Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set
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and was analyzed by appropriate methods to give
‘individual’ molecular species and also the distribu-
tion of fatty acids at the sn-1, 2, and 3 positions.
0009 In terms of molecular species it is to be expected
that in view of the high level of linoleic acid, the
dominant triacylglycerol molecules will contain at
least two linoleic chains, thus: LLLn (7.9%), LLL
(17.6%), LLO (15.3%). LLSt (4.2%), and LLP
(10.2%), making a total for this group of 55.2%.
Other triacylglycerols include LnLnL (3.1%),
LnLO (4.8%), LnLP (3.7%), LOO (6.3%), LOP
(6.9%), PLL (3.1%), OOO (3.3%), LOSt (3.7%),
OOP (3.4%), PLSt (3.1), others (3.4%) where Ln¼li-
linolenic, L¼linoleic, O¼oleic. St¼stearic, and
P¼palmitic. These three-letter symbols indicate only
the acids present, and not their position on the gly-
cerol backbone, so that, for example, LLO represents
three different isomers (LLO, LOL, and OLL), and
LOP represents the sum of six isomers. These results
were obtained by reverse-phase HPLC.
0010 The stereospecific analysis of the soybean oil gives
the results indicated in Table 2. As would be expected,
the sn-2 position has enhanced levels of oleic and
linolenic acid and lower levels of palmitic and stearic
acid. The results for linolenic acid are somewhat
unexpected, since all unsaturated acids are usually
enhanced in the sn-2 position. The two sets of results
for the sn-2 position agree reasonably well, except for
oleic and linolenic acid, when allowance is made for
the difficulties of these analytical procedures.
Other Components
0011 The AOCS publication on ‘Physical and Chemical
Characteristics of Oils, Fats and Waxes’ reports that
crude soybean oil contains 1.8–4.1 mg per kilogram
of sterols, which are mainly campesterol (16–24%),
stigmasterol (16–19%), and b-sitosterol (52–58%).
Tocopherol levels are given as 601–3363 mg kg
1
and include the a (9–352), b (0–36), g (89–2307),
and d (154–932) forms. (See Tocopherols: Properties
and Determination; Vitamins: Overview.)
Physical Properties
0012The same publication lists the following physical and
chemical properties properties: specific gravity at 20/
20
0.919–0.925, refractive index at 40
C 1.466–
1.470, iodine value 124–139, saponification value
189–195, unsaponifiable not above 1.5%.
Major Food Uses
0013Oils and fats are significant components of the diet
contributing 30–40% of caloric intake. They are con-
sumed in many different forms as: spreading or
yellow fats (butter, margarine, industrial margarine,
low-fat spreads), frying fats, salad oils, and mayon-
naise, and as an essential component of baked goods.
Refined soybean oil, before or after hydrogenation, is
used in these. As indicated later (Table 3), its contri-
bution is very high in the USA but somewhat lower in
other countries. In many cases, blends of two or more
oils are required to achieve the desired properties.
When considering the relative nutritional merits of
these preparations, it is important to note the extent
to which the various components have been hydro-
genated, that is to know the level of trans acids that
they contain.
0014Mayonnaise must contain at least 65% oil and
salad dressings at least 30%, though products with
lower levels of fat are also produced. These products
are generally refrigerated, so it is important that the
oil does not crystallize and break the emulsion. It is
therefore usual to use soybean oil that has been hy-
drogenated to IV 110–115 to reduce the level of
linolenic acid and then winterized to remove compon-
ents that would crystallize under refrigeration. Oils
used for mayonnaise or salad dressings must remain
clear when cooled in ice water (0
C) for 5.5 h. Soy-
bean oil treated as above remains clear, even after
24 h.
tbl0002 Table 2 Stereospecific distribution of fatty acids in soybean oil
Oil sn-1 sn- 2 sn- 3 sn- 2
a
16:0 10.2 18.2 1.9 12.0 3.7
18:0 4.1 5.4 2.7 4.5 3.4
18:1 23.4 15.9 28.4 25.0 21.4
18:2 52.8 47.8 64.1 48.3 65.0
18:3 8.3 12.9 2.6 10.3 6.4
minors 1.2
a
Results obtained by pancreatic lipase hydrolysis; other results obtained
by the method involving naphthylurethanes of diacylglycerols. The
original paper includes more detail and similar data for modified soybean
oils (Reske J, Siebrecht J and Hazebroek J (1997) Triacylglycerol
composition and structure in genetically modified sunflower and soybean
oils. Journal of the American Oil Chemists’ Society 74: 989–998).
tbl0003Table 3 Disappearance (million tonnes) of selected oils in
USA, EU-15, China, India, and Japan in 1999/2000
sbo sun rape palm pko coco
USA 7.42 0.13 0.68 0.15 0.20 0.48
EU-15 1.88 2.16 3.23 2.24 0.48 0.60
China 2.87 0.25 4.52 1.37 0.02 0.05
India 1.55 0.82 1.94 3.38 0.02 0.44
Japan 0.69 0.01 0.93 0.36 0.05 0.06
sbo, soybean oil; sun, sunflower oil; pko, palmkernel oil; coco, coconut oil.
Source: Oil World Annual (2000) Hamburg: ISTA Mielke.
SOY (SOYA) BEAN OIL 5377
0015 Frying oils, particularly for the preparation of fried
goods that will be stored, should not contain linolenic
as this will shorten the shelf-life. For such products,
it is usual to use a partially hydrogenated oil, and
the hydrogenated–winterized oil developed for may-
onnaise is often used for frying purposes also. For
fast-food purposes, where long-term storage is not
necessary, this additional processing of the oil is less
important.
