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

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Furthermore, texture in foods can be modified by

changing the texture of the soya bean materials.

Texturing

0043 Numerous ingenious methods have been patented to

add chewy textures into flours, concentrates, and

isolates. The most commonly used procedures are

extrusion and spinning.

0044 Extrusion is used mainly with flours and concen-

trates and is a method of both heating and forming.

The extruder is a screw or auger rotating within a

jacketed barrel. As the flour or concentrate is moved

through the auger, it is heated by friction and/or by

steam jacketing. High pressures are developed in the

nose of the barrel just before the exit. As the material

is forced through the exit port, it is shaped and puffed

due to the sudden drop in pressure.

0045 Spinning applies only to soya bean isolates. A con-

centrated solution of isolate is prepared and forced

through spinnerets (platinum plates with small holes)

into an acid bath. The protein precipitates in the acid

as a continuous fiber, and the spun fibers can be

wound together into a bigger ‘tow.’

0046 With both extruded and spun soya bean products,

flavors, colors, fats, etc., can be added to simulate

meats or seafoods.

Soyfood Manufacture

0047 Traditional soybean foods are classified into two

groups: nonfermented foods, including regular,

deep-fried, frozen-dried, roasted tofu, soybean pro-

tein film (yuba), and soybean sprouts; and fermented

soybean foods such as miso, soy sauce (shoyu), and

fermented whole soybeans (natto) and Tempeh.

Soymilk

0048 Soymilk is a very popular beverage with the Chinese,

but considerably less so with the Japanese and West-

ern populations. However, soymilk production has

increased in the USA due to lipoxygenase-null soya

beans and improved processing methods that remove

or limit the ‘beany’ flavor of the milk. The health

benefit of soy protein to reduce cholesterol (heart

disease) has also caused an increase in soymilk sales

(and soya used in foods) as the US FDA now allows a

health claim if the food contains at least 6.25 g of soy

protein with low levels of cholesterol, saturated fat,

and total fat. Soymilk is very important to tofu pro-

ducers because it is the intermediate product in the

manufacture of tofu.

0049 Many Japanese, like their Western counterparts,

find the odor of soymilk undesirable. This odor is

formed by the oxidation of specific unsaturated

fatty acids by the enzyme lipoxygenase during seed

grinding. Understanding how off-flavors and undesir-

able flavors interact with soy proteins and similar

seed constituents may lead to improved processing

systems. Breeding programs at Purdue University

(West Lafayette, IN), Iowa State University (Ames,

IA), and the Japanese Ministry of Agriculture, For-

estry, and Fisheries (Tsukuba, Japan) have developed

lipoxygenase-null varieties.

0050Additionally, odor formation may be circumvented

by heat inactivation of the enzyme before the beans

are ground (significantly lowering yields), or by mask-

ing the flavor with additives. (See Soy (Soya) Beans:

Properties and Analysis; Soy (Soya) Milk.)

0051Soymilk is traditionally made by soaking soybeans

in water overnight, then grinding the beans with

water added during grinding. Alternatively, full fat

flakes, grits, or flour can be used to produce the

soymilk slurry. The resulting slurry is boiled and

stirred for 1–30 min (depending on the temperature).

This heating step improves the nutritional value of the

milk (by inactivating trypsin inhibitors) and improves

the flavor (by inactivating lipoxygenase and volatiz-

ing some of the off-flavor compounds that result

during grinding). Heating also increases the shelf-life

of the milk by reducing its microbial load. The heated

slurry is then filtered through a cloth or nylon bag to

separate the undispersible fiber residue (okara) from

the soymilk. The resulting soymilk may then be

flavored, if desired. It may also be pasteurized,

homogenized, or sterilized before being bottled,

aseptically packaged, or retorted.

0052Typically, high-protein, clear or yellow hilum,

large-seeded soybeans are preferred for soymilk pro-

duction. Two hundred grams of soybeans will yield

about 1 l of soymilk. Soymilk can be made more shelf-

stable by spray-drying or roller-drying it into a dry

powder (as is done with cows’ milk). Spray-dried

soymilk can be instant in beverages, confections,

and meat fillers.

0053Although soymilk has a composition similar to

cow’s milk, the oil-to-protein ratio is lower. For this

reason, reconstituted soymilk is often supplemented

with oil. In addition, soymilk may be supplemented

with sugar to enhance its palatability. These soymilk

beverages often contain fruit juice, cocoa, flavors (ar-

tificial or natural), stabilizers, and other ingredients to

enhance customer acceptance by masking soy flavors.

Tofu

0054Tofu has been produced in Japan for more than 2000

years. It was introduced from China along with the

agronomic introduction of soybeans. The shelf-life of

tofu can be quite variable, ranging from 1 to 5 days

SOY (SOYA) BEANS/Processing for the Food Industry 5387

for fresh tofu, 3 weeks to 1 month for pasteurized

tofu in the package, and 6 months to 2 years for tofu

processed aseptically. The initial microbial load and

storage temperature largely govern the shelf-life.

Some products (such as silken tofu) are more difficult

to transport because they are susceptible to tempera-

ture abuse and physical damage.

0055 Large-scale factories in Japan consume 2–3 tonnes

of soybeans per day. These large manufacturers have

developed integrated production and marketing

systems. From the factory to the supermarket show-

case, superior product quality is ensured by sophisti-

cated, timely distribution using refrigerated transport

and display systems. Likewise, in Japan, some super-

market chains are now producing their own tofu in-

house, where it is kept in refrigerated display cases.

Aseptically packaged tofu gained popularity in the

USA because it has a longer shelf-life and can be

stored and transported easily.

