Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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See also: Amino Acids: Metabolism; Freezing: Structural

and Flavor (Flavour) Changes; Irradiation of Foods:

Basic Principles; Lactic Acid Bacteria; Pasteurization:

Principles; pH – Principles and Measurement;

Preservation of Food; Sanitization; Sterilization of

Foods; Water Activity: Effect on Food Stability; Wines:

Production of Table Wines; Production of Sparkling Wines

Further Reading

Deak T (1995) Methods for the detection and identification

of yeasts in foods. Trends in Food Science and Technol-

ogy 6: 287–292.

Deak T and Beuchat LR (1996) Handbook of Food Spoilage

Yeasts. Boca Raton, FL: CRC Press.

Fleet GH (1992) Spoilage yeasts. Critical Reviews in Bio-

technology 12: 1–44.

King AD, Pitt JI, Beuchat LR and Corry JE (eds) (1986)

Methods for the Mycological Examination of Food.

New York: Plenum Press.

Kurtzman CP and Fell JW (eds) (1998) The Yeasts. A Taxo-

nomic Study, 4th edn. Amsterdam: Elsevier.

Pitt JI and Hocking AD (1985) Fungi and Food Spoilage.

Sydney: Academic Press.

Samson RA, Hocking AD, Pitt JI and King AD (eds) (1992)

Modern Methods in Food Mycology. London: Academic

Press.

Skinner FA, Passmore SM and Davenport RR (eds) (1980)

Biology and Activities of Yeasts. London: Academic

Press.

Thomas DS (1993) Yeasts as spoilage organisms in

beverages. In: Rose AH and Harrison JS (eds) The

Yeasts, 2nd edn. vol. 5, pp. 517–561. London: Academic

Press.

Tudor EA and Board RG (1993) Food spoilage yeasts.

In: Rose AH and Harrison JS (eds) The Yeasts, 2nd

edn. vol. 5, pp. 435–516. London: Academic Press.

Spores See Allergens; Food Intolerance: Types; Food Allergies; Milk Allergy; Lactose Intolerance;

Elimination Diets; Microbiology: Classification of Microorganisms; Detection of Foodborne Pathogens and their

Toxins; Spoilage: Chemical and Enzymatic Spoilage; Bacterial Spoilage; Fungi in Food – An Overview; Molds in

Spoilage; Yeasts in Spoilage

Spray Drying See Drying: Theory of Air-drying; Drying Using Natural Radiation; Fluidized-bed Drying;

Spray Drying; Dielectric and Osmotic Drying; Physical and Structural Changes; Chemical Changes; Hygiene;

Equipment Used in Drying Foods

Squashes See Melons, Squashes, and Gourds

Squid See Marine Foods: Production and Uses of Marine Algae; Edible Animals Found in the Sea; Marine

Mammals as Meat Sources

SPOILAGE/Yeasts in Spoilage 5537

STABILIZERS

Contents

Types and Function

Applications

Types and Function

J E Fox, P Ingenpass and S Zachow, GC Hahn and

Company, Lubeck, Germany

This article is reproduced from Encyclopaedia of Food Science,

Introduction

That familiarity breeds contempt is an oft-quoted

maxim of political life, yet it might also be applied

to many of our foodstuffs, which have acquired the

epithet of common, basic, staple, or simple. The ma-

jority of these foods are, in a physicochemical sense,

far from simple. Almost all are complex multiphase

systems, in which gases, liquids, or solids are dis-

persed in a liquid continuous phase, typically aque-

ous, which itself contains a multitude of solutes.

Examples of such natural foods are milk and eggs,

whilst icecream and mayonnaise are representatives

from manufactured foods.

0002 Disperse systems are inherently instable, and this is

true for many of these complex foods. Thus, full-fat

milk spontaneously creams on standing, and acidified

milk irreversibly curdles. This instability can be

resolved into two principal processes:

0003 Flocculation of fine or colloidally dispersed par-

ticles to aggregates which, if liquid or gaseous,

may coalesce to form larger droplets or bubbles.

0004 Displacement of particles under gravity as a result

of density differences between the phases.

These processes can influence the appearance and

rheology of the food and may detract from its per-

ceived quality and acceptance. The precise effects,

however, will depend on the volume fraction of

the disperse phase, and will naturally be greater

where this is higher. Particularly in such foods, it is

important to control or inhibit flocculation and

gravitationally induced phase separation. (See Floc-

culation.)

0005 The word ‘control’ is included here by virtue of the

fact that, in some foods, it may be advantageous to

promote these processes. Thus, in fat-reduced

mayonnaise, an aggregation of fat droplets may be

required to give the product a structure and plasticity.

Aggregation and structure formation may also be

utilized to prevent phase separation. In fat-rich fresh

cheese products, a casein network prevents the

creaming of the fat, and a similar mechanism is op-

erative in the stabilization of foams by fat crystals.

Although contradictory in terms, a stabilizer may

achieve stability by controlled and partial destabiliza-

tion. (See Casein and Caseinates: Uses in the Food

Industry.)

0006Control of flocculation and separation can be

achieved by the judicious use of polysaccharide

gums, proteins, organic salts (and emulsifiers), alone

or more often in combination. In this role these sub-

stances have become known as stabilizers, a suitable

definition for which would be as follows: food addi-

tives which prevent or control phase separation in

foods consisting of two or more phases.

