4440 PECTIN/Properties and Determination

Jansman AJM, Hill GD, Huisman J and van der Poel AFB intake and effects on nutrition and health (review).
(eds) (1998) Recent Advances of Research in Anti- Journal of the Science of Food and Agriculture 80:
nutritional Factors in Legume Seeds and Rape Seeds. 1094–1117.
Wageningen, The Netherlands: Wageningen Pers. Savage GP (1988) The composition and nutritive value of
Martinez San Ireneo M, Ibanez Sandin MD and Fernandez- lentils (Lens culinaris). Nutrition Abstracts and Reviews
Caldas E (2000) Hypersensitivity to members of the (Series A) 58: 319–343.
botanical order Fabales (legumes). Journal of Investiga- Savage GP and Deo S (1989) The nutritional value of
tional Allergology and Clinical Immunology 10: 187– peas (Pisum sativum). A literature review. Nutrition
199. Abstracts and Reviews (Series A) 59: 65–88.
Rowland I (1999) Optimal nutrition: fibre and phytochem- Urbano G, Lopez-Jurado M, Aranda P et al. (2000) The
icals. Proceedings of the Nutrition Society 58: 415–419. role of phytic acid in legumes: antinutrient or beneficial
Sanchez-Monge R, Pascual CY, Diaz-Perales A et al. (2000) function? Journal of Physiology and Biochemistry 56:
Isolation and characterisation of relevant allergens from 283–294.
boiled lentils. Journal of Allergy and Clinical Immun- van der Poel AFB, Huisman J and Saini HS (eds) (1993)
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Santos-Buelga C and Scalbert A (2000) Proanthocyanidins in Legume Seeds. Wageningen, The Netherlands:
and tannin-like compounds. Nature, occurrence, dietary Wageningen Pers.

Pecans See Walnuts and Pecans

PECTIN

Contents
Properties and Determination
Food Use

Properties and Determination only started at the beginning of the twentieth century.
In this document we highlight the chemistry, origin
L Flutto, Danisco, New Century, KS, USA
and production, and the functional properties of
Copyright 2003, Elsevier Science Ltd. All Rights Reserved. pectin.

Introduction Chemistry
0001 Pectin is a high-molecular-weight carbohydrate poly-
The Homogalacturonic Acid Backbone
mer which is present in virtually all plants where it
contributes to the cell structure. The term pectin Pectin consists of a chain of galacturonic acid units 0003

covers a number of polymers which vary according which are linked by a-1,4 glycosidic bonds. The
to their molecular weight, chemical configuration, galacturonic acid chain is partly esterified as methyl
and content of neutral sugars, and different plant esters. Pectin molecules can have a molecular weight
types produce pectin with different functional prop- of more than 200 000, corresponding to a degree of
erties. The word ‘pectin’ comes from the Greek word polymerization up to 1000 units (Figure 1).
pektos which means firm and hard, reflecting pectin’s Though the esters are the most significant compon- 0004

ability to form gels. ents on the galacturonic acid backbone, other chem-
0002 The gelling properties of pectin have been known icals, such as acetyl, can be important in specific
for centuries, but the isolation of commercial pectin pectin types. Commercial pectin can also be partly
 PECTIN/Properties and Determination 4441

OH COOCH3 OH COOCH3 OH

O O O
O
OH OH OH OH OH
O O
O O O

COOH OH COOH OH COOCH3

fig0001 Figure 1 Pectin consists of long sequences of anhydro galacturonic acid completely or partly esterified with methanol.

tbl0001 Table 1 Classification of pectins However, 1,2-linked l-rhamnose is present in the

