Chapter 1 Pectin








1-1
1-2
1-3
1-4
1-5
1-6
1-7
1-8
Structure and Terminology
Production
Characterization of pectin gel
Factors affecting gelation
Chemical properties
Pectic enzymes
Structure and mechanisms of gel formation
Application
1-1 Structure and Terminology




Pectin is heterogeneous complex polysaccharide
Its composition varies with the source and the
conditions applied during isolation
All pectin molecules contain linear segments of
(14)-linked a-D-galactopyranosyluronic acid with
some of the carboxyl groups esterified with methanol.
Some of the hydroxyl groups of the galacturonosyl unit
(O-2 and O-3) are esterified with acetic acid.
Pectin molecule with methyl esterified
or nonesterified carboxyl groups
Amidated pectin has commercial
importance
Terminology




Protopectin
Pectinic acids
Pectic acids
Pectins

Degree of esterification (DE) > 50



High-methoxyl pectins (HM-pectins)
High concentration of soluble solids, low pH
DE < 50


LM-pectins
Divalent cations
1-2 Production

1-2-1 Raw materials



Citrus peel (20-30%), apple pomace(10-15%)
Sugarbeet waste, sunflower heads, mango waste
Sugarbeet pectin is inferior to citrus or apple
pectin



Presence of acetate esterification
A relatively low molecular mass
Presence of large amount of neutral sugar side chain
1-2-2 Extration, Purification, Modification

Two general processes
1. Separating the pectin from most other water-soluble
material by precipitation with an alcohol
2.Precipitating pectin as an insoluble salt with suitable
multivalent metal ions

1-2-2
Extration,
Purification,
Modification

Extraction:
50-90 , pH
1-3, Time
0.5-24h
1-2-3 Standardization





Uncontrolled variations in the raw materials will affect their
functional properties.
Reproducible performance from batch to batch of the final
products is a must.
Unstandardized HM-pectins are usually ‘diluted’ to a uniform
pectin grade (150 grade USA-SAG)
The grade USA-SAG is the number of parts of sucrose which,
under standard conditions, can be turn into a gel of standard
gel strength by one part of the pectin.
Standard conditions: refractometer soluble solids, 65%; pH
2.20-2.40; gel strength, 23.5% SAG in 2 min measured by
Cox and Higby (1944)
1-3 Characterization of pectin gel
1-3-1 gel strength and breaking strength


Some methods measure the gel strength within
the elastic limits of the gel
Other methods measure breaking strength
SAG determination method




The gel to be tested is prepared in a glass of
standardized dimensions
After curing, the gel is carefully removed from
the glass and allowed to stand without support
The height of the gel deformation by its own
weight is measured after a specified time
% SAG = 100 x (loss of height/original height)
Plunger methods




Strain is applied to the gel by means of a plunger--compression strain
Corresponding values of deformation are measured
Strain-versus-distance curve can be obtained while the
plunger is forced into the gel at a constant speed
Plunger methods are well suited for use in the jam and
jelly industry
1-3-2 Gelling time and temperature



Commercial high-ester pectins are usually
standardized to a certain gelling time or
temperature under specified conditions
Gelation of high-ester pectins may begin later
than instant when the gelling system was colled
below the gelling temperature
Gelling time is often measured rather than the
gelling temperature
Gelling time measurement

The test gel is prepared in exactly the same way
as for the SAG determination



The still liquid preparation is adjusted to 95 and
poured into a standard glass in a 30 water bath
The setting time is then taken as the time span from
the filling until visual signs of gelation appear
Setting time values are 50 sec for commercial
‘rapid-set’ pectins and 225 sec for ‘slow-set’ pectins
1-3-3 Factors affecting gelation










Temperature
Concentration of pectin
pH
Concentration of cosolutes
Concentration of ions
Molecular weight
Degree of esterification
Degree of amidation
Presence of acetyl groups
Heterogeneity and presence of neutral sugar residues
Temperature


A pectin gel is in most cases prepared hot and then
solidified by cooling
When cooled below the gelation temperature , systems
containing LM-pectin will gel almost instantaneously
whereas HM-pectin systems will gel after a time lag.



