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

Подождите немного. Документ загружается.

0081 Cider, malt and wine vinegars are more costly than

distilled vinegar, but have unique flavors which con-

tribute character to mayonnaise. Distilled vinegar is

used when a neutral flavor is desired. Lemon juice

may be used in place of, or in addition to, vinegar

when its flavor is desired.

0082 Egg Egg yolk is the emulsifying agent most often

used in the home for preparing emulsions requiring

stability. The fact that egg yolk is itself an emulsion

explains, at least in part, why it is such an effective

agent. (See Stabilizers: Types and Function.)

0083 Eggs for mayonnaise may be fresh, frozen, or dried.

Fresh broken eggs usually make a weak-bodied may-

onnaise, although the product may stiffen somewhat

during storage. Upon freezing and storing raw egg

yolk below 6



C, its viscosity increases and gelation

occurs. This irreversible gelation of egg yolk makes it

useless for mayonnaise production. The addition of

10% salt (sodium chloride) or 10% sugar will par-

tially inhibit the gelation. Mayonnaise made from

frozen salted egg yolk is thick and creamy. Dried

yolk disperses readily in the aqueous phase of mayon-

naise, and results in a thicker product than that

obtained from frozen egg when prepared with the

same total egg solids content.

0084 Egg yolk is the primary source of color in mayon-

naise. The intensity and tone of the yellow color of

the yolk determine the color of the finished product,

because no other coloring matter is permitted. In

mayonnaise formulation, sequestrants, including but

not limited to calcium disodium ethylenediaminete-

tra-acetate (EDTA) and/or disodium EDTA, may be

used to preserve color.

0085 Pasteurization of egg products in the USA became

mandatory on 1 June 1966 in order to eliminate

problems with salmonella. Eggs used for dressings

and mayonnaise must meet this requirement.

0086 Biopolymer Proteins and polysaccharides, such as

soy protein isolate, whey protein concentrate,

xanthan gum, sodium alginate, propylene glycol al-

ginate, locust bean gum, guar gum, gum arabic, gum

acacia, starch, modified starch and microcrystalline

cellulose, are the two most important types of bio-

polymers used as ingredients in mayonnaise and

salad dressings to enhance the texture, replace

part or all of the fat, and enhance the stability of

emulsions.

0087 Proteins can form a film around the surface of

fat droplets through three stages: (1) native protein

molecules diffuse to the interface; (2) protein pene-

trates the interface; and (3) molecules rearrange to

achieve minimum energy. Such actions not only

reduce the interfacial tension, but also form a physical

barrier to reduce the possibilities of flocculation

and coalescence of fat droplets. Gums and/or starches

are added to dressings possibly due to their thickening

and/or surface-active effect. Gums and/or starches

may improve the emulsion stability of the dressings

by making the continuous phase more viscous, redu-

cing the possibilities of fat droplets encountering each

other, and creating a yield stress which increases

emulsion stability by minimizing or eliminating

creaming of the fat droplets under gravity force.

0088Mustard Mustard flour is probably used in more

dressing formulae than any other spice. It is used

chiefly for flavor but contributes slightly to emulsifi-

cation. Oil of mustard can be used in place of mustard

flour without affecting the emulsion strength. Oil

of mustard must be obtained from mustard seed.

Synthetic allyl isothiocyanate is not permitted. (See

Mustard and Condiment Products.)

Procedures for Manufacture

0089Mayonnaise is prepared commercially by both batch

and continuous methods, and there are many vari-

ations with respect to order and rate of ingredient

additions. All equipment should be fabricated from

stainless steel since vinegar will corrode ordinary steel

and aluminum. Two-stage mixing is commonly

employed with high-speed turbine blades in the first

stage followed by more severe shearing of the oil into

fine droplets in the second stage. The second-stage

mixer may possess close-clearance whirling teeth as

in a colloid mill.

0090The Dixie–Charlotte system is probably the one

most widely used for the production of mayonnaise

and salad dressings. The system consists of two Dixie

mixers and a Charlotte colloid mill connected by

appropriate piping, valves, and a rotary positive dis-

placement pump. It is arranged so that one mixer

feeds premix to the mill while another batch of pre-

mix is being prepared in the other mixer. The Dixie

mixer is a deep circular tank fitted with three turbine

mixers mounted side-by-side on a horizontal shaft

close to the tank bottom. The shaft is turned by a

variable-speed motor. This mixer can prepare mayon-

naise requiring no further processing. The emulsion

will be similar to one made with a Hobart mixer. The

creamy texture of modern mayonnaise is obtained by

pumping this relatively soft, coarse emulsion through

the Charlotte mill. This equipment is available in a

number of sizes with capacities ranging from 60 to

760 l per batch and yielding 230–4540 l of finished

mayonnaise per hour. The system is arranged on a

continuous-batch basis and can be modified to be

operated as a truly continuous system.

1896 DRESSINGS AND MAYONNAISE/The Products and Their Manufacture

0091 Preparation of mayonnaise premix in the Dixie

mixer is started by adding mayonnaise from a previ-

ous run to a level which will reach the mixer shaft.

This gives the turbine blades a heavy material to work

against while shearing the oil into fine droplets. Egg

and dry ingredients are then added to the mixer with

low-speed agitation. Oil and vinegar are then pumped

or fed by gravity from supply tanks into the mixer.