0007Because stabilizers influence the structure of a

food, and because many of the additives used have,

in their own right, a thickening or gelling function,

the term stabilizer has become loosely used to

describe any additive that influences the rheology of

the products. This is a somewhat dangerous practice

as, in many countries, food-labeling law has led to a

legal definition of the term, and this usually restricts

its use to multiphase systems. It should also be

remembered that the term refers to a functionality;

therefore one and the same additive may not always

be properly described as a stabilizer. Thus, when car-

rageenans are used to prepare a clear jelly – a single-

phase system – it should be declared not as a stabilizer

but as a gelling agent. On the other hand, in chocolate

milk, where the gel serves to hold the cocoa par-

ticles in suspension, the former declaration would be

correct.

Flocculation

0008In order to illustrate how stabilizers influence floccu-

lation, it is necessary to review the forces which are

believed to be acting on dispersed particles. These

were first set out in the theory of Derjaguin Landau

Verwey Overbeck, which recognizes two types of

interparticle interactions:

5538 STABILIZERS/Types and Function

1.0009 Van der Waals forces.

0010 Electrostatic interaction.

Van der Waals forces are strong attractive forces

which are principally attributable to fluctuating po-

larization of the electron distribution in the molecule.

These forces decrease rapidly with distance, being

inversely proportional to the sixth power of the

separating distance.

0011 Dispersed particles may also carry surface charges,

with the resulting formation of an electrical double

layer of counterions in the proximal continuous phase.

When two similarly charged particles approach each

other, these ion layers begin to overlap and interact,

giving rise to repulsive forces. Typically, these forces

are stronger than Van der Waals forces at larger

separations, so resulting in a net repulsive force. As

separating distance decreases these repulsive forces

attain a maximum before Van der Waals attraction

causes flocculation (Figure 1). The height of this bar-

rier will naturally be dependent upon the magnitude

of electric double layer but, in order to limit floccula-

tion, it should be considerably larger than the thermal

energy of the system. The absolute magnitude of these

forces is generally related to the surface area of the

particle. They are therefore important where the ratio

of surface area to weight of the particles is large, and

therefore increase in importance with diminishing

particle size.

0012 From these considerations it follows that a col-

loidal dispersion may be stabilized by increasing the

surface charge and this, in turn, can be achieved by

the adsorption of polyelectrolytes. This approach is

particularly important in the stabilization of protein

dispersions, which tend to flocculation when the pH

of the continuous phase approaches their isoelectric

point. Here sodium carboxymethylcellulose (CMC)

has proved effective down to a pH of 4.2, below

which the polymer itself becomes increasingly insol-

uble. CMC offers the additional advantages that: (1)

its calcium salts are soluble, and there is therefore no

restriction on its use in calcium-rich systems, in par-

ticular milk, and (2) it is in itself a good thickening

agent, and when used in excess, it can retard gravita-

tionally induced phase separation. (See Colloids and

Emulsions.)

0013Below pH 4.2, pectin and, to a lesser degree,

alginate esters can be used. For stabilization, a

high proportion of the carboxylic acid residues

present in these molecules must be blocked, thus

only high-methoxy pectin, with a degree of esterifi-

cation (DE) above 70%, and propyleneglycol alginate

(DE > 60%) are effective. Polymers with a higher

proportion of free acid groups tend to facilitate

flocculation, presumably by bridging the dispersed

particles, and are calcium-sensitive. The esterification

of the acid also promotes the cleavage of the glyco-

sidic bond by b-elimination. These hydrocolloids

are therefore susceptible to thermal degradation,

particularly in neutral systems, and this can be a

handicap for their use in pasteurized and sterilized

products.

0014With these pectins and alginate derivates, a further

mechanism of stabilization may be operative. The

steric effects of the long molecules adsorbed on to

the surface of the particles may prevent their mutual

approach. In order to function in this way, the stabil-

izing polymer must have an appreciable portion of its

length as a fully solvated chain in the proximal solv-

ent (Figure 2). This requirement can rarely be met by

homopolymers and usually requires block polymer

species, such as high-methoxy pectin, containing

both lyophilic and lyophobic segments. This stabiliz-

ing mechanism will be affected by the solvent quality

with respect to the lyophilic portion; reducing the

quality will decrease stability. The stabilization also

requires that the surface be fully coated with polymer,

which should therefore be used in excess. If added

sparingly, lyophobic portions of the same molecule

may cause bridging between particles and thereby

induce flocculation.

Gravitationally Induced Phase Separation

0015Neglecting interparticle forces, the movement of par-

ticulate phase under gravity is governed ideally by

Stokes law. This law relates the terminal velocity u

of a spherical body to the viscosity of continuous

Electrostatic double-layer

repulsion

Resultant force with

energy barrier to flocculation

Interparticle

separation

Van der Waals

attraction

Attractive force Repulsive force

fig0001 Figure 1 Schematic representation of particle interaction. Re-

produced from Stabilizers/Types and Function, Encyclopaedia of

Food Science, Food Technology and Nutrition, Macrae R, Robinson

RK and Sadler MJ (eds), 1993, Academic Press.

