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

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illness with symptoms similar to those of staphylo-

coccal food poisoning are reported to the CDC, but

are not classified because of inadequate information

about the presence of staphylococci or enterotoxin in

the foods involved. (See Food Poisoning: Tracing

Origins and Testing.)

0002 Staphylococcal foodborne outbreaks vary in size,

and can involve one or two persons to as many as

over 1000 people. One outbreak in the USA involved

1300 people attending a picnic in Indiana. Baked ham

was the implicated food. An even larger outbreak

occurred in Japan, involving 1500 people who

became ill from eating contaminated rice balls con-

tained in lunch boxes prepared at one location. (See

Food Poisoning: Statistics.)

Symptoms of the Disease

0003 The major symptoms of staphylococcal food

poisoning, i.e., vomiting and diarrhea, occur within

1–6 h after ingestion of food containing enterotoxin.

A representative set of symptoms observed in 122

cases of illness that occurred among high-school

students after they had eaten cream puffs is given

in Table 1.

0004 Ninety-five (57%) of the 165 students who ate the

cream puffs became ill, whereas none of those who

did not eat them became ill. This is typical of out-

breaks involving a large number of people. The aver-

age onset time in the outbreak was also normal for

large outbreaks, with a few having earlier onset times,

usually because of consumption of large amounts of

toxin or increased sensitivity of some individuals, and

a few that have delayed onset times of 7–8 h. Al-

though vomiting is the symptom most frequently ob-

served, some individuals may have other symptoms,

such as diarrhea without vomiting. Diarrhea may

not be observed in milder cases, whereas vomiting

usually is. Changes in temperature and blood pressure

are not common, particularly with milder cases,

although it is known that in experimental cases a

change in temperature can occur, either up or

down; a drastic lowering of blood pressure may also

occur.

0005Death is uncommon with this type of food

poisoning, but deaths have occurred in children or

older individuals, often with other complications.

Two children, 3 and 4 years of age, died within 24 h

after each drank 125 ml of milk from a goat with

staphylococcal mastitis. The deaths of the children

and the results of the autopsy indicated that the chil-

dren received a relatively large amount of enterotoxin

in the milk they drank.

0006Several deaths of older people who consumed food

containing enterotoxin have been reported; the deaths

usually occurred after severe vomiting and diarrhea.

One elderly woman died of acute vascular collapse

secondary to fulminating gastroenteritis in an out-

break of staphylococcal food poisoning after eating

baked ham. Of 28 other people who were known

to have become ill with symptoms characterized

by vomiting, diarrhea, and severe prostration, six

individuals required hospitalization.

0007A 57-year-old woman reportedly in excellent

health died of shock within a few hours of the onset

of illness after eating a cold plate lunch at a restaur-

ant. Three other individuals developed severe gastro-

enteritis after eating plate lunches at the same

restaurant.

Requirements Necessary for Food

Poisoning

0008Certain conditions are necessary for staphylococcal

food poisoning to occur: (1) the food must be a good

medium for the growth of staphylococci and the pro-

duction of enterotoxin; (2) enterotoxigenic staphylo-

cocci must be present in the food; (3) the food must be

held at a warm temperature for several hours for

the staphylococci to grow to sufficient numbers to

produce enterotoxin.

Foods Involved in Outbreaks

0009A variety of foods can support growth of enterotoxi-

genic staphylococci. Foods involved in outbreaks are

usually rich in protein, and include meat and meat

products, poultry, milk and dairy products, salads

(tuna, chicken, ham, and potato), custards, pudding,

and cream-filled bakery products. (See Cream: Types

of Cream; Milk: Processing of Liquid Milk; Poultry:

Chicken; Ducks and Geese; Turkey.)

tbl0001 Table 1 Symptoms of staphylococcal food poisoning from 122

cases

Symptom Reaction

Cases

None Mild Severe

Vomiting 122 15 12 95

Pains in abdomen 122 6 40 76

Diarrhea 103 13 75 15

Headache 101 29 59 13

Muscular cramping 113 41 58 14

Includes 94 students, eight lunchroom supervisors who took cream puffs

home, and 20 cases resulting from the consumption of cream puffs sold at

three cafe

s and from a bakery truck.

Cases from which this information was available.

Data from Dennison GA (1936) Epidemiology and symptomatology of a

Staphylococcus food poisoning. American Journal of Public Health 26:

1168–1175.