0056 Different types of tofu can be made from the soy-

milk by altering the starting materials (beans, full fat

flakes, etc.), solids content, temperature of coagula-

tion, type of coagulant, breaking of the curds, and

pressing. Firm tofu (called momen in Japan) is more

cheese-like in texture, whereas Kinugoshi (silken or

soft) tofu has a much more homogenous, delicate

texture, is softer, and has a smoother feeling than

regular momen tofu. Reduced fat, grilled, backed,

and flavored tofus can be made by altering the

starting material or by grilling, baking, and flavoring.

Packed tofu differs from other forms because it is

processed within its sealed retail container. Asepti-

cally packaged tofus are packaged tofu products

made from all ingredients commercially sterilized

before aseptic packaging. Deep-fried tofu includes

three main types: namage (single-fried tofu), aburage,

and gan-modoki (double-fried tofus). Kori tofu is a

frozen, dehydrated tofu. Upon rehydration, its tex-

ture is very different from the original tofu in that it is

more meat-like in texture, and it acts as a sponge in

soups, etc.

Yuba

0057 Yuba is a soy protein film produced from the surface

of cooling soymilk. Some consumers use fresh film for

cooking, but others prefer dried yuba. It is packaged

in sheet form, small rolls, or pieces of various shapes

and sizes, and it can be used in a variety of food

applications.

Texturized Soy Protein Foods

0058 Texturized soy protein products, made by texturizing

whole soybeans, soy flour, concentrates, or isolates

with single and twin-screw extruders are used to

make meat analogs and snacks.

Fermented Soyfoods

0059Fermented soyfoods usually contain salt and the

byproduct of a desirable fermentation. They have a

relatively long shelf-life compared with fresh soy

products like traditionally prepared momen tofu.

Miso

0060Miso is made in Japan by mixing cooked soybeans

with rice koji (fermented rice started culture) and salt

water. This material is then fermented for several

months. There are several miso products that differ

in the type of koji starter (a high ratio of rice to

soybeans results in a more lightly colored and sweeter

miso) used for the fermentation. Miso is used in

soups, as a spice, and in coatings for vegetables and

meat products.

Soya Sauce (Shoyu)

0061Soy sauce (shoyu) manufacturing was modernized

much earlier than other soy foods. Defatted soya

flakes are used instead of whole soyabeans because

the soybean oil separates and collects on the surface

of the sauce. Both fermentation and acid hydrolysis

are used to produce different types of soy sauce that

are now commonly available around the world.

Natto

0062Natto is cooked whole soybean product fermented

with Bacillus natto. Small soybeans are often pre-

ferred for natto production. The soybeans are fer-

mented until a white, sticky glutamic acid polymer

is formed, which gives the natto a distinctive flavor

and sticky and stringy characteristics.

Tempeh

0063Tempeh is a fermented whole soybean product that

originated in Indonesia but is equally popular in Ma-

laysia. Tempeh is usually cooked before it is eaten.

Preparation usually involves frying, deep-fat frying,

or baking the product. It is also added to soups and

fast foods, and is used as a meat replacement in main

dishes.

See also: Dressings and Mayonnaise: The Products and

Their Manufacture; Emulsifiers: Uses in Processed

Foods; Fats: Uses in the Food Industry; Margarine:

Methods of Manufacture; Protein: Chemistry; Soy (Soya)

5388 SOY (SOYA) BEANS/Processing for the Food Industry

Beans: Processing for the Food Industry; Properties and

Analysis; Soy (Soya) Milk; Vegetable Oils: Oil

Production and Processing

Further Reading

Erickson DR (ed.) (1990) Edible Fats and Oils Processing:

Basic Principles and Modern Practices. Champaign, IL:

American Oil Chemists’ Society.

Erickson DR (ed.) (1995) Practical Handbook of Soybean

Processing and Utilization. Champaign, IL: AOCS Press

and St. Louis, MO: United Soybean Board.

Erickson DR, Pryde EH, Brekke OL, Mounts TL and Falb

RA (eds) (1980) Handbook of Soy Oil Processing

and Utilization. St. Louis, MO: American Soybean As-

sociation and Champaign, IL: American Oil Chemists’

Society.

Kinsella JE and Soucie WG (eds) (1989) Food Proteins.

Champaign, IL: American Oil Chemists’ Society.

Liu, KeShun (1997) Soybeans: Chemistry, Technology,

and Utilization. New York: Chapman & Hall, ITP

Publishing.

Snyder HE and Kwon TW (1987) Soybean Utilization.

New York: Van Nostrand Reinhold.

Weiss TJ (1983) Food Oils and their Uses, 2nd edn. West-

port, CT: AVI.

Properties and Analysis

E G Hammond, P A Murphy and L A Johnson, Iowa

State University, Ames, IA, USA

Background

0001 Soya beans vary widely in their appearance and

composition. The main constituents of soya beans,

in descending order, are protein, oil, complex carbo-

hydrates, oligosaccharides, simple sugars, and min-

erals. Phytochemicals in soybeans have gained

prominence in the last 10 years, especially isofla-

vones, saponins, and phenolic acids, because of their

potential health-protective effects. Soya isoflavones

in particular have been associated with a variety of

other improved physiological states, including re-

duced cholesterol levels, anticarcinogenicity, and im-

proved bone health.

0002 Most legumes contain 20–25% protein, but soya

beans typically contain 30–45% protein (moisture-

free basis), and average 35.35% at 13% moisture.

Levels as high as 55% protein (moisture-free basis)

have been observed. The oil content typically ranges

from 15 to 24% and averages 19.16% on a 13%

moisture basis. The composition varies with growing

area; for example, soya beans from northern and

midwestern areas of the USA typically contain 1.5–

2% less protein and 0.2% more oil than beans grown

in southern states. One Iowa soybean processor has

begun offering premiums for soybeans containing

higher-than-normal oil contents.