Agitation speed is usually increased periodically as

the level of the premix rises. If the oil is added too

slowly the premix will be thick and only partially

emulsified. The subsequent passage through the col-

loid mill causes an overemulsification, resulting in a

less viscous and stable mayonnaise. If the oil is added

too quickly, in relation to agitator speed, the premix

will develop an oily and curdled appearance; and, if

the rate is not reduced, the emulsion will reverse to

the water-in-oil type.

0092 The premix is pumped through the Charlotte mill

as soon as it is made. Timing should be such that the

alternate premix tank should have just finished

emptying. This is critical with many mayonnaise for-

mulations as the premix can gel in the dixie mixer.

The longer the premix is held in the mix tank prior to

milling, the softer the final product will be.

0093 Since salad dressings are similar to mayonnaise

except for the lower oil content and the added starch

paste, the ingredients function as in mayonnaise, and

principles with respect to mixing and emulsion stabil-

ity are similar. Special care must be given to starch

cooking to develop the desired degree of thickening.

0094 Raw starch is not water-soluble, but can be dispersed

in cold water. It requires cooking to form a thickened

suspension or paste. The sugar, salt, and vinegar are

also part of the paste. The process calls for cooking and

cooling the paste before combining it with the egg and

oil emulsion. In batch processing, some of the paste is

usually added to the egg before any oil is incorporated.

This weakens the egg. The oil is thereby prevented from

forming too tight an emulsion. The oil is not whipped

in as vigorously as with mayonnaise. When the balance

of the starch paste is mixed in after the oil is added, the

entire mass must be fairly soft so that it can be pumped.

The colloid mill yields a salad dressing with high vis-

cosity and smooth texture. If the premix is too stiff, it

will break down in the mill.

0095 A batch-type starch paste cooker is essentially a

jacketed vertical stainless-steel tank equipped with

single- or double-acting agitators having side-

scraping blades. A similar vessel is used for cooling

the paste in which cold water or brine solution is used

as the cooling medium. The most modern method for

processing starch paste is a continuous one employing

the concept of energy regeneration resulting from the

use of a plate heat exchanger.

0096No matter what process is employed, starch paste

should be used as soon as possible after preparation.

The longer it stands after cooling, the more readily it

will break down on being worked into the dressing.

This is especially true with high-amylose starches.

Cooking starch in vinegar solution tends to degrade

or hydrolyze the starch to some extent. Modified

starches are usually more resistant to breakdown

than unmodified types. Where feasible, it is best to

cook the starch with a minimum amount of vinegar

in the water solution. (See Starch: Modified Starches.)

0097The continuous method employed in the manufac-

ture of mayonnaise and salad dressing provides con-

tinuous automatic control so that one worker can

process up to 7570 l of mayonnaise, salad dressing,

and pourable dressings per hour. One operator can

monitor the entire system. Manual operation is

almost nonexistent now.

0098Formulae are monitored from a control center. In

the case of salad dressings, the system includes four

probe-controlled surge tanks: one for oil, one for

starch, one for egg, and one for the brine additive.

Each of the surge tanks is probed at a high and low

level so that, when a low level is reached, a signal is

sent to a pump, and the tank will be resupplied with

oil, starch, or egg until it reaches the high point. This

maintains a constant supply of ingredients. Should

any one of the tanks become empty, the entire system

halts. Each controlled surge tank leads to a metering

pump. Each pump is monitored from the control

center so that it delivers the desired volume within

0.5%.

0099By setting the predetermined speed of each pump,

the egg, brine, oil, and starch are metered accurately

at the proper flow rate ratio to the inline mixer or

preemulsifier where the ingredients are thoroughly

mixed and a preemulsion is created. The preemulsion

is then pumped with a sanitary pump to a colloid mill,

where an extremely fine globule emulsion is created,

and then on to the filler. Using this system, up to 25

different varieties of dressing can be made, all within

the accuracy of 0.5% in the formulation.

See also: Colloids and Emulsions; Emulsifiers: Organic

Emulsifiers; Fats: Fat Replacers; Hypertension:

Hypertension and Diet; Mustard and Condiment

Products; Soy (Soya) Beans: The Crop; Stabilizers:

Types and Function; Starch: Modified Starches; Vinegar

Further Reading

Anonymous (1975) Instructions for the Use of Dried Egg

Yolk in Mayonanise, Salad Dressing and French Dress-

ing. New York: Henningsen Foods.

Ford LD, Borwankar R, Martin RW , Jr. and Holcomb DN

(1997) Dressing and sauces. In: Friberg SE and Larsson K

DRESSINGS AND MAYONNAISE/The Products and Their Manufacture 1897

(eds) Food Emulsions, 3rd edn, pp. 361–412. New York:

Marcel Dekker.

Friberg SE (1997) Emulsion stability. In: Friberg SE and

Larsson K (eds) Food Emulsions, 3rd edn, pp. 1–55.

New York: Marcel Dekker.

Gorman JM and Ball HR, Jr. (1986) Quality control and

product specifications. In: Stadelman WJ and Cotterill

OJ (eds) Egg Science and Technology, 3rd edn, pp.

325–343.Westport: AVI.

Humphreys WM (1996) Fiber-based fat mimetics: micro-

crystalline cellulose. In: Roller S and Jones SA (eds)

Handbook of Fat Replacers, pp. 131–144. New York:

CRC Press.

