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sarcomas were produced at the site of injection

of aluminum-dextran in mice. However, since

subcutaneous injection of aluminum-dextran is a

rather irrelevant model to assess aluminum carcino-

genicity, the significance of the positive results

appears questionable. (See Carcinogens: Carcino-

genic Substances in Food: Mechanisms.)

0021 Since aluminum and aluminum compounds are not

carcinogenic, or even show some antitumor activity

in laboratory animals, the negative results in most

short-term in vitro and in vivo mutagenic assays

(except some experiments in plants) are not surpris-

ing. (See Mutagens.)

0022 According to experimental data together with cer-

tain epidemiological evidence, it can be concluded

that aluminum and its salts do not constitute a

carcinogenic or mutagenic hazard except, perhaps,

in cases of extremely high exposure.

Miscellaneous

0023 No significant aluminum toxicity was observed when

aluminum nitrate nonahydrate was given orally to

rats at 375, 750 or 1500 mg per kg of body weight

per day for 1 month or over a period of 100 days at

360, 720, and 3600 mg per kg body weight per day.

However, it has been suggested that oral aluminum

exposure may both stimulate and suppress the

immune system, depending on the exposure level and

the physiological state of the animal and the immune

response assessed. Recent studies in rats have shown a

slight stimulation of some immune functions in the

rats at aluminum plasma concentrations normally

found in healthy humans (< 10 ng ml

1

Aluminum Toxicity in Humans

Dialysis Encephalopathy Syndrome

0024 Although the possible human toxicity of aluminum

has been a matter of controversy for over 100 years,

the spectrum of clinical aluminum toxicity has

expanded gradually since its initial description as

the cause of dialysis dementia. In the 1970s, Alfrey

et al. suggested that dialysis encephalopathy, pre-

viously a uniformly fatal neurological syndrome,

resulted from aluminum intoxication. Based on add-

itional biochemical and epidemiological data, this

supposition was confirmed, and now it is quite

accepted that aluminum is the cause of the dialysis

encephalopathy syndrome, the main neurotoxic con-

dition of aluminum. This syndrome includes a mild or

severe speech disorder, hallucinations, twitching,

myoclonus, seizures, mental changes and typical elec-

troencephalogram abnormalities. Moreover, there is

little doubt that aluminum can also cause bone

disease and anemia in dialysis patients. Individuals

with dialysis osteomalacia typically present with

severe symptoms of axial skeletal pain, proximal

muscular weakness, and fractures of the ribs, among

other symptoms. In turn, aluminum has also been

implicated as the cause of a microcytic, hypochromic

anemia in patients with chronic renal failure. These

disorders can result from introduction of aluminum

directly into the blood stream via high aluminum-

dialysate or consumption of large oral doses of

aluminum-containing phosphate binders. The lack

of urine production, which is the major route for

aluminum excretion, contributes to the problems in

these patients. While the health threat from diffusate

fluids was significantly reduced by the recommenda-

tion that the diffusate contains less than 10 mgof

aluminum per liter, ingesting aluminum-containing

phosphate binders is still a matter of concern for

uremic patients.

0025On the other hand, several reports have described

aluminum accumulation and toxicity in individuals

without chronic renal failure but with iatrogenic

exposure to aluminum. These include preterm

infants, largely fed intravenously, patients on total

parenteral nutrition, subjects with severe burns, indi-

viduals receiving alum irrigation in the urinary blad-

der to prevent bleeding, and patients undergoing

cranial bone reconstruction with aluminum contain-

ing bone cement.

Occupational Exposure

0026Occupational exposure to aluminum occurs not only

in the primary refining of this metal but also in user

industries (e.g., aircraft, automotive, metal products).

Aluminum welding is also an important exposure

vehicle. Although there are only a few studies on the

influence of occupational exposure to aluminum on

a worker’s cognitive performance, a diverse range of

cognitive deficits, including visuomotor or visuo-

spatial problems, attention deficits, impaired verbal

or visual memory and learning, and problems with

‘concept formation’ have been reported. Recent in-

vestigations have also corroborated that exposure

to aluminum is associated with detrimental effects

on certain cognitive functions, with deficits in

memory attention, and visuomotor and visuospatial

abilities.

0027For biological monitoring, urinary aluminum

appears to be a more sensitive index to current expos-

ure than serum levels. Workers with occupational

exposure to aluminum have shown statistically sig-

nificant increases in urinary aluminum/creatinine

ratios in association with borderline changes in

serum aluminum values. The mean aluminum con-

centrations in a healthy nonexposed population who

164 ALUMINUM (ALUMINIUM)/Toxicology

did not use antacid drugs were 0.06 mmol l

1

(range

0.02–0.13 mmol l

1

) in serum, and 0.33 mmol l

1

(range 0.07–0.82 mmol l

1

) in urine, with the upper

reference limit for aluminum being 0.1 mmol l

1

serum and 0.6 mmol l

1

in urine.

