Karbohidrat II

5/28/2018 Karbohidrat II

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Carbohydrates

ADVANCED

FOOD CHEMISTRY
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Starches, which are assembled from-glucose units, are soluble and

easily digested. Cellulose, synthesized from -glucose

units, is insoluble and cannot be

digested as a food source by mostanimals.

Structural Representation(Haworth Projection)


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Disaccharides

Monosaccharides in the ring form can linktogether to form disaccharides or in greaternumbers to form polysaccharides.

Disaccharides are formed when twomonosaccharides are coupled together.

The coupling is of a specific type: an oxygenatom forms a bridge between the units coupled

together This oxygen atom must be part of an acetal or

ketal group.


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Linkage of two monosaccharide moleculesto form the disaccharides such as maltose,lactose and sucrose. The linkages are

designated as alpha () or beta ()depending on the orientation of the -OHgroup at the number C1 forming the bond.

The linkage are called glycosidic linkagesand are know as alpha () or beta () 1-2,1-3, 1-4, and1-6.

Disaccharides


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Disaccharides


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Oligosaccharides

Formed when small numbers ofmonosaccharides are coupled together.

Example: raffinose, stachyose, fructo-oligosaccharides, maltodextrin


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Polysaccharides

Starch (amylose & amylopectin)

Cellulose

Hemicellulose pectins, hydrocolloids


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Starch

The primary source of stored energy inplants

It occurs in nature as water-insoluble

granules and is available in unlimitedquantities

The most common starches used in the

food industries are extracted either fromcereals or roots and tubers


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Starch

Amyloplast (leucoplast): responsible for starchsynthesis

Hilum: where the synthesis of starch began

Starch is unique among carbohydrates because

it occurs naturally as discrete granules(orgrains), which is water-insoluble and is availablein unlimited quantities

The most common starches used in the food

industries are extracted either from cereals orroots and tubers


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Starch

In addition to their nutritive value,starches are used to affect the propertiesof many foods

They are used in gelling, thickening,adhesion, moisture-retention, stabilising,film forming, texturising, etc.


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Starch consists of two types of molecules, amylose(normally 20-30%) and amylopectin (normally 70-80%).Both consist of polymers of a-D-glucose units in theconformation (D-glucopyranose molecules).

In amylose these are linked -(14)-, with the ringoxygen atoms all on the same side, whereas inamylopectin about one residue in every twenty or so isalso linked -(16)- forming branch-points.

The relative proportions of amylose to amylopectin and -

(16)- branch-points both depend on the source of thestarch, e.g.amylomaizes contain over 50% amylosewhereas 'waxy' maize has almost none (~3%)

Starch


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Starch Production in Food Industry

Corn starch is extractedfrom the kernel through aprocess of wet milling.

The process employstechniques of grinding,

screening andcentrifugation to separatepurified starch from fiber,oil and tightly boundprotein. (Fig. 1).


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Amylopectin

A naturally occurring branchedpolymer of glucose found instarch whose linear portions areconnected by -1,4-glycosidiclinkages and the branch pointsare -1,6-glycosidic linkages

Amylose

A naturally occurring polymer ofglucose found in starch comprised

of anhydroglucose units with -1,4-glycosidic linkages in straightchain
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Amylose/amylopectin ratio

Generally, about one part of amylose to everythree parts of amylopectin for normal grainsources

Waxy varieties contain 0% amylose and 100%amylopectin used in non-gelling starchapplications, starch-thickened frozen products,and many modified starches

High amylose varieties: 60-85% amylose, therest in amylopectin. Useful as binders and filmformers


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The polymerization of glucose into amylose


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The difference between amylose and cellulose


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Polysacharides

Amylopectin


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Structure of Amylopectin


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Properties of starch components

Property Amylose AmylopectinGeneral structure Essentially linear Branched

Linkage - 1,4 - 1,4 and - 1,6

Average chain length 103 20-25Molecular weight


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Specific characteristics to differ

among starch

Granule size and shape

Amylose content

Gelatinization temperatureViscosity and pasting properties

Setback or cold viscosity

Gel strength Paste clarity


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Granules

This is the small (5-25 microns) grain-likeparticle in which amylose and amylopectinmolecules are deposited and stored by a

plant.

In the case of corn, they are located in theendosperm of the seed or kernel


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H

H

HH

H

H

HH

Structure of Starch Granules


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Granule size and shape

Starch granules come in a wide variety of sizes rangingfrom 3 microns to over 100 microns.

