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

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infections such as osteomyelitis, septic arthritis, and

soft tissue infections. Diagnosing infection with

Salmonella is dependent on culturing the organism,

usually from either stool or blood cultures. In the

case of nontyphoidal Salmonella, it is also worth

trying to culture organisms from the incriminated

food.

0017 Gastroenteritis from nontyphoidal Salmonella is

usually self-limiting, and rehydration is the most crit-

ical aspect of treatment. Antibiotic therapy is not rou-

tinely required for this aspect of Salmonella infection

and has in some instances been thought to promote

chronic carriage. When there is systemic invasion with

the bacteria and in cases of enteric fever, antibiotic

therapy is important. Third-generation cephalospor-

ins and quinolones are most frequently used, although

chloramphenicol has been the mainstay of treatment

for typhoid fever for many years and is still used in

many developing countries, but chloramphenicol does

carry a risk of complications.

0018 Antibiotic resistance has become a major problem

with many Salmonella serovars. Of particular con-

cern is the recent emergence and spread of Salmonella

DT104 that carries resistance to multiple antibiotics,

including, in some instances, to the fluoroquinolones

such as ciprofloxacin. In 2000, Salmonella strains

that were resistant to Ceftriaxone were also reported,

further raising the concern that the emergence of new

antibiotic resistance profiles were occurring.

Shiga Toxin-producing

E. coli

0019 Shiga toxin-producing E. coli (STEC) are relative

newcomers to the scene of foodborne pathogens.

The first STEC to be associated with disease in

humans was E. coli O157:H7 following two out-

breaks of hemorrhagic colitis in 1982. Since then, it

has been learned that there are in fact many different

serotypes of STEC, and at least 60 different types

have been associated with clinical disease. Recent

studies have suggested that around 1% of samples

submitted to clinical microbiology laboratories in

the USA contain STEC, of which around two-thirds

are O157:H7, the remainder being non O157. STEC

are present in the gastrointestinal tracts of many

mammalian species but appear to be especially

common in ruminants (cattle, sheep, deer, and

goats). Therefore, the main source of STEC in our

food supply is bovine products.

0020 Recently, there have been an increasing number of

reports associating STEC infection with fresh pro-

duce (lettuce, alfalfa sprouts, apple cider) and water.

This is thought to be mainly due to contamination

with fecal material from cattle pasture. Clinically,

STEC cause a variety of diseases ranging from

diarrhea, which may or may not be bloody, hemor-

rhagic colitis, and the hemolytic uremic syndrome

(HUS). HUS is a triad of renal failure, thrombocyto-

penia, and hemolytic anemia. Acutely, HUS has a

mortality rate of around 5%, and up to 50% of

HUS patients may have some degree of permanent

renal insufficiency. The main virulence factor from

STEC is the production of one or more bacterio-

phage-encoded Shiga toxins (Stx), which are of two

main types, Stx1 and Stx2. Following ingestion of the

bacteria, they colonize portions of the lower intestinal

tract and produce the toxins. Stx is then thought to

cross the intestinal epithelial cell barrier and damage

distant target sites, especially the kidney and brain, by

a direct effect on endothelial cells in the microvascu-

lature. The infectious dose of STEC may be very low,

in the region of 10–100 organisms in some instances.

Symptoms typically develop 2–4 days following in-

gestion but may occur in as little as 1 day or in as

much as 8 days. The diarrhea can be of variable type

(bloody or nonbloody) and may contain leukocytes.

The type of diarrhea is not a reliable indication of

who will go on to develop HUS. The mainstay of

treatment for STEC and its major complications is

supportive. There is a degree of controversy over

the use of antibiotics, and a number of studies have

suggested that certain antimicrobials (e.g., trimetho-

prim-sulfamethoxazole) actually increase the likeli-

hood that a patient will go on to develop serious

complications.

Yersinia

spp.

0021Of the three members of the genus Yersinia, Y. entero-

colitica and Y. pseudotuberculosis are considered to

be foodborne, whereas Y. pestis is not. Yersinia are

not very commonly found as causes of foodborne

illness compared with Salmonella or Campylobacter.

However, they are clearly transmitted in food and can

cause a significant gastrointestinal illness. The food

most frequently associated with yersiniosis is pork.

Swine are a major reservoir of these organisms, and

although they have been found in many other animals

(e.g., sheep, dogs, cats, and cattle), consumption of

undercooked pork is a common association. Milk

is another frequently reported source, and since

Y. enterocolitica can survive, and indeed multiply, in

milk at 4



C, small numbers of organisms can become

a significant health threat, even if the milk is refriger-

ated. Symptoms in Y. enterocolitica infection can

be prolonged, lasting several weeks or even longer.

Most infections are, however, self-limiting, although

complications may occur such as ulceration and in-

testinal perforation. A classic long-term complication

following yersiniosis is the development of reactive

EMERGING FOODBORNE ENTERIC PATHOGENS 2067

arthritis. As with other enteric pathogens, this is more

likely in patients who are HLA B27-positive.

Viral Foodborne Pathogens

0022 Viral agents are considered to be an increasingly

important cause of foodborne illness. A number of

different viral agents have been associated with food-

borne disease and cause a variety of illnesses varying

from a simple gastroenteritis to major systemic upset

such as hepatitis. Food and water are vehicles for

viruses, but viruses do not reproduce in food, and

nor do they produce toxins in food. Some viruses,

such as Norwalk, cause large outbreaks, and others

seem to be more frequently associated with sporadic

disease. Overall, the difficulty in diagnosing viral

illness has precluded the development of large

amounts of epidemiological data. It is beyond the

scope of this chapter to discuss all viral causes of

foodborne disease. However, Norwalk-like viruses

do deserve a specific mention.

