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

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amorphous regions of the starch granules and the

presence of strong binding forces which relax within

one temperature range.

0011 Large variation in nonstarch polysaccharides

(NSP), including fiber content (1.2–13.5%), has

been observed in selected types of legumes. A signifi-

cant proportion (80–93%) of the fiber is localized in

the seed coat. Beans possess relatively high levels of

soluble and insoluble fiber, and significant levels

of pectin. Cellulose is the major component of fiber

in smooth and wrinkled peas, red kidney, and navy

beans, while in other legumes (lupins, lentils, broad

beans, etc.), hemicellulose predominates. Cotyledon

cell walls contain higher levels of pectin than cellu-

lose. The seed coats are primarily composed of

cellulose (29–41%) with small amounts of lignin

(1.2–1.7%). Total dietary fiber is higher in cooked

beans than in raw beans. Water-soluble fractions can

be lost with cooking water, even though the beans are

intact, while long boiling may cause modifications in

certain constituents of other fiber fractions. (See Diet-

ary Fiber: Properties and Sources.)

Proteins

0012 Legumes are dense sources of plant protein that

ranges from 20% to 40% (dwb). The bean storage

(reserve) proteins are predominant in the globulin

fractions, while the metabolic (enzymatic) proteins

are primarily found in the albumin fraction. The

storage proteins have high affinity for water and con-

tribute dramatically to the nutritional and functional

properties of the cooked seed. Bean proteins are

relatively high in essential amino acids, in particular

lysine, threonine, isoleucine, leucine, phenylalanine

and valine. However, they are deficient in sulfur-

containing amino acids, in particular methionine

and cystine. This explains their association with

cereal grains that are deficient in lysine, but are a

substantial source of methionine. (See Protein: Food

Sources.)

0013The globulin fraction can be subdivided into globu-

lin I (GI: high salt solubility) and globulin II (GII: low

salt solubility). Phytohemagglutinin (PHA), the lectin

of dry beans, is identified as GII with two general

types of subunits: an erythrocyte reactive subunit, E,

and a lymphocyte-stimulating subunit, L. PHA has

relatively high levels of aspartic acid and serine, but

possesses very little cystine and methionine. It has the

ability to agglutinate red blood cells, disrupt the in-

ternal mucosa, and reduce nutrient absorption. Legu-

minosa lectins will bind both the storage protein and

the glycosidase enzymes. It has been suggested that

lectins act during the maturation of the plant to

contribute to an orderly arrangement of the storage

proteins in the protein bodies.

0014Total biological utilization of the legume protein is

relatively low, with digestibility less than 76%. Pro-

tein digestibility may be impaired by the presence of

numerous antinutritional compounds that must be

removed or destroyed during processing. There is

considerable variability in protein digestibility

among different commercial classes of Phaseolus

vulgaris, and also among cultivars within a class.

Heating for longer than 30 min at 121



C results

in lowered protein quality and decreased available

lysine in P. vulgaris. The protein efficiency ratio

(PER) of raw and cooked legumes is approximately

0 and 1.2, respectively.

Minor Constituents

0015Ash and minerals The total ash content of P. vul-

garis ranges from 3.5 to 4.1% (dwb). Beans are gen-

erally considered to be substantial sources of calcium

and iron. They also contain significant amounts of

phosphorus, potassium, zinc, and magnesium. Differ-

ences among bean classes and environmental factors

influence variability. Ash content decreases after

cooking because of leaching, with losses ranging

from 10% to 70%. The wide range of reported losses

could be due to different soaking and cooking

methods. (See Minerals – Dietary Importance.)

0016Vitamins Dry edible beans provide several water-

soluble vitamins (thiamin, riboflavin, nicotinic acid,

and folic acid) but very little ascorbic acid. However,

variability of vitamin content is high. Commercial

methods of preparation of canned beans cause a

significant loss of water-soluble vitamins. (See Vita-

mins: Overview.)

0017Lipids Neutral lipids are the predominant class and

account for 60% of the total lipid content. Phospho-

lipids comprise 24–35%, while glycolipids account

Epicotyl

Hypocotyl

Micropyle

Radicle

Hilum

Cotyledon

Seed coat

fig0001 Figure 1 Anatomical structure of a legume seed.

LEGUMES/Legumes in the Diet 3523

for up to 10% of the total lipid content of legume

seeds. Most dry beans possess relatively low total fat

content, generally 1–2%. The fatty acid composition

of legumes demonstrates a significant amount of vari-

ability; however, legume lipids are generally highly

unsaturated (55–85%), with linoleic acid present in

the highest concentration. Palmitic acid is the predom-

inant saturated fatty acid. (See Fats: Classification.)

0018 Tannins and polyphenols The procyanidin and con-

densed tannin content of dry beans ranges from 0.4%

to 1.0%. These compounds are localized in the bean

seed coat, with low or negligible amounts present in

the cotyledon. The hydroxyl groups of the phenol

ring enable the tannins to form cross-links with pro-

teins that may be implicated in postharvest seed

hardening or decreased digestibility. During cooking,

polyphenolic compounds are partially leached into

the cooking medium and may interact with cotyledon

constituents, yet complete destruction of the tannins

does not occur during heat processing. (See Tannins

and Polyphenols.)