STAPHYLOCOCCUS

/Food Poisoning 5557

Source of Contamination

0010 Staphylococci can be found in most raw foods. How-

ever, the most frequent source of contamination of

foods implicated in staphylococcal food-poisoning

outbreaks is the food handler. Most foods involved

in such incidents are cooked, and are recontaminated

in the final preparation for serving. A food handler

with any type of staphylococcal infection or one who

is carrying the organism in his or her nose is a likely

source of contamination.

0011 An outbreak occurred in California in 1983 involv-

ing several hundred children in an Easter-egg hunt.

The source of the contamination was an infected

lesion on the hands of the person who prepared the

eggs. Another outbreak involved packaged sliced ham

that was contaminated with staphylococci from the

nose of the person who packaged it. The ham was

packaged on a Saturday morning and sold through-

out the day without any of the consumers getting sick.

The unsold ham was stored in a relatively deep pan

and refrigerated overnight. Cooling might have been

quite slow because of the size of the pan. On Sunday

morning, the ham was warmed before being sold

around 11:00 a.m. People who bought the ham

on Sunday became ill with staphylococcal food

poisoning. Enterotoxin A (SEA) was isolated from

the leftover ham.

0012 Animals carry staphylococci in their noses and cer-

tain animal diseases, such as mastitis, are caused by

staphylococci. However, animals are less important

sources of contamination because, even though raw

meats and milk are usually contaminated with

staphylococci, cooking and pasteurization tempera-

tures will destroy the organisms. In addition, the

presence of other competing microorganisms in the

raw foods inhibits staphylococcal growth. An excep-

tion is when staphylococci are present in much higher

numbers than other organisms, as in the case of milk

from a mastitic animal, e.g., the two children who

died after drinking milk from a goat with mastitis.

0013 Equipment can sometimes be a source of contamin-

ation. An outbreak associated with baked ham

resulted from contamination of the ham with the

meat slicer. The same strain of enterotoxigenic

S. aureus was isolated from both the ham and the slicer.

Conditions Necessary for Growth and

Toxin Production

0014 In order for food poisoning to occur, the food con-

taining an enterotoxigenic staphylococcal strain must

be held at a warm temperature, usually room tem-

perature or above, for several hours (at least 4 h) for

the staphylococci to grow to sufficient numbers to

produce enterotoxin. Growth of staphylococci to a

population of 1 million or more organisms per gram

of food is assumed necessary to produce enough

enterotoxin to cause illness.

0015Care needs to be taken in interpreting the signifi-

cance of staphylococcal numbers in food when inves-

tigating an outbreak. Not all staphylococcal strains

produce enterotoxin. A large number of staphylo-

cocci in a food may indicate poor hygienic practices

but, to incriminate a food definitely as the cause of

food poisoning, it is necessary to demonstrate that the

staphylococcal isolate produces enterotoxin. Alterna-

tively, the lack of staphylococci or the presence of low

numbers does not indicate the absence of enterotoxin

in the suspect food. This is especially important in the

case of heat-processed foods. Absence of viable

staphylococci does not necessarily indicate a safe

product because preformed enterotoxin may not be

inactivated.

0016Data from outbreaks indicate that less than 1 mgof

SEA can result in illness. In a chocolate milk outbreak

in 1985, it was found that 100–200 ng of SEA was

sufficient to cause staphylococcal food poisoning in

children. SEA is the most toxic enterotoxin and the

one most commonly involved in staphylococcal food-

poisoning outbreaks.

Site of Action

Emetic Action

0017The site of the emetic action of enterotoxin in the

monkey is in the abdominal viscera, with the sensory

stimulus for emesis reaching the vomiting center of

the brain via the vagus and sympathetic nerves. This

is supported by experiments in which transthoracic

vagotomy partially protected the monkey from the

emetic action of enterotoxin given intragastrically

and, when coupled with abdominal sympathectomy,

the monkey was completely resistant to the emetic

action of enterotoxin. The monkeys with deafferen-

tated abdominal viscera still vomited as normal

animals when the emetic compound, Veriloid, was

administered. Bilateral destruction of the area post-

rema on the floor of the fourth ventricle (chemorecep-

tor trigger zone) made the monkeys completely

refractory to the emetic action of enterotoxin given

intravenously or intragastrically.

0018Attempts to determine the site of action of entero-

toxin in the intestinal tract have been unsuccessful.

Specific binding of enterotoxin to cells closely related

to intestinal epithelial cells that have been cited as

potential target cells for direct cytopathic effects of

the staphylococcal enterotoxins was not detectable.

Binding of SEA in the rat intestinal tract was not

5558

STAPHYLOCOCCUS

/Food Poisoning

detectable, but rather the enterotoxin passed through

the gastrointestinal mucous membrane within 15 min

after administration and was detected in the kidney.

