sanderson 1993

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ALGINATES AND GELLAN GUM: COMPLEMENTARY

GELLING

AGENTS

George

R.

Sanderson and David Ortega

Kelco Division of Merck and Co., Inc., San Diego, California, USA

ABSTRACT

Alginates and gellan gum both have a high affinity for calcium ions. Their ability to

form gels with these ions is not only well known but is also exploited in many applications.

Alginate gels are usually formed in the cold, without recourse to heating, while gellan gum

gels are normally prepared by heating and cooling. These two polymers can thus be

considered

to

be complementary rather than competitive gelling agents.

The similarities and differences between the monovalent alginate salts, notably sodium

alginate, and KELCOGEL gellan gum are discussed in terms of their properties and

applications. This information is useful to the end user when trying to decide which

of

the

two hydrocolloids should be used in a particular application. It has also enabled alginate

and KELCOGEL to be used effectively together in some products. Specific examples are

described.

INTRODUCTION

Alginates, derived from a variety of brown seaweeds, have been known for over a

century. They are linear polymers composed of the salts of Q-mannuronic and L-guluronic

acid. The properties of a particular alginate depend on the relative proportions of these two

monomers in the molecule and, more specifically, the size and distribution of the so-called

block regions. These block regions are segments of the polymer chain composed solely

of

either mannuronic or guluronic acid.

Hydrocolloids are frequently classified as thickeners or gelling agents. Alginate is

somewhat

of

an exception in that it functions both as a thickener and a gelling agent.

Although all polyvalent cations with the exception of magnesium are capable of forming

gels with alginate

l

,

the only ion of relevance for foods is calcium. It has been said that the

reactivity displayed by alginate towards calcium is its strength and weakness

2

.

Proper

control

of

calcium ions can enable a wide variety of products to be formulated

3

;

improper

control invariably leads to singular lack of success. Fig. 1 shows the effects obtained by

mixing different concentrations of calcium ions with different concentrations of an alginate

composed of a high ratio of mannuronic to guluronic acid. The term conversion refers to

the amount of calcium ion added relative to the amount required to theoretically convert

sodium alginate to its calcium form. Thus, a calcium conversion

of

1.0, for example, means

sufficient calcium to convert sodium alginate on a stoichiometric basis to its calcium form.

In practical terms, this amount is approximately 0.1 g

of

calcium ion per 1.0 g

of

sodium

alginate. As implied in the figure, increasing the calcium ion concentration progressively

Food Hydrocolloids: Structures Properties

and

Functions

Edited by K. Nishinari and

E.

Doi, Plenum Press, New York, 1994

83

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2.0

_ 1.0

:.Ii

c

o

'E

0.5

c

8

CD

iii

c

'0

«

0.2

0.1

L-_ . . . . L . -_ -1 . . . _ - - -L - . _ . . . . L . -_ . . . . L_

0.2 0.4

0.6 O.B

1.0

1.2

Calcium Conversion

Fig. 1 Influence

of

calcium

ion

level on alginate rheology

increases intermolecular assocIatIOn resulting

in

a progressive increase in viscosity.

subsequently the formation of thixotropic solutions. and ultimately gel formation. in which

interchain association is permanent.

In the preparation of alginate gels. calcium ion control is essential in order to avoid

premature gelation and the formation

of

undesirable. broken gels. There are three general

methods of making gels. namely diffusion setting. internal setting and setting by cooling.

The first procedure is the simplest and. as the name implies. gels are formed by allowing

calcium ions to diffuse into a solution

of

alginate. Diffusion setting is used in the

production

of

fabricated onion rings and structured pimiento strip for stuffed olives, and to

encapsulate various core materials in a gelled alginate skin. A simplified illustration of the

formation

of

blackcurrants consisting

of

blackcurrant puree encapsulated by an outer skin

of

alginate gel is shown is Fig. 2

4

, The rate determining step

in

the diffusion process is the

time taken for the calcium ions to diffuse through the alginate solution. The effectiveness of

84

I---- ? co-axial tubes

fruit

puree mix - - -H(: f - t+---a lg inate

mix

pulsed) continuous)

~

setting bath

containing calcium salt.

e.g.,

calcium lactate

I

/

Fig. 2 Co-extrusion system for preparing blackcurrants

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the technique

is

therefore limited to the setting

of

thin films, through which diffusion time

is

short.