Grading, Handling, and Storage

0019 Various genetic, cultural, and environmental factors,

including variety, seed source, agronomic conditions,

handling, and storage of the dry product, critically

affect the final quality of legume food products. Seed

germination and vitality are extremely vulnerable to

damage during handling and storage.

0020 Beans are not ready for harvest until the moisture

level drops to about 20%. Conditions best suited for

threshing (removal of seed from pod and separation

of plant residue) are seed moisture of 16–20% (on a

wet-weight basis) and pod moisture at least 4% lower

than seed moisture. Moisture content is also an im-

portant factor influencing postharvest storage stabil-

ity. Accumulation of moisture will result in high seed

respiration rates (heat) and subsequent mold develop-

ment can be a storage problem. Aeration of seeds

during storage provides moisture equilibration and

ability to inhibit localized ‘pockets’ of moisture. The

seed is vulnerable to mechanical damage, which can

result in split seed coats, so design of handling

systems (conveyors and augers) must minimize seed

dropping.

0021 Bean moisture control, storage temperature, and

relative humidity exert a major influence on dry

bean quality and on the final product. High moisture

and high temperature during storage will result in

brown, discolored, and off-flavored beans (‘bin

burn’). Beans subjected to adverse storage conditions

may undergo cooked-seed textural defects which se-

verely limit their food use. Legume seeds that will not

soften sufficiently because of a failure to imbibe water

during soaking are termed ‘hard-shell.’ Legume seeds

that absorb adequate water during soaking, but will

not soften sufficiently during a reasonable cooking

time, are designated as hard-to-cook (HTC).

0022The most noticeable structural changes caused by

HTC defect is a failure of cotyledon cells to separate

during cooking. Disintegration of cytoplasmic organ-

elles, with inclusions and loosening of attachments

between the cell wall and the plasmalemma, are ob-

served in HTC beans. Loss of plasmalemma integrity

is considered to be responsible for increases in

electrolyte leakage observed in HTC beans. Much

research has been directed toward understanding

and controlling these reactions.

Processing and Uses

0023Food legumes are an economical source of supple-

mentary protein for many populations lacking animal

protein. Legumes are currently of interest to the con-

suming public because they provide high nutrient

levels without supplying excessive calories, and the

perception of their food values has dramatically

shifted from the ‘poor man’s steak’ label.

0024The major physical constraints limiting the use of

dry beans are as follows:

0025Preparation: time, convenience, expense

0026Postharvest storage changes: seed hardening –

hard shell and HTC; moisture absorption; mold

growth; seed discoloration; flavor and odor

changes.

0027The major biological constraints limiting utiliza-

tion of dry beans are as follows:

0028Antinutrients: protease inhibitors and trypsin

inhibitors, lectins and PHA; amylase inhibitors;

phytic acid (mineral chelation and malabsorp-

tion).

0029Digestibility: procyanidin interactions (tannins

and condensed polyphenols, binding of proteins);

protein (limited proteolysis, amino acid balance);

starch (resistant granules, limited amylolytic

degradation).

0030Flatulence factors: oligosaccharides; nonstarch

polysaccharides; proteins; retrograded starch.

Figure 2 summarizes the processing and edible

byproducts of dry beans.

Soaking

0031Soaking of legume seeds may be used to moisten and

soften the seed to reduce cooking time or aid in seed

coat removal. Soaking also reduces the toxin content

and surface contamination. The time needed for

3524 LEGUMES/Legumes in the Diet

Agronomic production

Harvest

Industrial product systems

Dry-seed packaging

Canning

Precooked products

Milled flours and

concentrates

Dry pack, single class,

and mixtures

Cooking

Soaking/blanching

Fill bean and

sauce formulations

Forced-air

dehydration

Home consumption

of individual

recipes

Closure or thermal

process

Meals or

powders

Beans in brine

Beans in tomato sauce

Structured

formed

particles

Extrusion

Hydration and cooking

(Soak/blanch/cook)

West extraction

Pin-milled

Frozen

Air-

classified

Extracts

alkali

acid

salt

Pork and beans

Beans and franks

IQF Block

Fractions

Protein

Starch

Fiber

Ultrafiltration

Isoelectric

precipitate

Protein

isolates

Protein

concentrates

Whole beans

or pieces

LDC

(Intrinsic populations)

On-farm storage

(basket/drum/bin)

Central elevator

(silo/bin)

Cooperative/governmental

Processing mill

(village level)

Dehulling (dhal)

Meals, flours

Water cooking

(home)

Open fire,

kettle, or pot

Whole bean or mash

porridge or gruel

fig0002 Figure 2 Outline of primary dry-bean processing and end products. LDC, less developed countries; IQF, individually quick-frozen.

soaking varies with variety and species, and with

length and conditions of storage. Traditionally, dry

beans have been soaked overnight (8–16 h) in cold

water. High-temperature soaking accelerates hydra-

tion. Experimental methods designed to accelerate

seed hydration and tenderization include vacuum,

ultrasonic sound, the use of soak-water additive

(phosphates) and gamma-irradiation. Cracking or

scouring seeds with tough seed coats before soaking

assists moisture penetration. The degree and rate of

hydration of the starch–protein matrix influences the

cooking rate and final texture of cooked beans. The

content of total soluble sugars (reducing and non-

reducing) and soluble minerals in legumes decreases

during soaking because of leaching losses. In many

less developed countries (LDC), dry beans are cooked

without soaking because of water quality limitations.