Neuronal binding of SEA in the intestinal tract was

not demonstrated; this binding might have been

expected based on the finding that the sensory stimu-

lus for vomiting reaches the vomiting center by way

of the vagus and sympathetic nerves.

Diarrheal Action

0019 Diarrhea is the second most common symptom seen

in staphylococcal food poisoning. In outbreaks in-

volving a large number of people, as many individuals

develop diarrhea as have an emetic reaction. Stimula-

tion of this reaction is not understood because the

mechanism of action is apparently quite different

from that of the so-called diarrheal diseases such as

cholera and Clostridium perfringens and Bacillus

cereus food poisoning. The toxins responsible for

the diarrheal diseases elicit an ileal loop reaction in

rabbits, whereas the staphylococcal enterotoxins do

not. Enterotoxin B (SEB) had no effect on the absorp-

tive mechanism of the rat small intestine, but the

enterotoxin somehow triggered a secretory mechan-

ism that resulted in a net secretion of fluids. The

actual mechanism responsible for stimulating excre-

tion has not been elucidated. (See Bacillus: Food

Poisoning; Clostridium: Food Poisoning by Clostri-

dium perfringens.)

Enteritis

0020 Enteritis is another effect of enterotoxins taken orally,

but it is not easily observed except by special examin-

ation. Pseudomembranous enterocolitis was observed

to be associated with staphylococcal infections in

patients who had been administered antibiotics to

control infection during surgery. Many of these pa-

tients died before the cause of their illness was diag-

nosed. The staphylococci had become resistant to the

antibiotics used and grew prolifically in the intestinal

tracts of these patients because the normal flora had

been eliminated by the antibiotics. These staphylo-

cocci were potent producers of enterotoxin, later

identified as SEA and SEB. Experiments in animals

with SEB revealed that enteritis can be produced in

monkeys, dogs, and chinchillas, with the severity of

enteritis depending on the amount of enterotoxin

given intragastrically. Autopsy of dogs 24 h after

ingesting SEB revealed acute enteritis with edema,

hyperemia, and ulcerations of the mucosa, and

destruction of the surface of the epithelium. Severe

round cell infiltration of the mucosa and destruction

of the surface of the epithelium were observed

by microscopic examination. These observations in

animals were similar to changes characteristic of

acute exogenous gastritis in humans resulting from

staphylococcal food poisoning. These findings, deter-

mined by gastroscopic examination, include patchy

mucosal hyperemia, regional edema, muscular irrita-

tion, erosions, petechiae and purulent exudate.

Examination 48 h later revealed the stomachs had

returned to normal. Acute gastroenteritis was ob-

served in monkeys 2 h after intragastric administra-

tion of SEB, with the most severe changes occurring at

4–8 h postinoculation. The mucosa was again normal

after 72 h postinoculation.

Death

0021Death is uncommon in staphylococcal food poisoning,

hence there is little opportunity to observe the patho-

logical effects of enterotoxin. However, autopsy of

the two children who died after drinking milk from

a mastitic goat revealed a moderate amount of pul-

monary edema marked with congestion of the alveo-

lar vessels and, in a few areas, there appeared to be

hemorrhages into the alveolae. There was a small

amount of leukocytic infiltration in the periportal

areas of the liver. These findings are similar to those

observed in monkeys that received a lethal dose of

enterotoxins by intravenous injection; in these animals

there was a decrease in intravascular fluid volume

with an increase in lung weight. The fluid was con-

fined to the perivascular and peribronchial interstitial

space; the lymphatics in these areas were gorged. The

primary pathological change was degeneration and

necrosis of capillary endothelial cells, with some but

less frequent damage to the endothelium of venules.

Also noted were interstitial hemorrhage and edema, a

histolytic infiltrate, and a striking herniation of capil-

lary endothelium into the vascular lumen. Apparently

these changes were brought about by the enterotoxin

binding to leukocytes with subsequent sequestering of

toxin-bound leukocytes in the lungs.

Treatment and Course of Illness

0022The rapid development of the illness makes it impos-

sible to prevent the symptoms from developing after

the enterotoxin has been ingested; once the symptoms

have occurred there is no treatment that will counter-

act them. In most cases recovery is within a few hours

and no treatment is necessary; however, in severe

cases where vomiting and diarrhea are excessive,

treatment intravenously with fluids is beneficial,

particularly to restore the salt balance.

0023A misunderstanding of the disease by the medical

attendant can lead to unfortunate results. Such was

the case when a young man afflicted with the illness

was given antibiotics, with death as a result. If the

disease was due to the ingestion of the organisms,

STAPHYLOCOCCUS

/Food Poisoning 5559

treatment with the proper antibiotic may be desirable

but, because it is due to a toxin, antibiotic treatment

is of no benefit. However, it could have an adverse

effect, particularly if the staphylococci were resistant

to the antibiotic. In this case the natural flora of the

intestinal tract would be eliminated and this would

allow the staphylococci to grow uninhibited and pro-

duce enterotoxin. Staphylococci are not good com-

petitors and usually do not grow in the intestinal tract

in the presence of the natural flora.

Prevention

Temperature Control

0024 Most staphylococcal food-poisoning outbreaks could

be prevented if proper temperature controls were

observed during holding of the food after its prepar-

ation and before being served. One method is proper

refrigeration of susceptible foods after they are pre-

pared. The lower the temperature, the slower the

growth of the staphylococci, with little or no growth

at refrigeration temperatures. An excellent example

of the effect of refrigeration is an outbreak from

cream-filled coffee cake that occurred in Wisconsin

in 1970. Approximately 50 people became ill after

eating the cake, with differing severity of symptoms,

depending on the length of time the cakes stood

unrefrigerated before being eaten. The cakes were

made by a bakery and delivered to several stores at

5:30 a.m. on a warm Saturday morning; the cakes

were not refrigerated at the stores. Purchases were

made all day Saturday and on Sunday morning.

Many who bought the cakes on Saturday did not eat

them until Sunday morning, but in most cases the

cakes were refrigerated by the purchasers. Most of

those who bought the cakes early Saturday morning

and refrigerated them did not become ill. No one who

ate cakes purchased at the bakery became ill because

the cakes were refrigerated at the bakery. The source

of the staphylococci was from the throat of the food

handler who had placed the cream filling into the

cakes with his hand. The organisms isolated from

his throat and the cakes produced enterotoxin E; not

many staphylococci produce this enterotoxin and its

involvement in food poisoning is rare.

0025 Some of the largest outbreaks of staphylococcal

food poisoning have occurred at picnics, a number

of these from baked ham sandwiches. Baked ham is

an excellent medium for the growth of staphylococci,

which is not always appreciated because it is a cooked

food. However, if the ham is recontaminated after

the baking, the results can be tragic. Providing

refrigeration for such a large quantity of food is diffi-

cult at a large picnic and normally the food will be at

the picnic for a number of hours before being con-

sumed. In cases such as this, every effort should be

made to provide refrigeration for the food at the

picnic grounds or not to transport it to the grounds

until shortly before it is to be served. (See Pork.)

0026One error that is frequently made is to place the

food in large containers to conserve space before it is

placed in the refrigerator. Under these conditions,

cooling is very slow and allows sufficient time for

the staphylococci to grow and produce enterotoxin.

A staphylococcal food-poisoning outbreak, in which

104 of 231 inmates in a country jail in New York

became ill, resulted from inadequate refrigeration of

macaroni salad. It had been prepared the day before it

was served and had been stored overnight in two

large, deep containers in a walk-in cooler. Isolation

of over 10

staphylococci per gram from the maca-

roni salad indicated inadequate cooling.

Food-Handling Practices

0027In the New York jail outbreak described in the previ-

ous section, it was ascertained that the food was

prepared by inmates who were inadequately trained

and not well supervised. Many food-poisoning out-

breaks are a result of inadequate training and super-

vision of the individuals preparing the food. The

major conclusion from both the First and Second

National Conferences for Food Protection held in

Denver, Colorado, in 1971 and in Washington, DC,

in 1984 was the need to educate the food handler as

well as the consumer on food safety. Unfortunately,

very little has been done in this area.

Food-Handler’s Infections

0028One method of preventing staphylococcal food-

poisoning outbreaks is to prohibit food handlers

with infections from handling foods. In some coun-

tries food handlers who are staphylococcal carriers

are not allowed to handle foods as long as they are

carriers. In the UK an assistant cook, who carried the

same staphylococcal organism in her nose as the one

isolated from lemon snow pudding involved in the

illness of six adults and 101 children in a primary

school, was excluded from work until the organisms

were eradicated by treatment with gentamicin cream.