DE > 50% DE < 50% main polygalacturonic chain where it forms ‘kinks’
Low-ester pectin (LE) in the molecular chain. Xylose is also a very import-
High-ester pectin (HE) No amidation DA < 25% ant neutral sugar in apple pectin where it is attached
Conventional LE Amidated LE in the homogalacturonic backbone.
DE, degree of esterification; DA, degree of amidation.
It is well documented that neutral sugar side chains 0011

are concentrated in relatively short segments of the

galacturonic backbone, described as ‘hairy regions.’
The part of the molecule free of side chains is
amidated with ammonia to form galacturonamide described as the ‘smooth region.’ (Figure 2).
units in the molecular chain.
0005 Some neutral sugars are also included in the homo- Chemical and Physical Properties
galacturonic backbone. This is the case for rhamnose Solubility Pectin is soluble in water, but insoluble 0012
but also specifically in apple pectins for xylose. in most organic solvents. The solubilization rate in
0006 The percentage of galacturonic acid of the whole water is related to the degree of polymerization and
molecule is defined as the galacturonic acid content the number and distribution of methyl-ester groups.
(% GA), which is set at a minimum of 65% in the The pH, temperature, and ionic strength of the solu-
definition of pectin as a food additive. tion are of great importance to the rate of pectin
0007 The percentage of esterified or amidated galacturo- dissolution. The calcium content of the water used
nic acid units of the total number of galacturonic acid to dissolve the pectin is of special relevance as it is
units in the molecule are respectively defined as the common that a high-water hardness will translate
degree of esterification (DE) and the degree of amida- into an incomplete dissolution of pectin.
tion (DA) (Table 1). Regulations limit the DA to a
maximum of 25%. Rheology of pectin solutions Pectin solutions are 0013

viscous but pectin is not an especially effective visco-

Esterification Pattern sifier compared to other gums such as guar gum.
0008 In addition to the number of components on the Dilute pectin solutions are almost Newtonian, and 0014

backbone, their position is of significant importance they are only slightly affected by the presence of
to the functional properties of pectin. The distribu- calcium. However, solutions with more than 1%
tion of esters is of special importance as it affects the pectin exhibit pseudoplastic behavior and are strongly
local electrostatic charge density of the polymer and affected by calcium. There is a continuum in texture
so its interaction with other charged molecules, starting with water through thixotropic solutions
whether ions such as calcium, proteins, or other with yield value to stiff gels depending on the pectin
pectin molecules. type and concentration, level of calcium, and pH.
0009 In apple pectin subjected to a mild extraction pro-
Stability High-ester pectins are stable at pH levels of 0015
cess, the ester distribution is reported to be almost
2.5–4.5. Above a pH level of 4.5, b-elimination will
random, while citrus pectin tends to have a somewhat
occur, depolymerizing the galacturonic acid chain.
blockwise distribution.
This mechanism requires an esterified carboxyl
group next to the glycosidic bond to be cleaved
Neutral Sugars
(Figure 3), so low-ester pectins are more stable at
0010 Pectin always contains varying amounts of neutral higher pH values.
sugars such as d-galactose, l-rhamnose, l-arabinose, The pectin molecular structure is quite resistant 0016

and d-xylose. Some of these neutral sugars are con- to heat. At pH around 3.5 pectin is only marginally
stituents of side chains to the galacturonan backbone. depolymerized at high temperatures. The heat-stability
 4442 PECTIN/Properties and Determination

Hairy region
Galacturonic acid
Methylated galacturonic acid

Sm om
Rhamnose

h
oo oga
th lac
Arabinose or galactose

re tu
gi ro
on na
Xylose (high content in apple pectin)

, n
Acetyl group (high content in sugar
beet pectin)

COOCH3
OH O
OH
OH
OH

COOH
OH O
OH
OH
OH Rhamnogalacturonan

fig0002 Figure 2 Primary and secondary structure of pectin.

O O CH3
O CH3
OH C O
OH C
O OH
O O
OH OH
OH OH
O
O O
O
O C OH
O C OH
O CH3
O CH3

fig0003 Figure 3 b-elimination mechanism.

of pectin is greatly improved when the water activity neutralized with cations of calcium, potassium, and
of the system is lowered through the addition of magnesium which are present in the plant tissues.
sugar. Pectin is today commercially produced mostly 0018

from apple pomace and citrus peels by an extraction

process followed by separation, purification, isol-
Origin and Production
ation, and then drying, milling, and standardization
0017 Pectin is a natural component of plants, predomin- (Figure 4).
antly in the form of pectic substance or protopectin,
which is not soluble in water. The pectic substance is
Functional Properties
an essential part of the plant cell wall structure, acting
as a cement for the cellulosic network and a hydrating Pectins are used in a broad variety of food and 0019

agent. The exact nature of the pectic substance is not pharmaceutical products. Their principal properties
completely understood. It is, however, generally rec- are gel formation with both high- and low-ester
ognized that it is a complex structure in which pectin pectins, viscosity build-up, and protein stabilization
is attached to other cell wall components such as with high-ester pectins. As methods develop for
cellulose, hemicellulose, and proteins by covalent obtaining a better understanding of the pectin mol-
bonds, hydrogen bonds, and/or ionic interactions. ecular structure, it is likely pectin will be attributed
In the plant the residual carboxyl groups are partly new functional properties in the future.
 PECTIN/Properties and Determination 4443

Peel or pomace depend on the charge density of the molecule which

Extraction Water can be directly correlated to the pH of the medium
Acid and the frequency of free galacturonic acids of the
Separation polymer. The higher the pH and the lower the degree
of esterification, the higher the charge density and
Purification hence the stronger the repulsion.
This repulsion, but more importantly the impossi- 0024
Liquid concentration bility of forming hydrogen bonds between ionized
Alcohol Ammonia pectin chains, are the reasons why a low pH is re-
(added before or
after precipitation) quired for high-ester pectin gelling. At a low pH,
typically below 3.6, the repulsion is low enough for
Precipitation Amidation the distance between the pectin chains to be reduced
sufficiently and hydrogen bonding can occur. In order
Drying and grinding to achieve sufficient hydrophobic interactions to sta-
bilize the molecular network, the water activity of the
Standardization
system also has to be decreased. Sugars are usually
HE pectin added for this purpose.
LC pectin LA pectin So, typically, high-ester pectins will only form gels 0025

fig0004 Figure 4 Pectin manufacture flow sheet. HE, high-ester; LC,

when the pH is below 3.6 and soluble solids are above
low ester conventional; LA, low ester amidated. 55% (Figure 5).
Upon storage of a cooled gel, it is typical that the 0026

texture will still develop into a stronger final gel. This

corresponds to a slow reorganization of the network
Gelling of High-Ester Pectins involving the creation of new junction zones or an
enlargement of the existing junctions between the
0020 The ability of pectin to form gels in specific condi- pectin molecules.
tions has long been used in the production of jams
and preserves. The separation of high- and low-ester
pectins in accordance with the 50% esterification rule Parameters Influencing Gelling
proves somewhat arbitrary when dealing with gelling
The gelling and final gel structure of high-ester 0027
mechanisms. It is clear that the dominant factor in the
pectins is influenced by a great number of parameters,
gelling of pectin is highly dependent on its degree of
the main ones being the pectin concentration, the
esterification but the complex network structure is
degree of esterification, molecular weight, acetylation
most often the result of a combination of several
and branching of the pectin molecule and the pH,
mechanisms. The statement that high-ester pectins ionic strength, water activity, sugar type, and cooling
will gel with sugars and acid, while low-ester pectins
rate of the gelling medium.
gel with calcium, is certainly valid but certainly cal-
cium can alter the gelling of high-ester pectins, just as
Pectin concentration The concentration of high- 0028
pH and soluble solids will affect low-ester pectin
ester pectin will increase the final gel strength of the
gelling.
system due to the increase in the number of junction
Gelling Mechanism zones, increasing the number of chains with elastic
activity. An increase in molecular weight would have
0021 It is generally accepted that a high-ester pectin gel is the same effect. In addition to this expected effect, the
formed by the cross-linking of the polymer in junction gelation rate is also increased with increasing pectin
zones, in which mainly hydrogen bonds but also concentration and a power law can be calculated
hydrophobic attractions between the methyl-ester between the two parameters.
groups play a part. Calcium bridges may also partici-
pate, especially if the esters are distributed in blocks,
leaving large parts of the molecule as free acids. Degree of esterification The degree of esterification 0029

0022 Gelling will occur upon cooling of a media where of the galacturonic acids affects both the charge dens-
favorable conditions are met. Cooling is necessary to ity of the polymer and the number of sites for hydro-
decrease molecular movement and permit the forma- phobic interaction. As pectin molecules with a high
tion of intermolecular interactions. degree of esterification are less charged, they can
0023 As the pectin chains carry negative charges they form gels at a higher pH and will also start gelling
will tend to repel each other. This repulsion will at a higher temperature.
 4444 PECTIN/Properties and Determination

Independent molecules in solution Gel structure

Junction zone

H+
H2O
Sucrose

Hydrogen bonding

C C C
O O O O
O
H H H c
o o
H H
CH3
O CH3 Hydrophobic
O O O interaction
C C C H
o o
c

fig0005 Figure 5 High-ester pectin gels through hydrogen bonding and hydrophobic interactions in an acidic water and sugar matrix.