In

situations in which diffusion

is

not practical, internal setting can be used. This is

done by controlled release

of

calcium ions from particles

of

a calcium salt dispersed

throughout the system. Rate

of

calcium release depends on the inherent solubility

of

the

calcium salt used, the amount present, particle size and pH. Salts commonly used include

dicalcium phosphate anhydrous and calcium sulfate dihydrate. Calcium release can be

further controlled by inclusion

of

calcium sequestrants and the use

of

slowly dissolving

acids and short mixing times. Internal or bulk setting can be successfully used to prepare a

wide variety

of

food products. These include products which are prepared by reconstitution

of

a dry mix using water

or

milk. A prerequisite to success is designing the dry mix to

ensure that the alginate has time to hydrate before sufficient calcium to cause gelation is

released.

Table 1

Alginate dessert gel formulation.

Ingredients

Water

Sugar

Sodium alginate (KELTONE

HV)

Adipic acid

Sodium tripolyphosphate

Calcium carbonate

Color

Flavor

84.75

13.92

0.49

0.41

0.31

0.08

0.01

0.D3

100.00

A third but less common method

of

forming alginate gels is setting by cooling. Table

I shows a simple formulation for an alginate dessert gel, prepared by adding a mixture

of

the dry ingredients to boiling water and cooling. Although useful, the resulting gel is weak,

and a limitation to preparing alginate gels by cooling is the fact that it is not possible to

achieve the high degree

of

conversion from sodium to calcium alginate needed to give

strong gels since the required levels of calcium cause the alginate to gel, even at elevated

temperatures. These gels, however, tend to be thermodynamically more stable than internal

or diffusion set gels since the calcium required for gelation is present throughout the system

in

soluble form and

is

not fed progressively to the alginate from an external source as in the

case of diffusion setting or by diffusion from the surface

of

a dissolving particle of calcium

salt as in internal setting.

Unlike

alginates, geIlan

gum has only been known

for over a

decade. Despite

this

short existence, it has already been extensively researched and is approved for foods in

Japan. Approval in non-standardized jams and jellies and icings and frostings has also been

granted in the U.S. and approval for general food use is anticipated in the near future.

Fig. 3 Native geIIan

gum primary

structure

85

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Gellan gum, a microbial polysaccharide derived from the organism

Pseudomonas elodea

is

a linear polymer with a tetrasaccharide repeat unit consisting of glucose, glucuronic acid,

glucose and rhamnose

5

,6.

As

shown in Fig. 3, there

is

also one glycerate substituent per

repeal and one acetate approximately every second repeat. The form of the gum in which

the acyl substituents have been removed

is

marketed by Kelco as KELCOGEL gellan gum.

KELCOGEL reacts with mono- and polyvalent cations to form a gel. These gels are

normally prepared by adding the appropriate ion to a hot solution of the gum and cooling.

Divalent ions are much more efficient than monovalent ions and, by way

of

example, gels

of

optimal gel strength require around 0.4% sodium but only in the region

of

0.016%

calcium. Since low levels of dissolved calcium promote gel formation and hence inter

molecular association, they also prevent chain dissociation or hydration. This potential

problem is easily overcome by the inclusion of a calcium sequestrant such as sodium

citrate,7,8 and, by manipulation of the relative concentrations of dissolved calcium and

sequestrant, it is possible to hydrate KELCOGEL at any desired temperature. In other

words, if desired, KELCOGEL can be hydrated at room temperature. These solutions, like

their alginate counterparts, can be converted to a gel by diffusion setting. However, in the

case of the KELCOGEL solutions, the gelling ion can be not only calcium but other ions

such as sodium, potassium or magnesium.