Aluminum and Alzheimer’s Disease

0028 Although there are still many unanswered questions,

there are strong indications that aluminum may be

one of the factors resulting in Alzheimer’s disease and

perhaps other neurodegenerative disorders, including

amyotrophic lateral sclerosis. Aluminum has been

detected in both senile plaques and neurofibrillary

tangle-bearing neurons in the brains of people with

Alzheimer’s disease. Several epidemiological studies

have shown increased risks for Alzheimer’s disease in

populations exposed to elevated aluminum concen-

trations in public drinking water supplies. However, a

recent study indicated that any relation at aluminum

levels below 0.2 mg l

1

is weak. Other independent

lines of evidence supporting the hypothesis that

aluminum might play a role in the pathogenesis of

Alzheimer’s disease are: (1) studies on the effects of

intracranial aluminum on the cognitive and memory

performance of animals; (2) data showing that in

laboratory experiments aluminum aggregates Ab,

phosphorylates some sites on tau, the principal sub-

unit of Alzheimer’s disease tangles and assembles,

in vitro, Alzheimer’s disease hyperphosphorylated

tau into paired helical filaments which are indistin-

guishable from those of Alzheimer’s disease; and

(3) the slowing of the progress of the disease with

the use of desferrioxamine (or deferoxamine), an

aluminum chelating agent that removes aluminum

from the body.

0029 Almost certainly Alzheimer’s disease can result

from many factors, genetic and environmental, or a

combination of both. Although the participation of

aluminum cannot be discarded, it seems very unlikely

that a single environmental factor such as aluminum

can constitute a sufficient explanation. A possible

interpretation is that aluminum, which is definitely

neurotoxic, may have a dementing effect independent

of the pathological processes associated with Alzhei-

mer’s disease. In contrast to genetic risk factors for

which preventive measures cannot yet be instituted in

the foreseeable future, human exposure to aluminum,

especially in the aging population, could probably be

reduced. It would, perhaps, contribute to reducing

the incidence of at least some forms of dementia.

Treatment of Aluminum Overload

0030 Reduction of aluminum accumulation and toxicity

may benefit a variety of patient populations which

have different treatment needs. Prevention is the most

important issue to avoid aluminum overload. Because

of the propensity of uremic patients to retain alumi-

num, prevention is of special interest for these sub-

jects. In relation to it, a careful surveillance of the diet

of these patients (citrate, ascorbate, lactate, etc.) is

recommended. Moreover, sodium bicarbonate and

calcium carbonate or calcium acetate are adequate

substitutes for Shol’s solution and calcium citrate,

respectively.

0031Aluminum mobilization and removal are essential

in patients with aluminum toxicity. Currently, the

most effective treatment to remove aluminum from

the body is parenteral administration of desferri-

oxamine, an aluminum chelator. In recent years, a

number of experimental studies have shown that

oral administration of the chelating agent deferiprone

(L1) could be an alternative drug to desferrioxamine

for aluminum mobilization. However, the potential

use of deferiprone for aluminum removal in humans

is still controversial.

See also: Carcinogens: Carcinogenic Substances in

Food: Mechanisms; Emulsifiers: Uses in Processed

Foods; Leavening Agents; Mutagens

Further Reading

Alfrey AC, LeGendre GR and Kaenhy WD (1976) The

dialysis encephalopathy syndrome. Possible aluminium

intoxication. New England Journal of Medicine 294:

184–188.

Chadwick DJ and Whelan J (1992) Aluminium in Biology

and Medicine. Ciba Foundation Symposium. Chichester:

John Wiley.

Colomina MT, Sanchez DJ, Sanchez-Turet M and Domingo

JL (1999) Behavioral effects of aluminum in mice:

influence of restraint stress. Neuropsychobiology 40:

142–149.

Domingo JL (1995) Reproductive and developmental

toxicity of aluminium: a review. Neurotoxicology and

Teratology 17: 515–521.

Domingo JL (1996) Adverse effects of aluminium-chelating

compounds for clinical use. Adverse Drug Reactions and

Toxicological Reviews 15: 145–165.

Gomez M, Sanchez DJ, Llobet JM, Corbella J and Domingo

JL (1997) The effect of age on aluminium retention in

rats. Toxicology 116: 1–8.

McLachlan DRC (1995) Aluminium and the risk for Alz-

heimer’s disease. Environmentrics 6: 233–275.