With some starches the granule size is polymodal,meaning the granules can be grouped into more than

one size range. Wheat starch, for example, has adistribution of both large and small granules.

Some granules exhibit their shape smoothly, whileothers are polyhedrons with a faceted surface.

Not directly related to functional properties, but ususeful information along with size for identification of thespecies


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Corn Potato

Rice Tapioca

Starch Granules


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Starch Granules


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Starch GranulesMaltose cross(birefrigence)


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Physical properties of starch from

various sources

Type ofstarch

Granuleshape

Granule size( )

Ratioamylose/

amylopectin

Gelatinization temp (oC)

Sago Cut ellipse 20-60 27:73 60-72

Rice Polygonal 3-8 17:83 61-78

Maize Polygonal 5-25 26:74 62-74

Potato Round 15-100 24:76 56-69

Tapioca Ovoid 5-35 17:83 52-64

Wheat Ellipse 2-35 25:75 52-64

Sweet potato Polygonal 16-25 18:82 58-74


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Birefrigence

Indicates that starch granules are semi-crystalline

When ungelatinized starch is viewed undera microscope with a polarized light, theintact crystalline structure of the starchrefracts the light in a Maltose Cross

pattern


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Starch-lipid interaction

Cereals commonly contain a high percentage of lipids(0.8-0.9%).

The lipid molecules may form a complex (helix) withamylose molecules.

Effects of lipid: Repress the swelling and solubilization of starch granules.

Increase the pasting temperature and reduce the water-binding-ability of the starches

Causes turbidity and starch pastes and starch solution

opaque/cloudy The oxidation of unsaturated lipidformation of undesirable

flavors


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+

Dissolvedamylosemolecule

Free lipidmolecule

Amylose-lipidcomplex(helix)

Formation of amylose-lipid complex


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Swelling and disorganization of starch granulesheated in water

When starch suspension is heated, the granulesabsorb water swell in size irreversibly.

Measures of starch gelatinization:

Swelling of granules

Increased viscosity

Increased translucency

Increased solubility

Gelatinization


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Gelatinization

Starch gelatinization is the collapse of molecularorder within the starch granule manifested inirreversible changes in properties such asgranular swelling, native crystalline melting, lossof birefrigence, starch solubilization, increasedsuspension viscosity.

The point of initial gelatinization and the rangeof over which it occurs is governed by starch

concentration, method of observation, granuletype, and heterogeneities within the granulepopulation under observation.


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Gelatinization temperature

The temperature range over which starchlosses its crystallinity in a watersuspension. Above this temperature range

starch rapidly swells and absorbs water tobecome a viscous or colloidal dispersion.

Gelatinization temperature range is

characteristics for each type of starch, thatis for each botanical sources


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A. Starch granules prior toheating in excess water

B. Starch granules after heatingto a temperature that melts thecrystallites

C. The starch granules swellmore during processing becausethey absorbed more water, andare therefore more gelatinized.

D. Highly gelatinized starchgranules are ruptured due to over

processing. The starch granulescompletely disappear


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Steps of starch gelatinization

Granules hydrate and swell to several times theiroriginal sizes

Granules lose their birefrigence (optical propertyof starch)

Clarity of the mixture increases Marked and rapid increase in consistency occurs

and reaches a maximum Linear molecules (amylose) dissolve and diffuse

from the ruptured granules Upon cooling, uniformly dispersed matrix forms

a gel or paste-like mass


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Starch gelatinization, pasting,

gelling and retrogradation

The initial suspension of insoluble starch in watercontains crystalline amylose and amylopectin starchpolymers associating with each other via H-bondingwithin starch granules.

Heated starch undergoes gelatinization, losing its

crystalline order through melting and interpolymer H-bond breakage.

The system is a sol of low viscosity, consisting of a liquidcontinuous phase and a solid dispersed phase.

With continuous heating, the system becomes a paste,

and is less pourable due to an increase in viscosity asmolecular material enters the intergranule matrix whilethe granules become swollen with water.


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As the gelatinized paste cools, an elastic, two-phase system forms consisting of a solidcontinous phase of mainly amylose polymersholding a liquid dispersed phase, water, through

intermolecular H-bonds

starch gels. The gelatinized starch regions of high amylose

content revert back to more crystalline structureduring storage retrogradation.

Retrograded starch expels water from its three-dimensional structure via syneresis, whichcauses gel shrinkage and increased starchpolymer intermolecular associations.