HM-pectin gel cannot be remelted
LM-pectin gel is thermoreversible
It is often desirable to fill commercial containers at a
temperature close to the gelation temperature to prevent
flotation of particles (berries)
Concentration of pectin

Typical concentrations of pectin in jams and jellies
range from 0.3% to 0.7%




0.3% HM-pectin gelling at about 65% soluble solids
0.7% amidated LM-pectin gelling at about 35% SS
The pectin concentration used is inversely related to
the concentration of soluble solids
At fixed levels of all other parameters, increasing the
amount of pectin causes the gel strength of the
resulting gel to increase.
pH





A pH of about 3.0-3.1 is typical for high-sugar jams
(HM-pectin, 65% SS)
Low-sugar jams may be slightly less acidic for taste
reasons. (pH 3.1-5.5)
Low pH values tent to increase the strength of both
HM- and LM-pectin gels
Gels will generally not form above about pH 3.5 in the
case of HM-pectin and about pH 6.5 in the case of LMpectin
HM-pectin: lower DE need lower pH for gelation
Concentration of cosolutes

HM-pectins will gel only in the presence of large
concentration of materials that lower water
concentration /activity



The soluble solids must be at least 55% (w/w)
Increasing the soluble solids content causes the gelation temp.
and the gel strength of the resulting gel to increase
LM-pectins may be gelled at zero soluble solids, but
increasing the soluble solids will also positively affect
the gelation temp. and gel strength
Concentration of ions

Gelation of LM-pectin will only happen in the
presence of divalent cations




Except for pectates or very low ester pectins which may form
gels with K inos under certain conditions
Most divalent cations may be effective, but only Ca2+ is
used in food application
Increasing Ca2+ concentration results in increasing gel
strength and gelling temp.
Divalent cations are not necessary for the formation of
an HM-pectin gel
Molecular weight

Gels made from either LM or HM-pectin with
high molecular weights will be stronger than
gels made with pectins of lower molecular
weights
Degree of esterification

DE values for commercial LM-pectins range from 2040%


Those with the lowest DE-values show the highest gelling
temperatures and the highest sensitivity to Ca2+
In contrast, the highest gelling temp. and the fastest
gelation of HM-pectins are found with those that have
the higest DE



Rapid-set (70-75% DE) > medium-rapid-set (65-70% DE) >
Slow-set (55-65% DE)
Gel strength: Slow-set + lower pH = rapid-set
Gel strength: R > M > S (at same pH)
Degree of amidation (DA)




Most commercial LM-pectins are amidation
DA values range from 15-20%
Amidation causes the pectin to gel at higher
temp. compared to a nonamidated pectin under
the same conditions, and less Ca2+ is needed
Amidation has a positive effect on gel strength
Presence of acetyl groups

If some of the galaturonic acid subunits contain
acetyl group at O-2 or O-3, gelation will be
hampered


Every eight units is esterified this way
The presence of acetyl esters may be a
drawback to suggested alternative source of
pectin such as sugar beet pulp and sunflower
heads
Heterogeneity and presence of neutral
sugar residues


Two pectin batches may behave differently, even if
they are similar with respect to molecular weight and
DE
The distrubution of esterified and free carboxyl groups
has received much attention because it is different in
enzymicly deesterified pectins than it is in acid or
alkali deesterified pectins.


Gel strength: enzymicly deesterified pectins < acid or alkali
deesterified pectins
Heterogeneity has been reported to be advantageous to
the gel-forming ability of a pectin
Heterogeneity and presence of neutral
sugar residues


The rhamnose content has impact on the
flexibility of the molecules (rhamonse insertions
in the backbone)
The side chains of neutral sugar may sterically
hinder gelation or limit the size of junction zone
1-5 Chemical properties


Pectins are polyanions at neutral pH and
approach zero charge at low pH
Dissociations of the individual –COOH groups
are not independent: pK = 2.9-3.3


The pH at 50% dissociation of the pectin ranges
from 3.5 through 4.5
React with positively charged polymers, such as
protein at pH values less than their pI
Breaking strength of pectin gels as a
function of pH
Decomposed of pectins