Lopez A (ed.) (1981) Mayonnaise and salad dressing prod-

ucts. In: Processing Procedures for Canned Food Prod-

ucts, A Complete Course in Canning 11th edn, book II,

pp. 380–395. Baltimore: Canning Trade.

McClements DJ (ed.) (1999) Emulsion ingredients. In: Food

Emulsions. Principles, Practice, and Techniques. pp.

83–125. Boca Raton, Florida: CRC Press.

McWilliams M (ed.) (1985) Salads and salad dressings. In:

Food Fundamentals, 4th edn, pp. 99–119. New York:

Wiley.

Orthoefer FT (1988) Reduced-fat margarines and dressings.

Journal of the American Oil Chemists’ Society 65:

574–578.

Roller S (1996) Starch-derived fat mimetics: maltodextrin.

In: Roller S and Jones SA (eds) Handbook of Fat

Replacers, pp. 99–129. New York: CRC Press.

Tressler DK and Sultan WJ (eds) (1975) Standards of iden-

tity for mayonnaise and French dressing. In: Food Prod-

ucts Formulary, vol. 2, pp. 394–395. Westport: AVI.

Chemistry of the Products

S C Yang and L S Lal, Providence University, Taiwan,

Republic of China

Introduction

0001 Food emulsions, such as mayonnaise and salad dress-

ings, are two-phase systems of immiscible liquids

with limited stability. One phase is in the form of

finely divided droplets of diameters generally larger

than 0.1 mm. This dispersed, internal, or discontinu-

ous phase is suspended in the continuous or external

phase. Emulsion systems can be divided into two

categories: (1) those consisting of droplets of oil dis-

persed throughout an aqueous medium, which are

usually referred to as oil-in-water emulsions; (2)

those in which droplets of water are dispersed

throughout an oil or fat medium, which are termed

water-in-oil emulsions. Most food emulsions are of

the oil-in-water type. Emulsion properties generally

depend on the nature of the continuous phase and the

proportion of this phase to the dispersed phase. (See

Colloids and Emulsions.)

0002Standards of identity, in the USA, for mayonnaise

define the product as a semisolid emulsion made of

egg yolk, edible vegetable oil, and acetic or citric acid.

It may also contain salt, spices or spices oils, natural

sweeteners and various natural flavoring ingredients.

The oil content must be not less than 65% by weight,

and the product must contain at least 2.5% acetic

acid by weight. Citric acid in the form of lemon or

lime juice may replace the acetic acid at a minimum

level of 2.5%. The egg yolk may be in liquid, frozen,

and/or dried forms. This ingredient provides emulsi-

fying properties and gives the mayonnaise a pale

yellow color, which must not be intensified by any

other ingredient. Salad dressings are also oil-in-water

emulsions, but the concentration of oil is only about

30–45% as compared to 65–82% in mayonnaise. In

addition to yolk, stabilizers are permitted in this

product. Commercial products of reduced-fat may-

onnaise and salad dressings usually contain less than

half fat content as compared to regular product. Fat-

free products should contain no or physiologically

inconsequential amount of fat (< 0.5 g fat) per serv-

ing. All reduced/low-fat or fat-free products generally

rely heavily on hydrocolloids for viscosity and texture

characteristics. Table 1 shows the composition of

selected types of dressings and mayonnaise. Many

variations in formulations exist within each type of

product. (See Emulsifiers: Organic Emulsifiers; Uses

in Processed Foods; Stabilizers: Types and Function;

Applications.)

Physical Structure and Rheology

0003Reduction of interfacial tension is probably the first

step in the formation of an emulsion. Surface-active

agents form a film around the oil globules and pre-

vent their coalescence. In surrounding the oil drop-

lets, the lipophilic (oil-loving) portion orients itself in

the aqueous phase, forming a shell around the drop-

lets of the dispersed phase. By collecting itself at the

interface, the emulsifier prevents the dispersed par-

ticles from coalescing and separating out, thereby

increasing the emulsion’s stability.

0004The microstructure of mayonnaise, as revealed by

the scanning electron microscope, contains fat glob-

ules of various sizes (Figure 1a). Both the dispersed fat

and continuous phase are evident. The continuous

phase binds tightly to the fat globules (Figure 1b).

Several very small fat globules can be seen adhering

to the large globules. Under the high magnification of

1898 DRESSINGS AND MAYONNAISE/Chemistry of the Products

transmission electron microscopy, part of the inter-

facial film is visible surrounding the lipid droplets of

diluted mayonnaise (Figure 2). The electron-dense

material at the interface is the emulsifying material

from egg yolk. This material, which acts as a surface-

active agent, consists of complexes of egg yolk protein

fractions such as lipovitellin, livetin, and lipovitelle-

nin. (See Eggs: Structure and Composition.)

0005 In addition to functioning as an emulsifying agent,

egg yolk contributes viscosity to mayonnaise. Increas-

ing the amount of egg yolk from 5 to 12% increases

the thickness of the product. Viscous emulsions tend

to be more stable. However, amounts of yolk in

excess of 12% are not associated with a change in

consistency of the mayonnaise. It is essential that

there is a sufficient amount of aqueous phase (usually

vinegar) to surround oil droplets as they become

smaller and expose more surface during emulsifica-

tion. However, an excess of aqueous phase is not

conducive to a good emulsion.