120
DE = 63
% obtainable firmness

100
DE = 73
80 DE = 81

60

40

20

0
3.0 3.2 3.4 3.6 3.8 4.0
Jelly pH

fig0006 Figure 6 High-ester pectin: the degree of esterification (DE) determines the optimal pH for the gelation.

0030 This last effect forms the basis for the classification The effect of neutral sugars on high-ester pectin 0033

of high-ester pectins into rapid-set, medium-rapid- gelling can be twofold and would need to be studied
set, slow-set, and extra-slow-set pectins as the degree more extensively. Neutral sugars present on the pectin
of esterification is decreased from more than 70% to molecule could result in steric hindrance of inter-
50% (Figure 6). molecular interaction and thus decrease the ability
0031 The distribution of the ester groups on the back- of the pectin to form gels. However, they could also
bone will also affect pectin gelation, as a marked participate in gelling through hydrophobic inter-
blockwise distribution of esters will result in a signifi- action and contribute to an increased cohesion of
cant contribution of calcium gelling. This contribu- the gel.
tion of calcium gelling will significantly increase the
gelling temperature of the pectin (Figure 7). pH and ionic strength of the gelling system The 0034

lower the pH, the lower the repulsion between the

0032 Acetylation and branching Acetylation sharply pectin molecules and, thus, the easier it will be for
decreases the gelling ability of pectin as the size of them to interact. This means that a low pH will lead
the acetyl groups does not allow the pectin chains to faster gelling in high-ester pectins. However, below
to come close enough for interaction between the a critical level, the gel strength will be reduced as the
molecules. gelling is too fast to obtain a well-organized polymer
 PECTIN/Properties and Determination 4445

Rhamnose

Galacturonic acid

Methylated
Marked block
galacturonic acid
structure
Neutral sugar

Calcium

fig0007 Figure 7 Participation of calcium gelling in high-ester pectin gelation.

network and precipitation can occur. The optimum the cooling rate is increased, the gelation rate is also
pH for gelation is controlled by the degree of ester- increased. However, during rapid cooling and with a
ification of the pectin as well as the soluble solids low storage temperature, gelling can actually become
content of the medium (Figure 6). very slow, reflecting the difficult development of
0035 Through their effect on the neutralization of the hydrophobic interactions in these conditions. With
pectin molecule, cations present in the system will an intermediate cooling rate and temperature range,
affect gelling. High ionic strength shifts the optimum hydrogen bonds and hydrophobic interactions
pH range towards higher values. This is particularly together can contribute to the build-up of a network
visible with sodium ions. However, with ions such as with the highest elasticity.
calcium or potassium that can bridge high-ester
pectin molecules in areas with a low density of ester, Properties of high-ester pectin gels Due to the nature 0039

there is a possible increase in junction zones. This of the molecular interactions involved in high-ester
effect can become significant for high-ester pectin pectin gelation, gels made with these pectins will
with marked blockwise distribution of ester groups typically not be thermo-reversible or shear-reversible.
(Figure 7). When submitted to mechanical stress, the broken gel
will then show a high level of syneresis.
0036 Water activity and sugar types Water activity and
sugar types will both affect the way hydrophobic Gelling of Low-Ester Pectin
interactions can develop between the pectin mol- Low-ester pectin has traditionally been used for gel- 0040
ecules. As water activity is reduced, the hydrophobic ling food products when the conditions required to
interactions are easier to form, causing faster gelling achieve a gel with high ester pectin were not met.
to occur and the final gel strength to be increased. Recently however, low ester pectins have also found
0037 The commonest way of reducing water activity in a applications in high sugar and low pH systems
food system is through the use of sugars. The effect of because of their specific texture characteristics.
sugars on hydrophobic interaction and so on gel Though the same base mechanism applies, low 0041

structure will be specifically linked to their molecular ester conventional and amidated pectin differ in
conformation and their interaction with the neighbor- their gelling properties and offer a broad range of
ing water molecules (Figure 8). functional properties.