Dissolved pectins are decomposed spontaneously by
deesterification as well as by depolymerization





Factors: pH, Aw, Temperature
HM-pectins: stable at about pH 3.5- 4, sugars or other agents
that lower water activity reduces the rate of degradation
LM-pectins: stable at about pH 4-5,
In both acid- and base-catalyzed decomposition, the rate
of DEster is faster than the rate of DPoly
Highly esterified pectins are more prone to
depolymerization than are LM-pectins or pectic acids
Decomposed of pectins


DPoly. At low pH-values is a hydrolysis reaction
DPloy. At alkaline conditions is a beta-elimination
reaction


Glycosidic bonds to O-4 of an esterified galacturonic
acid subunit eliminate much more easily than those to
O-4 of an nonesteified subunit
The rate of beta-elimination is almost proportional to
the amount of remaining methyl ester groups and slow
down as they are saponified
Decomposed of pectins

Powdered HM-pectins slowly lose their ability to
form gels, especially if stored under humid or
warm conditions


Stored at < 20 C
LM-pectins are more stable, loss should not be
significant after 1 year storage at room
temperature
Analysis of pectins

Degree of esterification (DE)




Washing in 60% 2-propanol (isopropanol)/5% HCl
Several washing with 60% 2-propanol (isopropanol)
Titrate to the equivalence point with NaOH
Saponification
Analysis of pectins

Degree of amidation


Heating the sample with excess of NaOH and trapping
the evolved ammonia in a known amount of HCL
Acetyl content



Alkaline saponification
Acidification with dilute sulfuric acid and steam
distillation
The evolved acetic acid is trapped in a known amount
of NaOH and titrated
Analysis of pectins

Average molecular weight



Intrinsic viscosity method
Membrane osmometry
LC method
1-6 Pectic enzymes


Pectin esterases (PEs)
Polygalacturonases (PGs)



EC 3.2.1.67
EC 3.2.1.15
Pectate lyases (PALs)



Exo-PGs
Endo-PGs
EC 3.1.1.11
Exo-PALs
Endo-PALs
Pectin lyases (PLs)
EC 4.2.2.9
EC 4.2.2.2
EC 4.2.2.10
Pectin esterases (PEs)

Catalyze hydrolysis of methyl ester bonds



Fungal PEs -- optimum pH about 4.5
Bacterial PEs -- pH 6-9
Attack prevailingly next to an unesterified
galacturonic acid subunit
Polygalacturonases (PGs)

Catalyze hydrolysis of glycosidic bonds



Exo-PGs


The rate of reaction is inversely related to the DE
Optimum pH 4.0-5.5
Release mono- or di-saccharides from the nonreducing
end
Endo-PGs

Attact at random
Pectate lyases (PALs)

Catalyze depolymerization via b-elimination





Fig 5 273
Only glycosidic bonds to O-4 of an unesterified
galacturonic acid unit are attacked
Optimum pH 8-9.5
Exo-PALs
Endo-PALs
Pectin lyases (PLs)




Catalyze b-elimination at bonds to O-4 esterified
galacturonic acid units
Only endo-PLS are known
Optimum pH 5-6
Presence of Ca2+: optimum pH 8
Pectin lyases (PLs)




Catalyze b-elimination at bonds to O-4 esterified
galacturonic acid units
Only endo-PLS are known
Optimum pH 5-6
Presence of Ca2+: optimum pH 8
1-7 Structure and mechanisms of gel
formation


To take part in gel formation, a pectin module
must aggregate with one or more other pectin
molecules
The junction zones must be of limited size
because the molecules would otherwise form a
precipitate rather than a gel
Citrus, apple and sunflower pectins preparations with
acid under hydrolyzing conditions (Powell et al., 1982)



DP is about 25
Because bonds to rhamnose were assumed to be
more labile than ordinary glycosidic bonds in
the galacturonan backbone
One rhamnose unit for every 25 galacturonic
acid units(regularly distributed)
Apple pectins fractionated by DEAEcellulose



Rhamnose insertions are very unevenly distributed
along the galacturonan backbone (Vries et al., 1982)
Pectin consists of smooth regions and hairy regions
rich in neutral sugars predominantly present as side
chain
Neutral sugar content tends to be higher if mild
conditions have been employed for extraction

L-rhamnose, L-arabinose, D-xylose, D-galactose, D-glucose
Pectins from spinach and sugar-beet


Ester-linked ferulic acid
has been found in neutral
sugar side chains
Formation of a covalent
bond between ferulic
acid by the action of
hydrogen peroxide or
peroxidase
Model of a function zone in a highsolids pectin gel
Model of a calcium pectate junction
zone
Egg box model of a junction zone in a
calcium pectate gel
1-8 Application


Pectins are a constituent of all plants and is part
of the natural diet of man
Pectins are generally recognized as safe (GRAS)
1-8-1 Jams and Jellies

Pectin has a dominant position as a gelling
agent in jams and jellies because



The natural pectin content in fruits used for jam
making is responsible for the gelation of traditional
jam that has been produced for centuries
Pectin is compatible with a natural image of the
product
Pectin has good stability at the pH of jams and
jellies, even when hot
1-8-1 Jams and Jellies


The selection of suitable pectin for a particular application
is dependent upon the desired texture and the desired
gelling temperature
HM-pectins: rapid-set, medium-rapid-set, slow-set


The actural gelling rate is dependent on the application conditions
LM-pectins are the possibility if the pH of the product is
above approximately 3.5 and/or the soluble solids (SS)
concentration is below approximately 55%
Gelling temperature

Which gelling temperature is desired is determined
by the filling temp. and the presence or absence of
suspended fruit particles in the product


Jams should solidify as soon as possible after filling.
Fruit flotation is then stopped before it lead to a too
unenen distribution of the fruit particles in the product
Delayed gelation is desirable in the case of jellies so that
air bubbles will have time to escape
Filling temperature

The desirable filling temperature is in turn restricted
by the size of the jars used


Large jars cool more slowly than smaller jars, and
holding at elevated temp. is detrimental to product
quality
A relatively low filling temperature is consequently
necessary if the product is to be sold in large
containers
Which pectin type may be used？



The container size puts an upper limit to the filling
temperature
The filling temp. and the desirability or
undesirability of a lag before solidification
determine the desired gelling temperature
The desire gelling temp., together with composition
of the product, determines which pectin type may
be used

Jams, Jellies
and
Confectionery
Jellies
Preparations
1-8-2 Acidified Milk Drinks


Casein particles of unstabilized acidified milk
systems tend to aggregate, especially during heat
treatment
A sandy texture may develop and whey formation
separation may occur due to sedimentation of the
casein
1-8-2 Acidified Milk Drinks


A typical use level for pectin in acidic milk drinks is 0.5%
The necessary dosage is dependent upon pH, titer, protein
concentration, heat treatment and size of casein particles


pH 3.5-4.2
Best stability is achieved at relatively high titer value




Typical titers of fruit-flavored acid milk products are 100-120 (mL 0.1N
NaOH per 100 mL)
More casein or harsher the heat treatment  more pectin is required
Large casein particles can not be stabilized efficiently
Very small particles require much pectin
Theory of stabilization




In unstabilized acidified milk, casein particles that are below
their isoelectric pH are positively charged
A repulsion that is not strong enough to prevent aggregation
exists between these particles
When pectin is added, it reacts with the casein and
neutralizes the charge, increasing the tendency of particles to
aggregate
When even more pectin is added to the casein particles, a
new repulsion between particles results from a surplus
negative charge that is stronger than the original positive
charge
1-8-3 Other application





Different properties of pectin are utilized in application
related to beverages such as orange juice, orangeades, and
soft drinks
HM-pectin may be used to increase the viscosity of soft
drinks and improve the mouthfeel
It may be used to prevent sedimentation of suspended
material in orange juice concentrates with more than 45% SS.
Oil-in-water emulsions in cosmetics may be stabilized with
pectin
Numerous patents, most of which related to uses of pectin is
in food products
Chapter 2 Cellulose and its derivatives



1. Methylcellulose and its derivatives
2. Hydroxyalkyl and ethyl ethers of cellulose
3. Sodium carboxymethylcellulose
1. Methylcellulose and its derivatives




