Transcript Nutrition Lecture Three

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Types of Carbohydrates

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

Smallest sugar molecules
Sugar alcohols
Sugar acids
Sugar amines


Simple sugars
Complex sugars
polysaccharides
– Polymers of simple sugars

fibre
Simple Sugars
 Monosaccharides
 Smallest
sugars
 Can be absorbed without digestion
 Sweet tasting
 Can combine with others to make
larger molecules:
 Disaccharides
 Polysaccharides
Hexoses
•Hexoses
•C6H12O6
Glucose
Galactose

Galactose
Fructose
Monosaccharides
•Pentoses
C5H10O5
• Polymerise to form
 Pentosans
 DNA
& RNA
•Simple Sugars

Disaccharides
Maltose
•Formed by joining two
.
monosaccharides:
•Maltose
•from two Glucose
Lactose
•Lactose
•From glucose & galactose
•Sucrose
•From glucose & fructose
Sucrose
Use of Simple Sugars

Sweeteners
– good tasting

Consistency
– sauces, glazes, syrups
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Preservatives
– Cordials, glazed fruit, dried fruit
– jams, sweetened condensed milk
Problems with Simple Sugars
Absorbed too quickly form digestive
tract.
 Causes the pancreas to produce excess
insulin
 Tissues become insensitive to insulin
> Type II diabetes

More Problems with Simple
Sugars
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Encourages tooth decay bacteria

Empty kilojoules

Not enough vitamins & minerals as needed
for catabolism

Takes Vitamins away from growth & repair
Solutions to sugar problem
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Use artificial sweeteners
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Aspartame (nutrasweet), Saccharin,
Sucralose
• Some are banned in USA
• Don’t have consistency
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Use Polyols
• Not absorbed

Eat more fibre
• Slows rate of absorption
Sweetness Of Sugars
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The relative sweetness power (RSP) for
– five simple sugars in 5% solutions.
Sugar
RSP:
Lactose Galactose Glucose
0.25
0.50
0.56
Sucrose
1.00
Fructose
1.30
Sugar Acids

Found as units
of pectin (polymer)
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Glucuronic Acid

Glucuronic Acid Methyl
Ester
Sugar Amines
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Found as units of Polymers:
chitin and in bacterial cell walls
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Glucosamine

N-acyl glucosamine
Polyols (or "sugar alcohols")
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Sorbitol
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Iditol
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Manitol
Properties of Polyols
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Made from simple sugars
– Functional properties
– Vary in their sweetness and kilojoule density, but are
non-calarigenic because they are not absorbed
Polyol
Sorbitol
Isomalt
Lactitol
Mannitol
% Sweetness
60%
55%
40%
65%
kj/g
10.0
8.4
8.4
6.7
Complex Carbohydrates
Digestible
Complex
CHO
Indigestible
Fibre
a Links
b Links

Amylose --> straight chain

Amylopectin --> Branched chain
Digestible Complex
Carbohydrates
– All digested slower than simple sugars
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Starch - in plants
– Amylose ( Straight chain)
– Amylopectin ( Branched chain)
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Dextrin
– Smaller fragments of starch
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Glycogen - in meats
– branched chain
Indigestible Polysaccharides
(Fibre)
 Crude
Fibre and Dietary Fibre:

Insoluble and soluble fibre
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Crude fibre (Insoluble)
– Non-starch polysaccharide (NSP):
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Lignin
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Cellulose
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Chitin
Dietary Fibre
 Soluble
Fibre :
•Pectin
•Undigested starch
•Retrograded amylose
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b- Glucans
•Inulin
Inulin
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Polymer of Fructose
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found in:
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chicory, artichoke, dahlia , onion and garlic
Fibre Polysaccharides
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Pectins
– a dietary fibre
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Chitin
– a crude fibre
All have b - links
Dietary Need For Fibre
How much do we need?
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Digestible Carbohydrates
No daily allowance has been recommended
But we need a lot of it
Fibre
 20
to 30 gams per day
 Most Australians
eat less than half this.
Why do we need Digestible
Carbohydrates?
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Energy
– Brain, Red blood and Kidney Cells
use only Glucose for energy
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Anaplerosis
– Citric Acid Cycle intermediates are made
only from sugar
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NADPH
– Made via Direct Oxidative pathway from
glucose is needed for synthesis

Conversion to Pentoses
– Needed for DNA and RNA
Carbohydrate Catabolism