slice of yam can also be used).
  2. Place the slice in a very hot oven or a toaster.
  3. Leave until light turns light brown.

Observation

Light brown colour will be observed. The product is called Dextrin. The process is known as dextrinilation.

Moist Heat and Starch

  1. Place 2 teaspoonful of corn starch paste (akamu/ogi) in a bowl.
  2. Add 6-7 teaspoonful of cold water.
  3. Mix thoroughly to obtain a slightly liquid consistency.
  4. Pour boiling water rapidly onto the mixture.

Observation:

The starch will swell and a jelly substance will form. The process is called gelatinization. The product is a gel.

Dry Heat on Sugar

  1. Place about 50g of sugar in a small saucepan.
  2. Heat gently, do not stir.
  3. Continue heating until there is colour change.

Observation:

A brown honey-like substance is formed. This process of production of caramel is known as caramelization. Different shades of brown (from light to very dark brown) can be obtained depending on how long it is heated.

Moist Heat on Sugar

  1. Pour about 30g of sugar into a pot or a saucepan containing 150mls of water.
  2. Heat gently and allow the mixture to dissolve.
  3. Continue heating until syrup is formed.

Observation:

The syrup is formed as the liquid evaporates.

Effects of Heat on Fats and Oils
Solid fat melts when heated.
Oil expands when heated.
When fat and oil are heated to a very high temperature, they burn and can catch fire. Fumes and unpleasant odours are given out. These irritate the eyes and gives a choking sensation.

EVALUATION:    1. Outline the effects of dry and moist heat on

  1. carbohydrates(sugar, starch)
  2. proteins
  3. Fats and oils

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively