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

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found in starches from different botanical sources.

NMR can distinguish between anomeric protons in-

volved in alpha-1,4 and alpha-1,6 branching, and

small peaks found in

C NMR scans have been

associated with nonreducing ends. NMR has also

proven useful in understanding interactions between

starch and other chemicals such as sugars, proteins,

and fatty acids.

See also: Chromatography: High-performance Liquid

Chromatography; Spectroscopy: Nuclear Magnetic

Resonance; Starch: Sources and Processing; Functional

Properties

Further Reading

Hill RD and Munck L (eds) (1985) New Approaches

to Research on Cereal Carbohydrates. Amsterdam:

Elsevier.

Kulp K and Ponte JG (eds) (2000) Handbook of Cereal

Science and Technology. New York: Marcel Dekker.

Manners DJ (1985) Some aspects of the structure of starch.

Cereal Foods World 30: 461–467.

Radley JA (ed.) (1976) Examination and Analysis of Starch

and Starch Products. London: Applied Science.

Thomas DJ and Atwell WA (1999) Starches. St Paul: Eagen

Press/American Association of Cereal Chemists.

Whistler RL (ed.) (1984) Starch Chemistry and Technology,

2nd edn. Orlando: Academic Press.

Whistler RL and BeMiller JN (1997) Carbohydrate

Chemistry for Food Scientists. St. Paul: Eagan Press.

Whistler RL and Paschall EF (eds) (1965–1967) Fundamen-

tal Aspects, vol. 1. Industrial Aspects, vol. 2. Starch:

Chemistry and Technology. London: Academic Press.

Zobel HF (1988) Molecules to granules: a comprehensive

starch review. Starch/Starke 40: 44–50.

Sources and Processing

W S Ratnayake and D S Jackson, University of

Nebraska, Lincoln, NE, USA

Background

0001 Starch is found in almost all tissues (leaves, roots,

tubers, seeds, stems, flowers, etc.) in green plants.

Only a small number of plants, however, are commer-

cially grown for starch; they include cereal (such as

wheat, corn, sorghum, and rice), tuber (mainly

potato), root (tapioca and arrowroot), stem (sago),

and legume (mainly pea) crops. All starches occur as

minute granules in nature, but the size, shape, and

nature of molecular arrangement inside the granule

depends on the species and sometimes on crop culti-

var or variety. The processing methods employed for

starch extraction mainly depend on the nature and

composition of raw material, i.e., source of starch.

Cereal Starches

Corn and Sorghum

0002Corn (maize, Zea mays L.) has been grown for 5000–

7000 years and was probably first grown in Central

Mexico. That first corn was very different from

today’s varieties, which were evolved through muta-

tion, hybridization, and random and conscious selec-

tion. Among the types of corn available today are

popcorn, sweet corn, dent corn, flint corn, and flour

corn. The availability of dent corn at low prices, its

storability, and its high starch content have led to its

increasing use for starch production.

0003Grain sorghum (Sorghum bicolor), also known as

milo, was probably initially cultivated 5000–7000

years ago in eastern Africa. Although sorghum is a

major cereal crop and resembles corn in general com-

position, it is sometimes considered inferior to corn

for food, feed, and industrial uses. Compared with

corn, it can be grown effectively in more arid regions

and can be milled in a similar way. Sorghum starch

has properties similar to those of corn starch, and the

extraction procedure (wet milling) is similar to that

applied in corn starch extraction.

0004The corn kernel is a caryopsis (a berry), borne on

an inflorescence called ‘an ear.’ The caryopsis matures

approximately 60 days after pollination, and corn is

harvested in late summer or early autumn. In sor-

ghum, the seeds are borne in a terminal, bisexual

rachis (head). Waxy sorghum or corn starches are

produced by the varieties containing three recessive

wx genes.

0005The corn (and sorghum) wet milling process con-

sists of: (1) cleaning the grain, (2) steeping, (3) milling

and fraction separation, (4) starch processing, and (5)

product drying. Grain is initially cleaned by screening

to remove foreign material and broken kernels. The

grain is then steeped to soften the kernel. Sorghum

typically needs longer steeping times than yellow dent

corn. Steeping involves maintaining the correct bal-

ance of steeping water with regard to flow, tempera-

ture, sulfur dioxide concentration, and pH. Normal

steeping conditions are 30–40 h at 48–52



C. Sulfur

dioxide (c. 0.1%) was initially used in steep water to

prevent the growth of spoilage organisms but was

later recognized as an indispensable reagent to maxi-

mize starch yield. The effect of sulfur dioxide on the

protein matrix is apparently such that it disperses

the protein matrix by breaking disulfide bonds, thus

STARCH/Sources and Processing 5567

releasing more starch. The use of unusually high tem-

peratures and/or sulfites during steeping reduces the

starch yield. Proper steep temperature is also import-

ant, as steeping between 45 and 55



C promotes the

growth of indigenous lactic acid bacteria. Growth of

these bacteria lowers the pH of the steep, making the

antimicrobial action of SO

more effective, and is

helpful in softening the kernel structure. Lactic acid

also increases the absorption rate of sulfur dioxide

into the kernel. Steep-water pH is normally main-

tained at about 4.0 and is highly buffered.