0023 Norwalk virus is a small round-structured virus

(SRSV) and was the first virus to be clearly associated

with gastroenteritis. Norwalk is a calicivirus, and this

group of viruses causes disease worldwide and has

been associated with some large outbreaks, often in

confined environments such as cruise ships. Out-

breaks have been associated with contaminated

drinking water, swimming water, consumption of

undercooked shellfish, ice, and salads. As with the

other enteric viruses, fecal contamination of food or

water is usually found to be the ultimate source. The

incubation time following exposure is around 48 h,

and the clinical illness usually consists of vomiting

and diarrhea. The diarrhea is watery without red

cells, leukocytes or mucus. The disease is usually

self-limiting, settles in 24 h, and requires no specific

therapy. Specific diagnosis is difficult. A number of

assays are available (but not commercially), including

electron microscopy, enzyme immunoassays, and

reverse transcriptase–polymerase chain reaction.

Parasites

0024 Two emerging parasitic foodbrone pathogens that

cause predominantly watery diarrhea are Cryptospor-

idium parvum and Cyclospora cayetanensis. As can

be seen from Table 4, C. parvum causes a lot of

disease, but only 10% of it is considered to be food-

borne; in contrast, C. cayetanensis causes a lot less

disease, but 90% of it is considered to be foodborne,

much of which is based on outbreak data. Crypto-

sporidium parvum, for which proven effective ther-

apy does not exist, has gained notoriety for causing

persistent chronic diarrhea in immunocompromised

patients. C. parvum is endemic in cattle and is usually

acquired in humans from contaminated water, fresh

produce, unpasteurized milk, or person-to-person

spread. The incubation period is typically about a

week but can be as long as 28 days. C. parvum is

known to cause large outbreaks, the largest of which

was waterborne in Milwaukee, in which around

400 000 individuals became sick. C. cayetanensis in-

fection has been associated in the past with consump-

tion of imported berries most likely contaminated

with fecally contaminated water. More recently, it

has been linked with fresh basil. It can be diagnosed

by direct acid-fast microscopy of stools, but it is im-

portant to note that most microbiology laboratories

will not routinely look for C. parvum and/or C. caye-

tanensis, so they may be more common than we think.

Transmissible Spongiform

Encepalopathies

0025Mad cow disease or bovine spongiform encephalop-

athy (BSE) was first diagnosed in the UK in 1986. BSE

is a member of the family of transmissible spongiform

encephalopathies (TSEs) that are linked with neuro-

logical diseases in a variety of animals, including

humans, sheep, elk, and mink (Table 6). Historically,

TSEs were recognized in Europe as long ago as the

eighteenth century, when a neurological condition

known as scrapie was first described in sheep. How-

ever, TSEs did not become a public health or food

safety concern until the mid-1990s, when the link

between BSE and a condition in humans, known as

new variant Creutzfeldt–Jakob disease (nvCJD), was

made, and it became clear that the disease was due to

transmissible agents, that were given the name prions.

0026Although there are no clear answers as to the

origins of BSE, the generally held belief is that BSE

originated from feeding cattle rendered protein

produced from the carcasses of scrapie-infected

sheep or cattle. The rendering process involves pro-

cessing carcasses by boiling at atmospheric or higher

tbl0006Table 6 Types of transmissible spongiform encephalopathies

(TSEs) in animals and humans

TSEs in animals

Scrapie (sheep and goats)

Chronic wasting disease

Transmissible mink encephalopathy

Bovine spongiform encephalopathy

TSEs in humans

Crutzfeldt–Jakob disease

Kuru

Gerstmann–Straussler–Scheinker syndrome

Fatal familial insomnia

2068 EMERGING FOODBORNE ENTERIC PATHOGENS

pressures, which results in the generation of an aque-

ous protein solution under a layer of fat. The fat can be

removed and the protein solution further processed

into a meat and bone meal product for use as an

animal food. Changes were made in the rendering

process in the UK around 1980, and it is assumed

that this change allowed the survival of the etiologic

agent. The recycling of cattle carcasses through the

rendering process only served to concentrate the etio-

logic agent further that eventually led to the epidemic

of BSE in the UK in the late 1980s. Thus, the current

belief is that the etiologic agent can be delivered orally

and is concentrated in certain parts of an infected

animal’s body, especially central nervous tissues.

0027 In the year 2000, there were 1101 new cases of BSE

diagnosed in the UK, so infectious cattle still remain

in the UK. BSE has not been limited to the UK, and

there have been several hundred cases in other Euro-

pean countries and elsewhere in the world, although

some of these are imported rather than native cases.

Since 1994, when the first case of nvCJD was recog-

nized in the UK, there has been a steady increase in

the numbers of cases. Up to November 2000, there

had been 84 cases in the UK, and the trends in inci-

dence since 1994 indicate that the number of cases

and deaths per year are on the rise.

0028 Up to the time of this writing, there have been no

documented cases of BSE in the USA. The USDA and

FDA have taken action to prevent the importation of

BSE-contaminated material or animals into the USA.