STABILIZERS/Types and Function 5539

phase, Z, the radius of the particle, r, and the force

acting on the particle, f:

 ¼ð6f Þ=r

f ¼ð

 

r

The density of the particle is r

, and that of the

continuous phase is r

0016 It follows from these equations that the speed of

creaming or sedimentation increases with particle size

and decreases with the viscosity of the continuous

phase. This is, of course, the rationality behind the

use of homogenization to delay creaming in milk, or

the use of thickening agents to delay sedimentation.

0017 In order to have appreciable influence on stability,

the viscosity must be drastically increased and this

can best be achieved by the use of polysaccharide

gums. These substances are extremely efficient

thickening agents, being effective at concentrations

typically below 1.0%. (See Gums: Properties of Indi-

vidual Gums.)

0018 The effect on viscosity is believed to be the result

of nonspecific entanglement of the randomly coiled

polysaccharide chains. It follows from this model that

the more extended the polysaccharide molecules are

in solution, the more entanglement would be likely

and the higher the viscosity obtained. The extension,

and thereby the viscosity, is governed by size and

topology of the molecule, its flexibility, and its inter-

action with the solvent. Given the same molecular

weight, a linear molecule will be more extended and

more prone to entanglement than a highly branched

species. For linear molecules the extension should be

directly related to the molecular weight. (See Carbo-

hydrates: Classification and Properties.)

0019It is therefore not surprising to find that all com-

mercially important gum thickeners are linear poly-

mers, and that they are available in a wide range of

viscosities which reflect their degree of polymeriza-

tion.

0020The fact that these substances show a much larger

effect on viscosity as compared with equally large

synthetic polymers or proteins has been ascribed to

the bulky monomer sugar which restricts chain flexi-

bility. None of these polymers are rigid rods, however,

so that the quality of the solvent will influence the

degree of extension. In thermodynamically poor

solvents, and in the presence of salts which shield

electrostatic repulsive forces in polyelectrolytes, the

molecules tend to assume more compact conform-

ations and the efficiency of thickening will be

reduced. It also follows from the model of molecular

entanglement that the concentration must be such

that physical contact is possible. This condition is

usually satisfied when the concentration of hydrocol-

loid gums, c, is such that:

c:½4

In this equation, [Z] is the intrinsic viscosity of the

polysaccharide; c.[Z] is known as the overlap factor.

The intrinsic viscosity is a measure of the extension of

the molecule in solution and can be related to its

radius of gyration.

0021The flow properties of hydrocolloid-thickened so-

lutions are markedly pseudoplastic (Figure 3). Under

the influence of shear, the dynamic viscosity falls.

This is thought to be the result of orientation of the

extended molecules under the shear gradient, with a

concomitant reduction in entanglement. This prop-

erty can be used to great advantage in stabilizers. The

shear stresses operative in gravitational sedimenta-

tion or creaming are in the order of 10

10

mPa.

At these extremely low shear stresses, hydrocolloids

exhibit extremely high dynamic viscosities. A 1%

xanthan solution shows a viscosity of 10

mPa s

1

under a shear stress of 10 mPa. At shear rates of

between 10 and 50 s

1

, believed to be present in the

mouth during mastication, the viscosity of the same

Hydrated lyophilic

segments

Adsorbed lyophobic segments

(a)

(b)

fig0002 Figure 2 (a) Steric stabilization and (b) flocculation. Repro-

duced from Stabilizers/Types and Function, Encyclopaedia of

Food Science, Food Technology and Nutrition, Macrae R, Robinson

RK and Sadler MJ (eds), 1993, Academic Press.

5540 STABILIZERS/Types and Function

xanthan solution falls to 10

10

mPa s

1

. Thus,

foods thickened in this manner exhibit a light,

pleasant mouth feel.

0022 The same stabilization effect cannot be obtained

with a thickener showing Newtonic flow characteris-

tics in which viscosity is independent of shear. If the

high viscosities could be obtained at low shear then

the product would be unacceptably thick on eating.

This can be illustrated by honey, a Newtonic fluid

thickened by mono- and disaccharides, which has a

viscosity of only 10

mPa s

1

, independent of shear

rate. Organoleptically, such Newtonically thickened

solutions are perceived as long and slimy.

0023 This approach to stabilization, and the use of non-

absorbed polysaccharides in food in general, is

limited by thermodynamic incompatibility with

other colloidally dispersed polymers. This prevents

the polysaccharide and its incompatible neighbor

from occupying the same space, the so-called ex-

cluded volume, and can drive the excluded colloid

to flocculate or lead to phase separation. Such ther-

modynamic incompatibility is known to exist be-

tween proteins and polysaccharides and the effect is

therefore important in foods containing colloidally

dispersed proteins such as milk or gelatin solutions.

Thus, in milk, the addition of a low concentration of

hydrocolloid with a large hydrodynamic volume (i.e.,

extended conformations) will cause curdling, while

gelatin solution, in the presence of larger concentra-

tions, will exhibit phase separation. Indeed this effect

may be used to advantage in the gelatin encapsulation

of fats or, possibly, in the stabilization of foams.

(See Carbohydrates: Interactions with Other Food

Components; Protein: Interactions and Reactions

Involved in Food Processing.)

