School and Home Cooking

by Carlotta C. Greer

RELATED WORK

LESSON CXVI

MEASUREMENT OF THE FUEL VALUE OF FOODS

HOW FOOD IS ASSIMILATED.—The uses of the foodstuffs,—carbohydrates, fats, protein, ash, water, and vitamines,—were given. It was stated that these foodstuffs either (a) "burned" (i.e. united with oxygen) and produced energy, (b) built the body, or (c) aided in regulating body processes.

All parts of the body are composed of microscopic cells. By the process of digestion the foodstuffs are made entirely soluble (see Solution and Digestion); they are then further altered, i.e. split to their end products and absorbed through the walls of the alimentary canal. The blood carries the digestion products to all parts of the body. The blood also carries oxygen,—which has been breathed into the body from the air,—to all parts of the body. The body cells then select the foodstuffs that they need to carry on their work. Some cells pick out the fuel materials—carbohydrates, fat, or protein—and oxygen. Fuel foods when oxidized, produce energy. Other body cells select some of the body builders—protein or ash—and use these for building or repairing tissue. The cells which build bone choose ash and the other materials needed for building bones; the cells which build muscle choose protein and the other materials needed for building muscle.

Little is known regarding the use of vitamines by the body cells, other than that they are indispensable for the growth and maintenance of the body.

HOW ENERGY OR FUEL VALUE IS MEASURED.—It was stated that the human body could be compared to an automobile, i.e. the "burning" of the fuel foods in the body produced the ability to do work. The quantity of energy that fuel food is capable of giving off is termed the fuel value of that food. Energy has been defined as the ability to do work. Since heat is energy, the fuel value of foods shows, in part, [Footnote 85: Although ash, water, and vitamines nourish the body, it is impossible to measure their nutritive value in terms of fuel value. Fuel value expresses the nutritive value only of the combustible foodstuffs,—carbohydrates, fats, and protein. However, according to Sherman, "the most conspicuous nutritive requirement is that of energy for the work of the body." Hence, the fuel value of a food is often spoken of as its nutritive value (see "Chemistry of Food and Nutrition," Second Edition, by Henry C. Sherman, Ph.D., p. 138).] their nutritive value. If the quantity of heat that is produced by burning a food is measured, the measurement indicates the quantity of energy that the food is capable of giving to the body.

Heat cannot be measured by weight or length, but by the change in temperature which it produces in a given weight of a certain material. The heat unit is not a pound or yard, but a Calorie, or a definite quantity of heat, which, when applied to materials, will produce change of temperature in those materials. If the temperature of one pound [Footnote 86: NOTE TO THE TEACHER—The avoirdupois system of measurement and the Fahrenheit scale of temperature are used in this text. It is believed by the author that less than ten per cent of all pupils taking this course will enter college. Hence, the use of the measurements that are more in keeping with the pupils' practical needs. For the small minority who will enter college, a thorough drill in the metric system is urged. The following formula gives the necessary information for changing from the Fahreheit to the Centigrade scale: Subtract 32 and multiply by 5/9.] of water is 70 degrees Fahrenheit, and it is desired to increase the temperature of that water to 74 degrees Fahrenheit, a certain quantity of heat will have to be applied. It has been found that the quantity of heat required to raise the temperature of one pound of water through any four degrees of the Fahrenheit scale is practically the same, i.e. the quantity of heat required to raise the temperature of one pound of water from 32 degrees to 36 degrees F. is about the same as the quantity of heat that must be applied to raise the temperature of one pound of water from 60 degrees to 64 degrees F. The unit of measurement of heat is taken as the quantity of heat required to raise the temperature of one pound of water through about 4 degrees F.

The Calorie, [Footnote 87: I.e. greater Calorie, distinguished from the lesser calorie by the capital C.] used for food calculation, is approximately the quantity of heat required to raise the temperature of one pound (pint) of water through 4 degrees F. If one pint of water were placed over a lighted burner and heated until it increased four degrees in temperature, approximately one Calorie of heat would have been applied to the water (see Figure 82).

HOW THE FUEL VALUE OF A FOOD MATERIAL IS MEASURED.—Scientists have worked with care to obtain accurate data for the measurement of the heat produced by foods burning in the body. The data accepted to-day differ from those given by Rubner some years ago. [Footnote 88: See "Chemistry of Foods and Nutrition," Second Edition, by Henry C. Sherman, Ph.D., p. 143, "Physiological Fuel Values.">[

1 gram protein yields 4 Calories 1 gram fat yields 9 Calories 1 gram carbohydrate yields 4 Calories Expressing grams approximately in ounces, these data become: 1 ounce of protein yields 113 Calories 1 ounce of fat yields 255 Calories 1 ounce of carbohydrate yields 113 Calories

[Illustration: FIGURE 82.—ILLUSTRATING THE AMOUNT OF HEAT REPRESENTED BY
ONE CALORIE.]

In order to find the fuel value of foods, it is necessary to know their composition. For such data United States Department of Agriculture Bulletin No. 28 is a valuable source.