0006 Since salad dressing contains less oil than mayon-

naise, there are fewer lipid droplets, and a higher

concentration of amorphous material between drop-

lets. The amorphous material is assumed to be

cooked starch paste, a stabilizing ingredient added

to salad dressing but not to mayonnaise. Starch

paste also reduces the rate of lipid droplet coales-

cence in salad dressing. (See Starch: Modified

Starches.)

0007Sensory attributes of dressing emulsions, such as

creaminess, thickness, smoothness, spreadability, and

pourability, are related to their rheological properties.

The shelf-life of dressing emulsions also depends on

their rheological characteristics. Viscosities of dress-

ing emulsions depend on the shear rate applied. Pseu-

doplastic flow is the most common type. It manifests

itself as a decrease in the apparent viscosity as the

shear rate is increased and is therefore often referred

to as shear thinning. Viscosities of dressing emulsions

also depend on the shear time. Thixotropic behavior

is the most common type, in which the apparent

viscosity decreases with time when subjected to a

constant shear rate. Dressing emulsions that exhibit

this type of behavior often contain droplets aggre-

gated by weak forces. Shearing of the material causes

the aggregated droplets to be progressively deformed

and disrupted, which decreases the resistance to flow

and therefore causes a reduction in viscosity over

time. For example, pourable salad dressings, such as

French varieties, Thousand Island, and Creamy

Italian, are primarily viscous in their flow behavior,

but exhibit varying degrees of thixotropy and often

a measurable yield stress as well.

0008Some dressing emulsions are not purely viscous or

elastic, but instead partly viscous and partly elastic.

For example, mayonnaise and spoonable salad dress-

ings show viscoelastic rheological behavior and

also possess a yield stress. The viscoelastic behavior

tbl0001 Table 1 Composition of selected types of dressings and mayonnaise

Nutrient Amount per 100 g

Blue and Roquefort

(regular)

Cooked

(homemade)

French

(regular)

Italian

(regular)

Russian

(regular)

Mayonnaise

(soybean)

Mayonnaise

(low-cal)

French

(low-fat)

kcal 504 156 430 467 494 717 136 10

Moisture (%) 32.3 69.2 38.1 38.4 34.5 15.3 80.7 95.2

Protein (g) 4.8 4.2 0.6 0.7 1.6 1.1 1.1 0.4

Fat (g) 52.3 9.5 41.0 48.3 50.8 79.4 12.7 0.2

Carbohydrate (g) 7.4 14.9 17.5 10.2 10.4 2.7 4.8 1.8

Fiber (g) 0.1 0 0.8 0.2 0.3 0 0.5 0.3

Vitamins

A (IU) 210.0 411.0 690.0 280.0 220.0

C (mg) 2.00 0.60 6.00

Thiamin (mg) 0.01 0.06 0.05 0 0.01

Riboflavin (mg) 0.10 0.15 0.05 0 0.03

Niacin (mg) 0.10 0.25 0.60

Folic acid (mg) 3.00

Minerals

Calcium (mg) 81.0 84.0 11.0 10.0 19.0 18.0 18.0 11.0

Phosphorus (mg) 74.0 87.0 14.0 5.0 37.0 28.0 28.0 14.0

Sodium (mg) 1094.0 734.0 1370.0 787.0 868.0 568.4 118.0 787.0

Magnesium (mg) 10.0 2.0 10.0

Potassium (mg) 37.0 121.0 79.0 15.0 157.0 34.0 9.0 79.0

Iron (mg) 0.20 0.5 0.40 0.20 0.60 0.50 0.2 0.4

Zinc (mg) 0.11 0.08 0.11 0.43 0.16 0.18

Data pooled from Ensminger AH, Ensminger ME, Konlande JE and Robson JRK (1994) Food composition. In: Food and Nutrition Encyclopedia, 2nd edn,

vol. 1. Boca Raton, FL: CRC Press.

DRESSINGS AND MAYONNAISE/Chemistry of the Products 1899

could be characterized through creep tests or dynamic

tests. Creep test consists of the application of a con-

stant stress and ensuing study of the time-dependent

behavior of the strain. Dynamic experiment consists

of the application of a sinusoidal stress and the

resulting sinusoidal strain is measured or vice versa.

The amplitude of the applied stress or strain used in

this type of test is usually so small that the material is

in the linear viscoelastic region, and the rest state of

the material can therefore be successfully studied.

0009 The rheological properties of dressing emulsions

are a function of the continuous-phase viscosity, the

phase volume fraction of the dispersed phase, the

droplet size, and the nature of the colloidal inter-

actions. In general, the viscosity of an emulsion

increases as the continuous-phase viscosity increases.

Typically, gums and stabilizers that have non-

Newtonian rheology are added to pourable salad

dressings to impart the non-Newtonian character to

emulsions and increase the viscosity of the continuous

phase and hence the viscosity of emulsions. The emul-

sion viscosity generally increases with the phase

volume fraction of the dispersed phase in a nonlinear

manner, and decreases with increasing droplet size.

Rheological properties of an emulsion also depend on

the relative magnitude of the attractive and repulsive

10 µm

2 µm

(a)

(b)

fig0001 Figure 1 (a) The scanning electron microstructure of mayon-

naise reveals fat globules of various sizes. (b) Higher magnifica-

tion of part (a) showing the continuous proteinaceous phase

bound tightly to the fat globules. Reproduced from Dressings

and Mayonnaise: Chemistry of their products, Encyclopaedia of

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

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

1 µm

fig0002Figure 2 The transmission electron micrograph of mayon-

naise. The interfacial film is visible surrounding the lipid

droplets. The electron-dense material at the interface is the

emulsifying material from egg yolk. Courtesy of Scanning Elec-

tron Microscopy, Inc., Illinois.