1-1 Introduction
1-2 Manufacture
1-3 Properties
1-4 Application
1-1 Introduction




Etherification of cellulose provides a broad spectrum
of products that includes low-substituted alkyl ethers
that are insoluble in water and organic solvents
Alkyl ethers of intermediate substitution that are water
soluble
Highly substituted ethers that are soluble in organic
solvents but not in water
The methylcellulose and its derivative gums described
here are those that are water soluble and classified as
hydrophilic industrial gems
1-1 Introduction

The term methylcellulose gums is used to refer
to entire group of products including




Methylcellulose (MC)
Hydroxypropylmethylcellulose (HPMC)
Hydroxyethylmethylcellulose (HEMC)
Methylcellulose gums have broad commercial
application in a wide variety of uses and a
production of more than 76 x 10 exp 6 kg/year
1-2 Manufacture




Cellulose sheet pulp obtained from cotton or wood is
converted into alkali cellulose by reaction with sodium
hydroxide
Then, pressure reactors are used to etherify the alkali
cellulose with methyl chloride and , in some cases,
propylene oxide, ethylene oxide, or butylene oxide
Reaction times of 2-10 h
Purification takes advantage of the product’s thermal
gelation properties
1-2 Manufacture



The crude product is dispersed in hot water, in
which it is insoluble, and is then separated by
filtration or centrifugation
Additional washes may be used to improve
purity
The wet methylcellulose is dried and milled
Manufacturers of methylcellulose and modified
methylcelluloses
1-3 Properties

1-3-1 solid




Methylcellulose gum products are available in powder
and granular forms
The primary benefit of powder products is rapid
dissolution
Granular products have reduced dusting tendency and are
more easily dispersed
Both products may be treatment with dispersing agents to
make dissolution easier, but these products can’t be used
in foods or in contact with food products
Physical properties of methylcellulose
powder and granular products
1-3-2 To prepare solutions




Insufficient dispersion may lead to lumping and incomplete
dissolution
Application of high-shear mixing devices to help promote
dispersion can cause excessive foaming
It is generally recommended that the gum first be mixed
with a formulation ingredient, such as alcohol, glycol, or
salt solution. Water is then added to the mixture
The powder can be dispersed in water heated above the gel
temperature of the gum
1-3-2 To prepare solutions


Solution of methylcellulose gums are pseudoplastic
Solution rheology is dependent upon



the molecular weight of the gum
its concentration
presence of other solutes
Relationship between molecular weight
and aqueous solution viscosity
Viscosity as a
function of
concentration
for highviscosity
types of
Methocel
Viscosity as a function of concentration
for low-viscosity types of Methocel
Gel strength as a function of molecular
weight of Methocel products
1-4 Application





1-4-1 Salad Dressing
1-4-2 Dietetic Foods
1-4-3 Fried Foods
1-4-4 Bakery Products
1-4-5 Frozen Dessert
1-4-1 Salad dressing



MC and HPMC are used in pourable salad dressings,
such as French dressing, to stabilize the emulsion and
prevent separation.
Higher molecular weight versions of the gum are
preferred for the formulation with the purpose of
thicken and stabilize (0.3-1.0% gums)
Higher concentration are used in low-calorie, reducedoil dressings and in oil-free salad dressings
1-4-2 Dietetic foods


Bulking agent in low-calorie foods
Partial replacements of digestible carbohydrates with
low levels of nondigestible MC gums provides
desirable organoleptic properties with reduced calorie
content




Reduced-calorie salad dressing: 0.3-1.0% gums
Dietetic jellies and Preserves :0.5-1.0% gums, palatable
Artificially sweetened syrups: 1% MC, smoothness and body
Low-calorie beverages: 0.15-0.20% HPMC, mouthfeel and
body
1-4-3 Fried foods

In batters, dipping solution and sprayed-on
coatings for meat, fish and French-fried
potatoes



The gum reduces oil absorption through film
formation and thermal gelation
MC gums hydrophilicity helps to retain moisture
during the cooking process, preventing drying out of
the food
Batter formulation: 0.5-2.0%
1-4-4 Bakery products