0006 After steeping, the grain is milled to obtain as

complete a separation of components as possible.

Milling is usually done in an attrition mill (Bauer-

type) in preparation for germ separation. Once the

grain integrity is disrupted, it is a fairly simple process

to separate the lighter germ, an oil-rich fraction, from

the heavier starch and protein fractions by use of a

centrifugal hydroclone. Separated germ is cleaned by

washing and dewatered by mechanical squeezers in

preparation for oil recovery by hexane extraction. In

milling grain sorghum, starch and protein are more

difficult to separate, because the sorghum pericarp is

more fragile than that of corn. Separation is enhanced

if the kernels are dehulled prior to milling. This

gives a sharper separation of starch and gluten with

starch of whiter color and lower protein content.

Sorghum dehulling prior to milling also improves

germ separation.

0007 Free starch and protein from the first pass through

the mill are separated from unmilled endosperm and

fiber by screening. The unmilled endosperm–fiber

fraction is re-milled in a grinding mill to maximize

starch separation. Screening after this process separ-

ates the starch–protein fraction from the remaining

fiber fraction. The fiber fraction is dewatered and fur-

ther processed and often incorporated with other wet

milling end products (evaporated steepwater, spent

germ cake and protein) to produce feed fractions.

0008 The starch–protein mixture (mill starch) is separ-

ated by centrifugation. Protein (sometimes called

‘gluten’ in the corn processing industry) is less dense

(1.1 g cm

3

) than starch (1.5 g cm

3

), so that these

fractions may be easily separated. Starch obtained

has 1–2% protein, which is mainly removed by fur-

ther washing in a second centrifugal separator or set

of hydroclones to obtain a final protein content of

less than 0.38% (dry-weight basis). The pigments of

sorghum sometimes discolor (light pink or gray color)

starch. Bleaching with NaClO

or rinsing with

NaOH or methanol is done to reduce this discolor-

ation in isolated starch.

0009 The final starch slurry may be dried and sold as

unmodified starch, or the starch may be modified and

dried, gelatinized and dried, or hydrolyzed to a syrup,

which may be used directly or fermented to produce

ethanol or other chemicals.

0010Starch is usually dried by flash drying. The starch

slurry is dewatered by centrifugation or filtration, and

the moist starch is introduced into the bottom of a

stream of rapidly moving air (93–127



C). Drying is

rapid, and the product is collected in cyclones. Drying

conditions can be altered to control bulk density and

particle size. Wet milling is water- and energy-

intensive; the wet-milling industry is the second most

energy-intensive food industry in the USA.

Wheat

0011Wheat has been grown by man for 8000–9000 years,

its cultivation probably beginning in the Middle East.

The first commercial manufacture of wheat starch

was in England in the 1500s. Wheat is mainly har-

vested by mechanical means, and starch is separated

by one of several processing methods, such as the

Martin process, the Batter process, the Fesca process,

the ammonia process, the acid process, wet wheat

milling, whole wheat fractionation, the Rasio pro-

cess, or the hydroclone process. The first two pro-

cesses are the most commonly used. Wheat has

60–70% starch (on a whole-seed basis).

0012At present, low-grade flour (rather than wheat) is

used as the starting material for most wheat starch

production. There are two, somewhat similar pro-

cesses commonly used, i.e., Martin process and batter

process.

0013The Martin (dough ball) process was first used in

1835 and employs wheat flour as its raw material. It

consists of making a flour dough, washing out the

starch, drying the gluten protein, purifying the starch,

and drying the starch. Wheat flour and water (2:1)

are blended to form a stiff dough, and the dough is

then allowed to rest, hydrate, and strengthen the

gluten. The dough is then washed with water while

being kneaded or rolled, to remove the starch. Separ-

ated gluten is dewatered by roller compression and

dried in a flash-drier. Starch slurry overflow from the

dough washer is sieved to remove gluten particles and

then fine-screened to remove bran particles. Purifica-

tion and dewatering of the starch slurry are per-

formed by centrifugation to produce a high-solids

starch cake, which is then flash-dried. The final prod-

uct is dried to 10–12% moisture and contains ap-

proximately 0.3% protein.

0014The Batter process is a derivative of the Martin

process and differs in both the way the dough is

formed and the way it is treated. Wheat flour and

water (approximately 1:1) are mixed and the result-

ant dough allowed to rest for 30 min. This dough is

then vigorously mixed with additional water equal

to twice the weight of the original flour. Protein is

5568 STARCH/Sources and Processing

separated from this mixture by screening, and the

starch further purified from bran by additional

screenings. Centrifugal separation of the filtrate sep-

arates the large, lenticular starch granules (prime or

type A starch) from the type B starch (a mixture of

small granules, damaged granules, and pentosan

complexes – also called tailings or squeegee starch),

that is about 20% of the total starch. Type A starch is

essentially pure and is subsequently dewatered and

flash-dried. Type B starch is likewise processed but is

of low purity. Sulfur dioxide is not used in wheat

starch processing, as (1) it is not required to soften

the wheat flour particles because water alone can

soften the particles to an extent that protein is effect-

ively separated from starch, and (2) it would destroy

the desirable characteristics of the gluten.

