2.0 kimia makanan carbohydrates

8/3/2019 2.0 Kimia Makanan Carbohydrates

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Carbohydrates



Sources of Carbohydrates Animal products

Plants - major source

Photosynthesis

Minor except milk (lactose)

Starch: storage of energy

Cellulose: structural

6CO2 + 6H2O + 673 Kcal → C6H12O6 + 6O2



Nutrient Composition of an

Adult Steer

Water 54%

Fat 26% Protein 15%

Ash 4.6%

Carbohydrate <1% little stored in the

animal body



Carbohydrates (CHO) C:H:O (1:2:1)

The most abundant organic moleculesin nature

Sources

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

Sugars, starch, cellulose, gums



Carbohydrates Carbohydrates are polyhydroxy

aldehydes or ketones

Aldehyde Ketone



Classification Classified according to the number

of sugar molecules:

Most plants contain different typesof carbohydrates than animals

1.Monosaccharides - 1 unit2.Disaccharides - 2 units3.Oligosaccharides - 3 to 10 units

4.Polysaccharides - Greater than 10units



Monosaccharides (CnH2nOn) Classified by the number of

carbon atoms:

3-C triose

4-C tetrose

5-C pentose 6-C hexose

nutritionally important

Sugars that contain four or more carbons exist primarily in cyclic form



Monosaccharides Pentoses (5C)

Xylose and arabinose

Component in hemicellulose, glycoproteins

Ribose

Found in every living cell

Found in compounds involved in metabolism: ATP/ADP

Riboflavin

DNA/RNA



Monosaccharides Hexoses (6c)

Glucose

Component of starch, cellulose, andglycogen

Major end-product of carbohydratedigestion in monogastrics

Primary form of sugar used for energy

Glucose, fructose, and galactose are among the most important monosaccharides in living organisms



Monosaccharides 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

Lactose (galactose + glucose)

Maltose (glucose + glucose)

Milk sugar Found only in milk

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 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

Polysaccharide

Chain of 10+ sugar molecules



Polysaccharides Heteropolysaccharide - composed of

two or more types of monosaccharides

Homopolysaccharides - composed of one type of monosaccharide

Starch

basic unit: alpha-D glucose principal sugar form in cereals



Starch

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 -

indigestible crystalline formafter cooling



Starch Three forms of starch:

1. Amylose Apha 1-4 linkages

Straight chain

14-30% of total plant starch

Water soluble



Starch2. Amylopectin

Alpha 1-4 linkages

with alpha 1-6linkage at branchpoints

70-85% total plant

starch Not water soluble



Starch3. Glycogen

Animal starch

Small amounts in liver andmuscle

Highly branched

Water soluble



Carbohydrates



General characteristics the term carbohydrate is derived from the

french: hydrate de carbone

compounds composed of C, H, and O (CH2O)n when n = 5 then C5H10O5

not all carbohydrates have this empiricalformula: deoxysugars, aminosugars

carbohydrates are the most abundantcompounds found in nature (cellulose: 100billion tons annually)



General characteristics Most carbohydrates are found naturally in

bound form rather than as simple sugars

Polysaccharides (starch, cellulose, inulin, gums) Glycoproteins and proteoglycans (hormones, blood group

substances, antibodies)

Glycolipids (cerebrosides, gangliosides)

Glycosides

Mucopolysaccharides (hyaluronic acid)

Nucleic acids



Functions sources of energy

intermediates in the biosynthesis of other

basic biochemical entities (fats and proteins) associated with other entities such as

glycosides, vitamins and antibiotics)

form structural tissues in plants and in

microorganisms (cellulose, lignin, murein) participate in biological transport, cell-cell

recognition, activation of growth factors,modulation of the immune system



Classification of carbohydrates Monosaccharides (monoses or glycoses)

Trioses, tetroses, pentoses, hexoses

Oligosaccharides Di, tri, tetra, penta, up to 9 or 10

Most important are the disaccharides

Polysaccharides or glycans Homopolysaccharides

Heteropolysaccharides

Complex carbohydrates



Monosaccharides - simple sugars with multiple

OH groups. Based on number of carbons (3, 4,5, 6), a monosaccharide is a triose, tetrose,pentose or hexose.

Disaccharides - 2 monosaccharides covalentlylinked.

Oligosaccharides - a few monosaccharidescovalently linked.