Nieboer E, Gibson BL, Oxman AD and Kramer JR (1995)

Health effects of aluminium: a critical review with em-

phasis on aluminium in drinking water. Environmental

Reviews 3: 29–81.

van Landeghem GF, de Broe ME and D’Haese PC (1998) Al

and Si: their speciation, distribution and toxicity. Clin-

ical Biochemistry 31: 385–397.

ALUMINUM (ALUMINIUM)/Toxicology 165

Yokel RA and Golub MS (1997) Research Issues in Alumin-

ium Toxicity. Washington: Taylor & Francis.

Zafar TA, Weaver CM, Martin BR, Flarend R and Elmore D

(1997) Aluminium (

Al) metabolism in rats. Proceedings

of the Society for Experimental Biology and Medicine

216: 81–85.

Zatta PF and Alfrey AC (1997) Aluminium Toxicity in

Infant’s Health and Disease. Singapore: World Scientific.

AMARANTH

R Bressani, Instituto de Investı

gaciones, Universidad

del Valle de Guatemala, Guatemala

Background

0001 Amaranth, a legacy of the Aztecs, Mayas, and Incas,

continues to be an underexploited plant with a prom-

ising economic value due to the variety of uses it can

have and the benefits it can provide to producers,

processors, and consumers. Present interests have

developed because the plant offers leaves of a high

nutritional quality when used as a vegetable, because

the grains have a high protein content and quality,

and because the whole plant offers a highly accept-

able forage. The amaranth plant is also attractive

since it adapts itself to a large number of environ-

ments, grows with vigor, produces large amounts of

biomass, and resists drought, heat, and pests. Less

attractive features of the plant include leaves that

tend to accumulate nitrate and oxalates, and a very

small grain size, which necessitates a large labor force

when harvesting. With only a relative small research

effort, a strong knowledge base is being constructed

and is beginning to reveal the economic value and

nutritional benefits of this ancient legacy crop.

Origin and Distribution

0002 The Amaranthacea comprise over 60 genera, which

include around 800 species of dicotlyledonous, herb-

aceous plants, of either annual or perennial growth.

There are three species of the genus Amaranthus that

produce relatively large inflorescences with often

more than 50 000 edible seeds per plant. These are

A. hypochondriacus from Mexico, A. cruentus from

Guatemala and A. caudatus from Peru and other

Andean countries. Vegetable amaranths grow very

well in the hot, humid regions of Africa, South-east

Asia, Southern China, and India; they are represented

by various amaranth species, such as A. tricolor,

A. dubius, A. cruentus, A. edulis, A. retroflexus,

A. viridis, and A. hybridus. Grain amaranth was an

important crop for the preHispanic, New World civ-

ilizations. Its presence goes back some 4000 years bc

in the Tehuacan Valley in Mexico, also the most likely

site for the origin of maize. Its use is said to have

been highly associated with religious festivities,

which were forbidden by the Spanish conquerors

and resulted in the elimination of the crop. Its pro-

duction declined to small and insignificant levels, but

it did not disappear. From Mesoamerica and the

Andean region, grain amaranth was apparently

carried as a weed, ornamental, or grain to other

parts of the world. At present, there are three major

germ plasm collections: (1) USDA Plant Introduction

Center, Ames, Iowa, US; (2) Universidad del Cuzco,

Cuzco, Peru; (3) National Bureau of Plant Genetic

Resources, Shimla, India.

Classification

0003Amaranth is a dicotyledonous plant, not a grass like

most cereals, which are monocotyledonous; rather,

it is a pseudocereal. Amaranth shows an extreme

botanical plasticity in adaptation that contributes to

difficulties and confusion in its taxonomy. It is classi-

fied by means of flower structure, the form and pro-

portion of leaves and inflorescence. These highly

variable characters also allow for a high hybridiza-

tion frequency, and assure the availability of a large

germ plasm reserve.

Plant Description

0004Amaranths are broad-leafed plants that can grow to

about 1.5–3.0 m high. The plant has a variable

growth pattern in the type and number of branches,

all of which end with a small seed head, sometimes

maturing at the same time as the main seed head. Leaf

shape varies from lanceolate to ovate to elliptic. Leaf

number and size show great variability within and

between species. The leaves, stems, and flowers of

amaranth can be green, gold, reddish purple, or vari-

ous shades. The seed head, some 50–60 cm high,

varies from pendulous to spiked, and seed color is

usually black, gold, or cream.

166 AMARANTH

0005 Amaranths, like many cereals and grasses, carry

out photosynthesis by the C

pathway, which uses

carbon dioxide very efficiently by fixing it in the

chloroplasts of specialized cells surrounding the leaf

vascular bundles. This characteristic is also respon-

sible for lower water losses by transpiration in asso-

ciation with the stomata. C

plants also have the

capacity to photosynthesize at high rates at high

temperatures, and through osmotic adjustment, the

amaranth plants can tolerate some degree of lack of

water without wilting.