Preparation of gels by internal setting, although not impossible

9

, 10, is more difficult to

achieve with KELCOGEL than alginates. This is because inclusion

of

a sequestrant to

control the release of

the divalent ions in the system, so effective in preparing internal set

alginate gels, frequently in itself prevents hydration since the amount of sequestrant

required gives rise to too much sodium.

In summarizing a comparison and contrast of alginates and KELCOGEL in the context

of

food systems, the following key issues emerge. They both form gels with calcium ions.

Unlike alginates, KELCOGEL also forms gels with other ions, notably sodium, potassium

and magnesium. Excess

of

these ions can cause precipitation which can also be induced by

excess acid, i.e., hydrogen ions. (It has been suggested that precipitation with calcium

andlor

acid, as practiced in alginate production, could be used in the manufacture

of

gellan

gum.) Setting by cooling, diffusion setting and internal setting can all be used to produce

gels using either alginates or KELCOGEL. However, setting by cooling is usually the

method of choice with KELCOGEL while setting in the cold is frequently preferred with

alginates.

In view of the similarities between the two polymers, it seemed desirable to investigate

whether or not the two in combination could be used to advantage. In this respect, an

obvious area to study was mixed gels formed by cooling hot solutions.

MATERIALS AND METHODS

Gel Preparation

Gellan gum (KELCOGEL, Lot No. 86-0082) and sodium alginate (KELTONE HV,

Lot No. 85l20A), alone and in combination, were dispersed in cold deionized (Arrowhead)

water and the dispersions/solutions heated to 90°C under agitation in a Helmco-Lacy Hot

Cup. Calcium or magnesium ions were added using the appropriate quantities of 0.5M

stock solution. The hot polysaccharide solutions were then poured into ring molds (13mm

height, 28mm inside diam.), covered with plastic cover slips and allowed to stand overnight

at room temperature to cool.

Specific gum concentrations evaluated were in % by weight: 0.2% KELCOGEL,

0.6% KELTONE HV, and 0.2% KELCOGEL

+

0.6% KELTONE HV.

The specific calcium ion concentrations used were: 0, 2, 4, 6, 8 and lOmM; these same

concentrations were also used for the magnesium ion.

Gel Texture Measurement

After overnight storage at room temperature, the gel discs, in the cases where gels had

86

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formed, were carefully removed from the ring molds and evaluated using an Instron

Universal Testing Machine, Model No. 4201, as previously described

l l

.

RESULTS

AND

DISCUSSION

Using calcium ions, gels were formed with KELCOGEL. The textural parameters for

these gels are shown in Figures 4 - 6. The results are totally as expected

II,

12. Hardness

(Fig. 4) rapidly increases to a maximum and then gradually declines with increasing,

calcium ion concentration. Modulus (Fig. 5) shows

a

more symmetrical increase and

decrease while gel brittleness (Fig. 6) increases (lower % brittleness

=

more brittle) fairly

2.5

_ - -

D,

2

B

- G

...>-,

- ---G -

--- "

-

Q)

e----

u

' S-.

0

.2

U,

1.5

:§.

'"

[J

'"

J

c

"E

'

c

-0-

0.2 KGEL-Mg++

0.5

- - EJ-

0.2 KGEL-Ca++

0.2 KGEUO.6 KTHV-Mg++

0

0

2 4

6 8 10

12

Ion Concentration (millimolar)

Fig. 4 Influence of ion concentration (Ca++ or Mg++) on gel hardness

rapidly up to a calcium ion concentration

of

around 6mM and then starts to level

off

at

higher calcium. With solutions of 0.6% KELTONE HV, attempts to prepare gels with

between 2 and lOmM calcium were unsuccessful since as little as 2mM calcium resulted in

immediate precipitation of the alginate from the hot solution. Additional tests showed that,

even by reducing the alginate concentration to 0.2% and the added calcium ion con

centration to 0.5mM, gelation could not be prevented. These results demonstrate that,

unlike KELCOGEL, unbuffered sodium alginate has minimal to zero tolerance for calcium

ions at elevated temperatures. In other words, gelation cannot be prevented by use

of

4.5

4

3.5

ILl

/

C\I

E

3

. 2

/

'"