Germination, Sprouting, and Fermentation

0032 Soaking legume seeds and holding at ambient tem-

peratures will facilitate germination. Germination

has profound effects on the physicochemical compos-

ition changes and improves the nutritional quality of

legumes by increasing vitamins such as ascorbic acid,

riboflavin, choline, thiamin, tocopherol, and panto-

thenic acid. The sprouted grains may be consumed

fresh or, if followed by seed coat removal, can be

roasted or ground for use in soups or side dishes.

0033 In Asian countries, soybeans have been fermented

to produce a variety of nutritious food products.

Some important soybean-based foods are tofu

(soybean curd), natto (Japanese product), miso (soy

paste), tempeh (Indonesian product), shoyu (soy

sauce) and tamari. Fermented foods that are trad-

itional in India include idly (steamed) and dosai

(fried) from black gram, and dhokla (steamed) and

khaman from Bengal gram. Groundnuts are also fer-

mented with a mold to make ontjom, an Indonesian

product similar to tempeh.

Dehulling and Roasting

0034 Dehulling and splitting the cotyledons reduces

cooking time considerably. The ease of removing the

hull depends on the thickness of the seed coat and can

be achieved via wet or dry methods. The wet method

involves soaking the grain in water for a few hours,

draining, drying, milling, and winnowing to remove

the seed coat. In a large-scale dry method, oil is mixed

with the seeds by passing through emery-coated

rollers to abrade the surface. This is common practice

for legumes with particularly tough seed coats,

including velvet, hyacinth, and winged beans.

0035 Dehulling and splitting the cotyledons into halves

is a process traditionally practiced in Asia and Africa.

In India, nearly 70% of food legumes are milled to

make dehulled split cotyledons (referred to as dhal),

which is prepared by cooking until soft, mashing,

mixing with water, then boiling again to give a

porridge of uniform consistency. In addition, dhals

are cooked with vegetables, spice, and condiments.

Roasting and puffing involve the application of dry

heat to legume seeds using a hot drier at a tempera-

ture of 100–200



C for a short time (1–5 min) or by

direct heating with hot sand. Dhal or whole seeds are

roasted to obtain an appealing flavor and maintain

maximum protein quality.

0036Pigeon peas are usually consumed as dehulled splits

or dhal. The dhals are cooked until soft and served as

a sauce or boiled with rice. They are also incorpor-

ated in cereal legume mixtures to feed infants and

young children in LDC. Mature seeds can also be

soaked before boiling or pounding, then steamed

and fried. However, the green seeds, pods, or sprouts

may be eaten directly or canned.

Thermal Processing

0037Heating increases tenderization of the cotyledon, im-

proves flavor, and inactivates enzymes and intrinsic

toxic factors of legume seeds.

0038Cooking Whole legumes may be cooked either with

or without the seed coat, in boiling water or steam.

Traditionally, cold-water-soaked beans are simmered

at subboiling temperatures for several hours or until

adequately tender for eating. Cultivar variability,

hard-shell, and HTC storage defects may dramatic-

ally alter cooking time. The use of ‘crock-pot’ cookers

has also generated interest for preparing beans, al-

though this low-temperature cooking procedure may

not adequately inactivate PHA. There is loss of solids

from beans during cooking, with the amount

depending on species, variety, and cooking method.

Although cooking is essential in order to render the

beans palatable and inactivate toxic substances, ex-

cessive cooking results in loss of protein biological

value in the form of lysine and methionine.

0039Canning Industrial canning overcomes the long

period of time and high fuel costs involved in home

preparation of legumes. Hot-water hydration (final

moisture 53–57%) can be accompanied via serial

rotator blanchers with differential temperatures, or

continuous pipe blanchers. Hydrated beans may

be processed in a standard rotary water blancher for

3–8 min, then continuously washed with cold-water

sprays, utilizing rod washers or vibrating sieves to

facilitate removal of broken beans and skins. Beans

are generally processed in water or brine, tomato

sauce, or molasses. The beans will further hydrate

during the thermal process and equilibrate with the

3526 LEGUMES/Legumes in the Diet

sauce or brine to a final moisture content of 65–70%

within 2–4 weeks.

Food Ingredient Preparation: Bean Meals, Legume

Flours, Concentrates, and Powders

0040 Flours and concentrates made from legumes other

than soybeans have had little commercial success.

Initial efforts to produce bean ingredients were

focused to minimize cell rupture in order to retain

the same texture, appearance, and taste of conven-

tionally prepared beans. The compartmentalization

of protein and starch enables size reductions and

fractionation of dry beans into coarse and fine frac-

tions containing high starch and high protein, respect-

ively. Examples of high-protein food ingredient

products are flour processed by pin milling and air

classification, and concentrates and isolates pro-

cessed by alkali, salt, and acid extraction together

with isoelectric precipitation or ultrafiltration. Bean

protein concentrates containing 72–81% protein,

protein isolates containing about 90% protein, and

fractions containing 50% starch have all been pro-

duced using water extraction techniques. Instant

precooked bean powders have been prepared by

soaking, cooking, slurrying, and drum- or spray-

drying. Recent product development has included

the use of spray-dried powders from pea, imitation

milk replacers from pea and lentil, and protein curd

similar to tofu from pea. Ingredients from dry beans,

peas, and lentils have been used in pasta, noodles, and

spaghetti. Legume meals and concentrates have been

blended into ground-beef preparations. In addition,

the high-fiber or high-protein bean flour fractions

have been successfully substituted (20%) for wheat

flour to produce quality biscuits, doughnuts, quick

breads, and leavened doughs.

