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Pectin

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Pectin

Occurs in plant middle lamella

Gel former, e.g., fruit jelly

rom t e ree wor mean ng to congea

Pectin was discovered in 1790 by

Vauquelin and later (1825) crudely

characterized by Braconnot

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Pectic Substance Nomenclature

Protopectin-high methyl ester content

Pectinic acid-intermediate methyl ester

,

 –  Salts are pectinates

Pectin-intermediate methyl ester content,

colloidal

Pectic Acid-little methyl ester content

 –  Salts are pectates

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Pectin--Chemical structure

Some other sugars, mainly L-rhamnose, are also present

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Pectin structure

Other monosaccharides (L-rhamnose, L-

arabinose, D-xylose) in the structure may

limit the size of junctions zones that can

e orme an , us, a eas par a y

determine ultimate gel strength

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Carboxyl Substitution in Pectin

Degree of Methoxylation (DM)

 –  Protopectin 16%

 –   

 –  Low Methoxyl Pectin 2-4%

Degree of Esterification

 –  Protopectin 100%

 –  Normal Pectin 50%

 –  Low Methoxyl Pectin 12.5-25%

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High and low methoxyl pectins

If DE is greater than 50%, it is a high

methoxyl pectin (HM pectin)

If the DE is less than 50%, it is a low

methoxyl pectin (LM pectin)

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Degree of amidation (DA)

The DA value indicates the percentage of

carboxyl groups that nave been

converted to the amide form by ammonia

process ng

Amidated LM pectins may have a DA of

15-25%

Amidated pectins are especially sensitive

to Ca+2 (see W&B, Figure 13.5)

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Types of pectins

HM LM Amidated

LM

-COOCH3

 

-COOCH3

 

-COOCH3

 

-COOH

-COO-Na

+

 -COOH

-COO-Na

+

 -COOH

-COO-Na

+

-CONH2  (15-25%)

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Pectic Substances and Gelation

Normal Pectin –  Gels in the presence of acid and sugar

Low Methox l Pectin

 –  Doesn’t need sugar, but does need calcium ion

Pectic Acid

 –  Forms insoluble calcium pectate. This reaction is

responsible for the firming effect seen in certain

plant tissues, e.g., canned tomatoes

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Pectin gels

Atomic force microscopy image courtesy of Peter Cooke, ERRC, ARS, USDA

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Chemistry of pectic substances

OO

OO

O

H

Me

OO

O

O

OH

dilute acid

OO

H   H

OOH   H

or ase

dilute acid

high temperaturedepolymerization

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Commercial (Normal) Pectin

Liquid or powdered Source -- mostly lemon and lime peel (20-30%

pectin). This is the highest quality.

Some from apple pomace (10-15% pectin)

Pectin grade = number of pounds of sugar that

one pound of pectin can carry in a jelly

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Pectin production

Citrus peel is extracted at pH 1.5-3.0 and

60-100oC

Extract is filtered

Pectin is precipitated by addition of

isopropanol

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Commercial (Normal) Pectin

Grade is influenced by DE and molecular

weight

Gel strength -- measured by ridgelimeter

, , ,

texture analyzer.

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Low methoxyl pectin

Available commercially

Requires no sugar to gel

Requires calcium ion to gel

Preparation

 –  Pectin LM Pectin

 –  Acid preparation is best, produces firmer

gels

 –  Enzyme preparation is inferior as

demethylation is not random

Enzyme, acid, alkali

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Low methoxyl pectin

Range of pH for gel formation = 2.5-6.5

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Pectin uses

Principally used in jellies and jam

However, some is used in

 –  Confections –  Beverages

 –  Acidified drinks

See W&B, Table 13.2 for other uses of

pectins

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Jelly making

Need -- pectin + acid + sugar

Pectin

 –  0.5-1.0%

 –  If juice is low in pectin, may concentrate by

boiling or add more as commercial pectin

 –  Peach -- poor gel, pectin contains acetyl

groups

 –  Citrus -- forms a good gel

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Jelly making

Acid

 –  Contributes flavor

 –  pH optimum is 3.2

 –  If juice is low in acid, add lemon juice

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Jelly making

Sugar

 –  Preservative

 –  Micororganisms cannot grow due to thee y s g osmot c pressure

 –  Optimum sugar concentration is about 65%

soluble solids

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Jelly making

Sugar

 –  This is reflected in the final cooking

temperature (colligative properties) of 104.5o

 –  During this cooking some of the sucrose is

hydrolyzed to invert sugar which will

discourage sugar crystallization in the jelly

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Gel strength in normal

pectin jellies

Jelly strength

Continuity of 

structureRigidity of

structure

[Pectin]

Optimum is

about 1%

Acidity [Sugar]

Optimum is 3.2

Low-hard gel

High-no gel

Optimum 65%

Low-weak gel

High-crystalsform

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Setting times HM pectins

DE Setting time

Rapid set 72-75% 20-70 sec

Medium set 68-71% --

Slow set 62-68% 180-250 sec

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Setting times

Rapid set pectins are used in jams where

quick gelling is desired to preventflotation of the fruit

Slow set pectins are used in jellies to

provide time for bubbles to escape

High methoxyl pectin gels can not usually

be melted and reformed

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Theory of normal

pectin gel formation

A pectin junction zone

Hydrogen bonds

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Pectin junction zones

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OH

HH

H

OH

H OH

HO

O

HH

H

OH

H

O

O

O

HH

H

OH

H OH

HO

O

HH

OH

H

OH

H O

H

OHO O

CH3

CH3

OHO

O

HH

OH

H

OH

H O

H

O

O   O

HH

H

OH

H OH

H

O

O   O

HH

H

OH

H OH

H

O

O   O

OH

HH

H

OH

H OH

H

O

O

O

O

OHCH3

H

CH3   CH3

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Theory of low

methoxyl pectin gel formation

a c um on

Ionic

bonds

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LMP junction zones

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HH

OH

H

OH

H O

H

O-

O   O

HH

H

OH

H OH

H

OH

O O

HH

H

OH

H OH

H

O-

O   O

OH

HH

H

OH

H OH

H

O

O

O

O

O

H   CH3

O

OH

HH

H

OH

H OH

H

O

O

O

HH

H

OH

H OH

H

O-

O

O

HH

H

OH

H OH

H

O

O

O

HH

OH

H

OH

H O

H

O-

O

O

O

O

CH3H

CH3

Ca2+

Ca2+

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Theory of low

methoxyl pectin gel formation

 –  pH needs to be higher (3.2-4.0) because only

carboxylate (COO-) groups can participate

in these types of ionic bonds

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Methyl ester content

and gelling ability

   i   t   h   C  a   +   2

   A   b   i   l   i   t  y   t  o  g  e   l

0 20 40 60 80 100

DE

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Characteristics and uses

of low methoxyl pectin gels

 –  These gels can be melted and reformed

repeatedly

 –  No sugar is needed to form the gel, hence

products. In practice, a small amount of

sugar is left in the dietetic products as a

tenderizer/texturizer. When included in

these preparations, the resulting jellies are

not as brittle as they would be in the absence

of the sugar.

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Uses of low

methoxyl pectin gels

Fat mimetic

 –  From Hercules, this is a LM pectin gelled

with Ca+2 and microparticulated (particle

μ  μ

 –  Trade name is Slendid

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Labeling

Both HM and LM pectin may be labeled

pectin