Active surveillance for BSE is underway in cattle in

the USA with signs of neurological disease and cattle

that are nonambulatory at slaughter. Close to 12 000

brains have been examined so far, with no evidence of

BSE. Despite the lack of evidence of BSE in the USA,

there is concern that it will appear at some point. The

long incubation period and the difficulty in control-

ling all imports of potentially contaminated products

from different parts of the world make it possible that

BSE will appear in the USA, at some time in the

future. In the general context of food safety, the

risks and the likelihood of serious outcomes that are

associated with bacterial pathogens such as Campylo-

bacter, Salmonella, and E. coli are significantly

greater than the risk of developing nvCJD from BSE.

However, nvCJD is frightening, because it is incur-

able, inevitably leads to death, and there are currently

no assays available to test food for the BSE prions,

although new tests to determine the presence of ner-

vous tissue in meat products are becoming available.

See also: Bovine Spongiform Encephalopathy (BSE);

Campylobacter: Properties and Occurrence; Detection;

Campylobacteriosis; Escherichia coli: Occurrence;

Detection; Food Poisoning; Occurrence and Epidemiology

of Species other than Escherichia coli; Food Poisoning by

Species other than Escherichia coli; Food Poisoning:

Classification; Listeria: Properties and Occurrence;

Detection; Listeriosis; Parasites: Occurrence and

Detection; Illness and Treatment; Salmonella: Properties

and Occurrence; Detection; Salmonellosis; Viruses

Further Reading

Allos BM (2001) Campylobacter jejuni infections: update

on emerging issues and trends. Clinical Infectious

Diseases 32: 1201–1206.

Centers for Disease Control (2000) Surveillance for food-

borne disease outbreaks – United States, 1993–1997.

MMWR 49: 1–51.

Centers for Disease Control (2001) Diagnosis and manage-

ment of food borne illness, a primer for physicians.

MMWR 50: RR-2.

Guerrant RL, Van Gilder T, Steiner TS et al. (2001) Practice

and guidelines for the management of infectious diar-

rhea. Clinical Infectious Diseases 32: 331–350.

Hohmann EL (2001) Nontyphoidal salmonellosis. Clinical

Infectious Diseases 32: 263–269.

Kramer JM, Frost JA, Bolton FJ and Wareing DR (2000)

Campylobacter contamination of raw meat and poultry

at retail sale: identification of multiple types and com-

parison with isolates from human infection. Journal of

Food Protection 63: 1654–1659.

Mead PS, Slutsker L, Dietz V et al. (1999) Food-related

illness and death in the United States. Emerging Infec-

tious Diseases 5: 607–625.

Mosier DA and Oberst RD (2000) Cryptosporidiosis. A

global challenge. Annals of the New York Academy of

Sciences 916: 102–111.

Nataro JP and Kaper JB (1998) Diarrheagenic Escherichia

coli. Clinical Microbiology Reviews 11: 142–201.

Paton JC and Paton AW (1998) Pathogenesis and diagnosis

of Shiga toxin-producing Escherichia coli infections.

Clinical Microbiology Reviews 11: 450–479.

Prusiner SB (1998) Prions. Proceedings of the National

Academy of Sciences 95: 13363–13383.

Ranjitham M, Madan M and Chandrasekharan S (1999)

Cyclospora cayetanensis – an emerging coccidian

parasite. Journal of the Association of Physicians of

India 47: 1198–1199.

Slifko TR, Smith HV and Rose JB (2000) Emerging parasite

zoonoses associated with water and food. International

Journal of Parasitology 30: 1379–1393.

EMERGING FOODBORNE ENTERIC PATHOGENS 2069

Emission Spectroscopy See Spectroscopy: Overview; Infrared and Raman; Near-infrared;

Fluorescence; Atomic Emission and Absorption; Nuclear Magnetic Resonance; Visible Spectroscopy and

Colorimetry

EMULSIFIERS

Contents

Organic Emulsifiers

Phosphates as Meat Emulsion Stabilizers

Uses in Processed Foods

Organic Emulsifiers

T Kinyanjui and W E Artz, University of Illinois,

Urbana, IL, USA

S Mahungu, Egerton University, Njoro, Kenya

Background

0001 This chapter will narrowly focus on organic emulsi-

fiers, one category in the general class of compounds

called surface-active agents, rather than macro-

molecular stabilizers or any of the other components

involved in emulsion stabilization. Some familiar

emulsions include those occurring in foods (milk,

mayonnaise, etc.), cosmetics (creams and lotions),

pharmaceuticals (soluble vitamins and hormone

products), and agricultural products (insecticides and

herbicides).

0002 The discussion will be limited to food emulsifiers,

rather than the use of emulsifiers for nonfood

products, such as cosmetics, paints or drug-delivery

systems. Emulsifiers are substances that reduce the

surface tension at the interface of two normally im-

miscible phases, allowing them to mix and form an

emulsion. Representing one class of a broader group

of ingredients called surface active ingredients or sur-

factants, emulsifiers assert their effects at the interface

between oil, water, or air dispersed in a second

immiscible fluid. They promote the formation and

stabilization of emulsions as well as foams and sus-

pensions. There are several types of emulsions, in-

cluding oil in water (o/w) water in oil (w/o), oil in

water emulsion dispersed in oil (o/w/o) etc.