0041 When raw legumes are ground without pretreat-

ments, they develop undesirable odors and flavors.

Lipoxygenase has been held responsible for the

appearance of off-flavors by catalyzing formation of

hydrogen peroxides from unsaturated fatty acids.

However, treatment with dry heat for 6–8 min at

105



C completely inactivates this enzyme. It is there-

fore advantageous to apply a rapid heat treatment to

beans prior to bean flour production. The attractions

of conventional air heating are ease of handling and

lack of product contamination, but air does not pro-

vide a high rate of heat transfer. Instant navy bean

powders, obtained by roasting dry beans in a bed of

heated ceramic beads, followed by grinding, resulted

in functional food ingredients which showed:

(1) stable gel-forming capacity; (2) low trypsin inhibi-

tor and hemagglutinin activities; (3) increased water-

holding capacity and cold paste viscosities; (4) no

changes in available lysine; (5) limited degree of

starch damage; and (6) reduction of water-soluble

nitrogen content. Air classification of roasted beans

produced high fiber, starch, and protein fractions that

are suitable as food ingredients in a variety of food

products.

0042Groundnuts or peanuts are eaten raw, roasted, or

pounded into peanut butter, or processed as salted

peanuts, sweets, and snacks. They are also incorpor-

ated in soups and stews. In Africa, India, China, and

South-east Asia, the peanut crop is converted to oil

and cake. Edible peanut flour is prepared by grinding

peanut kernels in a hammermill or bar-cracking

machine. The ground seeds are conditioned to 10%

moisture and cooked in a stack cooker for 45–60 min

to attain an exit temperature of 116



C. An expeller is

used to reduce the oil content of the cooked meal to

8–12%. The meal is then ground, conditioned to

10% moisture, flaked, and extracted with hexane.

The defatted flakes are desolventized, then cooled

and ground to either flour or grits. Nutritious, low-

cost, peanut-flour-enriched wheat noodles have been

developed in Thailand.

0043Processing of full-fat, partially defatted or fat-free

flakes from peanut kernels includes grinding low-

moisture (6%) kernels to a flour consistency, mixing

with water to form an emulsion suspension, heating

this to 93–116



C to reduce lipoxygenase activity, and

drum-drying to form the peanut flakes. Peanut pro-

tein concentrate is prepared using defatted peanut

flour or meal with protein content between 45%

and 60%. The processes or techniques which can be

used to isolate peanut protein concentrate include

immobilization of the major protein fraction, air or

solvent classification, and wet milling.

0044Bambarra groundnut seeds have lower oil content

compared to groundnut, but are richer in protein and

calories. They are consumed fresh, grilled, or broiled,

or made into flour to form cakes. Immature shelled or

unshelled nuts are pounded and boiled into a stiff

porridge. They are also served as appetizers and

relishes.

Convenience Bean Products

0045Preparation and cooking time is a major constraint to

bean utilization, but numerous chemical and physical

processing techniques have been initiated to alleviate

this problem.

0046Quick-cook beans Bean products which cook in

less than 15 min have been developed using vacuum

infiltration of a solution containing sodium chloride

(NaCl), pentasodium tripolyphosphate (Na

sodium bicarbonate (NaHCO

), and sodium carbon-

ate (Na

). Further soaking of the beans in this

solution is followed by rinsing, drying and cooking or

LEGUMES/Legumes in the Diet 3527

freezing, depending on the intended use. These prod-

ucts have not been commercially developed, in part

because of the elevated sodium level associated with

the process.

0047 Frozen or dehydrated beans Numerous precooking

and dehydration procedures have been developed

which enable production of rapidly reconstituted

beans, bean pieces, or bean powders. Fully cooked,

dehydrated bean flours, bean ‘crumbles’ and refried

bean mixes are prepared for use in institutional food

service systems. Main-dish retail products with a

wide variety of styles and seasonings (barbecue,

Cajun, al presto) have recently entered the market.

0048 Partially or fully cooked beans marketed as indi-

vidually quick-frozen (IQF) or as a block-frozen

product are suitable as institutional food ingredients

or for direct retail distribution. Appropriate hydra-

tion and softening under low-temperature cooking

conditions prior to freezing provide products that

are readily suitable for use in recipe-based foods,

such as chilli con carne and acidified three-bean

salad dishes.

0049 Extrusion Extrusion utilizes continuous high-pres-

sure and high-temperature cooking of starch or flour

from legumes and cereals. The use of this technology

and proper ingredient formulation may provide pre-

cooked or quick-cook legume products. Starch gelat-

inization occurs primarily during the later stages of

cooking of the beans. The amount of water available

is critical to the gelatinization process. When the

cooking and extrusion processes are combined, the

increased pressure differential will facilitate expan-

sion of the final product. This formed product, of

open porosity, may require additional air-drying to

assure shelf-stability. The dry formed ‘bean’ will read-

ily hydrate and soften when reconstituted. Die con-

figuration can be designed to produce a variety of

intricate product shapes that can be further optimized

to produce simulated beans. Appropriate binders and

coating agents can be added to improve the appear-

ance of precooked or quick-cook bean products,

resulting in promising prototypes of extrusion-

cooked formed ‘beans.’ (See Extrusion Cooking: Prin-

ciples and Practice.)