0038 Influence of cooling rate and storage temperature Gelling mechanism The gelation of low-ester 0042

Cooling decreases molecular movement and allows pectins is the result of ionic linkage through calcium
polymer molecules to interact at close distances. As bridges between carboxylic groups from two pectin
 4446 PECTIN/Properties and Determination

High-fructose corn syrups

63 DE corn syrup

Sucrose 43 DE high-maltose corn syrup

Gel strength

42 DE corn syrup

3.0 3.1 3.2 3.3 3.4 3.5 pH

fig0008 Figure 8 Effect of various sugars on high-ester pectin gel strength. DE, dextrose equivalent.

OH O OH O OH O
HO COO− HO COO− HO COO−
O O O O O O
COO− HO COO− HO COO− HO
O O O

Ca++ OH Ca++ OH Ca++ OH

HO HO HO
O O O
OH COO− OH COO− OH COO−
O− O OH O −OOC O OH O −OOC O OH O
OOC
O HO O HO O HO

− C C C C C
O O H N O O O O O O
H H H H
Ca++
H H H
O
O C− O O O O O H
C C C C C

fig0009 Figure 9 Eggbox model. Schematic overview of established low-ester pectin gel mechanism, showing calcium-induced junction
zones. Inset shows detail of the various types of possible hydrogen bonding that participate in the junction zone, together with the
calcium chelation (far left).

chains with the participation of hydrogen bonding. many oxygen atoms and because of flexibility with
The linkage generally takes place upon cooling a regard to the direction of its coordinate bonds.
pectin and calcium system. The most commonly The exact calcium requirements to obtain a gel 0043

accepted model of association is the eggbox model highly depend on the degree of esterification of the
(Figure 9). In this model, pectin chains could be pectin, the recipe, and process parameters such as the
bridged by calcium ions, which incorporate in their rate of cooling. An increase in ionic strength, increase
coordination shells two polyanion oxygen atoms in pH, or decrease in the degree of esterification
from one pectin molecule and three from another lowers the amount of calcium required to achieve
chain. Even though a number of positive ions can sol–gel transition. An optimum calcium level can be
bridge pectin molecules, especially magnesium and defined for a given pectin in specific conditions.
potassium, calcium is particularly effective in com- Above this optimum level, pregelation will occur,
plexing with carbohydrates, largely because its ionic i.e., gelling will occur at too high temperatures to
radius (0.1 nm) is big enough to coordinate with obtain a coherent gel structure (Figure 10).
 PECTIN/Properties and Determination 4447

above 30%, the distribution of the esters may be of

Low-ester amidated significant importance as it will control the length of
pectin
possible junction zones and influence the gelling
temperature, the final gel strength, and texture.
Gel strength

Influence of amidation The amidation of pectins 0049

was developed in the 1940s as a means of modifying

Low-ester the functional properties of low-ester pectins in order
conventional pectin
to achieve better gelling control. The exact mechan-
ism by which the amide groups intervene in the
gelation remains to be fully explained. However, it
is generally accepted that amidation increases the
gelling power of low-ester pectins due to the possibil-
ity of hydrogen bonding involving amide groups. Gels
0 20 40 60 80 100 made with amidated pectins are firmer and require
mg Ca2+ g−1 pectin less calcium; they are also more thermo-reversible
than ones made with low-ester conventional pectins.
fig0010 Figure 10 Influence of calcium on low-ester pectin gels.
Influence of molecular weight As for any polymer 0050