0003The total crude fiber content of soya beans is about

4.4% at 13% moisture. These materials are predom-

inantly cellulose, hemicellulose, and pectin. The outer

hull, typically 8% by weight of the bean, is especially

rich in crude fiber (35%). Fiber is hard to digest and

contributes little to the nutrition of swine and poultry,

the primary markets for soya bean meal.

0004The total sugar content of soya beans is 4.9–9.5%

at 13% moisture. Of the total sugar content, about

60% is sucrose, 10% raffinose, and 30% stachyose.

Raffinose and stachyose are oligosaccharides, causing

flatulence (intestinal gas) in humans and reduced feed

efficiency in livestock.

0005Isoflavone content of soya beans varies from 800

to 4000 mgg

1

on an aglycon basis. Soya contains 12

isoflavones, namely genistein, daidzein and glycitein,

as b-glucosides, 6

-O-malonylglucosides, 6

-O-acet-

ylglucosides and aglycons. Soya saponin concentra-

tions vary in a similar manner to isoflavones ranging

from 2 to 12 mmol g

1

0006Because of the variety of glucoside forms of sap-

onins and isoflavones, their concentrations should be

expressed in micromoles. The isoflavones and sap-

onins fractionate with the seed protein and are not

lipid-soluble. As soya beans are fractionated into food

ingredients, the forms of the isoflavones and saponins

are rearranged depending on the extent of heat pro-

cessing and the method of protein fractionation.

0007Generally soya bean meal is sold on a 44% protein

basis and 48% when soya beans are dehulled (Hi-Pro

meal). The average price of soybeans during the

1997–98 crop year was $6.47 per bushel (0.259 kg).

Oil sells for about twice the value of meal. Typical

selling prices for soya bean oil were 25.7 cents per

pound (0.566 kg) and meal (44% protein) for $197

per ton or 9.9 cents per pound (0.566 kg) during

1998. The 2000 crop year prices were considerably

lower.

0008Recent developments in breeding and genetic

modification of soya beans have achieved: new fatty

acid compositions, e.g., < 2% linolenic acid and

> 80% oleic acid to improve oxidative stability;

removal of all lipoxygenase isozymes to improve the

flavor of soya protein ingredients; elimination of

oligosaccharides to eliminate intestinal gas; altered

protein and amino acid composition to improve

functional and nutritional properties; and inserted

SOY (SOYA) BEANS/Properties and Analysis 5389

vaccines for human and animal health. While genetic

engineering holds great promise for the future (health-

ier foods, reduced environmental impacts, increased

yield, and lower input costs), consumers have begun

to question the safety of this new technology.

Proteins

0009 Glycinin and b-conglycinin constitute 65–80% of the

protein fraction or 25–35% of the seed weight. Gly-

cinin is classified as a legumin, characterized by mo-

lecular weights of 300–400 kDa and sedimentation

coefficients of 11S + 1S. b-Conglycinin is a vicilin,

which is in the range of 150–250 kDa, is glycosylated,

and has sedimentation coefficients of 7S + 0.5S.

In soya beans, the major proteins, glycinin and

b-conglycinin, are frequently described by their re-

spective sedimentation values, 11S and 7S, but such

fractions are often impure. The 7S fraction of soya

protein contains, in addition to b-conglycinin, lectins,

lipoxygenase, and b-amylase.

0010 b-Conglycinin is a trimer and/or hexamer in solu-

tion and probably occurs in both forms in the seed.

Two similar peptides, a and a

(57 kDa), and a gly-

cosylated b peptide (42 kDa) are assembled in the

mature protein in a nonrandom set of seven forms,

, ab

, aa

b, a

, a

, and b

with molecular

weights of 125–171 kDa. The a and a

subunits have

1–2 mol of cysteine per mole of peptide, while the

b peptide has no cysteine.

0011 Glycinin is a hexamer, although in older literature,

it is referred to as a dodecamer. It is composed of six

nonrandomly paired acidic and basic peptides. The

acidic peptides have molecular weights of 44, 37, and

10 kDa; the basic peptides are 20 kDa. The acidic–

basic (AB) pairs have been identified in the experi-

mental line, CX635-1-1-1, and are shown in Table 1.

Seven acidic and eight basic peptides have been iden-

tified in 18 cultivars. There appear to be sulfur-rich

and sulfur-poor AB pairs.

0012 Soya beans contain two main classes of protease

inhibitors or trypsin inhibitors (TI), although there

appear to be many isogenic variants. The two

principal classes are the Kunitz inhibitor with a mo-

lecular weight of 21 500 and the Bowman–Birk in-

hibitor, with a molecular weight of 8000. The Kunitz

inhibitor acts only on trypsin, while the Bowman–

Birk protein inhibits both trypsin and chymotrypsin.

Moist heat treatment denatures about 90% of the TI

activity with the residual being heat-stable. TI affects

animals of guinea-pig size and smaller but has little

effect on larger animals, except for weanling pigs.

Recently, the Bowman–Birk TI has been demon-

strated to be an anticarcinogen and is currently in

Phase II cancer trials. There are reports that TIs

exert a carcinogenic effect on rodents. There has

been interest in recovering and purifying soya bean

protease inhibitors to treat AIDS patients.

0013The United States Food and Drug Administration

has approved a health claim for soya protein that, as

part of a heart-healthy diet, 25 g per day of soya

protein will contribute to improved cardiovascular

health. (See Trypsin Inhibitors; Protein: Chemistry.)

Lipid

0014Soya bean lipids contain about 2–5% phospho-

lipids, depending on the growing conditions, and

1.6% unsaponifiables. The balance is chiefly triacyl-

glycerols.