0024A further explanation for the flocculation of

colloidal particles has been proposed; this relies on

the driving force of the osmotic gradient, caused

by the exclusion of bulky polymer molecules from

the narrow gap between two approaching par-

ticles. This phenomenon, christened depletion floccu-

lation, has yet to be definitively observed in food

systems.

0025The seed gums, guar and locust bean gum (LBG),

which are both galactomannans, together with the

microbiological slime, xanthan, are the principal hy-

drocolloids used commercially for thickening foods.

Of these, xanthan shows the most pronounced and

desirable pseudoplastic flow and, in its purified form,

is colorless and tasteless. Although in many respects

an ideal stabilizer, xanthan is considerably more ex-

pensive than the seed gums and, presumably for this

reason, its use has been somewhat restricted. Guar

suffers from the problem of taste and, although it can

be reduced by steam treatment, this erodes the price

advantage. For LBG the critical quality characteristic

is the presence of dark specks, which originate

from the seed coat and which can prohibit its use in

white products. (See Gums: Nutritional Role of

Guar Gum.)

0026These hydrocolloid thickeners can be used indi-

vidually, but it is well known that galactomannans

interact with xanthan and other hydrocolloids. This

so-called synergism results, in the case of guar and

xanthan, in the mixture having a higher viscosity than

predicted on the basis of the individual concentra-

tions. In the case of LBG and xanthan, the mixture

gels. These effects are believed to be the result of

ordered associations forming cross-links between the

chains. The naked mannan segments of the galacto-

mannans are implicated in the formation of these

junction zones with xanthan, although their exact

form is at present unknown.

0027Generally speaking, viscosity increase should only

be used to stabilize suspensions in which the particle

size is small. With macroparticular suspension, such

as herbs in oil-free dressings or chocolate particles in

milk, greater resistance to movement is usually re-

quired and here the elastic properties of the continu-

ous phase should be augmented, i.e., the gel character

of the continuous phase increased.

0028The origin of gelling in polysaccharide solution is

believed to lie in formation of intermolecular cross-

links between the individual chains. With the onset of

cross-linking, the solution becomes progressively

more viscous until a distinct gel begins to form.

With increasing cross-linking the gel loses its elasti-

city, becomes more brittle, and exhibits syneresis.

Eventually, the hydrocolloids may precipitate out

of solution. The cross-links, or junction zones, are

Newtonian flow

Shear stress, τ

Pseudoplastic flow

Shear strain, d g

fig0003 Figure 3 Schematic representation of pseudoplastic and New-

tonian flow. Z ¼ t/dg, where Z is dynamic viscosity. Reproduced

from Stabilizers/Type and Function, Encyclopaedia of Food Sci-

ence, Food Technology and Nutrition, Macrae R, Robinson RK and

Sadler MJ (eds), 1993, Academic Press.

STABILIZERS/Types and Function 5541

complex, involving at least two polysaccharide

strands, and are believed to be crystalline in nature.

The driving force in their formation is hydrogen

bonding between hydroxyl groups and/or ionic

bonding where polyelectrolytes are involved.

0029 For the stabilization of liquid suspensions gener-

ally, a weak and, preferably, thixotropic gel should

be used, and the breaking strength should be chosen

so that the weakly gelled aqueous phase flows when

subject to the high shear stresses on pouring. In

principle, any gelling polysaccharide can be employed

but, in practice, carrageenans enjoy the widest

commercial use. At dosage levels of 0.5%, Jota carra-

geenans give a weak thixotropic gel suitable for

water-based dressings. It is a requirement of their

use, however, that the dressing is filled at a tempera-

ture of around 20



C. This may be bacteriologically

undesirable and, in such cases, a weakly gelling

xanthan galactomannan mixture may be used,

hot-filled. Where milk is the suspending medium, k-

carrageenans at dosage levels of 0.02% provide a

satisfactory gel.

Ostwald Ripening

0030 One further mechanism of destabilization is known.

0031 In polydisperse systems it can be observed that

larger particles grow at the expense of smaller ones.

This disproportionation phenomenon, which was

first described by Ostwald in crystallization pro-

cesses, is only important in the context of food

systems in the destabilization of foams. Gas trapped

in a foam bubble is subject to a pressure, the Laplace

pressure, due to the surface tension of the surround-

ing, typically aqueous, interface. The magnitude of

this internal pressure is inversely proportional to the

diameter of the bubble, i.e., the smaller the bubble,

the higher the pressure. If the gas is soluble in the

continuous phase then an equilibrium will be estab-

lished between the pressure of the gas in the bubble

and the concentration of dissolved gas in the continu-

ous phase immediately surrounding the interface.

This dissolved gas may diffuse away from the inter-

face or the continuous phase itself may be transported

in bulk through the foam. If this becomes adjacent to

a larger bubble with a lower Laplace pressure then

gas will be released from solution to reestablish the

equilibrium.

0032 The speed of Ostwald ripening in foams may be

reduced by decreasing the surface tension of the aque-

ous interface or decreasing the solubility of the gas in

the aqueous continuous phase. In practice, however,

longer-term stability can be conferred on the foam by

gelling the continuous phase so that bubble dispro-

portionation cannot take place.