Including cake, doughnuts, breads, cookies, fruit pie fillings…
Their thermal gelation is valuable in preventing boil-over of
pastry filling and aids in gas retention in cakes during baking
Low moisture migration due to their hydrophilic nature
improves shelf life and prevents icing dry out
Their surfactancy and thickening properties help assure
uniform consistency by improving emulsification, air
entrainment, and ingredient suspension
In frozen baked goods, MC gums retard water migration
during freezing and thawing and help inhibit phase separation
during freezing
0.07-0.3% base on total ingredients
1-4-5 Frozen dessert


MC gums are used in frozen desserts to control
ice crystal size and improve emulsification
during processing
0.2-0.5%
1-4-6 others



Beer foam stabilizer-- 100ppm or less
Barbecue sauce and relish formulations-- 0.31.5%
Sausage casings
2.Hydroxyalkyl and ethyl ethers of
cellulose



1-1 Introduction
1-2 Manufacture and Properties
1-3 Application
1-1 Introduction





The principal, commercial, water-soluble hydroxyalkyl
derivatives of cellulose are hydroxyethylcellulose (HEC) and
hydroxypropylcellulose (HPC)
The derivatives are readily soluble in water and are produced in
a wide range of viscosity grades
Their solutions are pseudoplastic, that is, they vary in viscosity
depending upon the amount of stress applied
HPC is cold water-soluble and is a true thermoplastic and can be
extruded, injection molded or compression molded into flexible
film
HEC is insoluble in hot water (> 42 C) and soluble in a broad
range of polar organic liquids.
1-2 Manufacture



Water-soluble hydroxyalkylcellulose are manufactured
by reacting alkali cellulose with alkylene oxides at
elevated temperatures and pressure in a mixture of
organic solvents and water
Each unit in the cellulose molecule has three reactive
OH groups. Reaction of ethylene oxide or propylene
oxide with cellulose also leads to formation of new OH
groups
Molar substitution (MS) or degree of substitution (DS)
Viscosity range of aqueous solutions of
hydroxyalkyl-celluloses at 25 C and various
concentrations
1-2 -1 Preparation of HEC


HEC is produced from alkali cellulose by reacting cotton linters
or high-alpha wood cellulose with aqueous sodium hydroxide to
produce alkali cellulose (soda cellulose), which is reacted with
ethylene oxide in the presence of a water-miscible diluent such
as isopropanol or tertiary-butanol
52 parts wood pulp + 450 parts isopropanol  + 126 parts 22%
aqueous caustic for 1h  + 51 parts ethylene oxide heated to 30
C for 1h  increase to 35 C maintained for 3h  filtered 
washed with methanol-acetone mixture  neutralized with
acetic acid  dried
1-2 -2 Properties of HEC

Solubility
MS > 1.6 : readily soluble in either hot or
cold water
 Low-viscosity types dissolve more rapidly
than high-viscosity types

Effect of temperature on viscosity -- HEC


The viscosity increases
when cooled and
decreases when warmed
A convenient nomograph


If a solution has a
viscosity of 60 cP at 25 C
The viscosity at 42 C
will be ?? cP
Effect of concentration on viscosity -- HEC
Effect of pH on viscosity -- HEC




HEC is a nonionic polymer and therefore
undergoes little viscosity change over a pH
range of 2 to 12
Solutions show best viscosity stability in the pH
range of 6.5 to 8.0
A drop in viscosity results from acid-catalyzed
hydrolysis below a pH of 3.0
At very high pH, alkaline oxidation accelerated
by heat and light may occur
Rheology of HEC


All solution of HEC
are psuedoplastic
Solutions of lowmolecular-weight
types exhibit less
pseudoplasticity
FDA status of HEC


For use in packaging adhesives and
resinous and polymeric coatings employed
on metal or paper for food packaging
HEC is not cleared as a direct food
additives
1-2 -3 Properties of HPC

Solubility



Commercial HPCs
have MS > 2.0
Soluble in water
below 38 C,
insoluble in water
above 45 C
Soluble in many polar
organic solvents
Effect of temperature on viscosity -- HPC