0016 Margarines have to meet certain physical specifica-
tions, particularly in respect of their appearance and
melting behavior between refrigerator (4
C) and
mouth temperature (37
C) as well as nutritional
guidelines. A variety of binary and ternary mixtures
of soybean oil and of soybean oils hydrogenated to
various iodine values have been used. The hydrogen-
ated oils contain trans acids, and attempts are being
made to reduce the level of these by developing pro-
cedures of hydrogenation that give less trans acids or
by blending nonhydrogenated oil with ‘hardstock,’
which may be a fully hydrogenated oil or palm stearin.
These products are improved by interesterification
of the blended oils. (See Margarine: Types and
Properties.)
0017 Industrial margarines used in the baking industry
need specific functionality. This requirement may
take precedence over nutritional factors since labeling
of baked goods does not include the content of trans
fatty acids, and blends used for this purpose frequently
contain hydrogenated soybean oils.
0018 Shortenings or baking fats used for biscuits, biscuit
fillings, and various kinds of pastry and bread have to
vary in their fat composition depending on their end
use and generally consist of blends of two or more
hard and soft fats, some or all of which may be
hydrogenated. Soybean oil and hydrogenated soy-
bean oil can be components of these blends.
Market Data
0019 Soybeans are used as beans in some animal feeds, but
for the most part, they are crushed and extracted,
either in the country of origin or after export
to another country. Production of soybean oil is
therefore not confined to those countries where the
beans grow. Extraction of soybeans gives *18% of
oil, and the balance is seed meal, which is also an
important commodity of world trade. The main
countries that produce, export, import, and use soy-
bean oil (for food or nonfood purposes) are shown in
Table 4. The figures cited are millions of tonnes for
the year 1999/2000. In respect of production, USA,
Brazil, Argentina, and China grow and extract their
own beans, though China is also a large importer of
beans for local crushing. The other countries listed in
Table 4 crush imported beans. Exports from some of
the producing countries/regions go to a wide range of
geographical locations, of which only the larger
importing countries/regions are listed. Soybean oil is
used in virtually every country in the world. The
major consumers include the producing countries,
except that Argentina has only a small population
so that only limited quantities of oil are consumed
locally.
0020As the major grower of soybeans, the major produ-
cer of soybean oil, and the major consumer of the oil,
the USA is a special case. The following information
is taken from SoyStats published by The United
Soybean Board (America). Edible oil consumed in
the USA is almost entirely soybean oil, as is apparent
from the following figures for 1999: total oil 6.93
million tonnes, including soybean (5.73), corn
(0.23), rapeseed (0.22), cottonseed (0.18), lard
(0.13), other (0.31). Thus, soybean oil represents
82.6% of US consumption, and no other oil exceeds
3.3%. The oil is consumed in a refined state, but
much of it is hydrogenated to a greater or lesser extent
before use. With brush hydrogenation, the level of
linolenic acid is reduced to around 3%, but other-
wise, the oil is hardly changed. With more extensive
hydrogenation, linoleic and linolenic acids decline
in level, and saturated acids and trans monoene
acids increase. Soybean oil is consumed in the USA
mainly in salad and cooking oils (*47%), for baking
and frying (*36%), and in margarine production
(*12%).
tbl0004 Table 4 Production, exports, imports, and consumption (million tonnes) in 1999/2000 by country/region
Total Major countries/regions
Production 25.21 USA 8.15, Brazil 4.24, Argentina 3.10, EU-15 2.87, China 2.20, Japan 0.69. Taiwan 0.41
Exports 7.15 EU-15 1.00, Argentina 3.00, Brazil 1.49, USA 0.58
Imports 7.21 Iran 0.82, China 0.80, India 0.74, Bangladesh 0.47, Pakistan 0.28, former USSR 0.24,
Venezuela 0.25, Morocco 0.23
Consumption (food and nonfood use) 25.02 USA 7.42, Brazil 2.88, China 2.87, EU-15 1.88, India 1.55, Mexico 0.71, Japan 0.69, Iran
0.67, Taiwan 0.47, Bangladesh 0.46, South Korea 0.33, former USSR 0.33, Pakistan
0.32, Venezuela 0.29, Canada 0.29, Mexico 0.26
Source: Oil World Annual (2000) Hamburg: ISTA Mielke.
5378 SOY (SOYA) BEAN OIL
002 1 Soybean oil does not hold the same dominant
position in other countries where there is a greater
use of palm oil, rapeseed/canola oil, sunflower oil,
and lauric oils.
Seealso: Fatty Acids:Properties; Margarine:Typesand
Properties; Palm Oil; Rape Seed Oil/Canola; Soy (Soya)
Beans:TheCrop; Sunflower Oil; Vegetable Oils:Types
and Properties
Further Reading
Hamm W and Hamilton RJ (eds) (2000) Edible Oil
Processing. Sheffield, UK: Sheffield Academic Press.
Official Methods and Recommended Practices of the
American Oil Chemists’ Society, Physical and Chemical
Characteristics of Oils, Fats and Waxes (1996) Cham-
pagne, IL: AOCS Press.
Oil World Annual (2000) Hamburg: ISTA Mielke.
Reske J, Siebrecht J and Hazebroek J (1997) Triacylglycerol
composition and structure in genetically modified sun-
flower and soybean oils. Journal of the American Oil
Chemists’ Society 74: 989–998.