0015Oleic (18:1), linoleic (18:2), palmitic (16:0), stearic

(18:0), and linolenic (18:3) acids are present in soya-

bean oil, along with traces (less than 1%) of myristic

(14:0), palmitoleic (16:1), heptadecanoic (17:0), eico-

senoic (20:1), arachidic (20:0), behenic (22:0), and

erucic (22:1) acids. The range of acyl groups present

in soya bean oil has been extended by mutation

breeding and selection to the values reported in

Table 2.

0016The acyl groups are distributed asymmetrically

in the triacylglycerols with all the saturates on the

sn-1 and -3 positions and linoleate concentrated on

the sn-2 position. Generally, the sn-1 contains more

palmitate and stearate than sn-3, and the oleate is

enriched on sn-3. Phospholipids contain the same

acyl groups found in the triacylglycerols, but the

tbl0001 Table 1 Glycinin acidic–basic complexes from CX635-1-1-1

Acidic^basic complex S-amino acids Molecular weight

14 57

12 57

14 57

962

367

From Nielsen NC (1985) Structure of soy proteins. In: Altschul AM and

Wilcke HL (eds) New Protein Foods Vol. 5. Seed Storage Proteins, pp. 27–64.

New York: Academic Press.

tbl0002Table 2 Range of acyl group percentages produced in soya

bean lipids by mutation breeding and genetic engineering, and

the composition of a typical unselected variety

Range Typical value

Palmitate 3.5–30 10

Stearate 2.5–32 4

Oleate 8.0–85 26

Linoleate 2.0–60 52

Linolenate 1.8–13 8

5390 SOY (SOYA) BEANS/Properties and Analysis

concentration of palmitate is generally higher

and that of oleate lower. Phosphatidyl choline

(50%), ethanolamine (26%), and inositol (18%)

are the chief phospholipid components along with

lower concentrations of phosphatidic acid and

phosphatidyl serine.

0017 The unsaponifiables contain sterols, hydrocarbons,

and tocopherols. The chief sterols (3.5 mg pergram of

oil) are b-sitosterol, campesterol, and stigmasterol.

The tocopherols (about 1.25 mg per gram of oil) are

typically more than 70% gamma with smaller

amounts of delta and alpha. (See Fats: Classification;

Fatty Acids: Properties.)

Methods to Measure Composition

0018 Proximate analyses for moisture, protein, crude free

fat, crude fiber, ash, and total carbohydrate have been

adopted by the American Oil Chemists’ Society, the

American Association of Cereal Chemists, and the

Association of Official Analytical Chemists. All com-

position values for soya beans are reported either on a

moisture-free basis or at 13% moisture.

0019 Several methods are acceptable for moisture deter-

mination, but the most widely used procedure

involves measuring the weight loss when drying the

ground sample for 3 h at 130



C. In South America a

Karl Fischer titration is frequently used.

0020 Protein is estimated from Kjeldahl nitrogen. The

nitrogen content is multiplied by a factor of 6.25 to

convert to protein values despite the major soya

protein, glycinin containing only 17.5% nitrogen

(equivalent to a N conversion factor of 5.7).

0021 Oil content is determined as crude fat by continu-

ously extracting dried ground samples with petrol-

eum ether for 5 h. Total fat, which includes bound

fat as well as free fat, requires acid hydrolysis of the

sample prior to extraction. In recent years, the use of

near-infrared reflectance and near-infrared transmit-

tance has become widespread for rapid estimation of

grain composition, especially moisture, protein, and

oil. These spectrophotometers must be calibrated

against the standard wet chemical methods described

above. Moisture is also routinely measured by

electrical capacitance.

0022Crude fiber is measured as the weight loss on incin-

eration of the oven-dried residue remaining after

digestion of the sample with boiling dilute sulfuric

acid followed by boiling dilute sodium hydroxide.

0023Ash is primarily composed of noncombustible min-

erals and is determined by heating the ground sample

in a muffle furnace for 2 h at 600



C. Soya beans

contain about 4.7% ash at 13% moisture. Total car-

bohydrate is often estimated as the difference after

subtracting other constituents. This method does not

discriminate between oligosaccharides and other

sugars, and it often gives inflated values. Sugars can

be extracted with hot aqueous ethanol and quantified

by gas or liquid chromatography.

0024Acyl group composition of soybean lipids generally

is determined by gas chromatography. Lipid classes

are separated by thin-layer or liquid chromatograms.

0025Qualitative and quantitative analyses of the

individual proteins have been performed by immuno-

electrophoresis and/or sodium dodecyl sulfate poly-

acrylamide electrophoresis.

0026Isoflavones are assayed by reverse-phase high-

performance liquid chromatography (RP-HPLC)

of 80% acetonitrile extracts and absorbance detec-

tion at 250–260 nm. Methanol and ethanol tend

to underextract some isoflavone forms. Saponin

analysis is typically by RP-HPLC with absorbance

detection at 290 and 205 nm, depending on the

form, although older methods used silica-based thin-

layer chromatography. The major impediment to

accuracy has been the lack of suitable standards,

although most of the isoflavone forms are now

available. (See Analysis of Food; Chromatography:

High-Performance Liquid Chromatography; Gas

Chromatography.)