See also: Carbohydrates: Classification and Properties;

Interactions with Other Food Components; Casein and

Caseinates: Uses in the Food Industry; Colloids and

Emulsions; Flocculation; Gums: Properties of

Individual Gums; Nutritional Role of Guar Gum; Protein:

Interactions and Reactions Involved in Food Processing

Further Reading

Dickinson E and Stainsby G (1988) Advances in Food

Emulsions and Foams. Essex: Elsevier Science Pub-

lishers.

Larsson K and Friberg SE (eds) (1990) Food Emulsions.

New York: Marcel Dekker.

Mitchell JR and Ledward DA (1986) Functional Properties

of Food Macromolecules. Essex: Elsevier Science Pub-

lishers.

Philips GO, Williams PA and Wedlock DJ (eds) (1989)

Gums and Stabilisers for the Food Industry, vol. 5.

Oxford: IRL.

Tanford C (1961) Physical Chemistry of Macromolecules.

Chichester: John Wiley.

Applications

J E Fox, P Ingenpass and S Zachow, GC Hahn and

Company, Lubeck, Germany

This article is reproduced from Encyclopaedia of Food Science,

Neutral Milk Products

0001The inhabitants of Normandy and Ireland’s west

coast were historically the first to use hydrocolloids

as food additives. With the help of calcium-sensitive,

gelling polysaccharides which were extracted from

red seaweeds, and which later became known as

carrageenans, a gelled milk pudding or blancmange

was prepared.

0002Carrageenans are still used in food in this capacity.

k-Carrageenan dosages between 0.2% and 0.3% pro-

duce a brittle-gelled pudding when hot-filled above

the gel melting point of about 70



C, but should the

product be subject to shear whilst gelling and cold-

filled, then a smooth, creamy, custard-type product

results. The consistency and mouth feel of both the

hot- and cold-filled products can be modified by the

incorporation of other polysaccharides. Starch, for

example, will improve the body and locust bean

gum (LBG) the elasticity. (See Gums: Properties of

Individual Gums.)

5542 STABILIZERS/Applications

0003 The classification of carrageenans as stabilizers is,

in these products, a somewhat moot point. There are,

however, two well-established applications of carra-

geenans in which their stabilizing functionality is

undisputed.

Ultra-heat-treated (UHT) Whipping Cream

0004 One aspect of the instability of milk, and particularly

cream, arises from the flocculation and creaming of

the milk fat. In short-life products, this can be ad-

equately controlled by homogenizing the product to

reduce the oil droplet size. However, this cannot be

done with long-life UHT whipping cream because it

would impair the whipping properties. The problem

can be solved by the incorporation of stabilizers

which form weak gels. (See Cream: Types of Cream.)

0005 Carrageenans have proved efficient here when

added at levels between 0.01% and 0.02%. The sta-

bilizer should be dissolved at 70



C in the skimmed

milk used to standardize the fat content, before UHT

treatment. In these systems, the casein micelles appear

to play an active role in the gel structure. The carra-

geenan becomes attached to the micelle surface by a

process other than that requiring the intermediacy of

calcium ions, and probably involving the cationically

charged section of the casein molecules. It is therefore

not surprising to find that the strength of the gel is

dependent on casein quality or, more precisely, on the

thermal history of the cream. Where the heat treat-

ment was prolonged or repeated, absorption or bind-

ing is poor and a higher dosage of carrageenan will be

required to obtain the required stability. Carragee-

nans are also amongst the most thermal-instable

hydrocolloids. Prolonged storage at elevated tem-

peratures is therefore to be avoided.

Cocoa Drinks

0006 A similar problem arises with chocolate milk. The

cocoa particles tend to sediment to the bottom of

the bottle, giving a deep brown, compact layer

below a somewhat pale (milk) fluid. This can be

corrected in the same way as the creaming in UHT

cream by the formation of a weak gel using about

0.02% of carrageenans. Other hydrocolloids may

also be included to improve the mouth feel of the

drink. The dosage of carrageenan is critical. Too

much carrageenan results in the formation of a gel

which is too strong and shows syneresis on standing,

leaving an almost clear serum at the top of the bottle.

Too low a dosage results in a gel which is insuffi-

ciently strong to support the cocoa particles which

sediment in the bottle. The quality of the cocoa can

also affect the stability. Cocoa which has been treated

with alkali to obtain a good color is difficult to

stabilize. (See Cocoa: Production, Products, and Use.)

0007To obtain stabilization, the UHT or sterilized drink

must also be bottled at a temperature below the gel-

ling point of the system, and ideally 24



C should not

be exceeded.

Foamed Milk Products

0008Two groups of foamed milk products may be recog-

nized: those containing fat in which the fat plays a

functional role in stabilization, and those based on

skimmed milk.

0009In fat-free systems, the milk proteins themselves are

sufficient to lower surface tension and form a stabil-

izing layer around the air cells. This can be reinforced

by the addition of other hydrolyzed proteins, and

thickening agents can be added to reduce the speed

of drainage of the aqueous phase from the lamellae

between the air cells, which would otherwise lead to

collapse of the foam. Thickening agents will not pre-

vent Ostwald ripening, so that to insure complete

stability the aqueous continuous phase must be gelled

as in a mousse-type product.