Polysaccharides - polymers consisting of chains

I

(CH2O)n or H - C - OHI

Carbohydrates (glycans) have the following

basic composition:



Monosaccharides

Aldoses (e.g., glucose)have an aldehyde group atone end.

Ketoses (e.g., fructose) have

a keto group, usually at C2.

C

C OHH

C HHO

C OHH

C OHH

CH2OH

D-glucose

OH

C HHO

C OHH

C OHH

CH2OH

CH2OH

C O

D-fructose



D vs L Designation

D & L designationsare based on the

configuration aboutthe singleasymmetric C inglyceraldehyde.

The lowerrepresentations areFischer Projections.

CHO

C

CH2OH

HO H

CHO

C

CH2OH

H OH

CHO

C

CH2OH

HO H

CHO

C

CH2OH

H OH

L-glyceraldehydeD-glyceraldehyde

L-glyceraldehydeD-glyceraldehyde



Sugar Nomenclature

For sugars with morethan one chiral center,

D or L refers to theasymmetric C farthestfrom the aldehyde orketo group.

Most naturallyoccurring sugars are Disomers.

O H O H

C C

H – C – OH HO – C – H

HO – C – H H – C – OH

H – C – OH HO – C – H

H – C – OH HO – C – H

CH2OH CH2OH

D-glucose L-glucose



D & L sugars are mirrorimages of one another.

They have the samename, e.g., D-glucose& L-glucose.

Other stereoisomers have unique names,e.g., glucose, mannose,galactose, etc.

The number of stereoisomers is 2n

, where n isthe number of asymmetric centers.

The 6-C aldoses have 4 asymmetric centers. Thusthere are 16 stereoisomers (8 D-sugars and 8 L-

sugars).

O H O H

C C

H – C – OH HO – C – H

HO – C – H H – C – OH

H – C – OH HO – C – H

H – C – OH HO – C – H

CH2OH CH2OH

D-glucose L-glucose

Hemiacetal & hemiketal



Hemiacetal & hemiketalformation

An aldehydecan react withan alcohol toform ahemiacetal.

A ketone canreact with analcohol to form

a hemiketal.

O C

H

R

OH

O C

R

R'

OHC

R

R'

O

aldehyde alcohol hemiacetal

ketone alcohol hemiketal

C

H

R

O R'R' OH

"R OH "R

+

+



Pentoses andhexoses cancyclize as the

ketone oraldehyde reactswith a distal OH.

Glucose forms anintra-molecularhemiacetal, asthe C1 aldehyde

& C5 OH react,to form a 6-member pyranosering, named after

pyran.

These representations of the cyclic sugars are called

Haworth projections.

H O

OH

H

OHH

OH

CH2OH

H

OH

H H O

OH

H

OHH

OH

CH2OH

H

H

OH

-D-glucose -D-glucose

23

4

5

6

1 1

6

5

4

32

H

CHO

C OH

C HHO

C OHH

C OHH

CH2OH

1

5

2

3

4

6

D-glucose

(linear form)



Fructose forms either

a 6-member pyranose ring, by reaction of the C2keto group with the OH on C6, or

a 5-member furanose ring, by reaction of the C2

keto group with the OH on C5.

CH2OH

C O

C HHO

C OHH

C OHH

CH2OH

HOH2C

OH

CH2OH

H

OH H

H HO

O

1

6

5

4

3

2

6

5

4 3

2

1

D-fructose (linear) -D-fructofuranose



Cyclization of glucose produces a new asymmetriccenter at C1. The 2 stereoisomers are calledanomers, & .

Haworth projections represent the cyclic sugars ashaving essentially planar rings, with the OH at theanomeric C1:

(OH below the ring)

H O

OH

H

OHH

OH

CH2OH

H

-D-glucose

OH

H H O

OH

H

OHH

OH

CH2OH

H

H

OH

-D-glucose

23

4

5

6

1 1

6

5

4

3 2



Because of the tetrahedral nature of carbon bonds,pyranose sugars actually assume a "chair" or

"boat" configuration, depending on the sugar.The representation above reflects the chair

configuration of the glucopyranose ring more

accurately than the Haworth projection.

