Download Carbohydrates

Nutritional elements
1. Water
2. Carbohydrates
3. Lipids
4. Proteins
5. Vitamins
6. minerals
Water
Water (moisture) is the predominant constituent in many foods .As a medium water
supports chemical reactions, and it is a direct reactant in hydrolytic processes. Therefore,
removal of water from food or binding it by increasing the concentration of common salt or
sugar retards many reactions and inhibits the growth of microorganisms, thus improving the
shelf lives of a number of foods. Through physical interaction with proteins, polysaccharides,
lipids and salts, water contributes significantly to the texture of food.
Water importance
1. most abundant compound in the world.
2. animals must have frequent intakes of water to remain alive.
3. provides basis for all of the fluid of the animal’s body.
4. bloodstream requires liquid for circulation.
5. digestion requires moisture for breakdown of nutrients and movement of feed.
6. needed to produce milk.
7. provides cells with pressure to allow them to hold their shape.
8. helps body to maintain constant temperature.
9. flushes the animal’s body of waste and toxic materials.
10.a loss of 20% of body water will result in death.
11.animals generally need about three pounds of water for every pound of solid feed they
consume.
Carbohydrates
Carbohydrates are ubiquitous. Every organism contains some carbohydrate.
Carbohydrates can range from a simple monosaccharide to a large complex
polysaccharide.
Polysaccharides in combination with proteins, lipids, and nucleic acids play an
important role in many plant and animal metabolic systems.
Carbohydrates have many roles in food systems, where they function to provide
flavor, structure, and texture to food and nutritional benefits to the consumer.
They have a central role in the metabolism of animals and plants. Carbohydrate
biosynthesis in plants starting from carbon dioxide and water with the help of light
energy, i. e., photosynthesis, is the basis for the existence of all other organisms which
depend on the intake of organic substances with food.
The term carbohydrate was originally coined because these molecules were believed
to be hydrates of carbon, having the general formula Cn(H2O)n
General characteristics
1. the term carbohydrate is derived from the French: hydrate de carbone .
2. compounds composed of C, H, and O.
3. (CH2O)n when n = 5 then C5H10O5.
4. not all carbohydrates have this empirical formula: deoxysugars, amino sugars .
carbohydrates are the most abundant compounds found in nature (cellulose: 100
billion tons annually).
 Most carbohydrates are found naturally in bound form rather than as simple sugars
1. Polysaccharides (starch, cellulose, inulin, gums).
2. Glycoproteins and proteoglycans (hormones, blood group substances,
antibodies).
3. Glycolipids (cerebrosides, gangliosides).
4. Glycosides.
5. Mucopolysaccharides (hyaluronic acid).
6. Nucleic acids.
Functions
1. sources of energy
2. intermediates in the biosynthesis of other basic biochemical entities (fats and
proteins).
3. associated with other entities such as glycosides, vitamins and antibiotics).
4. form structural tissues in plants and in microorganisms (cellulose, lignin, murein).
5. participate in biological transport, activation of growth factors, modulation of the
immune system.
Aldose sugars
H
(H
C
O
C
OH)n
H
CH2OH
C
O
C
OH
CH2OH
C
O
H
C
OH
H
C
OH
Aldotriose
n=1
Aldose
H
H
H
CH2OH
(H
C
O
C
OH)n
CH2OH
Ketose
C
OH
H
C
H
C
O
H
C
OH
OH
H
C
OH
OH
H
C
OH
H
C
OH
CH2OH
CH2OH
CH2OH
CH2OH
H
C
O
C
OH
CH2OH
Ketotriose
n=0
H
C
Aldohexose
n=4
O
CH2OH
O
Aldopentose
n=3
CH2OH
C
C
Aldotetrose
n=2
Ketose sugars
CH2OH
H
Ketotetrose
n=1
C
O
CH2OH
H
C
OH
C
O
H
C
OH
H
C
OH
CH2OH
H
Ketopentose
n=2
H
OH
C
OH
CH2OH
Ketohexose
n=3
Structure of a simple aldose and a simple ketose
Enantiomers and epimers
H
H
H
H
C
O
H
C
OH
H
C
OH
CH2OH
C
O
C
O
C
O
HO
C
H
HO
C
H
OH
C
H
HO
C
H
HO
C
H
OH
C
H
H
C
OH
HO
C
H
H
C
OH
H
C
OH
CH2OH
these two aldotetroses are enantiomers.
They are stereoisomers that are mirror
images of each other
CH2OH
CH2OH
these two aldohexoses are C-4 epimers.
they differ only in the position of the
hydroxyl group on one asymmetric carbon
(carbon 4)
Classification of carbohydrates
I.
Monosaccharides (monoses or glycoses)
1. Trioses, tetroses, pentoses, hexoses
II.
Oligosaccharides
1. Di, tri, tetra, penta, up to 9 or 10
2. Most important are the disaccharides
III.
Polysaccharides or glycans
1. Homopolysaccharides
2. Heteropolysaccharides
3. Complex carbohydrates
Monosaccharides
 also known as simple sugars.
 classified by :1. the number of carbons and.
