Carbohydrates
In general, Cho are natural chemical compounds containing the elements carbon,
hydrogen and oxygen and have the empirical formula (CH2 O)n where n is three or
more. However, some compounds with general properties of the carbohydrates also
contain phosphorus, nitrogen or sulphur; and other e.g. deoxyribose (C5 H10 O4 ) do
not have hydrogen and oxygen in the ratio as that in water. The Cho group contains
polyhydroxy aldehydes, ketones, alcohols and acids, their simple derivatives, and any
compound that may be hydrolysed to these.
Classification of carbohydrates:
 Monosaccharides : simple sugars.
 Disaccharides: contain two monosaccharides.
 Polysaccharides: contain many monosaccharides.
Monosaccharides
 Also known as simple sugars.
 Classified by: 1.The number of carbons and.
2. Whether aldoses or ketoses.
 Single-sugar units that consist of carbon, hydrogen, and oxygen atoms in ratio
of 1:2:1.
 6 carbons.
 12 hydrogens.
 6 oxygens.
 arrangement differs.
 About 70 known monosaccharides :Glucose, fructose, galactose, ribose,
arabinose,mannose, fucose, inositol, rhamnose…
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Glucose:

Is an aldohexose.

Mild sweet flavor.

Known as blood sugar and dextrose.

Essential energy source.

Found in every disaccharide and polysaccharide.

Found normally in bloodstream and tissue fluids.
Galactose:

Is an aldohexose.

Hardly tastes sweet.

Rarely found naturally as a single sugar.

It's one of the constituents of lactose.
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Fructose:

Is a ketohexose.

Sweetest sugar.

Found in fruits and honey.

Is commonly known as fruit sugar.

Added to soft drinks, cereals, desserts.

It's one of the constituents of sucrose.
Monosaccharides and its chemical reactions:
•
The hexoses either aldehydes or ketones can act as reducing agents
Hexose + alkaline Cu complex (Fehling s solution or Benedict s solution) →
A red-orange precipitate of Cu2O is formed
This reaction is the basis for the test for sugar in the
urine
•
Hexoses will ferment in the presence of enzymes found in yeast.
Disaccharides:

Pairs of the monosaccharides.

Glucose is always present.

2nd of the pair could be fructose, galactose or another glucose.

Taken apart by hydrolysis.

Put together by condensation.

Hydrolysis and condensation occur with all energy nutrients.

Maltose, sucrose and lactose.
Maltose:

2 glucose units.

Produced when starch breaks down.

Not abundant.
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Sucrose:

Fructose and glucose.

tastes sweet

fruit, vegetables, grains

Table sugar is refined sugar cane and sugar beets.

Brown, white, powdered.
Lactose:

Glucose and galactose.

Main carbohydrate in milk.
–
known as milk sugar
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Disaccharides and its chemical reactions:
•
Of the three disaccharides only maltose and lactose show reducing properties
with alkaline Cu complex ions.
•
Sucrose is not a reducing sugar.
•
Sucrose and maltose will ferment with yeast due to the presence of the
enzymes sucrase and maltase.
•
Lactose will not ferment with yeast because of the absence of the enzyme
lactase.
Polysaccharides:
- Polysaccharides are polymers of monosaccharides
- Hydrolysis of Polysaccharides → monosaccharides
- Three common polysaccharides:
Starch
Cellulose
Glycogen
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- Plants store their food as starch
-
Plants use cellulose as supporting and structural parts.
-
Animals use glycogen as a reserve supply of carbohydrate.
Properties of polysaccharides
•
Polysaccharides have a high molecular mass
•
Insoluble in water.
•
Tasteless.
•
Give negative tests for reducing sugars.
Glycogen:
1. Animal polysaccharide for glucose storage.
2. Found in liver and skeletal muscles.
3. All glucose is stored as glycogen
4. Many branch points allow for rapid break down for glucose to be released.
Starches:

stored in plant cells

body hydrolyzes plant starch to glucose

Sources: grains, dried beans, pasta, bread.
Cellulose:

Structural parts of plants, found in all plant derived food.

Bonds of fibers cannot be broken down during the digestive process.

Only digested and utilized by ruminants (cows, deers, giraffes, camels).
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
Most abundant of all carbohydrates.

Cotton flax: 97-99% cellulose.

Wood: ~ 50% cellulose.
Dietary Fiber
 Group of plant polysaccharides that are not digested or absorbed in the small
intestine but are broken apart by bacterial celluloses to yield glucose.
Dietary Fiber types:
1. Soluble fiber : Dissolves and thickens in water often forming a gel or colloid
like:
Pectin
2. Insoluble fiber: Does not dissolve in water but does hydrate like Cellulose
and bran.
Pectins:
 Pectin are heteropolysaccharides found in the pulp of fruits (citrus, apples).
 On hydrolysis pectin yield galacturonic acid, galactose, arabinose, methanol
and acetic acid.
 Pectin are composed of galactans and arabans .
 Used as gelling agents (to make jellies).
 Hydrolysis by enzyme called (Estrase mucopoly saccharide).
Lignin:
 Non-polysaccharide insoluble fiber embedded in the structural part of a
plant.
 Limits digestibility.
 Only certain fungi can digest.
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Factors affecting utilization of crude fiber:
1. In general, young animals are less efficient to digest cellulose than adults.
2. Ruminants (i.e. cattle, sheep and goat) are able to digest a large an amount of
crude fiber. This is because the microbes present in the ruminant's stomach
degrade the crude fiber and make digestion easier for the ruminant
3. Microbes present in the digestive tract, require other nutrients for efficient
utilization of crude fiber. Therefore, diets should be rich in proteins, vitamins
and minerals.
4. Digestibility of forage gradually declines as it becomes more matured.
Therefore, feeding tender forage is preferred.
Functions of carbohydrates
1. Carbohydrates are the main source of energy for animal body. This energy is
required for maintenance of body temperature and carrying out body
functions like digestion, respiration and blood circulation.
2. Performing physical activities like walking, grazing and maintaining
productive capacity.
3. Each gram of carbohydrate when oxidized provides 4.1 kilo calories (kcal) of
energy.
4. The small amount of carbohydrate reserve in the animal body exists in the
liver and the muscles in the form of glycogen, which resembles starch. It is,
therefore, frequently called "animal starch.
5. The excess of carbohydrate in diet are converted and stored as fat. When
there is lack of carbohydrates in body due to any reason, this fat is used to
supply energy to the animal body.
6. Deficiency of carbohydrate leads to inefficient utilization of protein and fats.
7. The monosaccharides (i.e. the simple sugars) are vitally important
constituents of DNA (deoxyribonucleic acid) and IRNA (ribonucleic acid).
These compounds possess and transfer the genetic characteristics of the cell.
8. Carbohydrates provide some fats and sweetness to milk as well.
9. In the ruminants, carbohydrates are required for the growth and
development of rumen microbes.
10. In younger animals, carbohydrates are helpful in absorption of calcium and
phosphorus.
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Deficiency of carbohydrates
From the above mentioned factors it can be easily ascertained that although very
little amount of carbohydrate is present in the animal body at any given time, yet
without the presence of this carbohydrate, the existence of any living organism is
doubtful.
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