0050 Microwave heating/cooking Several frozen bean

and refried bean products, as well as instant bean

flour mixtures for sauces and salsa, are commercially

available and can be prepared using a microwave

oven. Microwave treatment of whole soybeans after

soaking to prepare soy flour or soy grits without a

burnt odor was reported completely to inhibit trypsin

activity. Proper microwave treatment also reportedly

increased the in vivo digestibility and the metaboliz-

able nitrogen of soybeans.

0051Legumes are prepared, processed, and consumed

using a variety of locally and culturally adapted

methods or styles, and are important in subsistence

and industrialized economies. Research directed to

improve utilization of legumes has included removal

of constraints such as postharvest storage defects,

cookability, digestibility, and inactivation of anti-

nutritional and flatulent factors. New processes and

products may enhance the utility and acceptability of

these valuable food resources.

See also: Beans; Canning: Principles; Carbohydrates:

Classification and Properties; Extrusion Cooking:

Principles and Practice; Fats: Classification; Flour:

Dietary Importance; Legumes: Dietary Importance;

Peanuts; Protein: Food Sources; Pulses; Tannins and

Polyphenols

Further Reading

Aykroyd WR and Doughty J (1982) Legumes in Human

Nutrition, 2nd edn. Rome: Food and Agriculture Organ-

ization.

FAO (1998) Production Yearbook, vol. 52. Rome: Food

and Agriculture Organization.

Liu KS (1997) Soybeans: Chemistry, Technology and Util-

ization. New York: Chapman and Hall.

Matthews RH (ed.) (1989) Legumes: Chemistry, Technol-

ogy and Human Nutrition, pp. 187–196. New York:

Marcel Dekker.

Salunkhe DK, Kadam SS and Chavan JK (1985) Postharvest

Biotechnology of Food Legumes. Boca Raton, Florida:

CRC Press.

Sinha SK (1977) Food Legumes: Distribution, Adaptability

and Biology of Yield. Rome: Food and Agriculture

Organization.

Uebersax MA and Occen

a LG (1993) Suitability of

dry edible beans for world food relief programs: appli-

cations and nutritive value. Michigan Dry Bean Digest

18: 2–13.

Uebersax MA and Ruengsakulrach S (1989) Utilization of

dry field beans, peas and lentils. In: Applewhite TH (ed.)

Vegetable Protein Utilization in Human Foods and

Animal Feedstuffs, pp. 123–130. Champaign, Illinois:

American Oil Chemists’ Society.

Uebersax MA and Ruengsakulrach S (1989) Structural and

compositional changes during processing of dry beans

(Phaseolus vulgaris). ACS Symposium Series 405. In: Jen

JJ (ed.) Quality Factors of Fruits and Vegetables: Chem-

istry and Technology, pp. 111–124. Washington, DC:

American Chemical Society.

Uebersax MA, Ruengsakulrach S and Hosfield GL (1989)

Uses of common dry field beans. In: Lucas EW and

Erickson DR (eds) Food Uses of Whole Oil and Protein

Seeds, pp. 231–252. Champaign, Illinois: American Oil

Chemists’ Society.

3528 LEGUMES/Legumes in the Diet

Dietary Importance

Y Lam, Bio-Rad Laboratories, Hercules, CA, USA

B O de Lumen, University of California, Berkeley,

CA, USA

Introduction

0001 Since man settled down to practice agriculture, the

human diet has consisted mainly of cereals or starchy

roots and fruits, which are poor sources of protein.

With few exceptions, these classes of food crops have

been the basis of the human diet throughout record-

ed history, and this is still true today. As shown in

Table 1, legume cultivation and consumption are

widespread throughout many countries and cultures,

suggesting that legumes might have evolved to fulfill

human needs for proteins and other nutrients, com-

plementing cereals.

North America

0002 Common bean, lima bean, soybean, peanut, pea,

and lentil are the main legumes used in this region.

Common bean and lima bean are typically processed

commercially and canned or cooked at home. Peanut

is used roasted as whole seeds or as ingredients in

various products such as peanut butter. Pea is sold

commercially as green immature seeds in frozen form

or as dry mature seed. Lentil is usually used as dry

seeds and incorporated into a number of dishes. Soy-

bean is a major cash crop in the USA, where the

soymeal that remains after oil extraction is used

mainly for animal feed. The USA and Brazil are the

biggest producers and exporters of soybean. Soybean

in the USA is a major source of cooking oil, protein

concentrate, and protein isolates, which find uses in

many different products including meats. The market

for soy products is increasing at a rapid rate owing to

the health benefits attributed to consumption of soy

products such as reduction of cardiovascular disease

and prevention of cancer. Tofu (soybean curd), soy

sauce, miso, and nato are consumed by an increasing

number of the US population in addition to the Asian

American population already consuming them in

large quantities.