0003 Emulsions are a special kind of colloidal dispersion:

one in which a liquid is dispersed in a continuous

liquid phase of a different composition. The dispersed

phase is sometimes referred to as the ‘internal phase’

and the continuous phase as the ‘external phase.’

Structure

0004Food emulsifiers can be categorized (Table 1) on the

basis of several characteristics, including origin,

either synthetic or natural; potential for ionization,

nonionic versus ionic; hydrophilic/lipophilic balance

(HLB); and the presence of functional groups.

Lecithin and Lecithin Derivatives

0005The primary source of lecithin, the only naturally

occurring emulsifier used in any significant quantities

in the food industry, is soybeans. Soybean oil contains

anywhere from 1 to 3% phospholipids in the crude

oil. Other sources include corn, sunflower, cotton-

seed, rapeseed, and eggs. Lecithin is obtained by an

aqueous extraction of the oil extracted from soy-

beans. Phase separation occurs upon hydration of the

phospholipids, and the two phases are separated by

tbl0001Table 1 Some organic emulsifiers

Lecithin and lecithin derivatives

Monoglycerols

Sucrose esters of fatty acids

Hydroxycarboxylic acid and fatty acid esters

Lactylate fatty acid esters

Polyglycerol fatty acid esters

Ethylene or propylene glycol fatty acid esters

Ethoxylated derivatives of monoglycerides

Sorbitan fatty acid esters

Propylene glycol monoesters

Phosphated mono and diglycerols

Sodium stearoyl-2-lactylate

Calcium stearoyl-2-lactylate

Fruit acid esters

2070 EMULSIFIERS/Organic Emulsifiers

centrifugation. The crude extract, after water re-

moval, contains about 35% triglycerols and smaller

amounts of nonphospholipid materials. Extraction

with acetone is used to produce an oil-free lecithin.

The term ‘lecithin’ has been used to describe both

phosphatidylcholine and mixtures of phospholipids.

Current recommendations by the International Union

of Pure and Applied Chemistry–International Union

of Biochemistry suggest the use of 3-sn-phosphatidyl-

choline rather than lecithin to describe 1,2-diacyl-sn-

glycero-3-phosphatidylcholine. However, a commer-

cial, soybean-derived lecithin preparation contains

several different phospholipids, primarily phosphati-

dylcholine, phosphatidylethanolamine and phospha-

tidylinositol. The structures are shown in Figure 1.

(See Phospholipids: Properties and Occurrence.)

0006 Commercial lecithin preparations can be either

treated or modified chemically to provide a product

with altered functional characteristics. Treatment

with either hydrogen peroxide or benzoyl peroxide

will produce a lighter-colored product. The chemical

modification of lecithin by reaction with hydrogen

peroxide, plus lactic or acetic acid and water, will

produce a hydroxylated product. Hydroxylation

occurs at the double bonds, altering lecithin such

that its hydrophilic character is increased. The result

is a product with improved oil-in-water emulsifying

properties relative to unmodified lecithin.

0007 Triglycerols are soluble in acetone, whereas phos-

pholipids are not. Therefore, the greater the percent-

age of acetone-insoluble material, the greater the

phospholipid content in crude lecithin. Because of

this, one of the primary criteria for the evaluation of

lecithin is the percentage of acetone-insoluble mater-

ial. Lecithin is also evaluated on the basis of several

other parameters including acid value (an indication

of free fatty acids), hexane-insoluble matter (an indi-

cation of fibrous material), water, peroxide value and

metallic impurities. Individual phospholipids in soy

lecithin can be quantitated using HPLC.

Mono- and Diglycerides

0008Mono- and diglycerides are the most commonly used

food emulsifiers. They consist of esters synthesized

via catalytic transesterification of glycerol with trigly-

cerides, with the usual triglyceride source as hydro-

genated soybean oil. Mono- and diglycerides are also

synthesized directly from glycerol and fatty acids

under alkaline conditions. Molecular distillation is

used to prepare a purified product containing up to

approximately 90% monoglycerol. Monoglycerols

can be prepared from the reaction of glycidol (2,3-

epoxy-1-propanol) and carboxylic acids with a yield

in excess of 90%. Advantages of the process include

the synthesis of difficult to produce monoglycerides

and a good potential for continuous processing.

Mono- and diglycerols have also been obtained from

a butterfat fraction by chemical glycerolysis. The en-

zymatic preparation of mono- and distearin by gly-

cerolysis of ethylstearate and direct esterification of

glycerol in the presence of a lipase from Candida

antarctica has also been reported.

0009Several tests are used for characterizing commer-

cial sources of mono- and diglycerides, including total

monoglycerides, hydroxyl value, iodine value, and

the saponification value. With the monoesters, the

fatty acid can be attached at either the alpha or beta

positions, as with the diglycerides (see Figure 2).

Hydroxycarboxylic and Fatty Acid Esters

0010To produce an emulsifier with an increased hydroph-

ilic character relative to monoglycerides, small organic

acids are esterified to monoglycerols (Figure 3). Some

C(O) CH

C(O) O CH

O P(O) OCH

(CH

)

O P(O) OCH

C(O) O CH

−

C(O) O CH

O P(O) O C

−

(a)

(b)

(c)

fig0001 Figure 1 Primary phospholipids reported in commerical leci-

thin, where R

and R

are fatty acids: (a) phosphatidylcholine;

(b) phosphatidylethanolamine; (c) phosphatidylinositol.