10 µm

fig0003Figure 3 The broken structure of the lower layer of mayonnaise

resulting from freezing and thawing. Reproduced from Dressings

and Mayonnaise: Chemistry of their Products, Encyclopaedia of

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

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

1900 DRESSINGS AND MAYONNAISE/Chemistry of the Products

interactions between the droplets. Viscosities of

emulsions can be increased by adding biopolymers

to increase the depletion attraction or bridging floc-

culation, by altering the pH or ionic strength to

reduce electrostatic repulsion, and by heating pro-

tein-stabilized emulsion to increase hydrophobic at-

traction. Aggregation may increase the emulsion

viscosity. The aggregation state of an emulsion is

clearly dependent on the shear rate, and for thixo-

tropic (time-dependent) systems, on shear history.

Factors Affecting Physical Stability

Emulsion Stability

0010 The term ‘emulsion stability’ refers to the ability of an

emulsion to resist changes in its properties over time.

The more stable the emulsion, the more slowly its

properties change. All emulsions are thermodynamic-

ally unstable and, given enough time, undergo phase

separation. However, in a kinetic sense, the dressing

emulsions can be made stable over shelf-life, main-

taining appearance, texture, and flavor that are

desirable to the consumer. The stability of dressing

emulsions may range from seconds for a product like

separating Italian dressing, to years for a product

like mayonnaise. Semisolid dressings, such as mayon-

naise and spoonable salad dressings, are very viscous

emulsions. Due to the high oil content of the mayon-

naise emulsion, the oil droplets are forced close to-

gether. This close proximity precludes concern for

flocculation, and emulsion stability must instead be

concerned with preventing coalescence, which can be

delayed by employing tough, pliable membranes that

are formed from the protein and polar lipid compon-

ents of egg yolk around the oil droplets. Pourable

dressings are much less viscous than semisolid dress-

ings, and are susceptible to creaming. Since the oil

droplets are spaced apart from each other, floccula-

tion that could lead to coalescence is also of concern.

For low-fat and fat-free dressings, emulsion stability

is normally not a major problem due to the low

amount of oils. Special considerations have to be

given to impart a full-fat flavor and texture for these

products.

0011 The emulsion stability is influenced by a number of

factors, including the egg yolk, the emulsifying effect

of mustard, method of mixing, and storage condi-

tions. The stability of mayonnaise may be evaluated

by simply storing samples at room temperature until

visible separation occurs. Centrifugation of emulsions

hastens the formation of separate layers and is also a

useful test of stability. The stability index for mayon-

naise is calculated as the percentage of the sample

remaining emulsified after being centrifuged at

5000 rpm for 30 min and then allowed to stand for a

period of time.

Egg yolk

0012Egg yolk is itself an emulsion, and it functions as an

efficient emulsifying agent. Three types of egg yolk

are currently used in dressings and mayonnaise: liquid

egg yolk, frozen salted egg yolk, and dried egg yolk.

0013Liquid egg yolk The emulsifying ability of egg yolk

is affected by the age and genetic factors of the bird

from which the eggs were obtained. Decreased emul-

sifying ability is associated with eggs from older birds.

Also, low social dominant strains of the White Leg-

horn breed were found to produce eggs with greater

emulsifying ability than eggs from high social domin-

ant strains. The emulsification capacity of liquid yolk

decreases as dilution with albumen increases. This is

due to the lower solids content and to interactions

between albumen proteins and yolk fractions.

0014Pasteurization does not significantly affect the emul-

sification capacity of commercial fresh yolk containing

48–49% solids. Heating albumen-free yolk to 61



causes no significant change in emulsion stability, but

emulsification capacity is significantly increased by

heating the yolk to 63



C. Pasteurization temperatures

above 63



C cause a considerable increase in egg yolk

viscosity. However, salted (10% sodium chloride)

liquid egg yolk can be pasteurized at 62–78



Cfor

5 min without damage to emulsifying properties. In

the manufacture of oil-in-water salad dressings, the

addition of egg yolk and salt results not only in an

increase of emulsion viscosity, but also in a reduction

of oil droplet size. (See Pasteurization: Principles.)

0015Frozen salted egg yolk Viscosity increases and gel-

ation occurs in raw egg yolk subjected to freezing and

storage below 6



C. The addition of salt reduces

gelation and inhibits microbial growth during

thawing. Frozen yolk containing 10% sodium chlor-

ide is the most common form used in the dressings

and mayonnaise industry. Frozen salted egg yolk pro-

duces mayonnaise that is stiffer than that made with

fresh yolk. Freezing at 29



C and storage at 23



for 1–4 months is detrimental to both pasteurized and

unpasteurized salted egg yolk. Acidification in com-

bination with pasteurization, followed by freezing

and storage, also damages the emulsification ability

of salted egg yolk.

0016Dried egg yolk The advantages of using dried egg

yolk are threefold:

0017less storage space and transportation cost than

liquid or frozen egg yolk;

0018not susceptible to bacterial growth during storage;

DRESSINGS AND MAYONNAISE/Chemistry of the Products 1901

3.0019 good uniformity, easy to handle in a sanitary

manner.

