CBSE Notes – Tests of Carbohydrates, Fats and Proteins

Tests of Carbohydrates, Fats and Proteins in Pure Samples and Detection of Their Presence in Given Food Stuffs

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Food is a necessary material that must be supplied to the body for its normal and proper functioning.
The main functions of the food are:
1. to provide energy
2. to promote growth
3. to replace worn-out tissues
4. to sustain life
5. to regulate body processes like assimilation and digestion.
The essential constituents of food are:
1. Carbohydrates
2. Lipids (oils and fats)
3. Proteins
4. Minerals
5. Vitamins and
6. Water.

Carbohydrates

The name carbohydrate is used for the compounds having general formula, C_x(H₂O)_y. These are called carbohydrates because they can be treated as hydrates of carbon. For example, glucose (C₆H₁₂O₆), sucrose (C₁₂H₂₂O₁₁), etc. However, this definition of carbohydrates has lost significance because of the following two reasons:
(i) There are many compounds that have the general formula C_x(H₂O)_y but do not behave as carbohydrates. For example, oxalic acid (C₂H₂O₂), formaldehyde (CH₂O), etc.
(ii) There are many compounds that do not conform to formula C_x(H₂O)_y but possess characteristic properties of carbohydrates and are treated as carbohydrates. For example, rham-nose (C₆H₁₂O₅).
Carbohydrates are polyhydroxy aldehydes, polyhydroxy ketones, their derivatives, and the compounds that give them upon hydrolysis, according to a more relevant definition.
Ketone-containing carbohydrates are referred to as ketoses, while aldehyde-containing carbohydrates are referred to as aldoses. Glycose is the broad name for all carbohydrates.
Monosaccharides are carbohydrates that cannot be hydrolyzed into simple carbs. Glucose, fructose, and other sugars are examples.

The carbohydrates which contain two to ten monosaccharide units are called oligosaccharides. For example, sucrose (C₁₂H₂₂O₁₁), maltose (C₁₂H₂₂O₁₁), raffinose (C₁₈H₃₂O₁₆), etc.
The carbohydrates which contain more than ten monosaccharide units are called polysaccharides. For example, starch, cellulose, glycogen, etc. These may be represented by the general formula (C₆H₁₀O₅)n.
Sugars and non-sugars are a more general grouping of carbs. Sugars such as glucose, fructose, and cane sugar are crystalline, water-soluble, and sweet. Non-sugars, such as starch and cellulose, are amorphous, water-insoluble, and tasteless compounds.
Reducing sugars are carbohydrates that can reduce Tollen’s reagent or Fehling solution. Reduced sugars are found in all monosaccharides. The majority of disaccharides are also sugar reducers. Sucrose is a sugar that does not reduce.
Carbohydrates are generally optically active because they contain chiral centres.
Carbohydrates perform two important functions in the body:
(a) They act as biofuels to provide energy for the functioning of living organisms.
In the human system, all carbohydrates except cellulose can serve as a source of energy. Starch and various sugars which are taken as food are first hydrolysed to glucose by the enzymes present in the digestive system.
Glucose on slow oxidation to carbon dioxide and water in the presence of enzymes liberates a large amount of energy which is used by the body for carrying out various functions.
C₆H₁₂O₆+ 60₂ ——> 6C0₂ + 6H₂0 + 2832 kJ
In order to fulfill the emergency requirements, our body also stores some of the carbohydrates as glycogen in the liver. Glycogen on hydrolysis gives glucose.
It may be noted that cellulose cannot be hydrolysed in our body because enzymes required for its hydrolysis are not present in our body. However, grazing animals are capable of hydrolysing cellulose to glucose.
(b) They act as constituents of cell membrane.