The pudding contained large numbers of staphylo-

cocci (1.5 10

1

) that produced SEA and entero-

toxin D, as did the staphylococci isolated from the

nose of the assistant cook. Although it was feasible to

exclude the cook in this case, usually it is difficult and

impractical to bar workers who are carriers of

staphylococci in their noses or throats from handling

foods because approximately 50% of the population

are carriers. On the other hand, food handlers with

5560

STAPHYLOCOCCUS

/Food Poisoning

any type of infection should not be permitted to

handle foods, particularly if the food is for mass

feeding. The only viable solutions to this problem

are proper refrigeration of vulnerable foods between

preparation and consumption, or maintaining the

temperature above 45



See also: Bacillus: Food Poisoning; Cadmium:

Toxicology; Clostridium: Food Poisoning by Clostridium

perfringens; Cream: Types of Cream; Food Poisoning:

Tracing Origins and Testing; Statistics; Milk: Processing

of Liquid Milk; Poultry: Chicken; Ducks and Geese;

Turkey

Further Reading

Bergdoll MS (1979) Staphylococcal intoxications. In: Rie-

mann H and Bryan FL (eds) Food-Borne Infections and

Intoxications, pp. 443–494. New York: Academic Press.

Bergdoll MS (1983) Enterotoxins. In: Adlam C and Easmon

CSF (eds) Staphylococci and Staphylococcal Infections,

vol. 2, pp. 559–597. London: Academic Press.

Bergdoll MS (1989) Staphylococcus aureus. In: Doyle MP

(ed.) Foodborne Bacterial Pathogens, pp. 463–523. New

York: Marcel Decker.

Dack GM (1956) Staphylococcus food poisoning. In: Dack

GM (ed.) Food Poisoning, 3rd edn. Chicago: University

of Chicago Press.

STARCH

Contents

Structure, Properties, and Determination

Sources and Processing

Functional Properties

Modified Starches

Resistant Starch

Structure, Properties, and

Determination

D S Jackson, University of Nebraska, Lincoln, NE, USA

Starch Structure

Amylose and Amylopectin Polymers

0001 Starch is a mixture of two glucose polymers. These

polymers are initially enclosed within a semicrystal-

line granule formed inside starch-synthesizing plant

organelles. Amylopectin, the larger of the polymers,

is an alpha-1, 4-linked, alpha-1,6-branched (4–6%

branching) polymer with an average molecular

weight near 10

. Amylose, a smaller, mostly linear

polymer, is also composed of alpha-1,4-linked glu-

cose units; long chains are sometimes connected

with alpha-1,6 branches, although branching

probably accounts for < 1 % of the glucose unit con-

nections. The molecular weight of amylose is ap-

proximately 10

. The molecular weight of starch

polymers varies depending upon its plant source.

Amylopectins have been reported to vary from

50 10

to 500 10

, and amyloses from 1600 to

1 10

. The degree of branching also varies.

Common starches typically have 25–35% amylose

and 65–75% amylopectin.

Genetic Differences

0002Several genetically modified starches are available.

The most common forms are the waxy starches

and the high-amylose starches. Waxy starch, which

contains 100% amylopectin, is found in grains

(i.e.,maize, sorghum, and wheat) that have three

recessive waxy genes. Combinations of recessive

(wx) and dominant (Wx) waxy genes result in

starches with varying percentages of amylopectin

from 75 (WxWxWx) to nearly 100% (wxwxwx).

High-amylose (ae) starches are available with ap-

proximately 53 or 70% amylose.

Microscopy of Granules

0003Starch granules have unique microscopic structures

(Figures 1 and 2), and the source of starch can

frequently be determined by a trained observer. The

shape and size of starch granules differ according to

the botanical source and the environmental condition

under which a crop was grown. Typically, rice and

maize starch have angular (polyhedral) granules;

potato starch has oval-shaped granules. Wheat starch

STARCH/Structure, Properties, and Determination 5561

consists of spherical and flat circular (lens)-shaped

granules. Sizes also vary widely. Rice starch granules

are very small (6 mm diameter), while potato starch

granules can exceed 100 mm. The mean diameter of

maize starch granules is 35 mm; wheat starch has a

bimodal distribution of granular sizes – small (B)

granules average 4 mm, while the large (A) granules

average 14 mm. Granules can also have compound

structures (i.e., oats, rice) which appear as separate

starch grains in a single amyloplast enclosure.

0004 Several microscopic techniques have found wide-

spread use. When observed under polarized light,

undamaged starch granules (as defined by the reten-

tion of crystalline structure) exhibit a phenomenon

called birefringence (Figure 1). This birefringence is

the result of polarized light being bent as it traverses a

region of high molecular order. Scanning electron

microscopy (Figure 2), as well as other higher-

magnification techniques, have proven extremely

useful in identifying the three-dimensional structure

of starch granules, as well as showing the interrela-

tionships of starch granules and other chemical com-

ponents in cereal grains, tubers, and other food

systems.