Viscosity decreases with
increases in temp.
The polymer reversibly
precipitates from water
at 40-50 C, causing a
rapid loss in viscosity
5% NaCl reduced the
ppt temp. to 30 C
40% sucrose  20C
Effect of concentration and pH on viscosity
-- HPC


Viscosity increases rapidly with
concentration
HPC is nonionic and undergoes little
viscosity change over the pH range of
form 2-12
Thermoplasticity of HPC




HPC can be processed by all plastic fabrication
methods
The low-molecular-weight types are preferred in
injection and blow molding, where rigidity, hardness,
and dimensional stability are important
The medium- or high-molecular-weight types are
recommended for most extrusion systems where
greater flexibility and higher tensile properties are
desired
MW 50,000-1,250,000
FDA status of HPC


Purified HPC is approved as a direct food
additive
Toxicity tests indicate that the polymer is
physiologically inert
1-3 Application of HPC

Organic solubility properties




Thickener in solvent-based adhesives, alcohol-based hair
dressings, perfumes, inks,
HPC is widely used as a granulating agent for tablet
and capsule mixes in the pharmaceutical industry
HPC films– to coat nuts to prevent oxidative rancidity,
coat candies and other confections
Foaming aid and emulsion stabilizer in whipped
toppings
3. Sodium carboxymethylcellulose




3-1 Introduction
3-2 Manufacture
3-3 Properties
3-4 Applications
3-1 Introduction of sodium CMC




Sodium carboxymethylcellulose (CMC) is a watersoluble cellulose ether produced by reacting alkali
cellulose with soldium monochloroacetate
CMC was first used as a substitute for starch and
natural gums
The purified grade, known as cellulose gum, is used
extensively in the food, pharmaceutical, and cosmetic
industries
A GRAS product
3-2 Manufacture





The traditional process is accomplished in a sigma-blade
mixer
The cellulose is steeped in NaOH, pressed, and shredded
Sodium monochloroacetate or chloroacetic acid can be
mixed with the cellulose before or after alkali is added
The reaction product is neutralized, dried, and packaged
The crude product can be purified by the use of alcoholwater mixtures to extract salts without dissolving the gum
3-3 Properties

3-3-1 Degree of substitution (DS)




Each D-glcopyranosyl unit has three reactive OH
group
It is possible to introduce three sodium
carboxymethyl groups per unit  DS = 3.0
Commercial CMC  DS < 1.5
Most common  0.4 < DS < 0.8
Idealized structure of sodium CMC
with a DH of 1.0
3-3-2 Uniformity of substitution

The first element is the preparation of a uniform
alkali cellulose



The proper amount of caustic must be brought into
contact with the cellulose fibers in a fashion that
ensures uniform distribution
Care in detailed distribution of the monochloroacetic acid is less critical
NMR is used to determine the relative location
of the carboxymethyl groups in CMC
3-3-2 Uniformity of substitution


Derivatization of one
OH group on the Dglucopyranosyl unit does
not alter the relative
reactivity of remaining
OH group
The relative rate constant:

k2 = 2.14, k3 = 1.00, k6 =
1.58
3-3-2 Uniformity of substitution



The unsubstituted regions tend to interact through
hydrogen bonding and generate thixotropy (搖溶
性) in solutions
Increase in thixotropy with increasing
concentration is rough indicator of the relative
uniformity of substitution of a given sample of
CMC
The longer the average chain length, the more
viscous is the solution
3-3-3 Solubility


Low-substituted types (DS 0.3 or less) are
insoluble in water but soluble in alkali
DS > 0.4  water soluble, DS < 0.4 with high
uniformity of substitution  water soluble
Solubility of various sodium CMC-CMC films at various
pH values
3-3-4 Rheology of CMC


CMC is generally used to
thicken, suspend, stabilize,
gel, or otherwise modify the
flow characteristics of
aqueous solution or
suspensions
Pseudoplasticity: A CMC
solution will vary in
viscosity as different
physical forces are applied to
the solution (timeindependent shear-thinning)
3-3-4 Rheology of CMC