Grading Standards

0027Each exporting country has unique standards, but

the grade standards established by the Federal Grain

Inspection Service (FGIS) for the USA listed in Table 3

tbl0003 Table 3 Official grades and grade requirements of the Federal Grain Inspection Service, United States Department of Agriculture

Grade Minimum test

weight kg/L

(lbs/bushel)

Maximum limits

Damagedkernels Foreign

material (%)

Splits (%) Soyabeans of

other colors (%)

Heat-damaged (%) Total (%)

US No. 1 0721 (560) 0.2 2.0 1.0 10.0 1.0

US No. 2 0695 (540) 0.5 3.0 2.0 20.0 2.0

US No. 3 0669 (520) 1.0 5.0 3.0 30.0 5.0

US No. 4 0631 (490) 3.0 8.0 5.0 40.0 10.0

US sample grade

SOY (SOYA) BEANS/Properties and Analysis 5391

are typical. Soya beans are divided into two classes

based on color: yellow soya beans and mixed soya

beans. Each class is divided into four numerical

grades and a US sample grade. Special grades (e.g.,

garlicky, infested) are provided to emphasize special

qualities affecting the value, and are added to, and

made part of, the grade designation. Six factors are

considered in assessing a grade designation: test

weight, heat damage, total damage, foreign material,

splits, and soya beans of other colors. Although pro-

tein and oil contents are not part of the official

grading standards, they may be specified in some

markets. Near-infrared transmission is used for

rapid estimation of moisture, protein, and oil con-

tents.

0028 Test weight is determined on a 136 L sample

before removing foreign material using an Official

Test Weight Apparatus. Foreign material is deter-

mined by sieving. Splits are determined by sieving a

portion of the grain after removing foreign material.

Damaged kernels are determined by hand-picking

after removal of foreign material.

See also: Chromatography: Thin-layer Chromatography;

High-performance Liquid Chromatography; Dietary

Fiber: Properties and Sources; Fats: Occurrence;

Protein: Food Sources; Soy (Soya) Bean Oil; Soy (Soya)

Beans: The Crop; Processing for the Food Industry;

Dietary Importance

Further Reading

Brumm TJ and Hurburgh CR (1990) Estimating the

processed value of soybeans. Journal of the American

Oil Chemists’ Society 67: 302–307.

Erickson DR (ed) (1995) Practical Handbook of Soybean

Processing and Utilization. Champaign, IL: American

Oil Chemists Society.

Erickson DR, Pryde EH, Brekke OL, Mounts T and Falb RA

(eds) (1980) Handbook of Soy Oil Processing and Util-

ization. Champaign, IL: American Oil Chemists’ Society.

FGIS (1990) Federal Grain Inspection Handbook, Book II.

Washington DC: Federal Grain Inspection Service.

Hammond EG (2000) Genetic alteration of food fats and

oils. In: Chow CK (ed.) Fatty Acids in Foods and their

Health Implications, 2nd edn. New York: Marcel

Dekker.

Hurburgh CR, Brumm TJ, Quin JM and Hartwig RA

(1990) Protein and oil patterns in the U.S. and world

soybean markets. Journal of the American Oil Chemists’

Society 67: 966–973.

Murphy PA, Song TT, Buseman G et al. (1999) Isoflavones

in retail and institutional soy foods. Journal of Agricul-

tural and Food Chemistry 47: 2697–2704.

Nielsen NC (1985) Structure of soy proteins. In: Altschul

AM and Wilcke HL (eds) New Protein Foods Vol. 5.

Seed Storage Proteins, pp. 27–64. New York: Academic

Press.

Smith AK and Circle SJ (1978) Chemical composition of the

seed. In: Smith AK and Circle SJ (eds) Soybeans:

Chemistry and Technology, Vol. 1, Proteins, pp. 61–92.

Westport, CT: AVI.

USDA (1999) U.S. Department of Agriculture, Economic

Research Service. In: Golbitz P (ed.) Soya & Oilseed

Bluebook. Bar Harbor, ME: Soytech.

Wang HJ and Murphy PA (1996) Mass balance of isofla-

vones study in soybean processing. Journal of Agricul-

tural and Food Chemistry 44: 2377–2383.

Wu SW, Murphy PA, Johnson LA, Fratzke AR and Reuber

MA (1999) Pilot plant fractionation of soybean glycinin

and b-conglycinin. Journal of the American Oil Chem-

ists’ Society 76: 285–293.

Dietary Importance

A M Fehily, Tinuviel Software, Warrington, UK

Background

0001The soya bean (Glycine max) is a native of China,

where it has been part of the diet for several thousand

years. It has also been important in Japan and Korea

for almost as long. These beans are used to produce

foods that are important components of the diet in the

Far East, e.g., fermented soya products such as tofu,

miso, tempeh, and soy sauce. More recently, soya

beans have become widely used in the Western diet,

being used to produce a range of ingredients: soya

flour and soya protein, which are used to make food-

stuffs such as bread, other cereal products, meat

products, and vegetarian alternatives; soya oil, which

is widely used as a vegetable oil both in domestic

cooking and by the food industry and is also used in

the manufacture of spreadable fats; soya lecithin,

which is used as an emulsifier in many foods; and

soya milk, a vegan alternative to cow’s milk. Soya is

also used to produce infant formulas for those infants

who are intolerant to lactose or cows’ milk protein.

0002Soya can provide a valuable contribution to nutri-

ent intakes and may also have a number of potential

health benefits. This article discusses the composition

of soya beans, the role of soya in the diet, and its

potential health benefits.

Composition

0003Soya beans contain a wide range of nutrients. They

contain some ‘antinutrients’ and also contain other

components, e.g., isoflavones, which may have bene-

ficial effects on health.

5392 SOY (SOYA) BEANS/Dietary Importance

Nutrients

0004 Soya beans contain protein, fat, carbohydrate, vita-

mins, minerals, and fiber.