0003The kidney bean is the principal legume of Mexico,

occurring in several varieties. The dietary patterns of

the Native American population in Arizona and New

Mexico are similar to those of Mexico and Central

America. The average daily intake of the Pima

Indians in Arizona is 70 g per person, about four

times the average US daily intake, providing a high

percentage of the total protein. Kidney bean is again

the principal legume, but other beans such as lima are

also eaten.

Latin America

0004The common bean is the major legume in this region,

making up about 90% of the total legume produc-

tion, excluding soybean, which is produced in large

quantities in Brazil as an export cash crop. In South

and Central America, cowpea, pea, pigeon pea, and

lupine are also grown. Common bean is typically used

tbl0001 Table 1 Cultivation of economically important legumes in different regions of the world

Common names Latin name Areas of cultivation

Peanut, groundnut,

monkey nut,

pigeon pea

Arachis hypogaea Tropics and subtropics

Cajanus cajan Tropics and subtropics in Asia and Africa; widely cultivated in India and

Pakistan; introduced into tropical America, Pacific Islands, and Australia

Chick pea, Bengal gram Cicer arietinum Tropics and subtropics in Asia and Africa; widely cultivated in India and

Pakistan mainly as a cold weather crop; also cultivated in

Mediterranean countries and South America

Soybean Glycine max South and East Asia, particularly in China and Japan (but not in India)

and USA; other countries only on a limited, experimental scale

Lentil, split pea Lens esculenta Near east, North Africa, India, Burma, central and southern Europe

Lima bean, butter bean Phaseolus lunatus Tropical America, West Indies, tropical Africa, Madagascar, New Guinea,

and north Australia

Golden gram, green gram Phaseolus aureus South and East Asia, particularly India, East Africa

Black gram, mung bean Phaseolus mungo India, Africa, West Indies, South and East Asia

Kidney bean, French bean,

haricot bean

Pea, garden pea

Phaseolus vulgaris Throughout the world, particularly in the Americas

Pisum sativum Throughout temperate zone; in warm countries as a cold weather crop or

at high altitudes

Broad bean, horse bean Vicia fab a Temperate zone, particularly Mediterranean region, highlands in Asia,

Africa, and Central and South Americas

Cowpea, blackeye pea Vigna unguiculata Tropical Asia and Africa, West Indies, southern Europe, and the Americas

Bambara, groundnut, earth pea Voandzeia

subterranea

Tropical Africa

LEGUMES/Dietary Importance 3529

as a dry bean, cooked at home, and included in a

number of dishes.

Tropical Africa

0005 In addition to the dry seeds, other forms of legumes

are also consumed, such as the tender green shoots,

leaves, and immature green pods. The three major

legumes that are consumed locally are cowpea,

common bean, and pigeon pea. Peanut is also grown

but mostly exported.

Asia

0006 Legumes are the only high-protein sources of the

average diet in India, where they are eaten mainly

with rice, wheat, and other minor cereals. Chickpea

and pigeon pea make up 60% of the total legume

production in India, followed by pea and khesari

(Lathyrus sativus). The term ‘gram’ is applied to dry

legume seeds with the husk, whereas the split,

dehusked seeds are called ‘dhal.’ The most common

way of preparing dhal is to cook until soft, after

which they are mashed, mixed with water, and boiled

again to give a soup or gruel of uniform consistency.

These are eaten as part of meals composed of the

staple cereal of the locality, which is usually boiled

rice or chapatties made from wheat, sorghum, or

millet.

0007 Soybean, peanut, common bean, adzuki bean,

black gram, horse gram, green gram, fava bean, and

lima bean are grown and consumed to different

degrees in China, Taiwan, Japan, Korea, Myanmar,

Vietnam, Philippines, Malaysia, Indonesia, and Sri

Lanka. The legumes are consumed as dry seeds, im-

mature pods, sprouted and fermented. The winged

bean (Psophocarpus tetragonolobus L) is mainly

eaten as a green vegetable in the Philippines, Malay-

sia, Indonesia, Vietnam, and Sri Lanka. Because its

chemical composition is similar to that of soybean,

the winged bean has been promoted in its dry form as

a rich source of protein and oil.

0008 Soybean is the principal legume of East Asia

(China, Japan, and Korea) and is also widely used in

South-east Asia. It is consumed in forms that have

been used for centuries such as green, dry seed, fer-

mented, and germinated. Green immature soybean

has an attractive flavor, and the pods are usually

boiled in salted water, so that the beans can be easily

removed. Immature beans are used in salads or

cooked in vegetables dishes or in soups. The popular-

ity of green soybean in the USA is increasing, together

with other soy products.

0009 Sprouted soybeans are among the most popular of

Chinese vegetable dishes, which are either eaten raw

as a salad or included in cooked dishes. Tofu is the

most popular form of soy products in Asia. Typically,

the whole beans are soaked overnight, ground into an

emulsion, and strained to remove coarse particles,

and the mash is boiled or steamed and passed through

cloth filters. The curd is then precipitated from the

milky fluid, allowed to settle, transferred to boxes

lined with cloth filters, pressed with weights, washed,

and dried to various extents. The final product, with a

white color and delicate texture, contains 6–17%

moisture and is sold in slices or slabs. The curd is

included in a variety of dishes and is widely used as

food for children.