Grain Description

0006 It has been found that the main amaranth inflores-

cence may produce 49–89 g of grain (50 000–100 000

seeds). The grain is very small, lenticular in shape,

1–1.5 mm in diameter, and weighs 0.6–1.3 mg per

seed, with the structure shown in Figure 1. The

germ, which is circular in shape, encircles the peri-

sperm in one plane, and represents, together with the

seed coat, around 25–26% of the weight of the seed,

as obtained by milling techniques. This fraction is

relatively rich in fat and protein. The perisperm rep-

resents 68–78% of the weight of the grain. In cereal

grains, such as maize, the seed coat plus germ repre-

sent around 16–18% of the weight of the kernel, with

the endosperm representing about 65%.

Production

Grain

0007 Production depends on many variables, such as agro-

nomic practices, plant density per hectare, method

of harvest in which seed shattering is important,

uniformity of grain maturation, and the type of seed

head. Yields in some localities have ranged from 1.1

to 1.5 t ha

1

, but in Mexico, some reports indicate

yields of 3.0–5.9 t ha

1

Annual production has been

estimated at 470 10

t per year world-wide. High

yields can be obtained through high plant population

densities (320 000–360 000 plants per hectare), as

well as from the appropriate application of organic

and inorganic fertilizers. To increase yield, breeding

objectives include the development of early maturing

varieties, with a reduced plant height and resistance

to lodging with insect and disease tolerance and no

seed shattering. Likewise, the size of the seed should

be increased.

Whole Plant

0008With respect to vegetable production, yields between

1.4 and 11 t of dry matter per hectare at 4 weeks have

been reported. In one study, dry matter yields at

25, 40, and 60 days after emergence were 66.6,

681.8, and 3452.0 kg ha

1

, yielding 9.7, 154.3, and

514.7 kg of protein per hectare. Yields of edible leaves

are obviously much lower, with values varying from

0.30 to 0.70 t per hectare of dry matter. From a study

on 14 varieties, the average dry weight of the whole

plant prior to seed harvest, was 208.5 g, of which

40% was represented by the weight of the stems,

26% by the inflorescence, and 34% by the seed.

0009The amaranth plant may be cultivated as an inter-

crop with maize to provide a good-quality forage fed

fresh or ensilaged to swine and/or to cattle. Alone or

combined, it can be dehydrated or pelletized to be

used as feed for farm animals.

Vegetable Amaranth

0010The use of amaranth leaves as a vegetable has been

well established in a number of countries. A. tricolor

is the main vegetable species in Asia, whereas

A. hybridus and A. cruentus predominate in Africa

and Latin America. Today, there is probably more

amaranth consumed as a vegetable than as grain.

The young leaves and the softest sections of the

plant are boiled, sometimes in several changes of

water, and consumed often mixed with cooked toma-

toes and other condiments. Usual forms of consump-

tion include soups, salads, boiled, made into a pure

with tomatoes and consumed with cooked root crops

or lime-cooked tortillas. The flavor of cooked amar-

anth leaves and young stems is pleasantly mild and

not unlike that of similar greens.

Chemical Composition

0011The chemical composition of the vegetative part of

amaranth is variable, since the content of organic and

Procambium

Cotyledons

Perisperm

Procambium

Root

Seed

coat

Cotyledons

Starchy

perisperm

Vascular

bundles

Endosperm

Radicle

(root)

Procambium

Shoot

apex

Amaranth

fig0001 Figure 1 A. cruentus seed in (a) cross- and (b) longitudinal

sections as viewed in a light microscope, Source: Irving DW,

Betschart AA and Saunders RM (1981) Morphological studies

on Amaranthus cruentus. Journal of Food Science 46(4): 1170–1174.

AMARANTH 167

inorganic compounds changes as a result of climate,

plant nutrition, agricultural practices, physiological

stage, species and cultivar type, and position of leaves

taken for analysis (Table 1). The moisture content for

all species varied from about 70 to 94%, or from 6 to

30% dry matter. On a dry-weight basis (dwb), protein

varies from 18 to 38% and total crude lipids from 1.3

to 10.6%. The lipid fraction contains 53.6% non-

polar lipids, 33.8% glycolipids, and 12.6% phos-

pholipids. The main fatty acids include linolenic

(30–70%) and palmitic (13–14%) as well as oleic

and stearic acid (see Table 5).

0012 The variability in crude fiber is also quite large,

from 5.4 to 24.6% (dwb). This variability can be

explained on the basis of the age of the plant, with

old leaves and shoots showing the highest values.