O

H

HO

H

HO

H

OH

OHHH

OH

O

H

HO

H

HO

H

H

OHHOH

OH

-D-glucopyranose -D-glucopyranose

1

6

5

4

32



Sugar derivatives

sugar alcohol - lacks an aldehyde or ketone; e.g.,ribitol.

sugar acid - the aldehyde at C1, or OH at C6, isoxidized to a carboxylic acid; e.g., gluconic acid,

CH2OH

C

C

C

CH2OH

H OH

H OH

H OH

D-ribitol

COOH

C

C

C

C

H OH

HO H

H OH

D-gluconic acid D-glucuronic acid

CH2OH

OHH

CHO

C

C

C

C

H OH

HO H

H OH

COOH

OHH



Sugar derivatives

amino sugar - an amino group substitutes for ahydroxyl. An example is glucosamine.

The amino group may be acetylated, as inN -acetylglucosamine.

H O

OH

H

OH

H

NH2H

OH

CH2OH

H

-D-glucosamine

H O

OH

H

OH

H

NH

OH

CH2OH

H

-D- N -acetylglucosamine

C CH3

O

H



N-acetylneuraminate (N-acetylneuraminic acid,also called sialic acid) is often found as a terminal

residue of oligosaccharide chains of glycoproteins.Sialic acid imparts negative charge toglycoproteins, because its carboxyl group tends todissociate a proton at physiological pH, as shown

here.

NH O

H

COO

OH

H

HOH

H

H

R

CH3C

O

HC

HC

CH2OH

OH

OH

N -acetylneuraminate (sialic acid)

R =



Glycosidic Bonds

The anomeric hydroxyl and a hydroxyl of another

sugar or some other compound can join together,splitting out water to form a glycosidic bond:

R-OH + HO-R' R-O-R' + H2O

E.g., methanol reacts with the anomeric OH onglucose to form methyl glucoside (methyl-glucopyranose).

O

H

HO

H

HO

H

OH

OHHH

OH

-D-glucopyranose

O

H

HO

H

HO

H

OCH3

OHHH

OH

methyl--D-glucopyranose

CH3-OH+

methanol

H2

O



Structural representation of

sugars Fisher projection: straight chain

representation

Haworth projection: simple ring inperspective

Conformational representation: chair

and boat configurations



Rules for drawing Haworth

projections draw either a six or 5-membered ring

including oxygen as one atom

most aldohexoses are six-membered aldotetroses, aldopentoses,

ketohexoses are 5-membered

O O




projections next number the ring clockwise starting next

to the oxygen

if the substituent is to the right in the Fisherprojection, it will be drawn down in theHaworth projection (Down-Right Rule)

OO

1

23

4

5

1

23

4




projections for D-sugars the highest numbered

carbon (furthest from the carbonyl) is

drawn up. For L-sugars, it is drawndown

for D-sugars, the OH group at the

anomeric position is drawn down for and up for . For L-sugars is up and is down



Optical isomerism A property exhibited by any compound

whose mirror images are non-

superimposable Asymmetric compounds rotate plane

polarized light



POLARIMETRY Measurement of optical activity in chiral or

asymmetric molecules using plane polarized light

Molecules may be chiral because of certain atoms

or because of chiral axes or chiral planes

Measurement uses an instrument called a

polarimeter (Lippich type)

Rotation is either (+) dextrorotatory or (-)

levorotatory



polarimetry

Magnitude of rotation depends upon:

1. the nature of the compound

2. the length of the tube (cell or sample container) usuallyexpressed in decimeters (dm)

3. the wavelength of the light source employed; usually

either sodium D line at 589.3 nm or mercury vapor lamp

at 546.1 nm

4. temperature of sample

5. concentration of analyte in grams per 100 ml



[]DT

l x c

observed x 100=

D = Na D line

T = temperature oC

obs

: observed rotation in degree (specify solvent)

l = length of tube in decimeter

c = concentration in grams/100ml

[] = specific rotation



CH2OH CH2OH6 6



Cellobiose, a product of cellulose breakdown, is theotherwise equivalent anomer (O on C1 points up).

The (1 4) glycosidic linkage is represented as a zig-

zag, but one glucose is actually flipped over relative

H O

OH

H

OHH

OH

CH2OH

H

O H

OH

H

OHH

OH

CH2OH

H

O

HH

1

23

5

4

6

1

23

4

5

6

maltose

H O

OH

H

OHH

OH

CH2OH

H

O OH

H

H

OHH

OH

CH2OH

H

H

H

O1

23

4

5

6

1

23

4

5

6

cellobiose

Disaccharides:

Maltose, a cleavage

product of starch(e.g., amylose), is a

disaccharide with an

(1 4) glycosidic

link between C1 - C4OH of 2 glucoses.