0020 Compared to frozen and to freeze-dried egg yolk,

spray-dried egg yolk produces the least stable emulsions.

This detrimental effect of spray-drying on yolk is due

to the rapid increase in extractability of the free lipids.

Mustard

0021 Mustard has a slight stabilizing effect on emulsions.

This effect depends not only on the chemical and

physical properties of mustard, but also on the

method of incorporating mustard into the mayon-

naise. In general, mustard collects at the oil–water

interface and tends to prevent droplets of oil from

coalescing. (See Mustard and Condiment Products.)

Method of Mixing

0022 Introduction of oil beneath the emulsion surface pro-

vides mayonnaise with improved stability, consist-

ency, and homogeneity. Using this method, the best

mayonnaise can be produced when a small amount of

oil is first added to the emulsifying agent, followed by

the addition of acid, and then the addition of the

remainder of the oil.

0023 The appearance of the dispersed and continu-

ous phases in laboratory and commercially made

mayonnaises is different. This is due to the difference

in the degree of agitation. A colloidal mill is used to

prepare the emulsion of commercial products,

whereas a catering-type food mixer is used in the

laboratory. The colloidal mill results in uniformity

in the size and shape of fat globules and a continuous

phase with no separation from the fat globules. In

mayonnaise prepared in a food mixer, the fat globules

are irregular in both size and shape, and some glob-

ules seem to join together to form a continuous mass.

Other mixing factors that affect consistency of may-

onnaise include the amount and composition of the

aqueous phase added during the first stage of mixing,

the duration of beating and resting periods, and the

addition of vinegar at various stages in the process.

Storage Conditions

0024 Mayonnaise and salad dressing become increasingly

unstable when stored at 55



C for 3 days. The rate of

droplet coalescence in salad dressing may not be as

high as in mayonnaise due to the stabilizing effect of

the starch ingredients.

0025 Freezing usually causes the dispersed phase of

emulsions to coalesce. Thus, freezing and thawing of

mayonnaise result in collapse of the emulsion struc-

ture. The emulsion may separate into two layers, the

upper layer of oil and the lower layer probably con-

taining water, proteins, sugar, salt, and mustard

(Figure 3). The damage to emulsions that are broken

by freezing is related to the influence of freezing on

the emulsifying agent. (See Freeze-drying: Structural

and Flavor (Flavour) Changes.)

0026Salad dressing may be stable to frozen storage

when the oil does not crystallize, or crystallizes

slowly. Other conditions favoring stability include

use of a thickening agent such as waxy rice flour

and freshly salted unfrozen egg yolk, at a level of

5.3–8%, along with a decrease in oil. At storage

temperatures above 18



C, this combination was

stable for 6 months. Other factors affecting emulsion

stability include:

0027fermentation of the egg yolk with pancreatic

phospholipase A

;

0028acetylation and succinylation of egg yolk lipo-

proteins;

0029addition of 0.05% sodium 2-lactylate to egg yolk.

Storage and Shelf-Life

0030Most dressings and mayonnaise held at room tem-

perature have a shelf-life of approximately 7 months.

These products are preserved against microbial spoil-

age by their acid and sodium chloride content, but

they are very sensitive to oxidative deterioration in

flavor and should be refrigerated after their contain-

ers are opened. (See Storage Stability: Mechanisms of

Degradation.)

0031The acid and sodium chloride content protects

against spoilage by microorganisms such as Salmon-

ella and Staphylococcus species. Some lactic acid bac-

teria and yeast may survive at the low pH (pH 4.0) of

mayonnaise, but they are destroyed by pasteurization

at 60–63



C for 3–5 min. Care should be taken when

mixing dressing with mayonnaise to avoid growth of

microorganisms which might occur at the higher pH

of the mixture. (See Lactic Acid Bacteria; Spoilage:

Yeasts in Spoilage; Staphylococcus: Properties and

Occurrence.)

0032Oxidative rancidity is one of the major problems in

relation to the use of vegetable oils. Even a hint of a

rancid flavor can ruin an entire batch of salad dressing or

mayonnaise. A thin film of oil, such as might be left on

containers through inadequate washing, can become

rancid very quickly. Thus, all dressing containers must

be cleaned thoroughly, and a fresh batch should never be

poured into a container containing older dressing.

0033Time, temperature, light, air, surface exposure,

moisture, nitrogenous organic material, and traces

of metals are factors responsible for the rancidity of

dressings and mayonnaise. In salad dressing and may-

onnaise products, the oil is subjected simultaneously

to most or all of these adverse conditions:

1902 DRESSINGS AND MAYONNAISE/Chemistry of the Products

.0034 The emulsification process increases the exposed

surface area of the oil.

0035 On average, mayonnaise contains 10–12% air by

volume, although an inert gas such as nitrogen may

replace some of the air.

0036 Moisture is present.

0037 Nitrogenous organic material is dispersed in films

surrounding the oil globules.

0038 The products are packed in glass jars that are

exposed to light.

0039 In some production areas traces of metals may be dis-

solved out of the equipment by the vinegar, although

the use of stainless-steel equipment minimizes this.

0040 The temperature at which salad dressing and may-

onnaise are kept may be as high as 38



C or higher.