Sipos EF and Szuhaj BF (1996) Soybean oil. In: Hui YH
(ed.) Baileys Industrial Oil and Fat Products, 5th edn.
vol. 2, pp. 497–602. New York: Wiley.
2000 SoyStats, United Soybean Board www.unitedsoybea-
n.org
SOY (SOYA) BEANS
Contents
The Crop
Processing for the Food Industry
Properties and Analysis
Dietary Importance
The Crop
H E Snyder, University of Arkansas, Fayetteville, AR,
USA
This article is reproduced from Encyclopaedia of Food Science,
Food Technology and Nutrition, Copyright 1993, Academic Press.
Production
0001 The soya bean originated in the Far East and has
provided food for that part of the world for thou-
sands of years, but only during the past few decades
have soya beans become an important food crop in
the West. Table 1 shows how the production of soya
beans has increased since 1940. The newly recognized
value of the soya bean is in both the extracted oil and
the residual high-protein meal. The oil is widely used
as a food in margarines, shortenings, and salad oils.
The meal is valuable for its high-protein content as an
animal feed, particularly for poultry and swine.
0002The USA, Brazil, China, and Argentina produce
87% of the world’s soya beans. China has been a
major producer for a long time, but the USA reached
that status only in the 1940s, and Brazil and Argen-
tina only since the 1970s.
0003In comparison with grain production, annual soya
bean production of about 100 10
6
t is not large.
World production of coarse grains (maize, sorghum,
etc.) is about 800 10
6
t, while rice and wheat
amount to about 450 10
6
t each. Soya beans per
unit weight are worth about twice as much as grains.
(See Cereals: Contribution to the Diet.)
0004Soya beans are the predominant oilseed in the
world. About half of the world oilseed production
comes from soya beans, and this is more than the
combined production of the next four oilseeds:
cottonseed, peanut, sunflower, and rapeseed (canola).
Oilseeds vary widely in total oil content; the annual
vegetable oil production therefore differs from oilseed
production. Table 2 shows vegetable oil production
for the world during the 1980s. Palm oil comes from
palm fruit and is not classified as an oilseed, but palm
oil is produced in the largest quantities next to soya
tbl0001 Table 1 Soya bean production (10
6
t) by major countries
during the past 50 years
19 4 0 195 0 19 6 0 1970 19 8 0 19 9 0
USA 2.1 7.8 16.3 30.7 48.7 52.4
Brazil 2.1 15.5 20.0
China9.74.9
a
7.0 9.7 7.9 10.8
Argentina 3.4 10.5
World 11.9 17.8 28.1 45.2 81.2 107.1
a
Data for 1948.
SOY (SOYA) BEANS/The Crop 5379
bean oil. Most of the vegetable oils are increasing in
production to keep up with world demand, but cot-
tonseed, coconut, and olive oil production are rela-
tively stable. (See Ground Nut Oil; Palm Oil.)
0005 The increased use of vegetable oils for foods paral-
lels the growth of soya bean production. In the 1920s,
animal fats were predominant in human diets, but
since the 1940s, vegetable oils have steadily replaced
animal fats. The particular vegetable oil that is used
depends on the country. Soya bean oil makes up
about 75% of vegetable oil use for food in the USA.
Peanut oil is the oil of choice in India, and rapeseed oil
is important in Canada.
0006 Soya beans are annual legumes and were used at
first in the USA as a hay crop. Since legumes are
nitrogen-fixing plants, the hay crop could be used in
rotation with corn to replenish soil nitrogen. With
increased use of nitrogen fertilizers, the value of
soya beans for their nitrogen fixation decreased.
0007 Most of the spectacular recent increase in produc-
tion in the USA and South America (Table 1) is due
to increased area devoted to growing soya beans.
There has been a slow but definite increase in yield
per unit area, with an approximate doubling since
1940 to 2 t ha
1
in 1990 in the USA.
0008 The problems that producers face in trying to in-
crease yields of soya beans are the same as with any
agronomic crop. Pests such as birds and rodents may
eat planted seeds; diseases may slow down the growth
of roots, stems, or leaves; insects can cause damage as
well as transmit diseases; weeds compete for mois-
ture, soil nutrients, and sunlight.
0009 The flowers of soya beans are small and in-
conspicuous, making it difficult to produce hybrid
seed. Under normal conditions, soya beans are
self-fertilizing. The time of flowering is triggered by
lengthening nights, and different soya cultivars (culti-
vated varieties) respond to different night lengths.
Thus, it is important to select the proper cultivar for
the latitude in which it will be grown. If a cultivar
from southern latitudes is grown farther north, it will
not flower until late in the season and may freeze
before the seed matures. Conversely, northern culti-
vars grown in southern latitudes may flower before
the plant has reached full growth, thus greatly redu-
cing yield.
Morphology
0010Soya beans can range in weight from about 100 to
300 mg each, with diameters of 4–8 mm. They are
roughly spherical in shape when dry and swell to a
definite bean or kidney shape when wet. The morpho-
logical features of the whole bean (Figure 1) are the
hilum (point of attachment to the pod), the micropyle
(a small opening through which the germ tube grew),
and the chalaza (a small groove opposite the hilum
from the micropyle).