0015 Most wheat starch manufactured is sold unmodi-

fied and is mainly used in paper adhesives, laundry

sizing, and cotton finishing, rather than in food. In

foods, the thickening power of wheat starch is infer-

ior to corn starch, but paste texture and strength, as

well as paste clarity, are about equal to corn starch.

Wheat starch may be preferred for use in certain

baked goods owing to the lack of chemicals used in

its production. Some modified wheat starches show

emulsification properties in selected foods.

Rice

0016 Rice (Oryza sativa) cultivation probably originated in

Asia, and rice is still a staple food. In the USA, more

than 90% of the rice crop is produced in four states:

Arkansas, Louisiana, Texas, and California. The rice

grain consists of a hull and an edible berry (caryop-

sis). The outer fibrous layers cover the starchy endo-

sperm and the germ. The endosperm contains mainly

starch granules and protein bodies, with little matrix

protein in evidence.

0017 To isolate rice starch, broken rice is treated with

dilute (0.3–0.5%) sodium hydroxide for about 12 h

to soften the grain and aid protein removal. It is wet

hammer-milled, the cell walls are removed by

screening, and the protein is extracted. The rice starch

slurry is purified by further centrifugal washing and

then dried.

0018 Rice starch is little used, because of its high cost of

production relative to other commercial starches but

may be used as a custard or pudding thickener in

foods, as a dusting powder in cosmetics, and as a

stiffening agent in the cold-starching of fabrics. Rice

starch is used in Europe in baby foods, and in the

laundry and paper industries.

Potato

0019 Potato starch is extracted from the tubers of Solanum

tuberosum, which was first cultivated around ad 200

in Peru. Potato starch is mainly produced in Europe.

Starch is typically isolated from cull potatoes, surplus

potatoes, and waste streams from potato processing.

However, there are special cultivars developed for

starch manufacture. The tubers generally contain

65–80% starch (w/w).

0020Culled or surplus potatoes are washed with water

in a flume, to remove dirt and foreign matter. They

may be washed again on arrival at the processing

plant. They are then disintegrated by a saw blade

rasp or hammer mill, and the mashed product is

screened to remove skins and fiber. During the

disintegration process, sulfur dioxide is usually

added to preserve the color and inhibit oxidation.

Water-soluble impurities are separated by wash-

ing, and other impurities are separated by gravity

separation.

0021Screening, by using a screening battery, separates

the starch from the potato pulp, which can be

reground, and a second starch extraction made to

obtain a total yield of 12% starch based on raw

potatoes. Starch isolated from the screens or sieves

is reslurried in water to remove soluble material, and

then dewatered in a continuous centrifuge. Addition

of water, and concentration in a hydroclone is

followed by further batch centrifuge or tabling oper-

ations for final purification of the potato starch.

Starch slurry isolated from these operations is

dewatered by vacuum filtration and flash-dried

(< 175



C inlet temperature). Potato starch, dried to

17–18% or less moisture, is then screened and pack-

aged. Unmodified potato starch has a relatively low

temperature of gelatinization, and exhibits high vis-

cosity on gelatinization, but breaks down on further

heating and stirring. It can form useful films and has a

high binding power.

0022Potato starch is used unmodified, or it may be

pregelatinized, converted to a cationic form, dextri-

nized, or derivatized by hydroxyethylation, hydroxy-

propylation, or carboxymethylation. Large amounts

of potato starch are used in thickening commercial

soups, and pregelatinized potato starch is useful in

instant puddings. Other uses of potato starch include

pie fillings, sweets, chewing gums, and extrusion

cooking, and as a filtering medium in breweries,

where it is employed as a filter precoat when filtering

yeast from the wort.

Tapioca

0023Tapioca starch is obtained from the large, tuberous

roots of the cassava plant (Manihot utilissima,

Manihot esculenta), which grows in many equatorial

regions. Cassava roots may be either ‘sweet’ (contain-

ing less than 50 mg of potential hydrogen cyanide per

kilogram of fresh root) or ‘bitter’ (containing 250 mg

STARCH/Sources and Processing 5569

or more of hydrogen cyanide per kilogram of fresh

root). Sweet root varieties are grown for food pur-

poses and bitter varieties for other industrial uses. In

either case, the hydrogen cyanide is lowered to ac-

ceptable levels during processing.

0024 Harvesting of roots is often manual, and the yield is

usually 13–50 t ha

1

. Typically, roots contain 70%

water, 24% starch, 2% fiber, 1% protein, and 3%

fats, minerals, and sugars. Tubers should be processed

within 24 h of harvest, since deterioration sets in from

the time of root extraction and proceeds throughout

the process.