HO CH

OC(O)

(CH

)

(a)

HO CH

OC(O)

(CH

)

(b)

HO C

(CH

)

OC(O)

fig0002Figure 2 (a) Mono- and (b) diglycerides.

EMULSIFIERS/Organic Emulsifiers 2071

of the acids used are acetic, citric, fumaric, lactic,

succinic, and tartaric. Succinylated monoglycerols

are synthesized from succinic anhydride and distilled.

They are used by the baking industry as dough condi-

tioners and crumb softeners. Acetic acid esters of

mono- and diglycerides are synthesized from fatty

acids plus acetic anhydride or by transesterification.

The product is lipid-soluble and water-insoluble.

Functions in food include control of fat crystalliza-

tion and improvement of aeration properties of high-

fat foods. They are often added to shortenings or cake

mixes. (See Fats: Classification.)

0011 To synthesize other acid esters, citric acid esters of

mono- and diglycerides, glycerol is esterified with a

mixture of citric acid and fatty acids. It can also be

prepared by the direct esterification of citric acid with

glyceryl monooleate. The product is hot water- and

lipid-soluble. Functions in food include emulsifica-

tion, antispattering agent in margarine, improvement

of bakery product characteristics, a fat replacement in

high-fat foods and a synergist and solubilizer for

antioxidants.

0012 Diacetyl tartaric acid esters of monoglycerides

(DATEM) are synthesized from diacetyl tartaric acid

anhydride and monoglycerides. The emulsification

properties of DATEM depend primarily upon the

type of fatty acid and the percentage of esterified

tartaric acid. Emulsifier quality is based upon results

from the analyses for tartaric and acetic acid, acid

value, total fatty acids, saponification value, and

metallic residues.

0013 Lactic acid esters of mono and diglycerides consist

of a mixture of lactic and fatty acid esters of glycerin.

The emulsifier is dispersible in hot water. Important

qualitative parameters include the percentage of

monoglycerides, total lactic acid, acid value, free

glycerin, and the amount of water.

Lactylate Fatty Acid Esters

0014 Polymeric lactic acid esters of monoglycerides are also

available, commonly known as sodium or calcium

stearoyl-2-lactylates (see Figure 4). Typically, there

are two lactic acid groups per emulsifier molecule.

To produce the emulsifier, a mixture of the fatty

acid, polylactic acid, and calcium or sodium carbonate

is heated at about 200



C for about 1 h with agitation

in an inert atmosphere. The calcium salt is less dispers-

ible in water than sodium stearoyl-2-lactylate.

Polyglycerol Fatty Acid Esters

0015Polyglycerol esters (Figure 5) of fatty acid are also

used in food products, primarily in baked goods.

They consist of mixed partial esters synthesized from

the reaction of polymerized glycerol with edible fats.

Polyglycerols will vary in degree of glycerol polymer-

ization with an average specified. The source of fatty

acids as well as the degree of polymerization can vary,

providing a wide range of emulsifiers, from hydro-

philic to very lipophilic.

Polyethylene or Propylene Glycol Fatty Acid Esters

0016Fatty acids can be esterified directly to polyethylene

glycol ethers or by enzymatic preparation, which

allows better control of the reaction. Propylene glycol

fatty acid (C12, C14, C16, C18, and C18:1) mono-

esters (Figure 6) have been produced by lipase-

catalyzed reactions. Propylene glycol monoesters

of docosahexaenoic acid and eicosapentaenoic acid

that are potentially health-beneficial w/o emulsifiers

useful in the food industry have been synthesized

by lipase-catalyzed esterification. The HLB of the

emulsifier is altered by adjusting the degree of ethox-

ylation. Fatty acid polyglycol esters are good o/w

emulsifiers.

Ethoxylated Derivatives of Monoglycerides

0017Ethoxylated mono- and diglycerides are produced

from the reaction of several moles of ethylene oxide

and mono- or diglycerols under pressure. Ethoxyla-

tion of monoglycerols results in a product that is

much more hydrophilic relative to monoglycerols.

CCH

]

fig0005Figure 5 Polyglycerol esters of fatty acids, where R

, and R

are each a fatty acid and/or a hydrogen, and where the average

value of n is greater than 1.

O O

OHO

fig0004Figure 4 Sodium stearoyl-2-lactylate, where n normally

averages 2, and R is a fatty acid moiety.

fig0003 Figure 3 Organic acid ester of monoglycerol, where at least

one R is a short-chain organic acid, for example, acetic acid.

2072 EMULSIFIERS/Organic Emulsifiers

0018 The end product of the synthesis is actually a mix-

ture with a distribution range and peak; therefore,

many often vary among manufacturers.

Sorbitan Fatty Acid Esters

0019 Polyoxyethylene sorbitan esters are synthesized by

the addition, via polymerization, of ethylene oxide

to sorbitan fatty acid esters. These nonionic hydro-

philic emulsifiers are very effective antistaling agents

and, thus, are used in a wide variety of bakery prod-

ucts. These emulsifiers are much more widely known

as the polysorbates, e.g., polysorbate 20, 60, and 80

(Figure 7). Polysorbate 20, 60, and 80 utilize lauric,

stearate, and oleate, respectively, for the fatty acid

portion of the molecule. Polysorbate 60 is a mono-

stearate, whereas polysorbate 65 is a tristearate.