0041 It may be 3–6 months before these products are

consumed.

For these reasons, the oil used by the salad dressing

industry must be of high quality. Commercial salad

dressings are presently made with both unhydroge-

nated and hydrogenated soya bean oil. Whether or

not hydrogenation is necessary to prepare oxidatively

stable salad dressing is a controversial issue in the

industry. Hydrogenation of soya bean oil with copper

and nickel catalysts effectively increases the storage

stability of salad dressing at 21



C but not at 32



The use of butylated hydroxytoluene (BHT) as an

antioxidant in the oil, and ethylenediaminetetraacetic

acid (EDTA) as a metal scavenger in the starch base,

as well as nitrogen packaging, are effective in pro-

longing the storage stability of salad dressing made

with unhydrogenated soya bean oil. Therefore, these

additives or nitrogen packaging may provide eco-

nomic substitutes for hydrogenation of soya bean oil

used in salad dressing. (See Antioxidants: Synthetic

Antioxidants; Soy (Soya) Beans: The Crop; Vegetable

Oils: Oil Production and Processing.)

0042Separation of mayonnaise may occur as a result of

long storage, warm temperature, freezing, or consid-

erable shaking or agitation during shipping. This

problem is controlled commercially by fine division

of the oil droplets, use of an effective stabilizer, cool

storage temperatures (0–5



C), and protection from

air and light during storage.

See also: Antioxidants: Synthetic Antioxidants; Colloids

and Emulsions; Eggs: Structure and Composition;

Emulsifiers: Organic Emulsifiers; Uses in Processed

Foods; Freeze-drying: Structural and Flavor (Flavour)

Changes; Lactic Acid Bacteria; Mustard and

Condiment Products; Pasteurization: Principles;

Stabilizers: Types and Function; Applications;

Staphylococcus: Properties and Occurrence; Starch:

Modified Starches; Storage Stability: Mechanisms of

Degradation; Vegetable Oils: Oil Production and

Processing

Further Reading

Dickinson E (1992) Introduction to Food Colloids. Oxford:

Oxford University Press.

Hanson HL and Lorraine RF (1961) Salad dressings stable

to frozen storage. Food Technology 15: 256–262.

Harrison LJ and Cunningham FE (1985) Factors influen-

cing the quality of mayonnaise: a review. Journal of

Food Quality 8: 1–20.

McClements DJ (1999) Emulsion rheology. In: Food Emul-

sions. Principles, Practice, and Techniques. Boca Raton,

Florida: CRC Press.

Warner K, Frankel EN, Snyder JM and Porter WL (1986)

Storage stability of soybean oil-based salad dressings:

effects of antioxidants and hydrogenation. Journal of

Food Science 51: 703–708.

Yang SC (1988) Effect of types of salt on characteristics of

10% salted egg yolk in mayonnaise. Food Science

(Taiwan) 15: 304–313.

Dried Foods 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

DRESSINGS AND MAYONNAISE/Chemistry of the Products 1903

DRUG–NUTRIENT INTERACTIONS

B Caballero and K G Conner, Johns Hopkins

University, Baltimore, MD, USA

Background

0001 Understanding the interactions between dietary con-

stituents and pharmacological compounds is essential

to monitor drug therapy correctly as well as to assess

the potential nutritional impact of medications. Most

therapeutic agents exhibit some form of interaction

that ultimately affects the nutritional status of the

host, by altering absorption or utilization of nutri-

ents. Frequently, these changes are not readily identi-

fied or may be obscured by the underlying disease.

0002 The interactions between therapeutic agents and

nutrients are part of the large number of interactions

occurring between nutritional and nonnutritional

constituents of the human diet. These include all

substances added to the food chain – incidentally or

deliberately – during harvesting, processing, pack-

aging, distribution, and preparation of foods. Some

examples of this broad category would include

pesticides, food additives, antibiotics, hormones,

and environmental toxins.

0003 Drug–nutrient interactions operate in both ways:

drugs can have a significant impact on nutrient ab-

sorption and utilization. Also, the nutritional status

of the host certainly affects the ability of drugs to be

absorbed and transported, and to exert an effect at

the target tissues.

0004 Drug–nutrient interactions can be broadly classi-

fied in two categories: direct physicochemical inter-

action and physiological or functional interaction.

Drug–nutrient interactions can also be classified

according to the site of their occurrence: within the

food matrix, in the gastrointestinal tract, or during

transport, metabolism, and excretion. The mechan-

isms and sites of drug–nutrient interactions are listed

in Table 1.

Physicochemical Interactions

0005These usually involve some form of molecular inter-

action between the drug and a nutrient, and occur

primarily during digestion and absorption. The usual

consequence of this interaction is a reduction in the

bioavailability of the drug and/or the nutrient. A well-

known example of this mechanism is the binding of

metals by the antibiotic tetracycline.

Functional Interactions

Functional Interactions at the Gastrointestinal

Tract

0006These acquire particular significance because alter-

ations in gastrointestinal (GI) function are likely to

affect the digestion and absorption both of the drug

causing it and of a number of nutrients. The most

common GI functional effects altering those functions

are as follows.