0005 Protein Soya beans are a good source of protein,

containing 14 g per 100 g. This is more than that in

most other vegetables and more than that in most

other legumes (typically 5–9 g per 100 g), the excep-

tion being peanuts, which contain 26 g of protein per

100 g. In terms of protein quality, soya contains sub-

stantial amounts of most essential amino acids. When

compared with a reference protein (egg), soya pro-

tein, in common with other legumes, is deficient in

sulfur-containing amino acids (the essential amino

acid methionine and the nonessential amino acid cyst-

ine) and has a higher content of lysine. Combining

legumes with cereals provides a meal with a high

protein quality, as cereals have adequate amounts of

sulfur-containing amino acids but are deficient in

lysine. (See Protein: Food Sources.)

0006 Carbohydrate Soya beans contain 5 g of carbohy-

drate per 100 g. This is lower than that of many other

legumes. Of the total carbohydrate, 37% is starch,

41% is sugars, and 22% is oligosaccharides. The

sugars present are sucrose, fructose, and glucose.

(See Carbohydrates: Classification and Properties.)

0007 Fat Soya beans contain 7 g of fat per 100 g. This is

more than that in other legumes, most of which are

low in fat. The exception to this is peanuts, which

contain 46 g of fat per 100 g. The fatty acid compos-

ition of soya has a high ratio of unsaturates to satur-

ates. Of the fatty acids, 16% are saturates, 24% are

monounsaturates, and 60% are polyunsaturates. The

polyunsaturated fatty acids present are the essential

fatty acids linoleic acid (18:2n-6) and a-linolenic acid

(18:3n-3). (See Fats: Classification.)

0008 Minerals Soya beans contain significant amounts of

several minerals: calcium, iron, magnesium, potas-

sium, phosphorus, and zinc (see Table 1). One hun-

dred grams of soya beans provide about 12% of the

daily reference nutrient intake (UK) for calcium, 20%

of that for iron, 23% of that for magnesium, 15% of

that for potassium, 45% of that for phosphorus, and

13% of that for zinc (see Figure 1).

0009 Vitamins Soya beans contain a number of water-

soluble vitamins: thiamin, riboflavin, niacin, vitamin

and folate (see Table 1). One hundred grams of

soya beans provide about 15% of the daily reference

nutrient intake (UK) for thiamin, 8% of that for

riboflavin, 21% of that for niacin, 19% of that

for vitamin B

and 27% of that for folate (see

Figure 1). Soya beans also contain vitamin E: 1 mg

per 100 g. (See Vitamins: Overview.)

0010Fiber Soya beans provide a valuable source of fiber

in the diet: 6 g of nonstarch polysaccharides (NSP) per

100 g. Of this, 44% is soluble fiber, and 56% is insol-

uble fiber. One hundred grams of soya beans provide

0 1020304050

Folate

Niacin

Calcium

Iron

Magnesium

Potassium

Phosphorus

Zinc

Thiamin

Riboflavin

Vitamin B

fig0001Figure 1 Vitamin and mineral composition of soya beans in

relation to reference nutrient intakes (percentage of reference

nutrient intake provided by 100 g).

tbl0001Table 1 Vitamin and mineral composition of soya beans

Amount per 100 g as consumed

Sodium 1 mg

Potassium 510 mg

Calcium 83 mg

Magnesium 63 mg

Phosphorus 250 mg

Iron 3.0 mg

Copper 0.32 mg

Zinc 0.9 mg

Manganese 0.7 mg

Selenium 5 mg

Iodine 2 mg

Vitamin A (retinol equivalents) 1 mg

Vitamin D 0 mg

Vitamin E 1.13 mg

Thiamin 0.12 mg

Riboflavin 0.09 mg

Niacin equivalents 2.7 mg

Vitamin B

0.23 mg

Vitamin B

0 mg

Folate 54 mg

Pantothenate 0.18 mg

Biotin 25.0 mg

Vitamin C Trace

Source: McCance and Widdowson’s The Composition of Foods (1991) 5th edn.

Royal Society of Chemistry and Ministry of Agriculture Fisheries and Food.

Crown copyright is reproduced with the permission of the Controller of Her

Majesty’s Stationery Office. HMSO: London.

SOY (SOYA) BEANS/Dietary Importance 5393

33% of the daily dietary reference value (UK) for

fiber. (See Dietary Fiber: Properties and Sources.)

Antinutrients

0011 Raw soya beans contain a number of substances that

may have detrimental effects on digestion and other

metabolic processes (lectins, goitrogens, and digestive

enzyme inhibitors). These substances are, however,

inactivated by appropriate cooking of the beans or,

in the case of goitrogens, counteracted by adequate

iodine intake. (See Plant Antinutritional Factors:

Characteristics.)

0012 Lectins Lectins, also known as hemagglutinins, are

present in raw soya beans and in other legumes. They

are, however, heat-labile and are inactivated when the

beans are properly cooked. In experimental animals,

these polymeric proteins have been shown to cause

damage to red blood cells and intestinal mucosa, and

thereby impaired nutrient utilization and loss of body

weight. In humans, these compounds can result in

nausea, vomiting, diarrhea, and abdominal pain.

0013 Goitrogens Enlargement of the thyroid gland has

been shown to occur in rats fed soya bean meal. The

goitrogenic agent in soya beans is unknown. How-

ever, the effect is counteracted by adequate iodine

intake.

0014 Digestive enzyme inhibitors Raw soya beans con-

tain certain proteins (protease inhibitors) that react

with digestive enzymes (trypsin, chymotrypsin, or

salivary and pancreatic a-amylase), thereby interfer-

ing with the digestion of protein and starch. In

humans, raw soya or isolated protease inhibitors in-

creases levels of cholecystokinin (CCK) and pancre-

atic secretion. It is thought that chronic pancreatic

stimulation may lead to pancreatic hypertrophy,

hyperplasia, and possibly cancer. In rats, raw soya

has been shown to increase the risk of pancreatic

cancer. However, protease inhibitors present in raw

soya are inactivated by heat and are therefore not a

problem in cooked beans. For example, in countries

such as Japan, where soya foods are widely con-

sumed, the incidence of pancreatic cancer is similar

to, or less than, that for Western countries, where

soya forms a relatively small component of the total

diet.