2.5

"

;

0

2

/

::::;

1.5

I )

[']

/

- 0.2 KGEL-Mg++

rY'

- - 8 -

0.2 KGEL

-Ga++

0.5

0

2

4 6


Fig. 5 Influence of ion concentration (Ca++ or Mg++) on gel modulus

8

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45

-D-

0.2 KGEL-Mg++

40

0........

- - EJ-

0.2 KGEL-Ca++

Q

"'---

Q

0.2 KGEUO.6 KTHV-Mg++

35

"

'"

Gl

'

30

0-

'

- -S - _

25

'0

__

0

20

..

15

0 2

4

6 8

10 12


Fig. 6 Influence of ion concentration (Ca++ orMg++) on gel brittleness

elevated temperatures. Precipitation was also observed when 2 - lOmM calcium was added

to hot solutions

of

0.6% KELTONE HV

10.2

KELCOGEL. At the higher levels

of

added

calcium, precipitation was accompanied by gelation on cooling. These results strongly

suggested that the alginate was again precipitating from solution while, at higher levels of

added calcium, sufficient remained unbound by the alginate and available to cause the

KELCOGEL to gel on cooling. Thus, even in the presence of KELCOGEL, alginate still

displays minimal tolerance to added calcium at elevated temperature.

Interpreted superficially, these findings would argue against the practicality of

preparing useful alginate and mixed alginatelgellan gels by cooling in the presence

of

calcium ions. However, in the case of alginates, commercial products prepared in this

manner, such as the example in Table I, are well known. Useful combinations of alginate

and gellan gum that produce dessert gels on cooling have also been recently developed

13

.

A basic difference between these practical systems and the model gels described in this

paper is that the former are buffered with a sequestrant such as citrate or phosphate which

controls the calcium availability to the gelling polysaccharides. Another difference is that,

in the commercial gels, the calcium is frequently introduced through controlled dissolution

of calcium carbonate dispersed throughout the system while, in the model gels, the required

calcium is added in concentrated, predissolved form from a stock solution. Although, as

indicated, dessert gels containing both alginate and KELCOGEL have been formulated, the

nature of the resulting gels and how the calcium ions partition between the alginate,

KELCOGEL and sequestrant have still

to

be determined. This work is in progress.

With magnesium as the gelling ion, results are quite different. As anticipated, no gels

were formed with these ions and alginate. However, gels were obtained with both 0.2%

KELCOGEL and 0.2% KELCOGELlO.6% KELTONE HV. Figures

4 -

6 show that the

gels produced with magnesium and KELCOGEL are similar, although not identical, in

texture to those obtained with calcium, confirming that magnesium and calcium ions

interact similarly with KELCOGELi4. When magnesium ions were added to the

gellanlalginate combination, the gel strength peaks, for both hardness and modulus (Fig.

4

and 5), shifted to higher ion concentrations relative to the respective peaks for magnesium

and KELCOGEL. Similar behavior is observed for gels made with KELCOGEL in

combination with a sequestrant such as sodium citrate. It therefore appears that the

magnesium ions, although not able to promote interchain association and gelation of the

alginate, are nevertheless binding with the alginate to form a soluble complex. In other

words, the alginate is functioning as a sequestrant for magnesium ions. Inspection of the

viscosities of alginate solutions containing 0 - lOmM magnesium (Table 2) shows that

viscosity decreases with increasing magnesium ion concentration. This suggests increased

binding as the ion concentration is increased, with an accompanying increase in charge

8/17/2019 Sanderson 1993


screening and reduction in viscosity. The viscosity measurements also show that the

magnesium/alginate interaction

is

not time dependent, in keeping with magnesium s

inability to promote interchain association.