0025 The roots are initially washed to remove dirt and

other field debris, and then the outer skin is removed.

Breakage of root cell walls is accomplished by chop-

ping the root into small pieces and passing them

through a rasp disintegrator. During this process,

hydrogen cyanide is released and washed away.

Obtained pulp is washed on screens through which

starch passes, but fiber is held back. Fiber is generally

used in fertilizer or cattle feed. The starch slurry

(also called starch milk), after screening, is put

through a continuous centrifuge to separate the starch

from fine fiber and soluble material. This can also

be achieved by sedimentation. Starch thus collected

may be reslurried and put through a centrifugal

purification process as desired. Typically, sulfur diox-

ide (0.05%) is added to water used in the centrifuga-

tion purification processes to prevent microbial

growth.

0026 Starch slurry from the purification process is de-

watered by centrifugation or vacuum filtration

and then dried by drum, belt, tunnel, or flash

methods. Flash-drying is most common. The final

moisture content of the dried starch is in the range of

12–14%. Dried starch aggregates are pulverized

to obtain a free-flowing powder. Tapioca starch is

sold unmodified or is modified by derivatization,

pregelatinization, or cross-linking. The viscosity of

tapioca starch depends on plant variety, geography,

harvest time, age of roots, soil fertility, rainfall, and

manufacturing practices during production of the

starch.

0027 In some Asian countries, there is a commercial

product called ‘sago’ made from tapioca starch. This

‘sago’ has no relation to actual sago starch. It con-

tains starch pearls (0.5–1.0 mm diameter) made

from the extracted tapioca starch cake. During the

production, the starch cake is mechanically globu-

lated (or ‘pearled’) and then roasted to obtain a final

moisture content of 9–11% moisture.

Arrowroot

0028 Arrowroot starch is obtained from the root of the

tropical perennial, Maranta arundinacea. Roots are

harvestable after 6–12 months of growing and may

contain more than 20% starch, most of which is

extractable in the same manner, as previously de-

scribed for tapioca starch. The difference in process-

ing between the two roots is that arrowroot requires

more washing than cassava. In addition, the outer

skin of arrowroot root must be completely removed

to prevent the starch from having an off-color and

off-flavor. Arrowroot starch is principally produced

in China, Brazil, and St. Vincent in the West Indies.

Sago

0029Sago starch is derived from the stem of palms (princi-

pally Metroxylon spp., Arenga spp., and Maurilia

spp.) that are eight or more years old. The main

production areas are Sarawak and Papua New

Guinea; Metroxylon sagu is the popular species in

these areas. Starch production is primarily done at

the household level by hand. Cut palm trunks are

split, and the pith (which contains about 40% starch)

is scooped out. Kneading of the pith with water re-

leases the starch, which is sieved to remove fiber,

isolated by filtration, and dried. In commercial pro-

duction, starch extraction is conducted in a manner

similar to that of the household method. The pith of

the trunk is rasped out, and the kneading is done

mechanically. The crude, extracted starch is further

purified in factories by water washing and sieving,

and then dried using hot air. One palm trunk can yield

90–180 kg of sago starch, the granules of which are

large (20–60 mm in diameter). Sago starch is used in

foodstuffs or in textile sizings and adhesives.

Pea

0030Pea starch is extracted from the species Pisum

sativum. It is also identified by many other names

and produced throughout the world (field pea, garden

pea, green pea, yellow pea, smooth pea, and wrinkled

pea, etc.). The largest producer (25% of the total)

and the largest exporter (40% of the total) of peas in

the world is Canada. France produces about 17% of

the total.

0031Pea starch is mainly available as a byproduct of

protein extraction. Therefore, it is considered to be

a relatively cheap source of starch compared with

corn, wheat, and potato starches. Pea starch is pri-

marily used in industrial applications; its use in foods

is limited, owing to its poor functional properties.

0032The isolation of starches from peas is difficult,

owing to the presence of insoluble flocculent proteins

and fine fiber, which decreases sedimentation and

cosettles with the starch to give a brownish deposit.

Pea starches are isolated using aqueous techniques as

well as dry methods (pin milling and air classifica-

tion). Air classification is the most commonly used

5570 STARCH/Sources and Processing

commercial method for pea starch isolation. The pro-

cess requires a very high degree of particle size reduc-

tion (achieved by pin milling) in order to separate the

starch granules from the protein matrix. The major

fraction from the air classification process is the low-

protein-containing starch fraction, which is separated

from the fine protein fraction during the process. The

crude starch concentrate contains about 65% starch.

The residual protein associated with air-classified

field pea starch granules is derived from protein

bodies, agglomerates, chloroplast membrane rem-

nants (which enclose the starch granule), and a

water-soluble fraction that is presumably derived

from the dehydrated starch. Remilling and reclassify-

ing the starch fraction remove most of the protein

bodies and agglomerates, and water washing removes

most of the remaining attached protein. Purified, air-

classified starch contains 0.25% protein.

