Scientific study of food

Units of measurement

Energy value of food can be measured in calories or joules but a large unit of energy is measured in kilo-calories. It is the most common unit of measuring energy. The international unit of energy is “joule”. Therefore kilocalories is the amount of heat required to rise the temperature of a thousand gram (1000) of water by 1 degrees Celsius. For example one gram (gm.) of carbohydrate will produce four kilocalories of energy. One gram of protein will produce four kilocalories of energy and one gram of fat will produce nine kilocalories of energy.

Food weight: the raw or processed food can be measured in grams or kilograms.

1000 grams = 1 kilogram.

The macro nutrients are measured in grams while the vitamin and trace elements are measured in smaller units because they are required in relatively small quantity by the body and are also present in food in a small quantity.

Vitamins and trace elements are measured in milligrams (mg.) and micrograms (  g.).

1g     =     1000mg (10³mg)

1gm         =       1 000, 000  g (10⁶   g)

Or

1mg         =       0.001 or 10^-3gm

1  g         =       0.000001gm or 10^-6gm

Other units often used in measuring vitamins are the international unit (I.U) and standard unit (S.I).

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 -210^{0 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 acrolein.

Evaluation: mention the various measurements used for food stuffs

• What is the measurement of energy value of carbohydrates and vitamins.
• State the effect of dry heat on carbohydrates.

Assignment: state the metric equivalent of the following; a. evaporated milk

1. Satchet fat                         c. a gallon of vegetable oil                  d. a bag of rice
2. A pack of spaghetti