Finally, the ash content ranges from 7.6 to 22.2%.

Minerals and Vitamins

0013 The levels of calcium, potassium, and magnesium are

quite high, with calcium present in the largest amount

(2–3 g%; Table 2). Large quantities of phosphorus

are also found, with values ranging from 0.49 to

0.79 g%. There is a relatively high concentration of

iron, varying from 0.08 to 0.50 g% (dwb). Other

minerals have been reported in smaller amounts.

0014 The amounts of vitamins B

and B

, nicotinic acid,

and ascorbic acid are similar to those found in other

greens, but the content of b-carotene is as high as, or

higher than, that reported for other green vegetables

(Table 3).

Other Compounds

0015Amaranth, like many other fast-growing plants, has a

tendency to accumulate nitrates. Reported values

range from 0.27 to 0.74% nitrate (dwb) (0.046–

0.104% fresh weight; Table 1). There is a significant

variation among cultivars, also due to environmental

factors, since the same cultivar grown over different

years has different values. The stems contain about

twice as much nitrate as the leaves on a fresh-weight

basis (fwb). The levels of nitrate in amaranth leaves

are similar to those found in spinach and chard.

Nitrogen fertilizer increases nitrate accumulation

in green vegetables, including amaranth. Nitrates

seldom cause problems to consumers because of the

relatively low concentration and because, upon

cooking, they leach out of the vegetable.

0016Another compound of greater concern is oxalate,

which accumulates in leafy vegetables such as amar-

anths, particularly during dry weather. Oxalate levels

are nutritionally important because they can bind

essential divalent minerals, particularly calcium,

tbl0001 Table 1 Chemical composition of amaranth (grams per 100 g)

Vegetable Grain Forage

Moisture 85.0 + 4.4 9.9 + 2.0 87.8 + 0.76

Dry matter 15.0 + 4.4 90.1 + 2.0 12.2 + 0.76

Protein (N6.25) 24.1 + 4.2 15.2 + 1.7 19.2 + 5.6

Total lipids 3.8 + 0.68 7.0 + 1.6 2.9 + 1.3

Crude fiber 14.9 + 3.7 6.2 + 3.2 16.6 + 6.2

Dietary fiber 13.6 + 4.8

Ash 17.7 + 1.6 3.3 + 0.5 19.0 + 3.9

Carbohydrate 42.9 + 4.6 62.1 + 7.6 43.8 + 8.6

Amylose 6.1 + 1.2

Energy (calories

per 100 g)

284 366 337

Metabolic energy (kJ

1

) 12.2

Nitrate 0.55 + 0.19

Oxalate 4.5 + 1.8 5.86 + 1.89

Phytate 1.03 + 1.16

Tannins 0.18 + 0.14

Cell walls 63.5 + 7.7

Neutral detergent fiber 43.4 + 10.9

Acid detergent fiber 34.6 + 15.0

Acid detergent lignin 5.2

Cellulose 23.4

In vitro digestion (%) 60.0 + 4.1

Data, except moisture are given on a dry-weight basis. Moisture content

varies widely depending on processing.

tbl0002Table 2 Mineral content of amaranth

Mineral Vegetable

(gper100 g

)

Grain

(mgper100 g

)

Forage

(gper100 g

)

Phosphorus 0.66 + 0.22 578 + 38.9 0.70 + 0.28

Potassium 0.19 + 0.02 541 + 80.7

Calcium 2.57 + 0.62 212 + 66.0 2.45 + 0.76

Magnesium 1.10 + 0.30 327 + 42.8

Sodium 22.5 + 6.9

Iron 0.19 + 0.15 35.6 + 32.9

Copper 1.81 + 1.06

Manganese 3.42 + 0.90

Zinc 3.83 + 0.38

Sulfur 150

Aluminum 0.015 1.0

Selenium 0.003

dwb, dry-weight basis.

tbl0003Table 3 Vitamin content of amaranth (mg per 100 g

)

Vitamin Vegetable Grain

Thiamine 0.68 + 0.32 0.136 + 0.076

Riboflavin 2.24 + 0.43 0.223 + 0.056

Nicotinic acid 7.47 + 1.66 1.153 + 0.161

Biotin 42.5 + 1.5

Folic acid 43.8 + 1.5

Vitamin C 570.7 + 89.6 4.47

Carotene 33.3 + 16.68 4.6

dwb, dry-weight basis.