0033 The purity of pea starch obtained by wet milling is

higher than that obtained by air classification.

Repeated filtration through polypropylene screens

(20 and 70 mm) combined with alkaline treatment

(0.02% NaOH) causes substantial reduction in the

protein content of wet process extracted pea starch.

However, wet processing is not used to any great

extent at commercial levels.

0034 There is a slightly different procedure used for

wrinkled pea extraction. Wrinkled pea seeds are

steeped in warm water, followed by dehulling using

rubber rollers (to separate hulls from cotyledons), and

then the cotyledons are disintegrated by applying

high pressure. The slurry is suspended in water, and

the starch fraction is screened out. This process en-

ables up to 89% of the starch present in the wrinkled

peas to be extracted with a residual protein content of

around 1%.

Comparative Properties and Applications

0035Some comparative properties of various commercial

starches are given in Table 1. The general uses and

applications of major commercial starches are dis-

cussed under the specific sections above.

0036In general, the physicochemical properties of a

given starch vary depending on the source of starch

and often on the starch extraction method. Commer-

cially, wet milling techniques result in higher-quality

and purer starches compared with dry techniques, as:

(1) there is high starch granular damage in dry tech-

niques, and (2) most impurities are easily removed by

water washing in wet processing. Ultimately, how-

ever, the process chosen for starch extraction is usu-

ally determined by consumer/industrial demand,

availability of utilities, yield/quality considerations,

and various other economic factors.

Acknowledgement

0037This article is a revision of the first edition article by

J. R. Daniel and R. L. Whistler, Purdue University,

West Lafayette, USA from the Encyclopaedia of Food

Science, Food Technology and Nutrition, Copyright

1993, Academic Press.

See also: Cassava: Uses as a Raw Material; Flour:

Analysis of Wheat Flours; Oats; Potatoes and Related

Crops: The Root Crop and its Uses; Rice; Sago Palm;

Starch: Structure, Properties, and Determination;

Sources and Processing; Wheat: Grain Structure of

Wheat and Wheat-based Products

Further Reading

Balagopalan C, Padmaja G, Nanda SK and Moorty SN

(1988) Cassava in Food, Feed and Industry. Boca

Raton, FL: CRC Press.

tbl0001 Table 1 Comparative properties of some commercial starches

Source of starch Amylose

(%, w/w)

Amylopectin

(%, w/w)

Granule diameter

(mm)

Granule shape GTR

(



Normal corn 28 72 3–26 Round, polyhedral 62–72

Waxy corn 0 100 3–26 Round, polyhedral 63–72

High amylose corn (amylomaize) 50–70 30–50 3–24 Round, deformed 67–92

Sorghum 28 72 15 Round (compound granules) 71–80

Wheat 30 70 2–38 Lenticular, round 58–64

Rice 17 83 3–8

Polygonal, angular 68–78

Oat 16–29

71–84

3–10

Polyhedral 53–59

Potato 20 80 5–100 Oval, spherical 50–68

Tapioca 16 84 4–35 Oval, truncated 49–65

Arrowroot 21 79 15–70 Oval, truncated 62–70

Sago 26 74 5–65 Oval, truncated 60–77

Peas (normal)

33–49 51–77 5–40 Round, oval, spherical 55–61

GTR, gelatinization temperature range.

Individual (not compound) granules.

Depends on the variety.

Wrinkled peas and genetically modified varieties have different properties.

STARCH/Sources and Processing 5571

Inglett GE (ed.) (1970) Corn, Culture, Processing, Prod-

ucts. Westport, CT: AVI.

Hoseney RC (1986) Principles of Cereal Science and Tech-

nology. St. Paul, MN: American Association of Cereal

Chemists.

Kulp K and Ponte JG (eds) (2000) Handbook of Cereal

Science and Technology. New York: Marcel Dekker.

Pomeranz Y and Munck L (eds) (1981) Cereals: A Renew-

able Resource. St. Paul, MN: American Association of

Cereal Chemists.

Ratnayake WS, Hoover R and Warkentin T (2002) Pea

Starch: Composition, Structure and Properties – A

Review. Starch/Starke 54(6): 217–234.

Smith CW and Fredriksen RA (eds) (2000) Sorghum:

Origin, History, Technology and Production. New

York: John Wiley.

Talburt WF and Smith O (1987) Potato Processing, 4th

edn. New York: Van Nostrand Reinhold.

Van Beynum GMA and Roels JA (eds) (1985) Starch Con-

version Technology. New York: Marcel Dekker.

Watson SA and Ramstad PE (eds) (1987) Corn: Chemistry

and Technology. St. Paul, MN: American Association of

Cereal Chemists.

Whistler RL and Daniel JR (1985) Carbohydrates. In: Food

Chemistry, 2nd edn. New York: Marcel Dekker.

Whistler RL, BeMiller JN and Paschall EF (1984) Starch:

Chemistry and Technology. New York: Academic Press.