gel, the length of the polymer governs the number of

0044 Gelling is dependent on the length of the junction junction zones required to achieve a coherent net-
zones, that is, the number of galacturonic acid units work. Low-ester pectins with a high molecular weight
involved in electrostatic bonds with calcium. The will exhibit a higher gelation rate, lower calcium
bonds are stable when at least seven consecutive requirements for gelling, and an overall more cohe-
carboxyl groups from each chain are involved. If the sive and elastic gel structure with a reduced tendency
junction zones formed with calcium become too long, towards syneresis.
a pectin precipitate may be formed. This may occur
with pectin with a very low degree of esterification Influence of pH At low sugar content, as the pH is 0051
when large amounts of calcium are available. decreased, the pectin molecules are neutralized with
0045 The presence of ester or amide groups prevents the protons, decreasing the probability of junction zones
formation of junction zones in the interjunction seg- forming with calcium. This translates into higher
ments of the molecules, making them more flexible. calcium requirements and a looser gel texture at a
Side chains also prevent aggregation of the pectin low pH.
molecules through steric hindrance. On the other hand, when the water activity of the 0052
0046 The typical high-ester pectin gelling mechanism system is decreased by the addition of sugars, the
with hydrogen bonds and hydrophobic interactions high-ester pectin gelling mechanism will start to play
can also contribute to the final texture of low-ester a significant part in the gelling and the calcium
pectin gels, especially at low pH and with high soluble requirements will then be decreased when the pH is
solids concentration. lowered. In usual food systems, availability of natural
calcium will also be increased at a lower pH and thus
Parameters Influencing Gelling
may reduce the need for extra calcium addition
0047 Although the availability of calcium is a critical factor (Figure 11).
in the gelation of low-ester pectins, other parameters
in relation to the pectin molecule and media have a Influence of ionic strength An increase in gel 0053

significant influence on gelling and the final structure strength can be observed at a higher ionic strength.
obtained. The main parameters are the number and This is usually explained by the neutralization of the
distribution of ester and amide groups as well as the polymers by the extra ions, which allows the chains to
molecular weight of the pectin molecule and the pH, be closer, leading to a more organized and cohesive gel.
ionic strength, and water activity of the gelling
system. Influence of water activity As the solids level 0054

increases, calcium requirements decrease. However,

0048 Influence of esterification Because calcium bonds for most pectins, a higher solids level accelerates gel-
can only occur in esterification-free zones, gel ling, and increases the setting temperature and the
strength increases with a decreasing degree of esteri- final gel strength. It also reduces the optimum cal-
fication. For low-ester pectin with an average DE cium window, thus increasing the risk of pregelation.
 4448 PECTIN/Properties and Determination

160

140

120

Breaking strength (g)

100
100 mg Ca
80
200 mg Ca
60

40

20

0
3.10 3.30 3.50 3.70 3.90 410
pH

fig0011 Figure 11 pH influences on Ca-curves in low-sugar system (31% soluble solids), with high reactive amidated pectin. Triangles,
100 mg Ca; squares, 200 mg Ca.

In practice, this leads to a choice of pectin with a Due to the lower proportion of carboxyl groups, 0058

higher degree of esterification (less calcium-reactive) high-ester pectin has a weaker electrostatic inter-
at a higher solids level. action with protein than low-ester pectin but proves
to be more effective. Indeed, it seems to be important
Properties of Low-Ester Pectin Gels that significant parts of the pectin molecule do
not interact with the protein surface in order to
0055 The properties of low-ester pectin gels are very de-
achieve the steric repulsion effect. It is also the key
pendent on the type of pectin used (conventional or
to minimizing interactions between pectin and
amidated) along with the procedure and formulation
cations available in the system.
employed to make the gel. Typically, they are thermo-
Both the DE of the pectin and the distribution of 0059
reversible and show a high degree of thixotropy. In
the esters on the polymer affect its stabilization prop-
specific conditions it is however possible to obtain
erties. Excessively large blocks of carboxyl groups
heat-resistant or very brittle gels with no shear revers-
will tend to interact with the ions present in the
ibility.
system, such as calcium, rather than with the protein
– an interaction which will lead to an increase in
Protein Stabilization with High-Ester Pectins
viscosity or even gelation.
0056 In acidified conditions, casein and, more generally,
food proteins will tend to agglomerate and sediment Conditions Most food proteins (isoelectric point 0060

