1 Structure of Carbohydrates 大学动物营养学课件 英文版

Monosaccharides (CnH2nOn)
Classified by the number of carbon atoms:
3-C
triose
4-C
tetrose
5-C 6-C
pentose hexose
nutritionally important
Sugars that contain four or more carbons exist primarily in cyclic form
➢ Starch
▪ basic unit: alpha-D glucose ▪ principal sugar form in cereals
Starch
Three forms of starch:
1. Amylose
Apha 1-4 linkages Straight chain 14-30% of total plant star
Starch granules
Held together by H-bonds Insoluble in water
Raw starch is not well digested
Heat causes swelling of granules
‘Gelatinization’ Access for digestive enzymes Retrograded starch -
Heteropolysaccharide
Hemicellulose
Complex mixture of glucose, mannose, arabinose, and galactose
Beta 1-4 linkage Principal component of plant cell wall Degraded only by microbial enzymes
Polysaccharides
Heteropolysaccharides, cont.
Pectin
Polymers of 1-4 linked glucose Degraded only by microbial enzymes Found primarily in the space between
FOS are used as ‘prebiotics’
Promote growth of lactic-acid bacteria
(Lactobacillus and Bifidobacteria)
These bacteria utilize FOS for energy
Suppress growth of E. coli
Improve GI health
Homopolysaccharide
Cellulose
▪ Most important structural polysaccharide of plants
▪ Basic unit: beta-D-glucose ▪ Straight chain, beta 1-4 linkage ▪ Highly stable ▪ Cotton is purest form
Cellulobiose (glucose + glucose)
➢ Beta 1-4 linkage in cellulose ➢ Does not exist freely in nature
Oligo- and Poly-saccharides
Oligosaccharide
Chain of 3–10 sugar molecules
Sources
➢ Sugars, starch, cellulose, gums
Carbohydrates
Carbohydrates are polyhydroxy aldehydes or ketones
Aldehyde
Ketone
Classification
Classified according to the number of sugar molecules:
Monosaccharides
Pentoses (5C)
Xylose and arabinose
Component in hemicellulose, glycoproteins
Ribose
Found in every living cell Found in compounds involved in metabolism:
Hexoses (6c)
Fructose
75% of sugars in honey Found in fruits and cane sugar
Galactose
Component of milk sugar (lactose) May be metabolized to glucose
Mannose
Found after hydrolysis of plant mannosans and gums; legumes
Disaccharides
Two monosaccharide molecules linked by a glycosidic (or acetal) bond
Polysaccharide
Chain of 10+ sugar molecules
Polysaccharides
Heteropolysaccharide - composed of two or more types of monosaccharides
Homopolysaccharides - composed of one type of monosaccharide
Soluble: pectins, gums, and some hemicellulose
Hemicellulose
NSC
Structural Carbohydrate
Potentially degraded
Lignin
Indigestible
Structural Non-Carbohydrates
Lignin
Polymers of phenylpropane units Encases cellulose and hemicellulose to enhance
little stored in the animal body
Carbohydrates (CHO)
C:H:O (1:2:1) The most abundant organic molecules
in nature
➢ Major component of plant tissue ➢ Comprise up to 70% or more of dry matter of forages ➢ Make up less than 1% of the weight of animals
➢ Lactose (galactose + glucose)
▪ Milk sugar ▪ Found only in milk
➢ Maltose (glucose + glucose)
▪ Intermediate product of starch hydrolysis ▪ Found in starch from melting of barley ▪ Alpha 1-4 linkage fundamental for starch
Disaccharides
Sucrose (glucose + fructose)
➢ Common table sugar ➢ Produced in leaves and stems of plants ➢ Found in sugar cane and sugar beets
Disaccharides
rigidity to plant cells As plant matures it becomes “woody” Lignification reduces digestibility by acting as a
barrier to the plant carbohydrates No animal or bacteria can break these bonds
Found mainly in cell walls of barley, oats, yeast
Dietary Fiber for Monogastrics with Limited Post-gastric Fermentation
Cellulose, hemicellulose, lignin, gums, pectin
▪ Primary form of sugar used for energy
Glucose, fructose, and galactose are among the most important monosaccharides in living organisms
Monosaccharides
• Monosaccharides - 1 unit • Disaccharides - 2 units • Oligosaccharides - 3 to 10 units • Polysaccharides - Greater than 10
units
Most plants contain different types of carbohydrates than animals
Special Carbohydrates
Beta-glucans
Glucose with beta-1,4 and beta-1,3 bonds Absorb water and forms a gel
Reduces rate of passage (and feed intake) Prevents digestive-enzyme access Sticky or wet feces