0011The seed coat makes up about 9% of the weight of
soya beans and tightly encloses the two cotyledons
and embryo. The seed coat is not easily separable
from the intact dry seed, but if the seed is broken or
if it imbibes water, the seed coat separates readily. The
morphological features noted above (hilum, micro-
pyle, and chalaza) are part of the seed coat, which
tbl0002 Table 2 World vegetable oil production (10
6
t)
1980 1982 1984 1986 1988
Soya bean 12.8 13.8 13.4 14.8 15.0
Palm 5.2 5.6 6.9 7.9 9.0
Sunflower 4.7 5.8 6.1 6.6 7.0
Rapeseed 4.1 5.3 5.3 6.6 7.3
Cottonseed 3.2 3.4 4.2 3.2 3.6
Peanut 2.7 3.0 3.4 3.1 3.8
Coconut 2.9 2.7 2.8 2.8 2.6
Olive 1.9 1.9 1.7 1.9 1.8
Palm Kernel 0.6 0.8 0.9 1.0 1.3
Hypocotyl
Micropyle
Hilum
Chalaza
fig0001Figure 1 Morphological features of whole, mature soya beans.
The features shown are associated with the seed coat or hull.
Reproduced from Soya Beans: The Crop, Encyclopaedia of Food
Science, Food Technology and Nutrition, Macrae R, Robinson RK
and Sadler MJ (eds), 1993, Academic Press.
5380 SOY (SOYA) BEANS/The Crop
may be yellow, green, brown, or black, but the cotylc-
dons are green or yellow. United States grading stand-
ards discriminate against brown and black soya
beans. Since very little oil is present in the seed coat,
it is removed before oil extraction and may or may
not be added back to the defatted meal used as animal
feed.
0012 Several layers of cells make up the seed coat, and
cells of a distinctive type, termed hourglass cells be-
cause of their shape, are readily distinguishable by
light microscopy. The hourglass cells can be used as
qualitative markers to determine whether or not soya
bean meal has been added to other foods.
0013 If soya beans are soaked in cold water, a few,
perhaps 1%, fail to imbibe water and are called
‘hard seeded.’ The failure to imbibe water is a prop-
erty of the seed coat being completely intact and is
probably due to the outermost waxy layer, termed the
cuticle.
0014 The two cotyledons make up 90% of the soya
bean. The cotyledon cells are packed with protein
bodies and lipid bodies, the two principal organelles
(Figure 2). Early in the maturity of the cotyledons,
starch granules are prominent, but they decrease to
less than 1% of weight as beans mature.
0015Protein bodies are 2–20 mm in diameter and con-
tain principally the glycinin and conglycinin stor-
age proteins. Protein bodies are osmotically fragile
but can be isolated by using high-osmotic-strength
buffers at pH 5. In addition, heating (soaking soya
beans for a few minutes in boiling water) causes
protein bodies to be heat-fixed and not to disperse
in water.
0016Lipid bodies (0.2–0.5 mm) are much smaller than
protein bodies and are the sites of oil storage. Centri-
fugation of broken cotyledon cells separates lipid
bodies as a floating layer, but because of their phos-
pholipid-protein membrane, the smallest lipid bodies
sediment in a centrifugal field.
0017The hypocotyl of the soya bean has a different
composition to that of the cotyledon (less oil and
more carbohydrate), but since it makes up only
about 2.5% of the weight of the bean, the different
composition has little influence. The hypocotyl is
processed into oil and meal along with the cotyledons
after the seed coat is removed.
Composition
0018As a first approximation, soya beans contain 20%
lipid, 40% protein, 35% carbohydrate, and 5% ash
on a dry-weight basis. Considerable variability exists
in these numbers, depending on the cultivar and the
growing conditions. In the northwestern part of the
soya bean production area in the USA, protein con-
tent of soya beans is generally lower than in other
production areas. Protein content is known to be
inversely related to yield and to lipid content.
Lipids
0019The crude oil extracted from soybeans contains about
96% triglycerides. The fatty acid composition of the
triglycerides is approximately 11% palmitic (C16),
4% stearic (C18), 25% oleic (C18:1), 51% linoleic
(C18:2), and 8% linolenic (C18:3), with other minor
fatty acids also present. The fatty acid composition is
not fixed and can be changed by breeding new culti-
vars. (See Fatty Acids: Properties.)
0020Minor components in the crude oil include the
plant pigments lutein (3,3
0
dihydroxy a-carotene)
and chlorophyl. Also present are phospholipids, free
fatty acids, triglyceride hydroperoxides, sterols, sap-
onins, squalene, tocopherols (vitamin E), and flavor
compounds. During refining of the crude oil, phos-
pholipids, free fatty acids, pigments, and flavor com-
pounds are removed to produce an oil that contains
more than 99% triglyceride. (See Chlorophyl; Color-
ants (Colourants): Properties and Determination of
Pb D
CW
Pb
Lb
fig0002 Figure 2 Scanning electron micrograph of freeze-fractured
soya bean cotyledon. CW, cell wall; Lb, lipid body; Pb, protein
body; PbD, protein body depression. Reproduced from Soya
Beans: The Crop, Encyclopaedia of Food Science, Food Technology
and Nutrition, Macrae R, Robinson RK and Sadler MJ (eds),
1993, Academic Press.
SOY (SOYA) BEANS/The Crop 5381
Natural Pigments; Flavor (Flavour) Compounds:
Structures and Characteristics; Phospholipids: Prop-
erties and Occurrence; Triglycerides: Structures and
Properties.)
Protein
0021 Soya proteins have been separated in the ultracen-
trifuge and characterized as 2s,7s,11s, and 15s
fractions (s is a sedimentation constant, and larger
numbers indicate larger proteins). The 2s fraction
contains low-molecular-weight proteins, including
the Bowman–Birk and Kunitz trypsin inhibitors that
inhibit growth in young animals. Heating of soya
bean meal is necessary to denature trypsin inhibitors
and allow full utilization of the protein. (See Protein:
Chemistry.)