Miscellaneous Derivatives

0020 Fatty acids can be esterified directly to compounds

other than glycerol, for example, sugar alcohols like

sorbitol, mannitol, and maltitol, and sugars like

sucrose, glucose, fructose, lactose, and maltose.

0021 Sorbitol or sorbitan esters are formed from 1,4-

anhydro-sorbitol and fatty acids (see Figure 8). Typ-

ically, the emulsifier consists of a mixture of stearic

and palmitic acid esters of sorbitol and its mono- and

dianhydrides. Ethoxylated derivatives can also be

prepared by the addition of several moles of ethylene

oxide to the sorbitan monoglycerol ester and,

depending on the number of moles of ethylene oxide

added, have a wide range in HLB.

0022Lactitol (the hydrogenation product of lactose)

palmitate is synthesized by direct esterification at a

temperature of approximately 160



C. Workers have

reported the enzymatic synthesis of acetylated glu-

cose fatty acid esters. Two immobilized lipases from

Candida antarctica (SP 382) and Candida cylindra-

ceae catalyzed the synthesis of novel acetylated glu-

cose fatty acid esters with glucose pentaacetate and

Trisun 80 (80% oleic) vegetable oil or methyl oleate

as substrates in organic solvents. The incorporation

of oleic acid on to the glucose ranged from 30 to

100%. It was possible to catalyze the synthesis of

glucose fatty acid esters with free glucose as the

sugar substrate. Other researchers have reported the

synthesis of a novel nonionic surfactant, dialkyl glu-

cosylglutamate from d-gluconolactone, glutamic acid

and alkyl alcohols. Sucrose fatty acid esters (Figure 9)

can be synthesized using a variety of solvents or by

direct esterification. The first description of a prac-

tical commercial process for the preparation of su-

crose esters of fatty acids was reported in 1956.

Enzymatic synthesis of carbohydrate esters of fatty

acids has also been reported for the esters of sucrose,

glucose, fructose, and sorbitol with oleic and stearic

acid and fructofuranose. The reports by researchers

indicate the enzymatic preparation of three different

1,6-diacyl fructofuranoses. At low temperatures



C), the synthesis produces quantitative yields of

the diesters by simple addition of the original sugar to

a solution of the fatty acid in a solvent (acetone),

which is accepted by the European Commission

(EC) for use in the manufacture of additives. By

varying the degree of esterification, the HLB and,

hence, the functionality can be controlled. Sucrose

fig0008Figure 8 Sorbitan stearate, where R represents a fatty acid

moiety, for example, stearic acid, oleic acid, lauric acid, or

palmitic acid.

fig0006 Figure 6 Propylene glycol esters of fatty acids, where R

and

represent a fatty acid and/or a hydrogen, and where at least

one R represents a fatty acid.

(OC

)

fig0007 Figure 7 Polysorbates, where w þ x þ y þz ¼ 20 (approx.) and

Rs represent a single fatty acid and hydrogens for polysorbate

20, 40, 60, and 80. For polysorbate 65, each R represents a stearic

acid moiety. The fatty acids are lauric, palmitic, stearic, and oleic

acid for polysorbate 20, 40, 60, and 80, respectively.

EMULSIFIERS/Organic Emulsifiers 2073

monoesters have an HLB value greater than 16 while

the triesters have an HLB value less than 1. Monoe-

sters are particularly useful for the stabilization of

o/w emulsions, whereas diesters are best for w/o

emulsions. With esterification equal to or greater

than 5 moles of fatty acid per mole of sucrose, the

emulsification properties of sucrose fatty acid esters

are lost. But, at that degree of esterification, the su-

crose fatty acid polyester can be used as a low-calorie

fat replacement since it is neither digestible nor

absorbable.

0023 The consistency of both o/w and w/o emulsions can

be affected with the addition of ethylene or propylene

glycol monostearate. The most common ethylene and

propylene glycol esters used as emulsifiers are the

monostearate and monopalmitate.

Emulsion Stability

0024 Small droplets and the presence of an interfacial film

on the droplets in emulsions make them stable; that

is, the suspended droplets do not settle out or float

rapidly, and the droplets do not coalesce quickly.

0025 Emulsifiers are generally classified as: anionic

emulsifiers, cationic emulsifiers, amphoteric emulsi-

fiers and nonionic emulsifiers. Proteins (caseins) are

known to stabilize emulsions, owing to their ampho-

teric nature. The oil phase viscosity also contributes

to the stability of the emulsion stability, but this

depends on the adsorption and interfacial behavior

of the emulsifiers.

0026 One basis for a theory of emulsion stability con-

cerns the balance between the attractive and repulsive

forces of the particle. In other words, attractive (Van

der Waals forces or London dispersion forces) would

tend toward destabilizing an emulsion, whereas the

repulsive forces (electrostatic repulsion between elec-

trical double layers of like sign) would stabilize the

emulsion by keeping the droplets separated.

0027 There are several phenomena that can cause emul-

sion destabilization. Each is affected by the presence

of emulsifiers. To understand best the mechanism of

emulsion formation and ultimately the forces stabil-

izing emulsions, the mechanisms of destabilization

should be understood.

Mechanisms of Destabilization

0028Emulsion destabilization can be due to one or all of

five possible mechanisms; flocculation, coalescence,

sedimentation or creaming, Ostwald ripening, and

phase inversion.