Functional Properties

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

Introduction

0001 Starches are used in a wide range of food products.

They are sold to consumers as ingredients for

thickening, and are used by food companies as

thickeners, binding agents, stabilizers, texturizers,

fat replacers/enhancers, encapsulation agents, gelling

agents, film formers, moisture barriers, and crispness

enhancers.

Solution Properties

0002 Starches can be found in many physical forms. In

water they can be found as raw (uncooked) granules,

swollen (solvated) granules, granule pieces, entangled

polymer masses of amylose and/or amylopectin, or as

individual molecules of amylose and amylopectin.

The presence and proportion of the components con-

tribute to the unique functional properties of starch in

specific food systems. Undamaged (partially crystal-

line) starch granules are insoluble in cold water and

cannot be permanently dispersed in cold water

without the addition of solvents such as methyl sulf-

oxide (DMSO) or alkali. If granules are suspended in

water at 50–60



C, however, they swell considerably

and are partially dispersed. Upon prolonged gentle

stirring of swollen starch granules at temperatures

just below gelatinization, amylose is leached from

the granules. After 4 h of aqueous leaching at 85



approximately 29% of the total amylose in normal

dent corn can be solubilized. This fraction of the

amylose, however, is generally that which is exclu-

sively within the amorphous regions of the starch

granule. Specifically, without crystalline melting or

gelatinization, amylose that traverses crystalline

regions or whose movement is restricted within the

granule by crystalline regions would be unable to

leach from the granule. Upon vigorous agitation or

some other induction of shear, more amylose and a

small amount of amylopectin can also be solubilized

at this temperature.

0003At temperature above the point of complete crys-

talline melting, starches can be thoroughly dispersed

in water. Such a dispersion typically consists of

soluble amylose and amylopectin, entangled polymer

masses, and granule pieces consisting of mostly

amylopectin. Complete dispersion of most normal

starches (solubilized individual amylose and amylo-

pectin molecules, and entangled polymers) occurs at

autoclave temperatures without exposure to shear.

Solubilization of 80–90% of individual molecules of

amylose and amylopectin (no granule pieces or entan-

gled polymers masses) can be achieved when corn

starches (with amylose contents ranging from < 1 to

70%) are autoclaved (120



C) and subsequently

exposed to shear.

0004The degree of water solubility and dispersibility of

starch depend largely on the temperature at which

crystalline melting takes place. In the presence of

excess water, the melting of crystalline areas takes

place at relatively low temperatures (60–110



because water helps to plasticize these regions. In

water-limiting systems (including many foods), the

temperature of melting (and hence gelatinization) is

increased. Typical crystalline melting data, as deter-

mined by differential scanning calorimetry (DSC), are

shown in Table 1.

0005Individual crystalline regions within starch mol-

ecules melt within a specific narrow temperature

range, and the melting of some crystalline regions

probably facilitates the melting of adjacent regions

as amylopectin molecules that traverse the crystalline

regions become more mobile. The temperature at

which the first crystalline regions melt is referred to

as the endotherm peak start and the temperature at

which a tangent drawn along the steepest point of the

endotherm curve intersects the baseline is the onset

5572 STARCH/Functional Properties

temperature. The temperature at which the largest

quantity of crystalline regions is melting is at the

endotherm peak (often referred to as the gelatiniza-

tion point or gelatinization temperature), and the

temperature at which all crystalline regions have

melted is the endotherm peak end. Since complete

molecular solubility cannot be achieved without com-

plete crystalline melting, it is apparent that high-

amylose corn starches, whose endotherm peaks are

wider and end at higher temperatures than other

starches, are more difficult to solubilize completely.

Even after the temperature of crystalline melting is

exceeded, however, polymer entanglements must be

dislodged by either increased temperatures and/or

introduction of shear.

0006 When concentrated suspensions of starch granules

(i.e., 5%) are heated in water, complete solubilization

of individual molecules of amylose and amylopectin

is unlikely. When the granules swell, complete disrup-

tion of their original molecular structure may not take

place, even if all of the crystalline areas are melted.

The concentrated, dispersed polymers do not have

complete freedom of movement. They are easily en-

tangled with polymers and polymer segments within

their originating starch granule, from other starch

granules, and with molecules that leached from

granules during the initial stages of swelling and

gelatinization.

Gel Systems

0007 Upon cooling, hydrated cooked starches form com-

plex gel systems. The degree of association and the

final rigidity of the gel system are largely dependent

on the amylose/amylopectin ratio and the molecular

characteristics (chain lengths and degree of branch-

ing) of both polymers. The initial gel formation, how-

ever, is largely dependent upon amylose properties;

not only is linear amylose the primary component

solubilized but it is that component which forms

associations with other starch polymers most easily.