Changes during Hydration and Heating

0005 Starch granules, when exposed to water, undergo

swelling and upon heating undergo a process of irre-

versible swelling and crystalline melting called gelat-

inization. If the crystalline region is destroyed,

granular birefringent properties disappear. The tem-

perature at which birefringence is lost has been de-

fined by some as the gelatinization point. Since loss of

crystallinity causes loss of birefringence, additional

thermal disruptions of the granule still occur after

the gelatinization point as defined using microscopy

techniques. When starch granules are exposed to

liquid water below 40–50



C, the amorphous gel-

like portions of the starch granule absorb water, caus-

ing the granule to swell. When the temperature is

>40–50



C, and water is in excess, granules begin to

undergo reversible swelling and around 60–80



C lose

birefringence and undergo irreversible swelling.

During the transition from reversible swelling to loss

of birefringence, the amorphous regions have a

rubber-like structure and the specific volume of the

amorphous areas increases, as does the mobility of

molecular segments which are thermally softened and

plasticized by water. At the gelatinization tempera-

ture, the mobility of molecules increases rapidly.

Granule components are in a more flowable state.

The mobility of molecules in the amorphous regions

and the mobility of molecular regions which traverse

both crystalline and amorphous regions cooperatively

contribute to intergranular stresses. The continued

hydration of amorphous areas places additional stress

on those molecular regions (including regions within

the same molecule) which have remained crystalline.

These molecular movements have a cooperative effect

on granule swelling and the overall melting of starch

crystallites.

Starch Sources: Grain and Tuber/Root Structure

0006The majority of starch in cereal grains is located in the

endosperm. Many grains can be referred to as having

‘soft or floury starch’ or ‘hard or vitreous starch.’

Corn

Normal

light

Polarized

light

Potato

fig0001 Figure 1 Light micrographs (100) of corn (left) and potato starch (right) shown using normal (top) and polarized (bottom) light

microscopy.

5562 STARCH/Structure, Properties, and Determination

There is little evidence that the molecular components

of their starches are any different. The packing of the

starch granules within a kernel, however, is different.

Floury maize kernels have less protein binding the

starch granules together, and starch granules within

more flinty maize kernels are encased more tightly

within a protein matrix. Cereal starch is obtained

via wet milling; after the endosperm is disrupted, the

starch is collected by washing and centrifugation.

0007Cassava root, from which tapioca starch is pro-

duced, typically contains 25% starch. The roots

have a hard or cork-like outer layer which is usually

(a) (b)

(e) (f)

fig0002 Figure 2 Scanning electron micrographs (1000) of (a) corn, (b) oat, (c) potato, (d) rice, (e) tapioca, and (f) wheat starches.

STARCH/Structure, Properties, and Determination 5563

removed before starch processing. Starch is collected

by disrupting the cells, screening, and subsequent

collection by washing and centrifugation.

0008 Potatoes are also another important starch source;

they typically contain about 22% starch. Raw pota-

toes are ground to disrupt cell walls; the pulp is

washed, and screened. Starch is later collected via

centrifugation. Starch can also be obtained, as a by-

product, from commercial production of value-added

potato products such as french fries, instant potatoes

and potato chips (crisps).

Viscosity Measures

Amylograph/Rapid Viscoanalyzer

0009 The viscosity of cooked starches is important to the

food industry. One of the most important industrial

measures of starch properties uses amylograph or

Rapid Viscoanalyzer (RVA) instruments to measure

a starch’s thermal behavior. In the standard amylo-

graph, a 3–5% starch dispersion is mixed in a cylin-

drical bowl. Paddles mix the starch dispersion, and

the force these paddles encounter is recorded with a

computer. The test begins with the gradual heating

(1.5



C min

1

) of the starch dispersion. The starch

granules swell and the viscosity of the mixture in-

creases as the temperature increases because the

swollen granules occupy more area within the mixing

vessel. When the temperature reaches 95



C, the

starch mixture continues to be stirred while the tem-

perature is maintained for 60 min. When swollen un-

modified granules are exposed to shear, the viscosity

of the mixture decreases because the granules break

apart into smaller pieces. After the holding cycle, the

starch is subsequently cooled to 50



C (also at 1–5



min

1

) and a highly viscous gel structure can form by

hydrogen binding and water entrapment between

starch polymers. The RVA is a similar device that

uses smaller sample sizes and has programmable

heating, cooling, and stir speeds (the manufacturers

of the amylograph also make a instrument suitable

for analyzing small amounts of starch). Typical RVA

curves are shown in Figure 3.