2. whether aldoses or ketoses.
 most (99%) are straight chain compounds.
 D-glyceraldehyde is the simplest of the aldoses (aldotriose).
 all other sugars have the ending ose (glucose, galactose, ribose, lactose).
 Single-sugar units that consist of carbon, hydrogen, and oxygen atoms in ratio of 1:2:1.
 About 70 known monosaccharides :Glucose, fructose, galactose, ribose,
arabinose,mannose, fucose, inositol, rhamnose…
Glucose
 Blood sugar”.
 Most abundant monosaccharide in body.
 Provides a source of energy (ATP) to cells.
 Synthesizes other compounds in body.
i.e., glucose can be converted to some amino acids and fat for long-term energy
storage Glycogen.
Fructose
 Naturally occurring monosaccharide
 found primarily in honey, fruits, & vegetables
 Sweetest monosaccharide.
Galactose
1) Few foods contain this monosaccharide in its free state
2) Coupled with glucose to make lactose
3) Component of glycolipids & glycoproteins
4) Converted to glucose and used as energy
Disaccharides
 Consist of 2 monosaccharides bonded
together
1.
Lactose, sucrose, maltose
2.
Contain glycosidic bond
Types of Disaccharides
1. Lactose
2. Glucose + galactose
3. Source: milk
4. Sucrose
5. Glucose + fructose
6. Sources: sugar cane & table sugar
7. Maltose
8. Glucose + glucose
9. Sources: starch +infant formula
Oligosaccharides
1. 3-10 monosaccharides
Types: Raffinose . Stachyose .
2. Sources: dried beans, soybeans,peas, lentils, sweet potato.
3. Components of cell membranes and part of milk, particularly human milk.
4. Humans lack enzymes to digest oligosaccharides causing bloating, cramps, & gas.
5. An alpha-galactosidase from Aspergillus niger, a fungus Converts oligosaccharides into
simple sugars so gas is not produced by fermentation.
Oligosaccharides types:
1. Trisaccharide: raffinose (glucose, galactose and fructose).
2. Tetrasaccharide: stachyose (2 galactoses, glucose and fructose).
3. Pentasaccharide: verbascose (3 galactoses, glucose and fructose).
4. Hexasaccharide: ajugose (4 galactoses, glucose and fructose).
Polysaccharides
 >10 monosaccharides.
Most are made up of hundreds of monosaccharides bonded together
Types:
1. Starch: Storage in plants
2. Glycogen: Storage in animals
3. Dietary Fiber/cellulose: Not used for energy by humans but key for grazing animals.
Starch
1. Plant polysaccharide for glucose storage.
2. Amylose (α-1,4 glycosidic bonds) & Amylopectin (α-1,4 & 1,6).
3. Sources: grains, dried beans, pasta, bread.
Amylose and amylopectin are the 2 forms of starch. Amylopectin
is a highly branched structure, with branches occurring every 12
to 30 residues
Amylose and amylopectin are the 2 forms of starch. Amylopectin
is a highly branched structure, with branches occurring every 12
to 30 residues
Glycogen
1. Animal polysaccharide for glucose storage.
2. Found in liver and skeletal muscles.
3. Many branch points allow for rapid break down for glucose to be released.
Branching in Glycogen
1. Glycogen is more highly branched than amylopectin An α-1,6 branch every 4 to 8
glucose units
 for glycogen vs every 25th glucose unit for amylopectin
Dietary Fiber
 Group of plant polysaccharides that are not digested or absorbed in the human small
intestine but are broken apart by bacterial cellulases to yield glucose.
Dietary Fiber typs:
1. Soluble fiber : Dissolves and thickens in water often forming a gel or colloid like
Pectin Galactomannan (guar gum – a common thickening agent)
1. Insoluble fiber : Does not dissolve in water but does hydrate like Cellulose and bran
Pectins
1. pectins are heteropolysaccharides found in the pulp of fruits (citrus, apples).
2. on hydrolysis pectins yield galacturonic acid, galactose, arabinose, methanol and acetic
acid.
3. pectins are composed of galactans and arabans .
4. used as gelling agents (to make jellies).
Cellulose
1. Polymer of b-D-glucose attached by b(1,4) linkages.
2. Only digested and utilized by ruminants (cows, deers, giraffes, camels).
3. A structural polysaccharide.
4. Yields glucose upon complete hydrolysis.
5. Partial hydrolysis yields cellobiose .
6. Most abundant of all carbohydrates.
a) Cotton flax: 97-99% cellulose.
b) Wood: ~ 50% cellulose.
7. Gives no color with iodine.
8. Held together with lignin in woody plant tissues.
Lignin
1. Non-polysaccharide insoluble fiber embedded in the structural part of a plant
2. Limits digestibility
3. Only certain fungi can digest
Chitin
1. chitin is the second most abundant carbohydrate polymer.
2. Like cellulose, chitin is a structural polymer.
3. present in the cell wall of fungi and in the exoskeletons of crustaceans, insects and
spiders.
4. chitin is used commercially in coatings (extends the shelf life of fruits and meats).
5. A chitin derivative binds to iron atoms in meat and slows the rancidity process.