Amylose is usually the component that forms the

initial gel matrix which ‘entraps’ amylopectin and

incompletely solubilized granule pieces. Waxy starch

gels are far less rigid than normal starches or high-

amylose starch. The final rigidity of an unmodified

starch gel is largely dependent upon how closely

solubilized starch polymers can associate and hydro-

gen-bond with each other. Solubilized amylopectin

molecules, because of their highly branched nature,

cannot associate as closely as linear amylose mol-

ecules. Therefore, the polymers in high-amylopectin-

containing starches are prevented from establishing

long, close associations of parallel hydrogen-bonded

chains. The hydrogen-bonding that does take place

between amylopectin molecules and amylopectin–

amylose molecules results in water entrapment be-

tween the polymer chains. Linear amylose polymers,

however, can form rigid and closely hydrogen-bonded

associations (researchers often use a zipper analogy).

Nevertheless, in the initial stages of cooling (when

hydrogen bonds are being formed between amylose

molecules), water is also entrapped between the

polymers.

0008After prolonged cooling, the amylose–amylose,

amylose–amylopectin, and amylopectin–amylopectin

hydrogen bonding results in the squeezing out of

water between associated polymers. This weeping

process is referred to as syneresis. The process fre-

quently manifests itself as a layer of water on a food

product when unmodified starches are used to pre-

pare fruit pie fillings or starch puddings and these

gel systems are allowed to cool for several days

(or shorter times depending upon the amylose–

amylopectin ratio of the starches).

0009Because of differences in the closeness of associ-

ation and the amount of water entrapment, the

appearance of starch gels differs depending upon

the amount of amylose and amylopectin. High-

amylose starches are more white and opaque, while

tbl0001 Table 1 Typical differential scanning colorimetry starch crystalline melting (gelatinization) data when starch is exposed to excess

water

Starch Endothermpeakstart (



C) Endothermpeak

(



C) Endotherm peak end (



Waxy corn (< 1% amylose) 61.8 72.7 82.4

Normal dent corn (25% amylose) 61.8 71.4 80.1

53% Amylose corn 62.6 74.8 104.6

70% Amylose corn 62.3 92.2 108.4

Waxy sorghum (< 1% amylose) 70.8 76.1 82.7

Normal sorghum (24% amylose) 69.0 74.5 83.6

Waxy rice (< 1% amylose) 63.6 72.0 79.0

28% Amylose rice 68.6 77.5 86.2

Potato starch (16% amylose) 56.0 61.5 68.2

Endotherms peaks, depending upon convention, are displayed as either going upward from a baseline or as dropping below the baseline.

STARCH/Functional Properties 5573

high-amylopectin gels are more clear and have a

slightly gray-white appearance. Potato starch, be-

cause its amylose component has a significantly

higher molecular weight than that of other starches

(corn amylose 100 000–200 000; potato amylose

400 000), has gels whose physical/chemical character-

istics are closer to waxy starches than to cereal grain

starches with equivalent amylose contents. Some

amylose within potato starch associates by folding

back on itself. Because of intramolecular hindrance,

the association is not as tight as two separate amylose

polymers lined up parallel to each other.

Starch Gel Characteristics

001 0 In addition to differences in starch gelatinization

properties discussed elsewhere, native starches have

widely differing gel-forming properties. These prop-

erties are summarized in Table 2.

0011 The characteristics that starch imparts during gel-

atinization can be substantially influenced by chem-

ical or physical modification of the starches. Much of

the starch used in commercial food processing has

been modified in some manner to impart desirable

swelling, thickening, gelatinization, and retrograd-

ation properties. Chemical modification of native

starches can result in decreased swelling, changes in

gelatinization temperature, and increased or de-

creased gel and retrograded starch-forming capacity.

Most modifications, however, take advantage of the

inherent properties of the native starch that is being

modified.

Starch Inclusion Complexes

001 2 Starches form inclusion complexes with several

chemical constituents, including fatty acids and

mono- and diglycerides, emulsifiers, and many small

flavor compounds. In general, starch complexes are

formed when molecules bind within the alpha-helical

structures found in amylose and portions of amylo-

pectin polymers. Starch inclusion compounds, how-

ever, also encompass those instances when a

nonstarch chemical constituent is entrapped within

the three-dimensional network of starch polymers.

Starch–Iodine Binding

0013One of the simplest tests for identifying the presence

of starches is by the application of iodine solutions to

the sample in question. Since iodine can readily pene-

trate raw starch granules, gelatinization is not a pre-

requisite for staining. Starch will typically stain a

vivid purple-blue color; waxy starches stain red. A

central core is formed by amylose’s alpha-helical

structure; polyiodide ions are typically found within

this core. Similar binding also takes place with outer

chains of amylopectin, as well as smaller carbohy-

drates. The affinity of starch for iodine decreases as

the starch chain-length is decreased. Since linear por-

tions of starches are the primary binder of iodine,

isoamylase- or pullalanase (breaks alpha-1,6 branch

points)-treated starches show a far smaller decrease in

iodine affinity versus starches treated with acid or

alpha-amylases. Iodine complexing is also tempera-

ture-sensitive. Binding is reduced as temperatures

increase above 40



C; this corresponds to the change

in starch structure from helical to coil-shaped. If

allowed to cool, the iodine–starch complex reforms.

