Maharashtra Board Class 11 Food Science and Technology Chapter 5 Food Values PDF Download

Food Values

Can You Recall?

What is the difference between Calorie and Kilocalorie?

Can we measure the energy released from food?

Which nutrients in food give energy?

Can energy be stored in body?

5.1 Definition Of Kilocalorie

Energy is the ability to do work. The energy contained in food can either be trapped within the chemical constituents of the body or used to produce heat and body movement.

Energy is a precisely defined property of chemical compounds and other physical systems. The major sources to provide energy are carbohydrate, lipid and protein in the diet. Water, vitamin and minerals do not provide energy but they are important for other body activities. The energy of carbohydrate, lipid and protein is made available to the body, when these compounds are oxidised and release the energy during respiration / metabolism.

All forms of energy are interconvertible. The energy value of food is expressed in Kilocalories and determined by complete combustion of food in container surrounded by specific amount of water.

Definition: One Kilocalorie is defined as the amount of heat energy required to raise the temperature of 1Kg of water by 1°C from 15°C to 16°C at normal atmospheric pressure.

The unit of energy which has been used in nutrition for a long time is the Kilocalorie (Kcal). However, the International Union of Nutritional Science (IUNS) have adopted "Joule" as the unit of energy in place of Kcal.

Definition: A joule is defined as the energy required to move 1kg mass by 1 metre by force of 1 newton. One newton is the force needed to accelerate 1kg mass by 1 m/sec.

The international conversion factor is 1 Kcal = 4.184 Kilojoules (KJ)

Teacher's Note

Kilocalorie is a unit to measure energy in food. Just like we measure milk in litres, we measure food energy in kilocalories.

Exam Trick

Remember: 1 Kcal = 4.184 KJ. In your exam, just write this conversion formula and you will get marks easily.

Points to Remember

Energy is the ability to do work.
Kilocalorie measures how much energy is in food.
Carbohydrate, fat and protein give energy to our body.
1 Kilocalorie raises the temperature of 1 kg water by 1°C.
1 Kcal = 4.184 Kilojoules.

Physiological Fuel Value

The amount of energy actually available to the body from a given amount of nutrients is called physiological fuel value. Difference between the physiological fuel values and gross fuel values is as follows.

Teacher's Note

Physiological fuel value is the real energy our body can use from food. Gross fuel value is the total energy we burn in a machine, but our body cannot use all of it.

Exam Trick

Remember: Physiological = what body uses. Gross = what machine burns. Think of it like a car - gross value is total fuel, but your car uses less due to efficiency.

Points to Remember

Physiological fuel value is energy our body can really use from food.
Gross fuel value is energy released when food is burned completely.
Our body cannot digest fibre, so fibre energy is not used.
Carbohydrate gives 4 Kcal physiological fuel value.
Fat gives 9 Kcal physiological fuel value.

5.2 Methods To Determine The Calorific Values

The amount of energy released from foods and the amount of energy expended by an individual can be obtained by Direct and Indirect calorimetry.

Teacher's Note

Direct calorimetry means we burn food in a machine and measure energy. Indirect calorimetry means we measure how much oxygen a person uses while working.

Exam Trick

Remember: Direct = Direct burning in bomb. Indirect = Indirect measurement through oxygen and breathing. Think: Direct is like burning in a test tube, Indirect is like measuring a student's work.

Points to Remember

Direct calorimetry burns food in a bomb calorimeter.
Indirect calorimetry measures oxygen use in the body.
Bomb calorimeter measures energy value of food.
Benedict's oxy calorimeter is used for indirect calorimetry.
Douglas bag measures energy used during work.

Direct Calorimetry

a) Bomb Calorimeter

Principle: Direct Calorimetry

Purpose: Determination of energy value of food

Method: It consists of a heavy steel bomb with tight cover, which is placed inside a vessel of containing water. The foodstuff is placed in a small crucible inside the bomb is filled with oxygen at high pressure and the food stuff ignited by means of electric leads. The material in bomb burns and produces heat which is absorbed by water and results in rise in temperature which can be measured by following equation.

q = mc∆T

where q = the energy evolved (J)

m = mass of the water (g)

c = the specific heat capacity of the water = 4.18J/Kg

∆T = the temperature change in the water

b) Atwater And Rosa Respiration Calorimeter

Principle: Direct calorimetry

Purpose: Determination of Energy expenditure during BMR/ REE or a light activity.

Method: In this method the subject is placed in calorimeter, a small room with heavely insulated walls. The heat generated by the subject is taken up by water, pumped through the series of finned pipes which pass through the calorimeter.

Multiplying the difference in temperature between the incoming and outgoing water, by volume of water flowing, heat output can be obtained.

BMR - Basal Metabolic Rate

REE - Resting Energy Expenditure

Teacher's Note

Bomb calorimeter is like an oven where we burn food and measure heat. Atwater calorimeter is like a room where we measure how much heat a person makes while sitting.

Exam Trick

Remember: Bomb Calorimeter = formula q = mc∆T. Just memorize this one formula and write it in exam for bomb calorimeter questions.

Points to Remember

Bomb calorimeter burns food in a heavy steel container.
Heat from burned food is absorbed by water.
Temperature rise in water tells us energy in food.
Atwater calorimeter measures energy used by person.
Formula for bomb calorimeter is q = mc∆T.

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