MEASUREMENT OF FOOD ENERGY

MEASUREMENT OF FOOD ENERGY

The energy value of foods is determined in the laboratories by the use of special equipment called the bomb calorimeter. In the bomb calorimeter, the heat given off by a food in direct combustion or burning is measured under controlled conditions.

Energy value of a food can also be measured indirectly by measuring the oxygen used in burning a known amount of food.

The average fuel values of the energy giving components of foods have been found to be:

Carbohydrates     4.10 kcal / gm

Fats                      9.45 kcal/gm and

Proteins                 5.65 kcal/gm

The energy available from food in the body, called the psychological fuel value given above because:

• Some partially oxidized products are excreted.
• Some food is excreted in undigested form.

The carbohydrates and fats (after digestion) are completely oxidized in the body, but some partially oxidized end products of proteins are excreted in the urine. The energy value of these end products on an average is equivalent to 1.25 kcal/gm of protein consumed. This figure  is derived from a normal American diet about sixty years back. This correction is made in calculating energy available from proteins in the body.

The averages of coefficients of digestibility for the components of a typical dietary were:

Carbohydrates                         98 %

Fats                                         95 %

Proteins                                   92 %

The physiological fuel value (i.e., The energy available to the body) was calculated as follows:

Carbohydrates = (4.10) x 98 % = 4.01 kcal / g

Fats = (9.45) x 95 % = 8.98 kcal / g

Proteins = (5.65 – 1.25) x 92 % = 4.05 kcal / g  

For practical use these physiological fuel values were rounded off to the nearest whole number to get the kcalorie values we use in practical nutrition

Carbohydrates                         4 kcal / g

Fats                                         9 kcal /g

Proteins                                   4 kcal / g

Table: Calorie content of Dal

Components	Dal,   a	Calories per g,    b	axb
Carbohydrates	57.6	4	230.4
Fats	1.7	9	15.3
Proteins	22.3	4	0
Moisture	13.4	0	0
Minerals	3.5	0	0
Fiber	1.5	0	0
Calories per 100 g of dal		=	334.9

Please remember that these fuel values refer to the edible portion of the food.  Thus firstly, the energy content of the food related to  the food composition.

Secondly, energy value of food is affected by water or moisture content of food, as it is given in the food composition tables. As you may note from Table, water or moisture does not provide any energy. Therefore foods, which have a large percentage of water, have a low caloric content.

Thirdly, energy content of foods varies with their fat content.  As we learnt earlier, fat provides 9 kcal per gm, therefore foods with high fat content, have a high energy value.

The energy value of foods is affected by preparation or processing. As rice absorbs water, while cooking, cooked rice has about one-third the number of calories as an equal weight of raw rice. The reverse is the case when foods are dried. Dried fruits are connected source of energy as compared to fresh fruits. Seasoning with oil increases the energy content of salads, vegetables and dals. Frying foods such as papad, shev, wafers, invariably increases their energy content. Examples of effect of preparation on energy content of foods is preserved.

Thus any change in the composition during processing or preparation, affects the calorie content of the food product. It is important to take these changes into account, while calculating the energy content of food preparations, used in the dietary.

Table: Moisture, Fat and Caloric Content of Foods

Food	Moisture  %	Fats  %	Calories/ 100 g
Cucumber	96	0.1	13
Tomato	94	0.2	20
French beans	91	0.1	26
Orange, Carrot	88	0.2	48
Milk, cow’s	87	4.1	67
Grapes	79	0.3	71
Potato	75	0.1	97
Egg	73	13.3	173
Mutton, muscle	71	13.3	194
Wheat	13	1.5	346
Groundnut (Peanut)	3	40.1	567
Butter	19	81.0	729
Oil, Ghee or Vanaspati	0	100.0	900

Table: Change in Calorie Content with Preparation and Processing

Food	Moisture  %	Fat  %	Calories /  100 g
Rice, raw	13	0.5	345
Rice, cooked	71	0.2	115
Grapes	79	0.3	71
Raisins (Dry grapes)	20	0.3	308
Methi leaves, fresh	86	0.9	49
Methi leaves, fry	80	8.0	113
Papad	20	0.3	228
Papad, fried	3	26.0	512
Bengal gram dal flour	10	5.6	372
Shev (Made fro besan)	3	38	568