Starch gelatinization, pasting,

gelling and retrogradation
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Viscosity and granular changes

during pasting

Time/Temperature

Viscosity


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Relationship between starch gelatinization,

pasting, gelling and retrogradation

Raw, uncooked starch

granules heated in water Swelling is evident

H2O H2O


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Relationship between starch gelatinization,

pasting, gelling and retrogradation

Gelatinization and pasting

are complete

H2O

Some granules have

collapse


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Starch Gelatinization and Pasting,

Gelation, and Uglification

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Starch granules contain both linear amyloseand branched amylopectin.


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Raw, uncooked starch granulesheated in water


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Swelling is evident


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Notice loss of amylosefrom the granules

Some granules have collapsed


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Gelatinization and pasting are complete

Some granules have collapsed


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Now we start to cool

Gelation


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Notice areas of association. Theseare calledjunction zones


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This picture is not yet complete as we havent

accounted for the water in the system.


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water

water

water

waterwater

water

This is a starch gel

Uglification


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WATER

This picture ignores swollen and collapsed granules

Junction zones will naturally enlarge over time or

in response to processes such as freezing.

Uglification


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WATER

+ WATERof SYNERESISthat has beensqueezed out of the gel structure

The texture gets very ugly when this happens


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Pasting

Pasting is the phenomenon followinggelatinization in the dissolution of starch.

It involves granular swelling, exudation of

molecular components from the granule,an eventual, total disruption of thegranules.

P fil f t h l ti i ti


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Profile of starch gelatinization process

30 60 90 120 150150 180

1000

800

600

400

200

Corn

(40 g)

Potato (40 g)

Waxy sorghum (40 g)

50 65 80 95 95 80 65 50 50

0

Time (min)

Temperature (C)

Viscosit

y(BU)

Heating Cooling

Behaviour of Amylose in


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Behaviour of Amylose insolution

The amylose moleculeswill re-associate intoaggregates andprecipitate at lowconcentrations or set toa gel at higher amyloseconcentrations

G l ti


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Gelation

The formation of a gel from a cooled paste. A starch gel is rigid, thickened starch and water

mixture that has the properties of a solid. Starches with high amylose content form gels

more easily than do starches high inamylopectin.

Pastes derived from high amylopectin starchesare considered to be non-gelling but have a

gummy, cohesive texture. They are useful asthickening agents due to their ability to createan increase in viscosity.

G l ti


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Gelation

Amylose is the glue that holds geltogether

Therefore, waxy starches do not gel.

They form thick, cooked pastes and arefrequently the starting materials in theproduction of modified food starch

R t d ti


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Retrogradation

A process which occurs when the polymerscomprising gelatinized starch begin toreaasoaciate in an ordered structure.

In its initial phases, two or more amylose oramylopectin chains may form a simple juncturepoint which then may develop into moreextensively ordered regions

Retrogradation is especially evident whenamylose containing starches are cooled,resulting in water release (syneresis).

P t Cl it


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Paste Clarity

Influenced by the retrogradation tendencyof the starch, which also affects thetexture of the cooked structure

Ruber, tuber, and waxy starches haverelatively low retrogradation tendenciesand provide clearer gels

Cereal starches retrograde easily and givegels with less clear to opaque

Properties of starch water pastes with nearly


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Properties of starch-water pastes with nearly

the same maximum viscosity in viscometer

Starch%

(DB)

Cooked to max viscosity20 cooking beyond

maksimum

T (oC)Visc

(g-cm)

Gelstrength(g-cm)

T (oC)Visc

(g-cm)

Gelstrength(g-cm)

Potato 1.96 90 105 0 95 49 0Waxy corn 2.98 89 105 0 95 65 0

Tapioca 3.54 71 108 0 94 59 0

Corn 4.90 91 113 52 95 77 142

Rice 5.49 94 101 31 97 54 30

Wheat 6.44 92 105 345 94 62 440

Indicators of a proper starch cook


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Indicators of a proper starch cook

Under-cook Poor clarity

Low viscosity

Thin

Poor shelf stability Starchy flavor

Birefringence/incompletelyswollen granules

Proper Cook Clear

Full viscosity

Short, spoonable

Optimum stability Clean flavor

Fully swollengranules

Over-Cook Clear

Low viscosity

Cohesive

Poor stability Clean flavor

Fragmentedgranules

Effect of ingredients and


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Effect of ingredients and

conditions on gelatinization

Sugars

Acids

Enzymes

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Karbohidrat II