0010A number of fermented soybean products are

widely used in Asia. Soy sauce (shoyu) is produced

in large quantities in Asia and the USA. It is made

with a long, elaborate fermentation process with vari-

ous fungi, bacteria, and yeast. Soybean paste (miso)

is made from fermenting a mixture of soaked and

cooked soybean plus steamed rice inoculated with

Aspergillus oryzae. The final product, with a paste-

like consistency and containing about 10% protein, is

made into soups or served with rice and other foods

as a side dish or condiment. Natto is a Japanese

product made by fermenting whole soybeans through

the action of Bacillus subtilis using an ancient method

said to have been invented by Buddhist monks. The

finished product, which is eaten with rice, has a musty

flavor and gray color. A similar fermented product is

hamanatto, which originally came from Korea. Here,

the fermenting agent is a mold. Tempeh, an Indones-

ian product, is made by treating soybeans with the

fungus Rhizopus oryzae. This highly nutritious

product contains about 25% protein and is rich in

amino acids produced by the fermenting fungus. (See

Fermented Foods: Origins and Applications.)

0011Soy beverage is prepared as a white emulsion,

which has the appearance of milk. Typically, the soy-

beans are soaked and passed through a mill, emerging

as an emulsion. The emulsion is filtered, transferred

to a boiler, and boiled for 20 min after adding supple-

ments such as vitamins, sugar, salt, calcium, and fla-

vorings. The boiled mixture is finally passed through

a special emulsifier. The milk contains about 3.2%

protein, 3.4% fat, and 4.5% carbohydrates, with

contents of vitamins and calcium according to the

amounts added. In Asia, soy milk is used as a bever-

age for adults but not for infants. Various proprietary

formulations of soy milk are produced in the USA

mainly for use in feeding infants and young children

allergic to cows’ milk.

Middle East, North Africa, and Mediterranean

Countries

0012Populations in these regions consume legumes such as

fava bean, pea, lentil, lupine, and some species of

Lathyrus. In Africa, groundnut, mainly cultivated as

3530 LEGUMES/Dietary Importance

an oil-yielding cash crop, is also used directly as

human food. Cowpea is the next most widely used

legume in Africa. The common beans, particularly

kidney beans, are also grown extensively in hilly

regions with a good rainfall. Stewed broad beans are

commonly eaten as the first meal of the day in the

Middle East.

Europe

0013 Pea and lentil are produced and used extensively in

European countries. Common bean is also used in all

of Europe but is usually imported from Canada and

the USA. Lentil is also often imported.

Macronutrients

0014 The energy value and proximate composition of 10

species of legume seeds are shown in Table 2. The

largest component by weight in legume is carbohy-

drate averaging 53%. The second largest component

in legumes is protein, varying from 19.5 to 39.7% by

weight and contributing significantly to the seed

energy value. Lipids comprise on average 7% of the

seed weight. Most legumes are low in lipids, with the

exception of peanut and soybean, which are low in

carbohydrate but high in protein and lipids.

Protein

0015 Methionine is the first limiting essential amino acid in

legumes because the major storage proteins, the glo-

bulins, are low in this amino acid (Figure 1). Cysteine,

although not an essential amino acid, is included with

methionine, because it has a sparing effect on methio-

nine when added to the diet. This limitation, together

with its high lysine content, makes legumes nutrition-

ally complementary with cereals, which is first

limiting in lysine and relatively high in methionine.

This makes the overall protein quality of cereal–

legume mixtures better than that of either protein

source alone. (See Protein: Food Sources.)

0016Supplementation of legumes with free methionine

improves their value in supporting animal growth and

increases the efficiency of utilization of dietary pro-

tein. In the feeds of poultry and swine, where soybean

is the main protein source, methionine is used as a

supplement. Little practical use of supplementation in

human diets has been made, despite clinical studies

with humans demonstrating their effectiveness. (See

Amino Acids: Metabolism.)

0017Bioengineering (genetic engineering) is another

strategy to enhance the protein quality of legumes.

The sulfur amino acid requirements of humans vary

with age, with infants requiring the most, adults re-

quiring the least, and growing pigs requiring more

than human infants (Figure 1). The FAO recommends

using the essential amino acid requirement pattern of

2–5-year-old children to evaluate protein quality for

all ages, except infants. The methionine þcysteine

content of legumes has to be increased to approxi-

mately 25 mg per gram of protein for humans except

infants, to 42 mg per gram of protein for human

infants and to about 48 mg per gram of protein for

swine. The digestibility of legume protein, which

varies from 72 to 98%, also needs to be considered.

tbl0002 Table 2 Macronutrients contents per 100 g of edible legume seeds

Commonnames Energy (kJ) Water (g) Protein (g) Lipid (g) Crude fiber (g) Ash (g) Carbohydrate (g)

Soybean 1735 9.0 34.3 18.7 3.8 5.1 31.6

Peanut 2306 6.5 27.6 52.1 2.0 2.4 13.3

Pea 1453 10.5 24.5 1.1 4.0 2.5 62.0

Lentil 1453 10.5 27.7 1.0 4.1 2.6 61.2

Cowpea 1453 11.7 22.0 1.3 4.5 3.3 63.4

Chickpea 1546 10.7 19.5 5.7 4.0 2.7 61.7

Pigeon pea 1449 9.9 19.5 1.3 1.3 3.9 65.5

Fava bean 1470 10.6 24.8 1.4 7.0 3.3 60.4

Lupine 1596 10.7 39.7 9.0 12.5 3.5 35.0

Winged bean 1701 9.7 32.8 17.0 4.1 36.5

Mean 1537 10.0 25.8 7.0 6.0 3.4 52.3

Human

infant

met + cys mg/g protein

2−5

yr-old

children

Growing

pigs

Soybean Common

bean

Mung

bean

fig0001Figure 1 Methionine and cysteine contents of some legumes

compared with methionine and cysteine requirement for human

infants, 2–5 year-old children and growing pigs.