0029-Flocculation The adherence of droplets to form

aggregates or clusters and the buildup of these aggre-

gates are referred to as ‘flocculation.’ It occurs when

the attractive forces between the droplets exceeds that

of the repulsive forces, without a breakdown in the

structural integrity of the interfacial film surrounding

the droplets.

0030-Coalescence When aggregates or flocculates of the

dispersed phase combine to form a single, larger drop,

the phenomenon is referred to as ‘coalescence.’ Co-

alescence is really a reflection of the nature of the

interfacial film on the surface of the droplet. A strong,

stable film on the surface of the droplet, owing to

the addition of the correct concentration of the ap-

propriate emulsifier, will minimize this type of desta-

bilization.

0031-Ostwald ripening If the two phases forming the

emulsion are not totally immiscible, and there are

differences in droplet size within the emulsion, larger

droplets will form at the expense of smaller droplets

owing to a process known as ‘Ostwald ripening.’

Ostwald ripening is always a factor since variations

in initial droplet size always occur in macroemul-

sions, and both phases are never completely immis-

cible. The driving force for Ostwald ripening is the

difference in chemical potential between droplets of

difference sizes. Equilibrium will only exist when all

droplets are the same size, which really means a single

‘drop’ or the presence of two continuous and separate

phases.

0032-Phase inversion The viscosity of an emulsion will

increase gradually as more and more of a given phase

is added until a critical volume is reached. If more

of that same phase is added, exceeding the critical

volume, the emulsion will invert, i.e., the discontinu-

ous phase will become the continuous phase.

Mechanisms of Stabilization by Emulsifiers

0033There are several factors, some of which are depend-

ent on the emulsifiers and stabilizers added, involved

in emulsion stabilization. The first is the reduction of

interfacial tension by the emulsifiers. Next, is repul-

sion between droplets due to similar electrical charges

on the surface of the droplets. A third is the formation

of mesophases or liquid-crystalline phases, which will

OCH

fig0009 Figure 9 Sucrose fatty acid esters, where at least one of either

,orR

represents a fatty acid, and the remainder may

represent a fatty acid or a hydrogen; the degree of substitution

is 1–3.

2074 EMULSIFIERS/Organic Emulsifiers

provide the most stable configuration for a specified

set of conditions. A fourth is the addition of macro-

molecules or particulate material, which can substan-

tially increase emulsion viscosity and stability. An

increase in viscosity of the continuous phase adds to

the kinetic stability. However, without a concurrent

energy barrier, viscosity will have a small effect on

stabilization. Viscosity enhancers increase the stabil-

ity of the energy barrier. Stable oil-in-water emulsions

of argan oil with two different types of mixtures of

nonionic emulsifiers have been produced. Three dif-

ferent types of oil (Israeli argan oil, Moroccan argan

oil, and soybean oil) have been emulsified with mix-

tures of Span 80 and Tween 80. The optimum HLB

value for argan oil is 11.0. The argan o/w emulsions

are stable for more than 5 months at 25



C. Synergis-

tic effects have been found in enhancing the stability

of emulsions prepared with sucrose monostearate.

The origin of the oil and the internal content of

natural emulsifiers, such as monoglycerides and phos-

pholipids, have a profound influence on its interfacial

properties and on the stability of the argan o/w

emulsions.

0034 Emulsion stability is also dependent upon the con-

ditions under which the emulsion is formed. This

includes not only the constituents of the emulsion

but also the emulsifier concentration, emulsion tem-

perature, and physical state (crystalline vs. fluid) of

the emulsifier. The order of addition of the constitu-

ents is also an important factor. Addition of lecithin

to the lipid phase prior to the addition of the aqueous

phase can substantially alter the droplet size, liquid

crystal formation, and emulsion stability. Another

contributing factor is the nature of the internal and

continuous phases. Both affect emulsion stability.

Two types of emulsions, those prepared with unsatur-

ated emulsifiers and unsaturated oil and those pre-

pared with saturated emulsifiers and saturated oil, are

more stable than those prepared with emulsifiers and

oil of intermediate or mixed saturation.

Functions of Emulsifiers

Interfacial Tension

0035 The reduction of interfacial tension through the add-

ition of emulsifiers is a key factor in emulsion forma-

tion. It allows emulsion formation with considerably

less energy input than would be required without

the presence of an emulsifier. Once the interfacial

film consisting of emulsifier is formed, it acts as an

effective barrier to droplet coalescence. It has been

found that, in the presence of emulsifiers, the droplet

interface may acquire viscoelastic properties, which

are important in the prevention of coalescence. A

strong interaction between the hydrophilic portion

of the emulsifier and the aqueous phase leads to

a large reduction in the surface tension of the water;

this also affects the type of emulsion formed. A

weak interaction between water and the hydro-

philic portion of the emulsifier molecule will favor a

w/o emulsion, whereas a strong interaction will favor

a o/w emulsion.

Electrical Charge

0036Ionic emulsifiers provide an additional mechanism

for emulsion stabilization relative to nonionic emulsi-

fiers, through ion–ion and ion–solvent interactions.

In addition, the introduction of charged groups on the

surface of the emulsion droplets increases the repul-

sive forces. Ionic emulsifiers will form an electrically

charged double layer in the aqueous solution

surrounding each oil droplet.