0015 Phytic acid Phytic acid is present in soya beans and

also in other fiber-containing foods. It has been

suggested to reduce the absorption of calcium, iron,

zinc, and vitamin D from the diet. However, these

effects have been observed in in vitro experiments

and not in in vivo studies, even at fiber intakes at

the upper limit of the normal human consumption

range. In addition, levels of micronutrients tend to

be higher in fiber-rich foods than in fiber-poor foods.

Thus, adverse effects of phytic acid on nutrient

absorption are likely to be unimportant at the levels

of fiber normally consumed in the human diet. (See

Phytic Acid: Nutritional Impact.)

Isoflavones

0016Soya beans contain isoflavones, a group of com-

pounds that are structurally similar to estradiol (phy-

toestrogens). Soya beans contain high amounts of the

isoflavones genistein and daidzein (see Figure 2) and

smaller amounts of glycitein, primarily in the form of

glycosides: genistin, daidzin, and glycitin (total iso-

flavone content of 180 mg per 100 g). The glycosides

are hydrolyzed in the gut by a bacterial enzyme,

glucose being removed to produce the aglycone

forms (genistein, daidzein, and glycitein). Daidzein

and genistein have been shown to have a weak estro-

genic activity and are able to bind with a low affinity

to estrogen receptors, the affinity being greater for

b-receptors than for a-receptors. Compared with

17b-estradiol, daidzein and genistein have been

reported to have much less potency in producing

estrogenic effects, by about 1000-fold or more.

0017In the 1940s, it was reported that phytoestrogens

may exert adverse effects on uterine and ovarian

function. This was because sheep grazing on pastures

containing a particular type of clover (Trifolium sp.)

rich in formononetin, which is converted to daidzein

in the rumen, developed a widespread infertility. An

infertility syndrome has also been described in captive

cheetah, as a result of soya bean use, the syndrome

Daidzein

Genistein

OOH

fig0002Figure 2 Chemical structure of the main isoflavones present in

soya (daidzein and genistein).

5394 SOY (SOYA) BEANS/Dietary Importance

being reversed by removal of soya from the food. No

adverse effects of soya beans on human fertility have

been reported.

0018 More recently, it has been recognized that isofla-

vones may act either as weak estrogens or as anties-

trogens, competing for estradiol at the receptor

complex, yet failing to stimulate a full estrogenic

response after binding to the nucleus. This fact has

stimulated much research into whether isoflavones

may have a protective role in hormone-related

diseases such as breast cancer.

Role of Soya in the Diet

0019 Soya has been a staple in the diet of many Far Eastern

countries for centuries, e.g., foods such as tofu,

tempeh, and miso. In Western countries such as the

USA and UK, the amount of soya consumed is much

less than in countries such as Japan. In Western coun-

tries, these traditional soya foods are not very widely

consumed but are sometimes used as an alternative to

meat. Soya beans are, however, extremely versatile,

providing a wide range of ingredients that can be used

in foods for most meal occasions, e.g., soya flour,

soya protein, soya oil, soy sauce, and soya lecithin.

For this reason, consumption of foods containing

soya has increased in Western countries over the last

50 years. Nevertheless, soya still forms only a small

part of the total diet. It is noteworthy that of the soya

beans grown world-wide, only about 10% of the total

is used in foods for humans, the majority being used

as feed for animals.

0020 Soya beans can be an important component of a

normal healthy diet, as they are low in saturates,

provide a source of fiber, and contain a wide range

of other nutrients. Soya beans are also the main source

of phytoestrogens in the diet. In addition, soya beans

may have a number of potential health benefits, and

these are discussed in the following sections.

0021 For vegetarians, and particularly for vegans who

eat no animal products, soya beans play a very

important role in the diet. They provide a valuable

source of protein that can be of high quality if soya

beans are combined with cereals, since the amino acid

compositions are complementary. They also provide

an important source of iron. Low iron intake can lead

to iron-deficiency anemia. Ensuring adequate iron

status can be difficult for vegetarians as, in general,

iron from vegetable sources is less well absorbed than

that from animal sources. However, soya beans pro-

vide a source of iron that can be absorbed as well as

that in meat.

0022 For infants intolerant to cows’ milk protein or to

lactose, soya-based infant formulae can be an invalu-

able alternative to cows’ milk-based formulae. For

older children and adults who are allergic to cows’

milk or intolerant to lactose, drinks and other foods

made from soya can be very important components of

the diet, helping to ensure that nutrient intakes are

adequate for the maintenance of health.

0023In common with other legumes, soya beans are also

of agricultural importance, as they increase the nitro-

gen content of the soil. Although green plants cannot

utilize nitrogen in the atmosphere, there are several

species of bacteria, fungi, and blue–green algae that

are able to transform nitrogen in the air into a form

that can be used by plants. An important genus

of nitrogen-fixing bacteria is Rhizobium, which

forms nodules in the roots of legumes. These bacteria

live symbiotically with the legumes, the bacteria

obtaining food from the green plant, and the legumes

obtaining abundant usable nitrogen compounds from

the bacteria.

Soya and Coronary Heart Disease

0024Coronary heart disease (CHD) is a major cause of

death in many countries. For example, in the UK,

CHD accounts for about 30% of male deaths and

23% of female deaths.

0025The level of cholesterol in the blood is a major risk

factor for CHD. Soya protein substituted for animal

protein in the diet results in reductions in total plasma

cholesterol (by 9% on average), low-density lipopro-

tein cholesterol (LDL-C) (by 13% on average) and

triacylglycerols (by 11% on average). High-density

lipoprotein cholesterol (HDL-C) is unchanged or

may be slightly increased. The amount of reduction

in blood lipids tends to be greater among those with

the highest plasma cholesterol levels at baseline.