0010An entirely different situation exists in fat-contain-

ing products. Here the fat displaces the protein from

the air surface and prevents its stabilization of the

foam. In such products, the foam is stabilized by an

entirely different mechanism. An emulsifier, typically

an acetic acid or lactic acid ester of a mono- or

diglyceride, which is capable of displacing the protein

from the oil-water interface, is included in the stabil-

izing system. On whipping or aeration, the emulsi-

fiers promote coalescense of the fat globules, and the

fat crystals, which must be present in the fat phase at

the aeration temperature, form a supporting network

around the air cell. Such a mechanism is operative in

artificial cream, icecream, aerosol cream, cream top-

pings, milkshakes, and other products. (See Emulsi-

fiers: Uses in Processed Foods.)

0011In addition to emulsifiers, a variety of gums are

added to these stabilizer systems to modify the rhe-

ology of the aqueous phase. This is particularly

important where the fat content is low or the crystal-

lization poor. In cream toppings for desserts and

cakes, 1.0–1.5% gelatin is added directly before aer-

ation to stabilize the foam. In addition, carrageenans,

guar, and starches may be added to influence the

eating quality of the topping. In aerosol cream in

spray cans, the cream must remain fluid in the can,

and this system therefore cannot be used. Here the

protein content of the cream is enhanced and a low

dosage of gelling polysaccharide, carrageenan, or

pectin added.

0012Surface-active polysaccharides, such as propylene

glycol alginate or methylcellulose, may be used to

enhance foaming and foam stability. Where the

foam must be stable at elevated ambient temperature,

STABILIZERS/Applications 5543

the gelatin may be totally or partially replaced by

xanthan or gelling mixtures of xanthan and LBG.

Icecream

0013 Hydrocolloids and gelatin are also widely used in

icecream, and are customarily described and declared

as stabilizers, although their funtionality here has

little in common with stabilization in its strict sense.

Depending upon the type of icecream to be produced

and its fat content, typically between 0.5% and 0.8%

of a stabilizer mixture is used. Of this, about 50–60%

is a monoglyceride emulsifier to destabilize the fat

globules; the remaining 0.2–0.4 % is hydrocolloid,

of which about 80% is a thickening gum such as

LBG, guar, or sodium carboxy-methylcellulose

(CMC), and 20% a gelling agent, such as alginate or

carrageenan (0.01–0.03%). The gums serve to im-

prove mouth feel and limit ice crystal growth on

freezing and storage. The gelling agents are added to

prevent whey separation on thawing and give a slow

meltdown. (See Ice Cream: Methods of Manufacture;

Properties and Analysis.)

Sour Milk Products

Yogurt

0014 On approaching the isoelectric point, the casein mi-

celles in milk flocculate to give a delicate gel structure

typified by natural yogurt. With the natural solid

content of milk, the gel formed is extremely weak

and fragile and unsuitable for commercial exploit-

ation. The mouth feel is also poor and watery. The

addition of 2–5% milk solids as milk powder to the

base milk before incubation can remedy this situ-

ation. However, the problem remains that on aging

or exposure to high ambient temperature the casein

gel shows syneresis or wheying-off. To inhibit this,

the milk powder may be totally or partially replaced

by modified starches, gelatin, isolated milk protein,

or combinations thereof. Although from an economic

point of view the use of chemically modified starches

is very attractive, too high a dosage gives the

product a heavy, pasty and, for yogurt, very unchar-

acteristic mouth feel. Gelatin typically endows the

product with a smooth, light texture. (See Starch:

Modified Starches; Yogurt: The Product and its

Manufacture.)

0015 Polysaccharide hydrocolloids are not generally

employed because of their flocculation of milk pro-

teins at the isoelectric point, owing to the excluded

volume effects when added at effective concentra-

tions. The exception is the use of low-methoxy pectin,

at low dosages of about 0.1%, to promote floccula-

tion and thereby strengthen the gel.

0016Set yogurts, fermented in the tub, are inefficient to

produce on an industrial scale. Much more suitable to

the restraints of an industrial process are stirred

yogurts, in which the fermentation can take place in

larger vessels under carefully controlled conditions.

Unfortunately, however, once the yogurt gel is broken

by stirring, pumping, and filling, it will only partially

reform in the tub. This situation can be remedied

by the use of stabilizers which, if they are to be

added to the milk before culture, are limited to

those used in set yogurt, although they differ qualita-

tively from these.

0017With yogurt as a pumpable liquid, it becomes pos-

sible to pasteurize or even sterilize it in a plate heat

exchanger. This removes one of the major hurdles to

wide-scale distribution, i.e., the limited shelf-life. At a

pH not far below the isoelectric point of the proteins,

the stability of the dispersed protein is delicate and

thermal energy can easily lead to flocculation. This

flocculation is manifested as an unpleasant, sandy

texture in thermized yogurt. This phenomenon can

be delayed by the addition of high-methoxy pectin,

typically at levels between 0.5% and 0.7%, before

pasteurization. Pectin is believed to function by

forming a protective layer on the surface of the casein

micelles. A finer dispersion with a larger surface will

therefore require a higher dosage. The dosage is also

related to the thermal stress which the product must

survive. Indeed, under ideal technology and recipe, a

commercially satisfactory thermized product may be

manufactured with almost no stabilizer. However, if

the product is kept at elevated temperature over

hours, no amount of protective colloid can prevent

unacceptable sandiness. At extremely high dosage,

pectin also causes flocculation owing to excluded

volume effects. As an alternative to pectin, propylene

glycol alginate can be, but seldom is, used commer-

cially. CMC may be used above pH 4.2. (See Pectin:

Food Use.)