LEGUMES/Dietary Importance 3531

Taking soybean as an example with an average

methionineþcysteine content of 22 mg per gram of

protein, this value has to be increased by 14% (for

humans), by 91% (for infants), and by 118% (for

swine). Figures would have to be higher if protein

digestibility is taken into consideration and for other

beans (Figure 1), whose methionineþcysteine con-

tents are generally lower than those of soybean. In

any case, animal feeding trials need to be carried out

to establish the actual nutritional value of transgenic

seeds.

0018 Soybean is a primary target for genetic engineering,

since it is the single largest source of protein in animal

feed. In feed formulations where corn is added to

soybean meal to provide methionine, increasing the

methionine content of corn would be desirable, al-

though its protein quality would not be significantly

improved. Other legumes that are lower in methio-

nine content than soybean should also be targeted.

0019 There are basically four types of bioengineering

strategies to increase the methionine content in

legumes: (1) introduce methionine residues or me-

thionine-rich peptides into nonconserved, and pre-

sumably noncritical, regions of storage protein;

(2) transfer genes coding for methionine-rich protein

(MRP) from other species, i.e., heterologous genes

into legume of interest; (3) increase the level of non-

abundant, endogenous MRP in the target plant; and

(4) manipulate the key enzymes in the biosynthetic

pathways of essential amino acids. The transfer of

heterologous MRP genes into legumes is the most

widely used and has been successful in increasing

the methionine content of soybean by 26% and

lupine by 94%. The transgenic soybean containing

the Brazil nut MRP is allergenic to individuals who

are allergic to Brazil nut, demonstrating that the

Brazil nut MRP is a major allergen in Brazil nut and

that allergens can be transferred from one food source

to another through bioengineering. In feeding trials

with rats, the transgenic lupine seeds have statistically

significant increases in live weight gain, true protein

digestibility, biological value, and net protein utiliza-

tion compared with wild-type seeds. The strategy of

cloning nonabundant, MRP in soybean led to the

discovery of lunasin, a unique soybean peptide that

has been shown to have anticancer properties (see

section Bioactive Phytochemicals).

Digestibility of Legume Proteins

0020 While the amino acid pattern of legumes is the most

important index of protein quality, digestibility and

bioavailability of the constituent amino acids are the

next important factors. Differences in protein digest-

ibility may be due to the nature of the protein, the

presence of nonprotein components (dietary fiber,

tannins, phytates), the presence of antinutritional

factors, and processing conditions. The true digest-

ibility of legumes varies from 73% (canned pinto

beans) to 98% (soy protein isolate). Recognizing the

importance of digestibility in evaluating protein qual-

ity, the recommended method is to combine amino

acid score with digestibility data in what is called

protein digestibility-corrected amino acid score. (See

Protein: Quality.)

Carbohydrates

0021The total carbohydrate content of legumes is typically

60%, and these carbohydrates are generally well

absorbed and utilized. Starch accounts for the major

portion of legume carbohydrates, ranging from 24 to

56%. The oilseeds have lower carbohydrates content,

with values such as 14% for peanuts and 32% for

soybean. Oligosaccharides of the raffinose family

(raffinose, stachyose, verbascose, and ajucose) ac-

count for 31–76% of the total sugars. The resistance

of the raffinose oligosaccharides to human and mono-

gastric animal digestion presents a problem to certain

individuals sensitive to flatulence. It is estimated that

reducing the raffinose oligosaccharide content of soy-

bean used for livestock feed by 1% would result in an

additional total value of $101 million per year (1990

value) owing to improved nutrition and reduced

flatulence. (See Carbohydrates: Classification and

Properties.)

Lipids

0022The lipid content of legumes is generally 7%. Excep-

tions are the oilseeds peanut and soybean, which con-

tain about 52 and 20% oil, respectively. Soybean oil is

the most widely used cooking oil. Winged bean is po-

tentially a rich source of oil because of its similarity

with soybean in chemical composition, but has not

been exploited commercially. Peanut and soybean oils

provide essential fatty acids to the human diet. Peanut

contains 22% linoleic, whereas soybean has 54% lino-

leic and 8% linolenic. (See Fats: Classification.)

Micronutrients

0023Selected mineral and vitamin contents of 10 species of

legume seeds are shown in Table 3.

Vitamins

0024Legume seeds are excellent sources of folate, which,

in addition to being an essential nutrient, is thought

to reduce the risk of neural tube defects. One serving

of beans provides more than half of the current rec-

ommended dietary allowance (RDA) for folate. Beans

are also good sources of thiamin and pantothenic

3532 LEGUMES/Dietary Importance