0026A great deal of research has been done to identify

the component(s) of soya protein responsible for its

effect on blood lipids. Studies using a mixture of

amino acids that duplicates the amino acid profile of

soya protein have found that this does not have the

same effect on blood lipids as the intact protein.

However, studies of soya protein with isoflavones

intact have shown that this has a lipid-lowering

effect, whereas soya protein with isoflavones re-

moved has no significant effect. It has been suggested,

therefore, that the isoflavones present in soya protein

are largely responsible for the lipid-lowering effect of

soya protein. The benefits of isoflavones present

in soya protein on cholesterol lowering have been

suggested to be mediated through upregulation of

LDL-receptor activity. Nevertheless, studies of isol-

ated and purified isoflavones have failed to show that

these have a lipid-lowering effect.

0027Soya may reduce the risk of CHD through several

mechanisms in addition to its ability to lower blood

SOY (SOYA) BEANS/Dietary Importance 5395

lipids. For example, soya isoflavones are known to

act as antioxidants and have been suggested to reduce

oxidative damage to LDL-C. A decrease in oxidized

LDL particles, which are considered atherogenic, may

reduce the risk of atherosclerosis.

0028 A study of young cynomolgus monkeys showed

that the size of atherosclerotic lesions was 70% less

in those fed on a diet containing soya protein with

isoflavones present compared with those fed on a diet

containing soya protein with isoflavones removed.

This suggests that isoflavones may inhibit atherogen-

esis. In another study of surgically postmenopausal

cynomolgus monkeys, soya protein with isoflavones

intact was found to reduce the progression of athero-

sclerosis. The magnitude of the effect was reported to

be comparable with that of postmenopausal estrogen

therapy.

0029 Soya bean isoflavones, in particular genistein,

impact beneficially on vascular reactivity. Genistein

has also been shown, in vitro, to have a number of

other effects whereby the development of atherogen-

esis may be delayed: inhibition of the migration and

proliferation of smooth muscle cells; inhibition of

platelet activation and aggregation; and reduction in

platelet serotonin uptake.

0030 In 1999, in response to the available evidence on

the benefits of soya protein, the USA Food and Drug

Administration (FDA) announced that it would allow

food manufacturers to label products containing

6.25 g of soya protein per serving as helping to reduce

risk of heart disease, as part of a balanced diet low in

fat and saturates.

Soya and Cancer

0031 Cancer is a major cause of morbidity and mortality.

For example, in the UK, about one in three people

will develop cancer at some time during their life, and

cancer accounts for about one in four of all deaths.

There are marked differences in death rates from

several types of cancer between Asian countries and

many Western countries. The differences are more

striking for hormone-dependent cancers of the pro-

state, breast, and colon/rectum. For example, the

risk of dying from prostate cancer among Japanese

men is only one-fifth that of men in the USA, and

Japanese women have a breast cancer mortality

rate that is only one-quarter of that of women in

the USA.

0032 Countries where mortality from prostate and

breast cancers is low have considerably higher intakes

of soya than those countries where mortality from

these cancers is high. In animal models, studies inves-

tigating the effects of soya beans on prostate cancer or

breast cancer have shown reduced tumorigenesis. In

humans, however, evidence is inconclusive. Epidemi-

ological studies of prostate cancer conducted in Japan

and in Japanese migrants to Hawaii have shown no

significant effect of soya consumption. However, a

recent study in the USA reported that men who

drank one cup of soya milk per day had a risk of

developing prostate cancer that was 70% lower

than that of controls. For breast cancer, although

some studies have shown that soya can help prevent

breast cancer, others have found no significant effect.

An increase in menstrual cycle length has been ob-

served in some studies, in response to soya bean con-

sumption, although no change was observed in

others. Such an effect is of potential relevance to the

hypothesis that soya may be protective against breast

cancer, because some data indicate that longer cycles,

which are typical of Asian women, are associated

with a reduced risk of breast cancer.

0033For colorectal cancer, data are also inconclusive:

some studies showed no significant effect, some

reported a protective effect of soya, and others ob-

served an increased risk with soya consumption. For

cancers at other sites, data tend to show that in-

creased soya bean consumption may be protective

against lung and stomach cancer. Much more

research is needed to confirm whether soya has a

protective effect against cancer in humans. (See

Cancer: Diet in Cancer Prevention.)

0034Isoflavones appear to be the components of soya

that would be most likely to account for any protect-

ive action of soya against cancer, especially in inhibit-

ing the initiation stage of carcinogenesis. Genistein

has been shown to suppress the growth of a wide

range of cancer cells. It inhibits certain enzymes that

could affect the onset of cancer or the growth of

tumors: tyrosine protein kinase, mitogen-activated

protein (MAP) kinase and ribosomal S6 kinase.

Genistein also inhibits the DNA repair enzyme topoi-

somerase II and acts as an antioxidant, thus poten-

tially preventing oxidative DNA damage. It increases

in vitro concentrations of transforming growth factor

b, which is thought to inhibit the growth of cancer

cells. In addition, genistein has also been shown to

inhibit angiogenesis, the formation of new blood

vessels, an abnormal event that occurs as part of the

growth and expansion of malignant tumors. How-

ever, many of these effects have been shown with

very high concentrations of genistein and not in cells

treated with levels likely to be achieved in plasma of

human subjects eating soya foods.

Soya and Bone Health

0035Osteoporosis is a clinical condition in which there is

a reduced amount of bone per unit volume and an

5396 SOY (SOYA) BEANS/Dietary Importance