0018Pasteurization also presents the opportunity to add

new sterile ingredients to the sour product before

thermization. Thus low concentrations of gums, typ-

ically guar and LBG at 0.1% dosage levels, can be

added to improve the mouth feel of the product. (See

Pasteurization: Principles.)

Quarg and Fresh Cheese Products

0019The problems associated with the production of fresh

cheese products have their roots in the same phenom-

ena as those that destabilize yogurt. (See Cheeses:

Quarg and Fromage Frais.)

0020Collapse and contraction of the casein gel lead to

syneresis or wheying-off, and heating of the casein

enhances flocculation and causes sandiness in the

product. Both these effects can be eliminated or

5544 STABILIZERS/Applications

reduced by the use of stabilizers; the type and dosage

depend greatly on the recipe, on the technology, and

the type of product to be manufactured. A typical

thermized quarg stabilizer contains 0.3% gelatin,

0.3% starch, and small amounts of gum, including

CMC, guar, and LBG. Gelatin gives the quarg a

pleasant, smooth, and light mouth feel and appears

to function, at least partially, as a protective colloid

for underefficient thermization processes – such as

those occurring in a scraped-surface heat exchanger

– and in the presence of moderate amounts of fat, no

sandiness occurs.

0021 When the product is subject to high thermal stress,

such as prevails in a batch process with a long cooling

time or when the product is fat-free, other protective

colloids, such as CMC, may have to be included.

Starches are usually included to give the product

body. Gums confer viscosity on the product. This is

of special importance in hot-whipped products,

where the viscosity of the hot quarg would be insuffi-

cient to sustain a foam. In whipped products a higher

dosage of gelatin is also used to stabilize the foam

when cold.

Sour Milk Drinks

0022 Compared to yogurt or quarg, sour milk drinks con-

tain appreciably less protein, and the problem is

not so much one of stabilizing a casein gel network

as maintaining the individual casein flocculates in

suspension. To this end, almost all sour milk drinks

are homogenized under high pressure to break down

the casein flocculates and give a stabilizable par-

ticle density. The resulting high surface area dictates

that a higher than normal concentration of protective

colloids must be employed. Typically, this is high-

methoxy pectin for drinks below pH 4.2, and CMC

for a pH above 4.2. Below pH 4.2, CMC becomes

increasingly insoluble, and chain association leads

to flocculation enhancement. Above this pH, how-

ever, CMC has the added advantage of increasing

viscosity and thereby slowing sedimentation. With

pectin, other gums may be added to increase vis-

cosity.

Emulsified Foods

0023 Two types of emulsified foods can be recognized:

those such as mayonnaise and dressings, in which

the oil is dispersed in a continuous aqueous phase

(o/w), and those typified by such products as butter

and margarine, which are water-in-oil (w/o) emul-

sions. Both these systems are inherently unstable

owing to their high surface energy content and density

differences between the phases.

Oil-in-water Emulsion

0024Traditional mayonnaise is an o/w emulsion contain-

ing 80% oil, in which egg yolk serves as an emulsifier.

The short plastic structure of this product is attribut-

able to three factors:

0025The fine oil droplet size, 1–10 mm, results in a

relatively high Laplace pressure which resists

droplet deformation.

0026The high volume of oil is somewhat in excess of

the optimal packing condition, thus forcing the

droplets to be in intimate contact.

0027Attractive forces between proteins on the aqueous

face of the droplet surface cause adhesion and

restrict movement. (See Dressings and Mayon-

naise: The Products and Their Manufacture;

Chemistry of the Products.)

With no room for gravitational separation and an

adequate protein layer around the droplets, mayon-

naise represents a perfectly stable system. The

modern consumer, aware of the dangers of a high-

lipid diet, has shied away from such products and

demanded surrogate products showing identical

rheological behavior, but with 50%, 30%, and even

15% oil contents. Although milk powder or case-

inate, which promotes droplet adhesion, is used as

the emulsifier, the volume of oil is too low either to

form a continuous agglomerated network and to

endow the product with stability against creaming,

or to give the desired rheological properties. This

problem may be solved by including a starch paste

(10–12% solids) to replace the oil in a 1:1 ratio. This,

especially in very-low-oil emulsions, gives the prod-

uct a cheap and pasty mouth feel. A better and more

acceptable salad or low-energy mayonnaise can

be stabilized by replacing some of the starches by

hydrocolloids. For example, for the cold preparation

of a 30% emulsion, a blend of either LBG or guar

gum and xanthan at a total dosage of 0.4–0.6% can

be used in combination with starch. Guar gum or

CMC can be used in addition where the fat content

is very low in order to achieve a mayonnaise-like

consistency. The stabilizers can be used with emulsi-

fiers such as milk protein or egg yolk.