Liquid Crystal Stabilization

0037Macroemulsions, although thermodynamically un-

stable, can attain rather long-term stability, strongly

suggesting an intermediate stability level. This was

attributed to the formation of a liquid crystalline

state by the emulsifier. It has been shown that the

presence of a liquid crystalline state reduces the rate

of coalescence, even if droplet flocculation occurs.

(See Crystallization: Basic Principles.)

Stabilization by Macromolecules and Finely Divided

Solids

0038Emulsion stability can be increased by the addition of

macromolecules like gums and protein. Colloids like

xanthan gum, carboxy methyl cellulose and guar gum

significantly increase emulsion stability. With both a

constant emulsifier and colloid concentration, emul-

sion stability is enhanced by increased emulsification

temperature, increasing the degree of shear, and

increase pH, in the range of 3–6. Colloids act by

either increasing the viscosity or partitioning into

the o/w interface and providing a physical barrier to

coalescence.

0039To evaluate emulsion stability and thereby charac-

terize the potential of an emulsifier, the rate at which

the combined destabilization phenomena occur must

be determined. These rates can be determined from

the changes in the size and distribution of the oil

droplets with time. There are several methods avail-

able for this determination. Nuclear magnetic reson-

ance is often preferred as a better indication of

stability to HLB values. Other methods, used to evalu-

ate the effects of processing on emulsion stability,

include centrifugation, turbidity light micoscopy

scanning electron microscopy, etc.

EMULSIFIERS/Organic Emulsifiers 2075

Emulsifier Selection

0040 Emulsifier selection is based upon the final product

characteristics, emulsion preparation methodology,

the amount of emulsifier added, the chemical and

physical characteristics of each phase, and the pres-

ence of other functional components in the emulsion.

Food emulsifiers have a wide range of functions. The

most obvious is to assist stabilization and formation

of emulsions by the reduction of surface tension at the

o/w interface.

0041 Perhaps the most important factor in preparing an

emulsion is the selection of the appropriate emulsifier.

Several methodologies have been developed to assist

in such an endeavor. These include the HLB system

of Griffin, the H/L numbers, the water number, the

phase inversion temperature, and the emulsion inver-

sion point. Even with the best of methods, selection

can be very difficult, except perhaps for the few foods

that are relatively straightforward emulsions, like

mayonnaise and margarine. Often, one of the best

sources of information is the emulsifier manufacturer.

Several parameters should be considered during

emulsifier selection. These parameters include: (1) ap-

proval of the emulsifier by the appropriate govern-

ment agency, (2) desired functional properties, (3)

end-product application, (4) processing parameters,

(5) synergistic effect of other ingredients, (6) home

preparation, and finally (7) cost.

0042 Obviously, before an emulsifier can be used in a

food product, it must be approved by the appropriate

regulatory agency. Assuming this criterion is met, the

most important considerations would be both the re-

quired functional properties of the selected emulsifier

and the application. Delineating the required func-

tional properties such as emulsification, starch com-

plexation and crystallization control and the specific

end-product application are the two major factors in

emulsifier selection. An exact determination of these

two parameters should focus attention on a limited

number of emulsifiers. The processing methodology

and equipment available in the processing facility

could further limit the range of emulsifiers that are of

potential use. It is at this stage that ingredient sup-

plier(s) could begin to provide helpful assistance.

0043 By far, the most widely used rule for the selection of

food emulsifiers is the HLB number. The HLB index is

based upon the relative percentage of hydrophilic to

lipophilic groups within the emulsifier molecule. The

assigned values range from 1 to 20. Lower HLB values

indicate a more lipophilic emulsifier, whereas higher

values indicate a more hydrophilic emulsifier. Emulsi-

fiers with HLB numbers in the 3–6 range are best for w/

o emulsions, whereas emulsifiers with HLB numbers

in the range of 8–18 are best for o/w emulsions.

Depending upon the application and the types of

oils to be emulsified, there is an optimum HLB.

0044There is an equation that can be used to determine

the HLB number for several types of nonionic emulsi-

fiers, particularly the ethoxylated alcohols and the

polyhydric fatty acid esters. To determine the HLB

for the fatty acid ester type, the following equation

can be used:

HLB ¼ 20ð1  S=AÞ,

where A is the acid number, and S is the saponification

number of the ester.

0045For the polysorbate type of emulsifier, the HLB

value can be determined from the equation:

HLB ¼ðE þ PÞ=5,

where E is the weight percentage of oxyethylene, and

P is the weight percentage of polyhydric alcohol.

0046However, there are several factors that reduce the

utility of the HLB selection system. One factor is that

the HLB system does not work well for ionic emulsi-

fiers, a problem further complicated by the fact that

the charge varies with pH. Another factor is that com-

mercial preparations usually contain two or more

emulsifiers. These emulsifiers can have a significant

synergistic effect that makes it very difficult to apply

the HLB system. Another limitation is due to the fact

that the HLB system is based upon the molecular

structure of the emulsifier and does not take into ac-

count the combined oil/aqueous phase/emulsifier

system. In addition, once the appropriate emulsifier

has been selected, the correct concentration can not be

determined from the HLB value. The concentration

required is really a function of the droplet size. The

smaller the droplet, the greater the surface area and,

therefore, the greater the amount of emulsifier that is

required for monolayer coverage of each droplet. In

spite of these limitations, the HLB is still the most

widely used index of emulsifier functionality.

See also: Colloids and Emulsions; Fatty Acids:

Properties; Phospholipids: Properties and Occurrence