Starch–Lipid Complexes

0014Inclusion complexes similar to those involving iodine

also form between starch and lipid components. This

effect was first noticed when it was discovered that

tbl0002 Table 2 Starchpropertiesduringcookinginwater(5%starchconcentration)

Starchproperty

duringcooking

CornWaxycornandsorghumHigh-amylosecorn

PotatoTapiocaRiceWheat

Rateofgranular

swelling(onsetof

thickening)

SlowerSlowerVeryslowFastFastFastSlower

Extent of granule

swelling and solubility

(viscosity during cooking)

Moderate High Low to moderate Very high Moderate Moderate Low

Swollen granule fragility

(cooked starch susceptibility

to shear)

Moderate High Moderate High Moderate Moderate Very low

Retrogradation of linear

polymers (gel viscosity)

Very high Very low Extremely high Low Low Low Moderate

High-amylosestarchesrequiremoreextensivecooking(togelatinize)thanregularstarches(see Table 1). Table 2 dataassumeextensivecooking.

When not fully cooked, high-amylose corn starch paste viscosities are substantially lower than for cooked regular starches.

Certain data adapted, in part, from Zobel HF (1984) Gelatinization of starch and mechanical properties of starch pastes. Starch Chemistry and Technology,

2nd edn. Orlando: Academic Press.

5574 STARCH/Functional Properties

lipids interfere with amylose–iodine complex forma-

tion. The carbon-chain segment of a lipid is located in

the alpha-helical structure of amylose molecules and

in long, linear segments of amylopectin (or amylopec-

tin-like ‘intermediate material’) molecules. Hence,

the binding of lipid is somewhat dependent on the

molecular availability or solubility of starch poly-

mers, especially amylose. If starch is fully gelatinized

(amylose-solubilized), as the chain-length of satur-

ated fatty acids increases, the amount of starch-lipid

binding also increases. Also, there is less binding of

lipids (given equivalent lipid solubility) to previously

gelatinized starch as the temperature of starch–lipid

mixtures increases. This is in contrast to an increase

in binding that occurs between starches and lipids

during the gelatinization process. Since starch–lipid

binding is not a surface effect, amylose molecules are

not readily available for binding with lipid if they are

not gelatinized. Therefore, as the starch granule

swells during gelatinization, more amylose is molecu-

larly available for binding with lipid.

0015 Monoglycerides generally bind less to starch

than their corresponding fatty acid. A combinat-

ion of lower lipid solubility and a slightly increased

three-dimensional incompatibility between the

monoglyceride and central binding core found within

helical amylose probably account for this difference.

Incompatible molecular shape also accounts for the

decrease in lipid binding of unsaturated lipids as

compared to their saturated counterparts; double

bonds found in unsaturated lipids decrease subtle

molecular movements in solution and form a molecu-

lar shape that may partially interfere with lipid

inclusion within the amylose core.

0016 The binding between starch and lipids has practical

implications in the formulation of several starch-

containing food products. For example, various sur-

factants (mono- and diglycerides) and fats are widely

used to reduce bread staling. During the breadmaking

process, starch granules become swollen in the pres-

ence of amylose-complexing lipid components. Since,

during baking, starch–lipid interactions take place

while the granule is swelling (50–60



C), but before

gelatinization, lipids can complex with amylose prior

to its becoming soluble. As a result, starch granule

swelling and gelatinization are reduced. Thus, less

free amylose is subsequently available to hydrogen-

bond (retrograde) with other amylose molecules. In

addition, because of the reduced swelling, the mois-

ture distribution between the wheat gluten and starch

is altered, contributing to a softer crumb structure.

Interestingly, the softening of crumb structure by

amylose–surfactant complexing does not significantly

affect the mechanism by which bread firms, i.e., the

retrogradation of amylopectin. Surfactants have only

a low affinity for complexing with amylopectin, al-

though they may act via other mechanisms to retard

staling.

Other Starch Inclusion Compounds

0017Flavor compounds and similar low-molecular-weight

organics also readily complex with starch. The pri-

mary binding mechanism, as with iodine and lipids, is

the formation of an inclusion complex within the

helical structure of amylose. In addition, some flavor

molecules may become physically entrapped by the

long polymer chains of starches, although these mol-

ecules would be less likely to be retained during stor-

age. The commercial application of flavor inclusion

complexes is the preparation of dry flavor com-

pounds using starch and liquid flavor ingredients.

Inclusion compounds are most likely to form when

starch is molecularly dispersed in the presence of

flavor molecules. When hot water is used as a dispers-

ant, the reformation of helical segments (from a coil)

in amylose forms inclusion complexes in the presence

of flavor compounds. Commercial application of this

property includes the encapsulation of pollen flavor

for Honey Bee food, and the encapsulation of thou-

sands of flavoring substances for dry flavoring mixes

for direct consumer use and as an aid in commercial

food processing. The inherent property of starches to

form inclusion complexes can be enhanced or re-

duced by chemical modification.

See also: Iodine: Properties and Determination; Starch:

Structure, Properties, and Determination; Sources and

Processing; Modified Starches; Resistant Starch