0028For the stabilization of hot-prepared dressings and

mayonnaises, guar gum and xanthan in the ratio of

3:1 at an addition of about 0.50% can be employed.

The viscosity can be adjusted by varying the combin-

ation and quality of raw material and stabilizer(s).

0029Mayonnaises are widely used for the preparation

of salads. There are three special applications of

hydrocolloid stabilized products. When marinated

fish or fresh vegetables are included they tend to

lose appreciable amounts of cell fluids which can

STABILIZERS/Applications 5545

form unsightly pools in the mayonnaise. The incorp-

oration of gums can help bind this water. For

example, guar gum is used in combination with

xanthan, LBG, and propylene glycol alginate. For

dressings with high fat or cream contents, milk pro-

teins, especially whey protein and caseinates, are

widely used.

0030 Fresh fruit and vegetables often contain amylases

which attack and hydrolyze the starch in the mayon-

naise with the concomitant loss of viscosity and sta-

bility. For such applications, special mayonnaises

have been developed which are wholly stabilized by

enzyme-resistant hydrocolloids. Typical are blends

of guar gum and xanthan in the ratio of 3:1 at an

addition rate of 0.50%. The water-binding ability

and ‘cling’ of the dressing will be increased by adding

CMC to this blend. Where the oil content of the

mayonnaise has been reduced in the formulation of

a calorie-reduced or ‘light’ product, the consequent

reduction in opacity can be compensated by the

addition of milk proteins.

0031 In some salads, where the proportion of mayon-

naise is low, it must be prevented from running-off the

other components. This feature, known as cling, is

important in such products as coleslaw and may be

achieved by improving the pseudoplastic flow char-

acteristics of the emulsion by the use of stabilizers.

Good cling to salad ingredients, also to hot salads,

will be obtained by using balanced combination of

water-binding and gellifying hydrocolloids.

Water-in-Oil Emulsions

0032 Those arguments which led to the introduction of

low-oil mayonnaises have also promoted the develop-

ment of fat-reduced spreads. In butter or traditional

margarine, the distribution of the finely dispersed

aqueous phase is stabilized by the crystal matrix in

the fat. With half-fat products and spreads containing

more than 60% aqueous phase, the crystal matrix is

depleted and insufficient to insure stability. Hydro-

colloid stabilizers are, of course, unable to influence

the rheology of the fat phase. The usual approach is

therefore to prevent coalescence of the droplets by

increasing their viscosity or gelling. The viscosity

can be raised by the addition of proteins or gums.

The use of 2% caseinate in combination with other

milk proteins at a total dosage of about 4% is neces-

sary for the stability of the emulsion, possibly in

combination with fatty acid emulsifiers. The quality

of the product with regard to melting and spreadabil-

ity can be improved when adding hydrocolloids such

as carrageenan and xanthan. For gelling, gelating is

customarily used by virtue of its low melting tempera-

ture. (See Margarine: Types and Properties; Methods

of Manufacture.)

Deep-Frozen Foods

0033The crystallization of both oil and water phases in

deep-frozen products presents a special stabilization

problem. In addition to damaging and weakening cell

structures, crystal growth also physically concen-

trates the dispersed phase and thereby promotes ag-

glomeration. Icecream is typical of the foods in which

this can occur. In an analogous manner, ice crystal

growth within polysaccharide gels forces the chains

together; these may then form macroscopic, solid-

phase regions between the crystals which will not

rehydrate on thawing. The effect is most pronounced

in native starch gels where, after freezing, the gel

resembles a sponge from which the water can be

removed by simply squeezing. This situation can

be remedied by the addition of low levels of a hydro-

colloidal gum to the paste. Typically, 0.15% xanthan

and CMC is used. Alternatively, chemically deriva-

tized starches which show little or no retrogration,

such as hydroxypropyl derivatives, can be used. The

addition of emulsifiers and special starch-degradation

products counteracts crystallization. (See Freezing:

Principles.)

0034This behavior is not restricted to starch. Where the

chemical nature of the gelling polysaccharide is con-

ducive to ordered association, considerable syneresis

results from a freeze–thaw cycle. Such gels are, by

virtue of their propensity to cross-linking, naturally

strong and brittle. As with starch, syneresis can be

limited by the addition of small amounts of nongel-

ling gums. With k-carrageenan – a typical brittle,

freeze–thaw-unstable gel – small additions of LBG

may be used, but this will also influence gel rheology.

As would be expected, weak, elastic, and preferably

thixotropic gels may survive freeze–thaw cycles un-

damaged. Commercially, i-carrageenans are widely

used in this role.

0035Crystallization of the fat in an o/w emulsion usu-

ally results in a penetration of the protective layer

around the oil droplet with subsequent coalescence

on thawing. Provided that the oil content remains

low, preferably < 20%, emulsions which do not

break can be prepared by using propylene glycol al-

ginate as the emulsifier in combination with xanthan

as the stabilizer at levels of 0.5–1.0%.

Miscellaneous Applications

0036More than 10 years ago, the first oil-free dressing

appeared on the market in which the herbs were

suspended in a clear aqueous phase. In these products

the herbs are held in a suspension by a weak, prefer-

ably thixotropic gel, usually based on carrageenans.

This technique may be applied to a wide range of

5546 STABILIZERS/Applications