168 AMARANTH

making it nutritionally unavailable. On a dry-weight

basis, the oxalate in amaranth ranges from 1.1 to

7.9% (0.20–1.02% fwb); the stems contain signifi-

cantly lower amounts than the leaves. The variability

is a result of both the genetic make-up of the plant

and environmental factors. The oxalate in amaranth

is bound to sodium, potassium, calcium, and magne-

sium, but about 40% is free and therefore capable of

binding other minerals. During processing in boiling

water, oxalates are removed when water is changed,

so that an intake of 100 g of cooked amaranth would

provide approximately 0.2–1.0 g of oxalic acid. As-

suming that 40% of oxalate is free and lost during

cooking, the level drops to 0.12–0.6 g, which is non-

toxic. Toxic levels for humans have been indicated to

be 2–5 g per day. For populations consuming low

levels of calcium, some of this mineral would become

unavailable because of its complexing affinity to

oxalic acid.

Other Uses

0017 Amaranth leaves have been used in the preparation of

leaf protein concentrates. These represent 24–36% of

the leaf protein and contain 61–80% protein, which

is of a light color, almost odorless, and nonbitter.

Their essential amino acid content is attractive and

high in lysine, but the sulfur amino acid content is low

(Table 4).

Nutritional Value

0018 The chemical composition of amaranth leaves shows

that they provide a relatively good nutritional value.

The iron and b-carotene contents are highly available.

Not much information is available on the quality of

the protein in amaranth leaves, but they make a very

good supplement to maize and rice, either alone or

with common beans at levels of up to 5% (dwb),

because of their relatively high content of lysine, an

amino acid that is lacking in both cereal grains

(Figure 2). At this level of supplementation, amaranth

leaves can provide substantial levels of vitamins and

minerals to cereal/bean diets.

Grain Amaranth

Chemical Composition

0019The gross chemical composition of amaranth grain is

shown in Table 1. The crude protein content ranges

from 11.8 to 17.6%. The reasons for the large vari-

ation amongst the different species are not known.

While it may be of a genetic nature, it may also be due

to environmental conditions and cultural practices.

Nitrogen fertilization of amaranth has not consist-

ently increased the crude protein in the grain.

0020The variability in total lipid content for all species

is 4.8–8.1%. Nutritionally, a high lipid content is of

interest for the high energy that grain amaranth can

provide in comparison with cereal grains and food

legumes.

0021Dietary fiber data for grain amaranth are lacking.

Values for A. caudatus have been reported to vary

from 7.6 to 16.4%.

0022The ash concentration is relatively constant among

species, and the variability for each element is also

small.

0023Vitamin contents appear to be relatively constant

among species. Some of the vitamins, e.g., nicotinic

acid, are low in comparison with the nicotinic acid

content in cereal grains, which show values about two

to three times higher.

tbl0004 Table 4 Essential amino acid content of amaranth (milligrams

of amino acid per gram of nitrogen)

Essential amino acid Vegetable Grain

Leucine 421 + 76.5 356 + 17.6

Isoleucine 327 + 38.7 226 + 15.9

Lysine 300 + 34.9 351 + 21.4

Methionine 78 + 43.6 124 + 17.7

Cysteine 24 + 8.1 124 + 6.4

Phenylalanine 314 + 78.0 270 + 40.1

Tyrosine 232 + 48.7 220 + 32.6

Threonine 356 + 75.9 238 + 21.3

Tryptophan 80 76 + 12.3

Valine 355 + 31.4 256 + 14.1

0135

Percentage amaranth leaves

Maize Rice

Weight gain (g)

fig0002Figure 2 Supplementary effect of amaranth leaves to maize

and rice.

AMARANTH 169

0024 Starch is the most abundant chemical component

in amaranth grain; the content varies from 48 to

69%. It occurs as very small polygonal or spheric

granules (1–3 mm in diameter), and is readily digested

by a-amylases. The starch is present mainly as highly

branched amylopectin, but some varieties of amar-

anth grain contain 4.8–7.22% of amylose, a linear

starch. Other carbohydrates include sucrose, raffi-

nose, stachyose, and maltose in small but variable

amounts. Microgranule starches, like those in

amaranth, are being studied for paper coatings, fat

substitutes, and biodegradable applications.

Fatty Acids

0025 Amaranth seed oil is rich in the essential fatty acid,

linoleic acid, with values ranging from 43.4% in

A. cruentus to 51.4% in A. hypochondriacus. Oleic

acid content is second in concentration, with values of

21.3% for A. hybridus and 31.9% for A. cruentus.

Amaranth oil contains 18.6–21.3% palmitic acid.

The reported variability suggests differences between

species and also differences between varieties of the

same species. Other lipid classes include sterols, of

which spinasterol is found at around 0.20% of the

crude oil. In the unsaponifiable fraction, the isopre-

noid, squalene, is found in relatively large amounts,

around 6.8%. The total unsaturated fatty acid con-

tent is around 77% for amaranth oil (Table 5). (See

Fatty Acids: Dietary Importance.)