0022 The 7s fraction includes a storage protein, b-
conglycinin, with a molecular weight (M) of about
180 000. b-Conglycinin is a trimer with a, a
0
,andb
subunits, which, in different combinations, give six
distinct b-conglycinins. Also present in the 7s fraction
are hemagglutinins (lectins) and lipoxygenases. Hem-
agglutinins are glycoproteins that can cause agglutin-
ation of red blood cells and can be toxic, but are
probably heat-denatured along with trypsin inhibi-
tors and have no toxic effects when fed. Several
lipoxygenases have been characterized that catalyze
the removal of hydrogen and addition of molecular
oxygen to linoleic and linolenic fatty acids to yield
hydroperoxides. The hydroperoxides can break down
to yield off-flavor compounds associated with oxida-
tive rancidity. (See Oxidation of Food Components.)
0023 The 11s fraction is glycinin, a hexamer (M,
360 000). Each of the six subunits consists of acidic
polypeptides (M, 32 000–36 000) and basic polypep-
tides (M, 19 000–20 000). The 15s fraction is a dimer
of glycinin.
0024 Associated with protein in soya beans is phytin, the
calcium and magnesium salt of hexaphosphoryl ino-
sitol. Phytin strongly chelates divalent cations and has
been implicated in decreased availability of iron in
diets with soya protein. (See Phytic Acid: Properties
and Determination.)
Carbohydrate
0025 Insoluble carbohydrate includes the pectin, cellulose,
and hemicellulose that are associated with cell walls
in soya bean cotyledons. This is also the dietary fiber
component, which is increasingly recognized as an
important part of the human diet. The fiber is more
prevalent in soya bean seed coats (hulls) than in coty-
ledons. (See Carbohydrates: Classification and Prop-
erties; Cellulose; Hemicelluloses.)
0026 The soluble carbohydrate in soya beans is about
10% by weight of the dry bean and includes about
5% sucrose, about 4% stachyose, and about 1%
raffinose. Raffinose is a trisaccharide, and stachyose
is a tetrasaccharide, neither of which can be digested
by humans. As a result, microbial fermentation of
these sugars in the intestine produces gas (flatus),
which leads to gastrointestinal distress.
Handling and Storage
0027As soya beans are harvested and moved from the field
into storage, conditions have to be controlled to
minimize deterioration. The moisture content of the
beans should be 14% or lower to prevent microbial
growth. Also, the cleanliness of the beans is impor-
tant to avoid insect or other contaminants, which
may provide moisture and be a focus for microbial
growth. If deterioration does start, bacterial or mold
growth will generate higher temperatures and mois-
ture so that the process becomes autocatalytic. The
best control procedure in storage is to have tempera-
ture sensors spread throughout, and quickly mix
beans that show generation of hot spots. (See Spoil-
age: Bacterial Spoilage; Molds in Spoilage.)
0028Much of the crop from the USA and Argentina is
exported as beans. As the beans are transported by
truck, train, barge and ship, and they are transferred
into and out of storage, they tend to break, and the
pieces are known as splits. Splits are a factor in
grading, and the oil extracted from splits tends to
have greater amounts of free fatty acids and phospho-
lipids than oil from intact beans.
0029Much of Brazil’s crop is crushed in the country, and
oil and meal are exported. In handling oil, it is neces-
sary to minimize exposure to oxygen of the air during
transfer. Any outlet spouts should be below the sur-
face to prevent air incorporation in the oil, and blan-
keting the surface with nitrogen is a good protective
measure. Storage tanks must be kept clean. This is
particularly important for the tanks in ship’s holds or
for tankers, both of which may carry many different
liquid cargoes. Cross-contamination between cargoes
is avoided by careful cleaning of the tanks.
Grading
0030In the USA, there are four numerical grades and
sample grades for those beans that have the lowest
quality. The factors used for grading are test weight,
splits, heat damage, foreign material, and color. These
are similar criteria to those used for grains, and the
grading systems in other countries rely on the same
criteria, although the actual grades and maximum
limits may differ. The economically valuable constitu-
ents, protein and oil, are not part of the grading
system.
5382 SOY (SOYA) BEANS/The Crop
0031 Until recently, there have been difficulties in meas-
uring protein and oil quickly and accurately enough
to be part of the grading system. Infrared spectropho-
tometers now perform excellent analyses for protein,
oil, and moisture of either whole or ground samples.
Consequently, there is a renewed interest in using the
protein and oil content of soya beans to provide
premiums or discounts in pricing. Aside from the
analysis problem, other problems exist in keeping
high-oil or high-protein beans segregated as they
move through marketing channels.
See also: Carbohydrates: Classification and Properties;
Cellulose; Chlorophyl; Colorants (Colourants):
Properties and Determination of Natural Pigments; Fatty
Acids: Properties; Flavor (Flavour) Compounds:
Structures and Characteristics; Hemicelluloses;
Oxidation of Food Components;
Phospholipids: Properties and Occurrence; Phytic Acid:
Properties and Determination; Protein: Chemistry;
Spoilage: Bacterial Spoilage; Molds in Spoilage;
Triglycerides: Structures and Properties
Further Reading
Anonymous (1990) Soya Bluebook. Bar Harbor, ME: Soya-
tech.