Chemical Methods

Determination of Total Starch

0010 There are several chemical methods available to

measure the total amount of starch in a sample. For

samples high in starch content (cereal grains, tubers,

and their products), starch’s optical rotation in solu-

tion can be determined using a polarimeter. Samples

are initially extracted with ethanol to remove

optically active soluble materials and the remaining

starch is suspended in a calcium chloride solution and

placed in a boiling water bath. Proteins are removed

in the procedure with stannic chloride-phosphotungs-

tic acid. The resulting filtered solution’s optical rota-

tion is measured in the polarimeter and used to

calculate percent starch; a similar optical procedure

uses hydrochloric acid and a saturated lead solution.

More recently developed methods of starch analysis,

however, usually rely on the ability of the enzymes

alpha-amylase and amyloglucosidase to degrade

cooked (or chemically treated) starch to glucose.

These methods often have the advantage of being

applicable to a wider range of starch-containing

products. For these procedures, it is usually essential

to gelatinize fully (cook/disperse) the starch. For

common materials without extensive resistant starch

(fiber-like starch), the sample can be gelatinized in an

autoclave. For more difficult-to-gelatinize samples,

starch can be dispersed in methyl sulfoxide (also

known as dimethyl sulfoxide or DMSO) prior to

enzymatic digestion.

0011After the starch is digested with enzymes to glu-

cose, most methods subsequently convert the glucose

solution into a colored product that can be measured

colorimetrically in a spectrophotometer. In fact, how-

ever, many of the glucose measurement techniques

can be used at this stage. The percentage of starch is

calculated by multiplying the measured amount of

glucose evolved from the enzymatic treatment. Total

glucose is multiplied by 0.9 to determine total starch;

this calculation accounts for the difference in molecu-

lar weight between individual glucose units and

glucose polymers. In addition to these chemical total

starch methods, indirect procedures using near

024681012

Time (min)

Temperature (⬚C)

5050 50 95 95 50

Potato

Wheat

Waxy corn

Corn

Rice

53% Amylose corn

fig0003Figure 3 Representative Rapid Viscoanalyzer curves for

potato, wheat, corn rice, waxy corn, and 53% amylose corn

starches.

5564 STARCH/Structure, Properties, and Determination

infrared spectroscopy (NIR) technology (especially

for grain/cereal crops) have proven to be very useful.

While NIR methods must rely on these chemical pro-

cedures for method development and subsequent ma-

chine calibration, when used appropriately they are

extremely rapid and can be performed by personnel

not necessarily trained in complex chemical analyses.

Determination of Percentage Amylose

0012 Since amylose and amylopectin have unique physical

and chemical properties, and their relative propor-

tions influence the overall properties of starches, the

determination of the ratio of these polymers becomes

important. Potentiometric titration is considered one

of the better techniques for determining the percent-

age of linear components (i.e., amylose) in starch. It

relies on the affinity between amylose and iodine.

Potato and wheat starches have typical iodine affin-

ities of approximately 19.9%, whereas maize starch

has an iodine affinity of 19.0%.

0013 Colorimetric tests for the percentage of amylose

are also widely used. Solutions of amylose and iodine

result in a deep blue-purple color. Amylopectin and

iodine show only a slight affinity towards each other;

their solutions have a reddish color. The blue value

test relies on these properties; starch samples are dis-

persed in a sodium hydroxide solution and, after

neutralization, the samples are allowed to react with

an iodine solution. The absorbance (usually at 620–

680 nm) of the solutions is measured to calculate blue

value, and the apparent percentage amylose content

can be determined by developing a blue value stand-

ard curve with ‘purified’ amylose. Unfortunately,

commercially available amyloses are usually not

exactingly pure, nor is such a pure amylose available

for every kind of starch. Accurate chemical determin-

ations of amylose content from different starch

sources is made more difficult because not only do

amyloses from different botanical sources have differ-

ent iodine affinities, but different amylopectins will

also bind a small amount of iodine and thus cannot be

discounted in amylose determinations. A newer pro-

cedure for amylose determination relies upon the

complexing action of concanavalin A (A) with amy-

lopectin. The procedures precipitate amylopectin

from starch solutions, leaving only amylose. The

amylose is thus subsequently analyzed in much the

same way as for total starch determinations.

Instrumental Methods

Differential Scanning Calorimetry

0014 The differential scanning calorimeter (DSC) is widely

used to determine the crystalline melting temperature

of various starches (Figure 4). Small samples of

starches are heated at a constant rate and the endo-

thermic heat flow is recorded. Melting of crystalline

sites (or some starch chemists postulate melting of

crystalline sites and unfolding of double helices)

results in a thermal event typically recorded as

an endotherm. Usually, a broad crystalline melting

range is recorded; sites of crystallinity melt at differ-

ent temperatures depending upon their individual

structure, the action of solvent (usually water), and

the interaction of individual polymers which are con-

tained and traverse crystalline sites. DSC can also be

used to examine the recrystallization of gelatinized

starches. Most notably, DSC is used to study the

retrogradation process under various environmental

conditions of time and temperature, and the inter-

actions of starch with complexing agents and crystal-

lization promoting or inhibiting ingredients.