if the viscosity of the system is low enough. In these around 5) can form complex coacervates with anionic
conditions the proteins are also very sensitive to polysaccharides such as pectin (isoelectric point
dehydration and can easily become sandy after heat around 3.5) in the intermediate-pH region, where
treatment. With the rapid development of acidified the two macromolecules carry opposite net charges:
dairy beverages worldwide, now expanding with pH above the isoelectric point of the polysaccharide
other protein sources such as soy, the need for effect- but below that of the protein.
ive protein stabilizers in a low-pH environment is In the case of pectin–protein interaction, the 0061

growing strongly. High-ester pectin has proven to be strength of the complex will depend on several
a very useful stabilizer in these conditions. factors, such as the distribution of the carboxyl
groups on the galacturonic acid backbone, but also
0057 Mechanism It is generally accepted that, at suffi- on the three-dimensional protein structure and the
cient pectin concentrations, the adsorption of the distribution of ionizable groups on its surface. The
carboxyl blocks of the pectin molecule to the protein whole interaction will also depend on several system
surface will stabilize the protein system through steric parameters such as pH, ionic strength, presence of
repulsion (Figure 12). So, the presence of blocks of sugars, or fat.
free carboxyl groups on the galacturonic backbone Through its role in the ionization of both the protein 0062

has an important influence on the protein-stabilizing and pectin molecules, pH is the most significant factor
property of pectin. affecting electrostatic pectin–protein interactions. It
 PECTIN/Food Use 4449

Rhamnose

Galacturonic acid

Lack of binding sites Methylated

galacturonic acid

Neutral sugar

Part of casein

Optimal binding site

Hairy surface provides steric stabilization

Marked block
structure

fig0012 Figure 12 Theoretical picture of interaction between pectin and protein.

also plays a very significant role in the protein struc- Rheology of Liquids; Stabilizers: Types and Function;
ture and how proteins interact in a complex system Applications
such as milk.
0063 The optimum pH range for interaction between Further Reading
high-ester pectin and casein is 3.6–4.5. At a lower
pH, the block structures of the high-ester pectin Dickinson E (1998) Stability and rheological implications
will not be sufficiently ionized for proper protein of electrostatic milk protein–polysaccaride interactions.
Trends in Food Science and Technology 9: 347–354.
binding as the pH is too far below the pKa of the
Kravtchenko TP, Voragen AGJ and Pilnik W (1994) Char-
pectin. Above the isoelectrical point of the protein,
acterization of industrial high methoxyl pectins. Gums
the protein–polysaccharide complex is very weak or and Stabilizers for the Food Industry 7: 27–35.
nonexistent and the electrostatic protein–protein May CD (1990) Industrial pectins: sources, production and
repulsion is dominant. It is, however, clear that application. Carbohydrate Polymers 12: 19–99.
this repulsion is not sufficient to stabilize the proteins. Rolin C and De Vries J (1990) Pectin. In: Harris P (ed.) Food
Gels, pp. 401–434. London: Elsevier.
Thakur BR, Singh RK and Handa AK (1997) Chemistry
Conclusion and uses of pectin – a review. Critical Reviews in Food
0064 Pectin exhibits a wide range of functional properties Science and Nutrition 37: 47–73.
and enjoys a very good public image as a natural Walter RH (ed.) (1991) The Chemistry and Technology of
Pectin. London: Academic Press.
product derived from fruit. Today it is widely used
as a textural ingredient and stabilizer in a variety of
food applications, and there is little doubt that its
usage will grow as new functionalities are revealed.
Food Use
See also: Cholesterol: Absorption, Function, and
L Flutto, Danisco, New Century, KS, USA
Metabolism; Citrus Fruits: Composition and
Characterization; Dietary Fiber: Physiological Effects; Copyright 2003, Elsevier Science Ltd. All Rights Reserved.
Fermented Milks: Types of Fermented Milks; Gums:
Properties of Individual Gums; Food Uses; Dietary
Importance; Jams and Preserves: Methods of Introduction
Manufacture; Chemistry of Manufacture; Pectin: Food
Use; Protein: Interactions and Reactions Involved in Food Pectin has been used traditionally in food ever since 0001

Processing; Rheological Properties of Food Materials; man started cooking fruits and vegetables. As a