Protein

0026 Protein distribution in the grain The endosperm of

the grain contains 35.0% of the total grain protein,

while the remainder is in the seed coat and germ or

embryo. This distribution is quite different from that

found in maize, sorghum and rice, wherein the germ

contributes between 12.5 and 18.5%, and the endo-

sperm between 81.5 and 87.5% of the total protein of

the grain. The physical distribution of the protein in

amaranth is responsible for its higher total protein

content, as compared with common cereal grains,

since the protein concentration in the germ is higher

than the concentration in the endospem. (See Protein:

Requirements.)

0027Protein fractions in amaranth A few studies have

been carried out on amaranth protein fractions. The

quantity of albumin was found to vary between 19

and 23%, and that of the globulins between 18 and

21%. The alcohol-soluble prolamines have been

found to vary from 2 to 3%, and alkali-soluble

glutelin-like proteins from 42 to 46%. Values of

around 5–14 g per 100 g of protein have been

reported for nonprotein nitrogen. The data available

suggest that there are no great differences in the

quantity of protein fractions among species or

among cultivars. Recently, a purified albumin frac-

tion, 35-kDa monomer, is being used to insert it into

potato and rice protein by biotechnological tech-

niques because this albumin fraction has an excellent

essential amino acid pattern.

Amino Acids

0028Table 4 presents average values for all species. Com-

parison of the essential amino acid content in grain

amaranth with the Food and Agriculture Organiza-

tion/World Health Organization (FAO/WHO) 1973

reference pattern reveals that the most deficient

amino acid is leucine. Nevertheless, other amino

acids such as valine, isoleucine, and threonine could

be limiting. Biological tests, however, have revealed

that threonine, rather than leucine, is the most

limiting essential amino acid. Amaranth protein is

a good source of lysine, tryptophan, and sulfur

amino acids. In contrast, cereal grains are deficient

in lysine. The essential amino acid balance of

grain amaranth protein is significantly better than

that of many other proteins of vegetable origin.

Since germ proteins are richer sources of essential

amino acids (as compared with the storage proteins

of the endosperm), the higher proportion of germ

proteins in amaranth may explain the higher con-

centration of lysine in amaranth grain than that

in cereal grains. (See Amino Acids: Properties and

Occurrence.)

Antinutritional Factors

0029As indicated above, amaranth is consumed as a vege-

table and as a grain. There are various reports that

indicate that both food forms contain antinutritional

factors or toxic compounds that could interfere with

food uses and limit nutrient utilization. The toxic

factors in vegetable and grain amaranth include

saponins and phenolic compounds, phytic acid, oxal-

ates and nitrates, protease inhibitors, lectins, alka-

loids, and polyphenolics. Appropriate processing,

however, has been shown to reduce or eliminate

such compounds. (See Plant Antinutritional Factors:

Characteristics.)

tbl0005 Table 5 Fatty acid content of amaranth (grams per 100 g)

Fattyacid Vegetable Grain

Myristic acid 14:0 1.1 0.53 + 0.3

Palmitic acid 16:0 13.3 20.4 + 2.0

Stearic acid 18:0 4.6 3.5 + 1.5

Oleic acid 18:1 4.7 26.1 + 5.6

Linoleic acid 18:2 6.4 48.0 + 7.3

Linolenic acid 18:3 34.4 1.43 + 0.8

Arachidonic acid 20:0 0.5 1.6 + 0.9

170 AMARANTH

Processing

0030 Amaranth grain has been processed by a relatively

large number of techniques such as wet and dry cook-

ing, which include atmospheric and pressure cooking,

nixtamalization, drum drying, extrusion cooking,

and puffing; by biological approaches such as germin-

ation, malting, and enzymatic hydrolysis, and by

physical means, which include milling, physical frac-

tionation, and starch and protein extraction.

Nutritive Value

Oil

0031 The digestibility of amaranth crude oil varies between

91.7 and 94.1% at the 5% level of addition and

between 91.1 and 93.8% at the 10% level. These

results are significantly lower than those from refined

cottonseed oil at both levels of addition. The lower

digestibility is probably caused by the presence of

sterols (0.37% total) and unsaponifiable matter

(1.4%) in crude amaranth oil; however, no deleteri-

ous effects from its consumption have been reported.

Metabolizable Energy of Amaranth Grain

0032 The two main sources of energy in amaranth grain are

the carbohydrate fraction and the oil content. The

metabolizable energy (ME) of light- and dark-colored

A. cruentus grain is 11.8 and 11.72 kJ g

1

(2.81 and

2.79 kcal g

1

), respectively. Heat processing increases

the value for both seed colors, with extrusion cooking

giving the highest values of 17.72 and 14.11 kJ g

1

(4.22 and 3.36 kcal g

1

), respectively.