Table

2. Effect

of

magnesium ion concentration on the viscosity

of a 0.6% KELTONE HV solution.

Brookfield L VT Viscosities (6 rpm. spindle

no.

I)

Added Mg++ (mM)

o

hrs. 2 hrs. 24 hrs.

0

101

98

105

2

75

71

74

4

65

58

65

6 54

51

56

8 51

50

53

10 53

49

53

These studies highlight the difficulty associated with forming alginate gels by cooling.

High temperature does not prevent the strong association between alginate and calcium ions

and, unless a buffer

is

included to reduce the free calcium to a low level, precipitation

of

the

alginate results. It has also been shown that, when magnesium

is

used instead

of

calcium,

gels can be produced by cooling solutions containing KELCOGEL in combination with

alginate. In these gels, the alginate functions as a magnesium ion sequestrant and texture

modifier.

In summary, although KELCOGEL rather than alginate

is

the more logical choice for

gels formed by cooling, it

is

possible, from an understanding of the principles

of

gelation, to

make useful gels by cooling solutions containing both KELCOGEL and alginate.

For

completeness, it should also be mentioned that diffusion setting in the cold, normally the

province

of

alginate, can be used to form films from solutions

of KELCOGEL or

KELCOGEL and alginate

l5

.

A particular advantage

of

KELCOGEL

is

that these films can

be formed using sodium ions, from a source such as common salt, to bring about setting.

REFERENCES

I.

R.H. McDowell. Properties of Alginates, Kelco International, London (1986).

2.

W. Bryden, personal communication.

3. W Bryden and G.R. Sanderson. Structured Foods with the Algin/Calcium Reaction, Kelco Division of

Merck and Co., Inc., San Diego (1982).

4. M.E. Sneath, Artificial fruit berries,

British Patent

1,484,562 (1977).

5. M.A. O'Neill , R.R. Selvendran, and V.J. Morris, Structure of the acidic extracellular gelling

polysaccharide produced by

Pselldomollas elodea Carbohydrate Res.

124:

123

(1983).

6. P.E. Jansson, B.Lindberg, and P.A.Sandford, Structural studies of gellan gum, an extracellular

polysaccharide elaborated by Pselldomonas elodea Carbohydrate Res. 124: 135 (1983) .

7.

V.L. Bell,

D.

Ortega, and G.R. Sanderson. The Preparation of KELCOGEL Gellan Gum Gels, Kelco

Division

of

Merck and Co., Inc., San Diego (1989).

8.

V.L. Bell, D. Ortega, and G.R. Sanderson, A comparison of gellan gum, agar, K-carrageenan, and algin,

Cereal Foods World 34

:991

(1989).

9.

J.K. Baird and J.L. Shim, Non-heated gellan gum gels,

U.S.

Patellt 4,503,084 (1985).

10.

J.K. Baird and J.L. Shim, Non-heated gellan gum gels,

U.S. Patellf

4,563,366 (1986).

II. G.R.Sanderson, V.L. Bell, R.C. Clark, and D. Ortega, The texture of gellan gum gels, ill: Gums and

Stabilisers for the Food Industry 4, G.O. Phillips et aI., eds., IRL Press, Oxford (1988).

12.

G.R. Sanderson, Gellan gum,

in:

Food Gels, P.Harris, ed., Elsevier Applied Science, London (1990).

13.

Anon., Use of gellan/algin gum combinations

in

water dessert gels, Research Disclosure 333:69 (1992).

14. G.R. Sanderson and R.C. Clark, Gellan gum, Food Techllology 37:63 (1983).

15. W.F. Chalupa and G.R. Sanderson, patent pending (1992).

KELCOGEL and KELTONE are trademarks of Merck and Co., Inc. (Rahway, New Jersey), Kelco Division,

U.S.A., and are registered

in

the U.S. Patent and Trademark Office.

89

sanderson 1993

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