Erickson DR (ed.) (1990) Edible Fats and Oils Processing:
Basic Principles and Modern Practices. Champaign, IL:
American Oil Chemists’ Society.
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 Associ-
ation. Champaign, IL: American Oil Chemists’s Society.
Heatherly LG and Hodges HF (eds) (1999) Soybean Pro-
duction in the Midsouth. New York: CRC Press.
Snyder HE and Kwon TW (1987) Soybean Utilization. New
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Wilcox JR (ed.) (1987) Soybeans: Improvement, Produc-
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Processing for the Food
Industry
H E Snyder, University of Arkansas, Fayetteville, AR,
USA
L A Wilson, Iowa State University, Ames, IA, USA
Copyright 2003, Elsevier Science Ltd. All Rights Reserved.
Background
0001 Soya beans are seldom simply cooked and eaten.
They are traditionally processed into soyafoods or
into food ingredients. This article covers soyfood
processing and the initial separation of soybeans
into oil and meal by solvent extraction and then the
further processing of oil and meal. Oil needs to be
refined to remove minor components and is then
processed to make products such as margarines,
shortenings, and salad dressings. The protein-rich
meal is mainly used as animal feed but can be pro-
cessed into food ingredients such as flours, con-
centrates, and isolates. The protein products may
also be textured in various ways to simulate meats
or cheeses.
Oil Separation
0002The first step in processing most soya beans is to
separate the oil, either by solvent extraction or by
expelling. The processing companies that do the sep-
aration are called crushers, and each of the 100 or so
crushers in the USA processes on average about 1000
tonnes of soya beans daily. (See Vegetable Oils: Oil
Production and Processing.)
Preparation
0003Before solvent extraction, soya beans are cleaned and
cracked into several pieces (meats). The hulls are
removed by aspiration, and the meats are conditioned
by warming and by adding moisture. Conditioning is
necessary to make a cohesive flake. The conditioned
meats are put through smooth rollers that make
flakes of approximately 0.025 cm thickness. Making
flakes is advantageous for uniform penetration of
solvent in deep beds (minimal channeling) and for
disruption of the soya bean tissue so that solvent can
penetrate and dissolve the oil.
0004A recent development is to put the flakes through a
cooking extruder (expander) to yield collets. The
collets are pieces of the ‘rope’ exiting the outlet of
the expander. This processing gives a porous but still
high-density collet that extracts more readily than
flakes. Also, the collet holds less solvent that the
flake, thereby minimizing the energy needed for
removing the solvent.
Solvents
0005The solvent of choice is commercial hexane, a pet-
roleum fraction with a boiling range of 65–70
C.
Commercial hexane is a mixture of n-hexane, cyclo-
hexane, and methylpentanes. It has low viscosity and
a low heat of vaporization. The main disadvantages
of hexane are its flammability and the safety precau-
tions needed for safe handling.
SOY (SOYA) BEANS/Processing for the Food Industry 5383
0006 Chlorinated hydrocarbons are equally good
solvents for soya bean triglycerides, but the use of
trichloethylene led to toxic soya bean meal during
the 1940s, and this has discouraged further use of
these solvents.
0007 Ethanol and isopropyl alcohol are effective trigly-
ceride solvents when hot, and cooling can be used to
separate the dissolved triglyceride from the solvent.
Isoflavones are also extracted by alcohol. However,
alcohol solvents are not being used in commercial
extractions.
Extraction
0008 The full-fat flakes (or collets) are loaded into the
extractor to make beds over which the solvent
flows. Extractors may have deep (1.2 m) or shallow
(0.6 m) beds, and are always arranged so that solvent
flows countercurrent to the movement of the beds.
Thus, the fully extracted flakes are contacted by fresh
hexane entering the extractor, and full-fat flakes
are contacted by the full miscella (solution of crude
oil in hexane) just before it leaves the extractor.
The temperature of extraction is about 60
Cto
speed up diffusion of solvent and to lower the
miscella viscosity, both of which enhance the extrac-
tion of oil. Solvent extraction is capable of reducing
the residual oil in the soya flakes to less than 1%.
Removal of Solvent
0009 Upon completion of extraction, the solvent has to be
removed from both the oil and flakes. The full-fat
miscella contains 25–30% oil, and solvent is removed
by two stages of rising-film vacuum evaporators
followed by a third-stage stripping column. At the
end of this process, the crude oil contains about
1000 p.p.m. of hexane, which corresponds to a flash
point for the oil of 121
C.
0010 The flakes are treated in a desolventizer-toaster by
direct contact with steam first to remove the hexane
and second to heat treat the flakes for trypsin in-
hibitor destruction. After leaving the desolventizer-
toaster, the flakes are cooled and ground to a meal
for use as a high-protein feed ingredient. The protein
content is 44% with hulls added or 47.5–49%
protein without hulls.
0011 If flakes are to be used to produce soya bean pro-
tein isolates or soluble soya bean concentrates,
the solvent has to be removed with minimal heat to
maintain protein solubility. Flash desolventizers are
available in which superheated hexane is used as
the heat-transfer medium to evaporate hexane. The
flakes are kept dry and, with this system, protein
solubility is preserved.