Thixotropy: When long chain polymers
associate intermolecularly, there tend to develop
a three-dimensional structure and exhibit
thixotropy (time-dependent shear-thinning)
Solution of medium- and high-viscosity CMC


0.9 < DS < 1.2  pseudoplastic
0.4 < DS < 0.7 with slightly less uniformly
substituted  thixotropic
Pseudoplastic vs Thixotropic

Thixotropic solutions show
hysteresis (遲滯現象) loops



The increased shear stress required
to break the thixotropic structure
reduces the resistance to flow
A pseudoplastic CMC solution
instantly reverts to its at-rest
viscosity after shear removal
A thixotropic CMC solution
requires time for return to its atrest state
Left thixotropic and right nonthixotropic solution of CMC
3-3-5 Effect of trivalent metal ions



Gelation of CMC solution can be controlled to form
soft, pourable or very firm gels
Gradual release of aluminum ions to a CMC solution
results in uniform crosslinking
The stiffness of gel depends on the amount of the
crosslinking




Concentration of polymer
Metal cation to carboxylate anion ratio
pH
Polymer chain-length
Aluminum-CMC gels



Resistant to nonchelating acids but dissolve slowly in
alkaline solutions
High concentration of aluminum salts give more
brittle gels
Low-DS CMC solutions without salt addition also
could form the gel


More crystalline regions are present in low- than high-DS
CMC
Gel formation is probably the result of disaggregation of
the fringed micelles in the crystalline regions, which
provides more potential crosslinking points

3-3-6 Effect of temp. on
viscosity


Temp. variation has no
permanent effect on
viscosity
However, long periods of
heating at high temp. tend
to depolymerize and
degrade CMC
3-3-7 Effect of pH on viscosity



CMC solutions exhibit
maximum viscosity and
best stability at pH 7-9
pH > 10  some
decrease in viscosity
pH < 4.0  less soluble,
increase in viscosity
3-3-8 Effect of concentration on
viscosity

In concentrated solution


There is little tendency for the
counter ions (Na) to move out
of the sphere of influence of
the charges on the polymer
molecules
In dilution solution


The cations tend to move away
into the aqueous interpolymer
regions, leaving a net charge
on the molecules
As dilution continue , the
charge density on the chains
increase, and the chains
continue to uncoil
3-3-8 Effect of concentration on
viscosity

At higher concentration



Viscosity increases as an exponential function of
concentration
A doubling of the concentration causes a tenfold increase in
viscosity
Because viscosity is determined in large part by the
length of polymer molecules, a wide range of viscosity
types of commercial CMC are available

MW 40,000-1,000,000
3-3-9 Compatibility


CMC is compatible in solution with most watersoluble nonionic and anionic polymers and gums,
proteins, carbohydrates, salts, and solvents.
Monovalent cations usually form soluble salts


Generally, divalent cations will not form crosslinked
gels with CMC


Little effect on solution viscosity, clarity
Forming hazy solutions with reduced viscosity
Trivalent cations form insoluble salts

Compatibility
of CMC with
inorganic salt
solution
Compatibility with water-soluble
polymers

CMC is compatible with most water-soluble
gums over a wide range of concentration


Low-viscosity types > high-viscosity types
In non-ionic polymer


Guar gum , hydroxyethylcellulose, HPC
A synergistic effect on viscosity
Synergistic effect on viscosity

Compatibility
with solvents
Compatibility with others

With carbohydrates



CMC gum thoroughly dissolve in water and sugar is then
added  increase of viscosity
Dry gum is added to the sugar solution  decrease of
viscosity
With protein


CMC helps to solubilize various proteins and to stabilize
their solutions
CMC inhibits precipitation of casein in its isoelectric pH
region and produces high viscosities
Interaction of sodium CMC (DS 0.7)
and soy protein
3-4 Applications



Food-grade CMC is widely used because of its
ability to thicken water, act as a moisture binder,
dissolve rapidly in both hot and cold aqueous
systems
And because it is tasteless, odorless, and forms
clear solution without cloudiness or opacity
And because it is physiologically inert and
noncaloric

Cellulose
gum food
applications
and
properties
utilized