Flour.—The fuel content of flour is (see United States Department of Agriculture, Bulletin No. 28, p. 58, All Analyses Average):

10.6 per cent protein; 1.1 per cent fat; 76.3 per cent carbohydrates. Then, 1 ounce of flour contains, 0.106 ounce of protein; 0.011 ounce of fat; 0.763 ounce carbohydrates.

The protein in one ounce of flour yields (113 x 0106 =) 11.97 Calories.

[Illustration: FIGURE 83.—COMPARATIVE WEIGHTS OF 100-CALORIE PORTIONS OF
FOODS.]

The fat in one ounce of flour yields (255 x 0.011 =) 2.80 Calories. The carbohydrates in one ounce of flour yield (113 x 0.763 =) 86.21 Calories.

Total Calories furnished by 1 ounce of flour are (11.97 + 2.80 + 86.21 =) 100.98.

Butter.—The fuel content of butter is (see United States Department of Agriculture, Bulletin No. 28, p. 54):

1 per cent protein; 85 per cent fat; no carbohydrates.

1 ounce of butter contains 0.01 ounce of protein, 0.85 ounce of fat, and no carbohydrates.

The protein in one ounce of butter yields (0.01 x 113 =) 1.13 Calories.

The fat in one ounce of butter yields (0.85 x 255 =) 216.75 Calories.

Number of total Calories furnished by one ounce of butter is (1.13+216.75=) 217.88.

Sugar.—The fuel content of sugar is (see United States Department of Agriculture, Bulletin No. 28, p. 65) no per cent protein; no per cent fat; 100 per cent carbohydrates.

1 ounce of sugar contains no protein, no fat, and 1 ounce carbohydrates. 1 ounce sugar yields (113 x 1 =) 113 Calories.

HOW THE WEIGHT OF FOOD MATERIALS PRODUCING 100 CALORIES IS MEASURED.—For practical work in computing the fuel value of foods, it has been found more convenient to reduce all data to terms which express equal fuel value instead of equal weight as in the foregoing paragraph. One hundred Calories is the unit chosen. The weight of a food which, when "burned" in the body, will produce one hundred Calories is the desired data. This weight is termed a standard portion or a 100-Calorie portion (see Figures 83 and 84).

From the previous work, it is a simple matter to compute in ounces the quantity of food materials which will yield 100 Calories.

If 1 ounce of flour yields 100.98 Calories and x represents the number of ounces of flour which will yield 100 Calories, then x/1=100/100.98 or x=0.99, the number of ounces of flour which yield 100 Calories, i.e. a 100-Calorie portion of flour.

If 1 ounce of butter yields 217.88 Calories and x represents the number of ounces of butter which will yield 100 Calories, then x/1=100/217.88 or x=0.45, the number of ounces of butter which yield 100 Calories, i.e. a 100-Calorie portion of butter.

[Illustration: FIGURE 84—100-CALORIE PORTIONS OF FOODS. a, banana, b, butter, c, eggs d, meat; e, bread.]

If 1 ounce of sugar yields 113 Calories and x represents the number of ounces of sugar which will yield 100 Calories, then x/1=100/113 or x=0.88, the number of ounces of sugar which will yield 100 Calories, i.e. a 100-Calorie portion of sugar.

HOW THE FUEL VALUE OF A COMBINATION OF FOOD MATERIAL IS MEASURED.—It is possible to compute the fuel value of a food that is made up of several food materials. To do this one must know or find:

(a) Recipe for food. (b) Weight and measure of combustible food materials. (c) Number of Calories yielded by one ounce of each of the combustible foodstuffs.

The recipe for one loaf of bread is:

1 cupful water 1 teaspoonful salt 1 teaspoonful sugar 3 1/2 cupfuls flour 1/2 tablespoonful butter 1/4 cake compressed yeast 1/4 cupful water

By weighing and measuring one finds:

1 pound sugar measures 2 cupfuls 1 pound butter measures 2 cupfuls 1 pound flour measures 4 cupfuls

Then,

1 teaspoonful sugar weighs 0.16 ounce 1/3 tablespoonful butter weighs 0.25 ounce 3 1/2 cupfuls flour weigh 14.0 ounces

(From data of How the Fuel Value of a Food Material is Measured.)

1 teaspoonful sugar yields (113 x 0.16 =) 18.08 Calories 1/2 tablespoonful butter yields (217.88 x 0.25 =) 54.47 Calories 3 1/2 cupfuls flour yield (100.98 x 14 =) 1413.72 Calories 1 loaf of bread yields (18.08 + 54.47 + 1413.72 =) 1486.27 Calories

For the practical method of calculating diet (which is more fully treated in Lesson CXXXI), it is convenient to have the 100-Calorie portion of a recipe, or a "made" food.

The 100-Calorie portion of bread is estimated from the result above in the following manner:

Since 1486.27 Calories are yielded by one loaf of homemade bread, then 100 Calories are yielded by (100/1486.27 =) .06 or 6 per cent of a loaf of homemade bread; hence, 1/16 (6 ) or 1 slice of homemade bread yields 100 Calories.