0007Changes in GI motility A reduction in transit time

may lead to a decreased absorption. A large number

of drugs have an effect on gut motility, whether this is

their primary therapeutic effect or not. Conversely,

food composition affects motility as well. Dietary

fiber not only increases motility but also may trap

other nutrients and drugs and reduce their availability

for absorption.

tbl0001 Table 1 Mechanisms and sites of drug–nutrient interactions

Site Mechanism Effect

Food matrix Binding and chelation Decreases bioavailability

Gastrointestinal (GI) tract Changes in GI motility Increase in transit time reduces absorption

Binding and chelation Decreases bioavailability

Change in bile acid concentration Reduces absorption of fat-soluble nutrients

Gastric pH Affects absorption of iron, vitamin B

, and others

Circulation Albumin concentration Decreases transport of bound substances

Competitors for albumin binding Displaces albumin-bound nutrients (fatty acids, tryptophan, etc.)

Target tissues Antagonistic effects May increase requirements for antagonized nutrient

Enzyme activities Reduces concentration of enzyme product

Excretion Renal function Increased excretion may lower nutrient levels, increase

requirements

Sequestration Same as above

1904 DRUG–NUTRIENT INTERACTIONS

0008 Changes in gastric acid output A reduced chloride

production with a subsequent increase in gastric pH

retards gastric emptying and may alter the balance

between ionized and nonionized forms of therapeutic

agents.

0009 Reduction in the concentration of bile acids This

affects the absorption of most fat-soluble com-

pounds. Lower bile acid concentration may result

from increased binding and excretion or decreased

production. For example, the antibiotic neomycin

binds to bile acids and increases their fecal excretion,

thus reducing their luminal concentration, and in so

doing decreasing the absorption of fat-soluble vita-

mins. This interaction, like many others, can be used

therapeutically to reduce bile acid turnover in certain

liver diseases, and to lower cholesterol levels by

reducing their reabsorption.

0010 Alterations in the GI microflora This may affect the

availability of nutrients produced by the normal gut

flora, such as vitamin B

. Since many drugs are

susceptible to bacterial metabolism, changes in the

gut flora may also affect drug bioavailability. In cer-

tain cases, drug cleavage by intestinal microorgan-

isms is an expected and necessary step for adequate

drug action. For example, the antiinflammatory agent

5-aminosalicylic acid is given as its precursor sulfasa-

lazine, which is converted to the active compound by

colonic bacteria. An altered colonic flora affects the

production of the active compound. Drugs can also

inhibit nutrient absorption by directly affecting pro-

tein synthesis in the enterocyte. Since most transport

systems require active protein synthesis and turnover,

such inhibition would result in a decreased rate of

nutrient absorption. Furthermore, certain drugs

undergo initial metabolism in the enterocyte, before

reaching the bloodstream. Alterations in protein syn-

thesis at the enterocyte, or an impaired turnover of

the intestinal epithelia, also affect this process.

Interactions Affecting Transport,

Metabolism and Excretion

Functional Synergism or Antagonism

0011 The biological actions of nutrients and drugs can be

synergistic or antagonistic, occur in different time

periods after exposure, and affect a variety of target

tissues. Some of the most common mechanisms are as

follows.

0012 Alterations in drug transport Drugs circulate in the

bloodstream as free compounds or bound to other

blood constituents, usually proteins. Drugs vary

greatly in their propensity to bind to circulating pro-

teins, virtually covering the entire spectrum from zero

to 100%. For a given drug, the bound fraction tends

to be relatively constant under physiological condi-

tions, but responds to changes in pH, electrolyte bal-

ance, and the presence of competing molecules. The

major transport protein in plasma is albumin, and its

concentration and the presence of other compounds

with affinity for albumin binding affect the amount

of drug that ultimately will be transported by this

protein.

0013Increase in nutrient catabolism Certain drugs stimu-

late detoxifying systems such as the cytochrome P-

450 pathway. Activation of this system may result in

an increased catabolism of certain nutrients. In other

cases, drugs have a direct action on nutrient catabol-

ism, as in the case of anticonvulsant drugs, which

stimulate vitamin D catabolism in the liver.

0014Biological antagonism This occurs when a drug and

nutrient have opposite biological actions, as is the

case, for example, of vitamin K and salicylates in the

coagulation process.

0015Increased nutrient losses Many drugs enhance dir-

ectly or indirectly the urinary excretion of nutrients.

Examples include the increased urinary losses of elec-

trolytes caused by aminoglycoside antibiotics, and the

increase in urinary ascorbic acid excretion induced by

barbiturates.

Host-related Functional Interactions

0016Nutrients and nutritional status can conversely also

affect drug action and disposition. Perhaps the most

significant host-related factor affecting drug dispos-

ition is protein synthesis. An altered protein synthesis,

usually resulting from deficient dietary protein intake

or severe diseases, will affect absorption, transport,

metabolism, and excretion, all protein-dependent

processes. The role of plasma albumin in drug trans-

port was discussed above, and is certainly affected by

impaired albumin synthesis and/or sequestration in

the extravascular space, as seen in protein–energy

malnutrition. It should be noted, however, that mal-

nutrition affects many aspects of drug metabolism,

not all in the same direction. For example, drug deliv-

ery may be reduced by impaired albumin concentra-

tion, but drug concentration in the bloodstream may

be increased, owing to impaired clearance, which is

also affected by malnutrition.

0017The plasma amino acid profile may affect the effi-

cacy of drug entry into the central nervous system. At

the blood–brain barrier, certain drugs are transported

DRUG–NUTRIENT INTERACTIONS 1905