Expelling
0012The original methods for recovering oil from oil seeds
were designed to exert pressure on the seeds and
express the oil. The modern technique for exerting
pressure is an expeller: a motor-driven auger rotating
within a cage of narrowly spaced metal bars. As the
oil seed flakes move through the expeller, pressure
exerted by the auger forces oil out through the bars,
while the defatted flakes are pushed by the auger to
the opening at the end. Considerable heat is generated
by expellers, and often the protein meal is of a lower
quality than the solvent-extracted meal because of
excess heat. Also, the residual oil in expeller meal is
3–4%. Nevertheless, expellers are widely used when
it is necessary to handle a variety of oil seed in one
facility. Expellers can handle as much as 50–80
tonnes of oil seeds per day. The soya bean preparation
for expelling is similar to that for solvent extraction.
Recent interest in extruding or expressing has
increased the number of small operations that can
produce ‘crude’ oil and reduced-fat flour.
Soya Oil Refining
0013After extraction and removal of solvent, the crude
soya bean oil needs to be refined to convert it to edible
products. (See Vegetable Oils: Oil Production and
Processing.)
Degumming
0014The crude oil contains about 1–3% phospholipids,
known in the industry as gums. The phospholipids
act in conjunction with tocopherols as antioxidants,
but they will also precipitate out of the oil, making a
sludge that is difficult to remove from storage tanks,
road tankers, or ship holds. Therefore, crude oil is
often degummed by the crusher before shipping or
storing.
0015The degumming process involves adding 1–3%
water to hydrate the phospholipids, followed by
centrifuging to remove the hydrated material. The
phospholipids are removed in the water phase and
either recovered to be sold as a food ingredient, leci-
thin, or added to the meal portion to be sold as animal
feed. Phospholipids remaining in the oil are said to be
nonhydratable, and are largely calcium and magne-
sium salts of phosphatidic acid. An acid treatment of
the crude oil makes these phospholipids removable by
water washing. About half of the soya bean oil in the
USA is degummed before going to the refiner.
Alkali Refining
0016The purpose of alkali refining is to remove free fatty
acids from the crude oil (if the oil has not already been
5384 SOY (SOYA) BEANS/Processing for the Food Industry
degummed, phosopholipids are also removed by
alkali refining). Free fatty acids are undesirable be-
cause they lower the temperature at which the oil
begins to smoke and flash (ignite) when heated, as
in frying. The fatty acid content of crude soya bean oil
is 0–0.7%, and alkali refining yields oil with < 0.05%
free fatty acids.
0017 The process washes the oil with a 12% sodium
hydroxide solution followed by centrifugation. Fatty
acids are converted to sodium soaps and separate
with the water phase. Invariably, some oil is lost
with water phase (neutral oil loss), and the greater
the amount of free fatty acids, the greater the neutral
oil loss. After washing with dilute alkali, the oil is
washed once with water to remove residual soaps and
vacuum-dried to a moisture content of 0.1%.
0018 The fatty acids may be recovered by acidifying and
centrifuging the water phase. Fatty acids can be used
for soap manufacture but are often added to the soya
bean meal to serve as additional feed energy.
Bleaching
0019 Crude soya bean oil is darker in color than desired by
consumers, and bleaching is used to lighten the color.
Bleaching is achieved by the addition of bleaching
earth (adsorbent clays usually acid-treated) to the
hot oil under vacuum. The main pigments in soya
bean oil are carotenoids and chlorophyll, and these
are adsorbed on bleaching earths, which are separ-
ated from the oil by filtration.
0020 In addition to removal of pigments, the bleaching
process adsorbs oxidation products and the prooxi-
dant metals, iron and copper. Thus, bleaching plays
an important role in stabilizing the oil regarding oxi-
dation as well as lightening the color.
Hydrogenation
0021 Soya bean oil is highly unsaturated and, to make prod-
ucts such as shortening and margarines, hydrogen is
added to double bonds in the triglycerides to increase
their melting points. Hydrogenation is also used to
saturate partially double bonds in soya bean oil, so
that the oxidative stability is increased. (See Vegetable
Oils: Oil Production and Processing.)
0022 Hydrogenation is usually done in batches (al-
though continuous equipment is available), and the
requirements are a nickel catalyst, hydrogen gas
under pressure, vigorous agitation, and soya bean
oil at 120–200
C. The temperature, pressure, degree
of agitation, and amount of catalyst are variables that
affect the rate of hydrogenation and the degree of
selectivity. Selectivity refers to the increase in hydro-
genation rate of linolenic acid to linoleic acid to
avoid off-flavor generation from oxidation of lino-
lenic acid.
0023During hydrogenation, isomerization of fatty acids
takes place to give double bonds in new positions and
to shift double bonds from cis to trans. This process
reduces the amount of o-3 fatty acids (linolenic).
Melting point increases result both from saturation
of double bonds and from isomerization of cis to
trans double bonds.
Deodorization
0024The development of hydrogenation and deodoriza-
tion in the early 1900s made it possible to substitute
vegetable oils for animal fats in human diets. Hydro-
genation controlled the texture, and deodorization
controlled the flavor of vegetable oils.
0025Deodorization is steam distillation at a high tem-
perature under a vacuum. By this process, unwanted
flavors are removed, and some bleaching of remaining
carotenoid pigments occurs. The distillation tempera-
tures range from 204 to 275
C at 6 mmHg vacuum.
Under these conditions, not only flavor compounds
but free fatty acids and about half of the tocopherols
are distilled out of the soya bean oil.
0026If the oil to be deodorized is sufficiently devoid of
phospholipids (less than 5 p.p.m. phospholipid phos-
phorus), free fatty acids can be removed by distilla-
tion rather than by alkali refining. Such removal is
known as physical refining. The phospholipids must
be present in low concentrations because they brown
severely at high temperatures.