X-Ray Analysis

0015X-ray analysis of starch is useful in determining the

extent of crystallinity and crystallite structure, the

botanical origin of starches, the formation of starch

complexes, and can be used in structural studies to

determine spacing within starch helices. Unlike DSC,

X-ray diffraction is less subject to scientific debate

regarding the ‘true’ measurement of starch crystallin-

ity. The diffraction patterns (groupings of spectral

lines) of native starches have been broadly classified

as A, B, C and V (Figure 5). Researchers have also

proposed variants on these patterns. Cereal grain

30 40 50 60 70 80 90 100

Temperature (⬚C)

Wheat

Waxy corn

Rice

Regular corn

Potato

End

Start

Gelatinization

temperature

fig0004Figure 4 Differential scanning calorimetry (DSC) endotherms

of wheat, waxy corn, rice, corn, and potato starches (scanned at



C min

1

, > 60% water). The figure shows the start of crystal-

line melting, point of maximum endothermic energy (gelatiniza-

tion temperature), and temperature at which all crystals have

melted.

STARCH/Structure, Properties, and Determination 5565

starches generally have the A pattern, although defat-

ted high-amylose starches have a B pattern. Bean and

cassava starches have a C pattern and potato starch

has a B pattern. Complexes between fatty acids and

amyloses, seen especially strongly in some high-

amylose maize starches, exhibit a characteristic V

pattern.

Chromatography

0016 Size exclusion chromatography has been important in

determining the fine structure of amylose and amylo-

pectin molecules, as well as the relative proportion of

those molecules in food materials. In addition, chro-

matographic techniques have proven useful in deter-

mining the relative solubility of starch polymers in

solution and the percentage of amylose in starches.

Chromatography can be conducted using conven-

tional gel filtration techniques (soft gels), or more

rapid high-performance liquid chromatography me-

thods with rigid stationary-phase material (Figure 6).

Starch samples are first dispersed (usually in methyl

sulfoxide, also known as DMSO, NaOH, or water)

and injected into a chromatographic system. The

amylopectin usually elutes at or extremely close to

the void volume of most modern column systems, and

the smaller amylose elutes later. The molecular

weight of these materials can be determined by

coupling the chromatographic system to a laser

light-scattering detector, or can be estimated by

employing known-molecular-weight standards of

pure carbohydrate polymers. The relative molecular

weights or sizes of starch polymers can be compared,

as well as the relative effect of various food-

processing unit operations on starch structure. The

extent of starch depolymerization caused by food or

industrial processing is also easily measured using

size exclusion liquid chromatography. Amylases

can be used, coupled with chromatography and

postchromatographic chemical analysis, to determine

the extent and length of polymer branches, and other

details about the fine structure of particular starches.

Nuclear Magnetic Resonance Spectroscopy

0017Nuclear magnetic resonance (NMR) is a powerful

tool that has been used to understand starch–water

interactions and the molecular relationship between

chemical groups in starch molecules. For example,

wide-line

H NMR has been used to characterize

the mobility of water associated with starch pre-,

post-, and during gelatinization; these results have

confirmed the notion that gelatinization is a melting

phenomenon. In addition, both

H and

C NMR

have been used to study the degree of branching

3 13182328

A (Corn)

B (Potato)

C (Bean)

V (Lipid complex)

2Θ

fig0005 Figure 5 X-ray diffraction patterns (40 kV, 30 mA, Cu K-alpha

radiation, 2-theta diffraction angle) of a lipid complexed corn

(V-pattern), bean (C-pattern), potato (B-pattern), and corn (A-

pattern) starches.

Potato

Wheat

Rice

70% Amylose

Waxy corn

Regular corn

Amylopectin

Amylose

Decreasing (log) molecular size

fig0006Figure 6 Typical high-performance size exclusion chromato-

grams (HPSEC) of potato, wheat, rice, 70% amylose, corn, waxy

corn, and corn starches. The figure shows amylopectin and

amylose peaks. Starch was dispersed in methyl sulfoxide

(DMSO) before injection into the HPSEC system consisting

of four columns linked in series. Carbohydrate was detected

using a refractive index detector.

5566 STARCH/Structure, Properties, and Determination