It is the anomer

(C1 O points down).



Other disaccharides include:

Sucrose, common table sugar, has a glycosidicbond linking the anomeric hydroxyls of glucose & fructose.

Because the configuration at the anomeric C of glucose is (O points down from ring), the linkageis (12).

The full name of sucrose is -D-glucopyranosyl-(12)--D-fructopyranose.)

Lactose, milk sugar, is composed of galactose & glucose, with (14) linkage from the anomeric

OH of galactose. Its full name is -D-

CH2OH CH2OH CH2OH CH2OHCH2OH6



Polysaccharides:

Plants store glucose as amylose or amylopectin,

glucose polymers collectively called starch.

Glucose storage in polymeric form minimizesosmotic effects.

Amylose is a glucose polymer with (14) linkages.It adopts a helical conformation.

The end of the polysaccharide with an anomeric C1

not involved in a glycosidic bond is called the

H O

OH

H

OHH

OHH

O H

H

OHH

OHH

O

HH H O

O

H

OHH

OHH

H H O

H

OHH

OHH

OH

HH O

O

H

OHH

OHH

O

H

1

5

4

3

1

2

amylose



Amylopectin is a glucose polymer with mainly(14) linkages, but it also has branches formed by

(16) linkages. Branches are generally longer thanshown above.

The branches produce a compact structure & provide

multiple chain ends at which enzymatic cleavage can

H O

OH

H

OHH

OH

CH2OH

H

O H

H

OHH

OH

CH2OH

H

O

HH H O

OH

OHH

OH

CH2

HH H O

H

OHH

OH

CH2OH

H

OH

HH O

OH

OHH

OH

CH2OH

H

O

H

O

1 4

6

H O

H

OHH

OH

CH2OH

HH H O

H

OHH

OH

CH2OH

H

H

O

1

OH

3

4

5

2

amylopectin

CH2OH CH2OHglycogen



Glycogen, the glucose storage polymer in animals,is similar in structure to amylopectin.

But glycogen has more (16) branches.

The highly branched structure permits rapid glucoserelease from glycogen stores, e.g., in muscle duringexercise.

The ability to rapidly mobilize glucose is moreessential to animals than to lants.

H O

OH

H

OHH

OH

CH2OH

H

O H

H

OHH

OH

CH2OH

H

O

HH H O

OH

OHH

OH

CH2

HH H O

H

OHH

OH

CH2OH

H

OH

HH O

OH

OHH

OH

CH2OH

H

O

H

O

1 4

6

H O

H

OHH

OH

HH H O

H

OHH

OHH

H

O

1

OH

3

4

5

2

glycogen

CH2OH CH2OH CH2OH CH2OHCH2OH6



Cellulose, a major constituent of plant cell walls,consists of long linear chains of glucose with

(14) linkages.

Every other glucose is flipped over, due to linkages.

This promotes intra-chain and inter-chain H-bonds

and

cellulose

H O

OH

H

OHH

OHH

O

H

OHH

OHH

O

H H O

O H

OHH

OHH

H O

H

OHH

OHH

H

OHH O

O H

OHH

OHH

O

H H H H

1

5

4

3

1

2

van der Waals interactions,that cause cellulose chains

to be straight & rigid, andpack with a crystallinearrangement in thick bundles - microfibrils.

See: Botany online

Schematic of arrangement of

cellulose chains in a microf ibril.

http://web.chemistry.gatech.edu/~williams/bCourse_Information/6521/carbo/glu/cellulose_int_2.jpg

http://www.biologie.uni-hamburg.de/b-online/e26/26a.htm


































Multisubunit Cellulose Synthase complexes in theplasma membrane spin out from the cell surfacemicrofibrils consisting of 36 parallel, interactingcellulose chains.

These microfibrils are very strong.

The role of cellulose is to impart strength andrigidity to plant cell walls, which can withstand highhydrostatic pressure gradients. Osmotic swelling isprevented.

cellulose

H O

OH

H

OHH

OH

CH2OH

H

O

H

OHH

OH

CH2OH

HO

H H O

O H

OHH

OH

CH2OH

H

H O

H

OHH

OH

CH2OH

H

H

OHH O

O H

OHH

OH

CH2OH

HO

H H H H

1

6

5

4

3

1

2






















































































2.0 kimia makanan carbohydrates

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