0027The distillate remaining from deodorization is a
valuable byproduct because of the relatively large
content of tocopherols (vitamin E). Batch, semi-
continuous, and continuous equipment is available
for deodorization.
Soya Oil Products
0028After sufficient refining, soya bean oil is used to pro-
duce shortening, margarines, salad dressings, and
cooking oils of various types. (See Dressings and
Mayonnaise: The Products and Their Manufacture;
Fats: Uses in the Food Industry; Margarine: Methods
of Manufacture.)
0029For plastic products such as shortenings and mar-
garines, the texture is achieved by a mixture of trigly-
ceride crystals plus oil. To avoid a large crystal size
and grainy texture, it is necessary to have a mixture of
fatty acids. For soya oil products, this means adding
oils that contribute palmitic acid to achieve small
crystals. In addition to the familiar plastic shortenings
produced for home use, dry shortenings are manufac-
tured for incorporation into various bakery mixes,
SOY (SOYA) BEANS/Processing for the Food Industry 5385
and liquid shortenings are used for ease of metering in
automated baking processes.
0030 For margarines, the solids content at various tem-
peratures (solid fat index) is an important quality
criterion. If the margarine is to be used in the home,
manufacturers want a product that spreads easily at
refrigerator temperatures and melts completely in the
mouth (body temperature). These texture character-
istics are achieved by blending hard and soft fats and
oil. The crystal formation for both shortenings and
margarines is achieved by cooling mixtures rapidly
while mixing in scraped-surface heat exchangers.
0031 Cooking oils based on soya oil are usually partially
hydrogenated to minimize the linolenic acid content
and to minimize oxidative rancidity in the hot oil.
Soya Bean Protein Products
0032 Although an estimated 90% of the soya bean defatted
protein meal goes to animal feed, a variety of food
products and ingredients are produced from the
remainder. These include soya bean flours, ranging
from full fat to defatted, soya bean protein concen-
trates, soya bean protein isolates, and various
textured products simulating meats, seafoods, and
cheeses.
Soya Bean Flours
0033 By grinding defatted soya bean flakes to flours (or
grits, if the particle size is larger), a product is pro-
duced that is used in the baking industry for its mois-
ture sorption capability. Soya bean flours and grits are
also used in meat emulsions for the emulsifying ability
in addition to moisture sorption. (See Emulsifiers:
Uses in Processed Foods.)
0034 Full-fat flours are produced by grinding dehulled
soya beans. The unheated flours have active lipoxy-
genase and are used to bleach wheat flours used in the
baking industry. The oxidative action of lipoxygenase
both bleaches the carotenoids in wheat flour and
oxidizes the proteins to improve machinability. Full-
fat flours can be heat-treated to produce enzyme
inactive flours where less ‘beany’ flavors with more
cereal/nutty flavors are desired.
0035 A range of soya bean flours between defatted and
full fat can also be produced by adding soya bean
oil and lecithin in varying amounts to defatted
flours. These products are used mainly in the baking
industry.
0036 If the soya bean flours are used in substantial con-
centration in food products, soy beany flavors can
become a problem. The presence of indigestible oligo-
saccharides, raffinose and stachyose, that cause flatus
can also be a problem. To avoid the flavors, heated
soyflours and lipoxygenase-null soybeans have been
developed. Reduction of the oligosaccharides has
been accomplished by the development of soya bean
protein concentrates. (See Soy (Soya) Beans: Process-
ing for the Food Industry.)
Soya Bean Protein Concentrates
0037The processing of defatted soya bean flakes into con-
centrates requires the protein to be rendered insoluble
and extracting the soluble sugars (sucrose, raffinose,
and stachyose) with water. The protein can be made
insoluble by heat treatment, by aqueous ethanol
treatment, or by adjusting the pH to the isolectric
point of 4.5. The water extraction leaves complex
carbohydrates and protein, and the protein concen-
tration has to be 70% to be classified as a concen-
trate. The use of water extraction retains more of the
isoflavones than traditional ethanol extract concen-
trates. Both types of concentrates are currently in the
market place.
0038In some food applications (a high-protein drink,
for example), soluble protein may be needed, and
this can be achieved by using a pH to render the
protein insoluble followed by pH increase after ex-
tracting the sugars. Protein solubility is measured by
the nitrogen solubility index (NSI) or protein disper-
sability index. The indices give the percentage protein
remaining in solution or suspension after centrifuga-
tion. (See Protein: Chemistry.)
0039Soya bean protein concentrates are used in the
baking and meat industries for their moisture sorp-
tion and emulsifying properties.
Soya Bean Protein Isolates
0040For those food applications in which only soya bean
protein is suitable, soya bean isolates are available.
Isolates contain 90% soya bean protein and are
prepared from defatted flakes with a high NSI. The
protein is dissolved with dilute alkali, separated from
the remaining cellular material, and precipitated by
adjusting the pH to 4.5. The protein can be recovered
as spray-dried isolectric protein (no pH adjustment
and low solubility) or as soluble proteinate after rais-
ing the pH. About one-third of the original flake is
recovered as protein isolate.
0041Soya bean protein isolates can be used for moisture
sorption and emulsification in baked goods and meat
emulsions. They can also provide textural improve-
ment through gelation and adhesion properties or
serve as primary nutrients in infant formulae.
0042Soya bean flours, concentrates, and isolates may
modify texture in foods by increasing viscosity, by
holding moisture or fat, or by adhesion and cohesion.
5386 SOY (SOYA) BEANS/Processing for the Food Industry