Protein

0033 A number of researchers have uncovered an import-

ant conclusion: the protein value (protein efficiency

ratio) of the raw amaranth grain does not reflect the

amino acid pattern of the protein. Furthermore, am-

aranth grain processed by wet cooking gives a higher

protein quality value than that of the raw grain in all

amaranth species. When processed under conditions

that do not damage the availability of essential amino

acids, its protein quality is very close to that of casein

or milk protein. The effect of processing is evident in

both the consumption of the diet and the weight gains

of test animals. This effect is still unexplained and

deserves some research. It has been suggested that

the presence of antiphysiological factors that are in-

activated by heat may be responsible; well-known

antigrowth factors such as trypsin inhibitors, tannins,

and lectins are present at low levels in amaranth

grain.

0034Some processes, such as expansion, flaking, and

wet cooking, apparently do not affect protein digest-

ibility. However, the product from toasting gives an

equal or lower protein digestibility than the raw

grain. Table 6 lists the protein quality values of amar-

anth grain protein and that of other cereal grains.

With the exception of quality protein maize, also

high in lysine, all other cereal grains have a protein

quality below that of amaranth grain.

tbl0006Table 6 Protein quality of amaranth and various common

cereal grains

Grain Condition Protein quality

(percentage of casein)

A. cruentus Raw 74.8 (NPU)

A. cruentus Popped 74.4 (NPU)

A. caudatus Drum-dried 89.1

A. cruentus Drum-dried 86.1

A. hypochondriacus Drum-dried 85.0

Pearl millet Raw 55.8

Finger millet Raw 50.0

Teff Raw 56.2

Maize Raw 45.0

Sorghum Lime-cooked 30.6

QPM Raw 72.6

QPM Raw 82.9

Rice Lime-cooked 60.0

Wheat flour Raw 26.0

Barley, common Raw 53.2

Barley, Hiproly Raw 70.8

QPM Raw 70.0

Whole wheat Raw 37.2

Oats Raw 73.6

Rye Raw 52.0

Opaque-2 maize Raw 96.9

Opaque-2 maize Lime-cooked 92.4

NPU, net protein utilization.

tbl0007Table 7 Minimum nitrogen intake to obtain nitrogen equilibrium

from various food sources

Protein source Nitrogenintake

Nitrogen absorbed

Cheese 71 49

Extruded amaranth 80 51

Popped amaranth 84 52

Milk 75–86 48–60

Casein 94 64

Texturized soy protein 97 70

Soybean isolate 87 62

Meat 85 64

Soy/meat 92 68

Maize/beans 97 67

Beans 116 71

Rice/beans 96

Plantain/beans 112

Milligrams of nitrogen per kilogram body weight per day.

From Bressani R et al. (1993) Plant Foods for Human Nutrition 43: 123.

AMARANTH 171

0035 Although human studies on grain amaranth pro-

tein quality have been conducted, data are not readily

available. Some results with adult human subjects

indicate that extrusion-cooked grain amaranth has a

protein value of 89% relative to the value of cheese,

whereas the popped material has a value of 81% of

the value of cheese. Digestibility values follow the

same order. Table 7 summarizes the protein quality

of various protein sources as evaluated in humans.

The quality is expressed as the amount of nitrogen

ingested from the food protein source needed to

obtain nitrogen equilibrium in nitrogen-balance stud-

ies. A smaller value indicates a higher protein quality.

In studies with rats, amaranth containing diets

reduced cholesterol levels in blood as well as in the

liver. In the colon, amaranth diets induced similar

changes to those from cellulose feeding, but did not

reduce the pH and did not increase cecum surface

area. These observations suggest that the soluble

and insoluble fiber of grain amaranth behave as that

is these fractions of other cereal grains.

Supplementary Value

0036As a result of its high lysine content, the addition of

amaranth grain to cereal flours improves the quality

of the mixture (Figure 3). The available data show an

increase in protein quality of 62% for wheat flour,

40% for maize, and 25% for rice, from the addition

of 30% amaranth flour to 70% of each cereal grain.

The high protein quality of amaranth means that it

can be used alone or as a fortifier in cereal grain

mixtures.

Grain Uses

0037Popped and parched amaranth are time-honored

edible forms of whole amaranth. The methods of

preparation have persisted for centuries in Mexico,

Peru, and India. In recent research, grain amaranth

flour has been tested as a supplement to wheat, maize,

and rice flours for use in pastries, baking mixes,

pasta products, tortillas, and similar products Like-

wise, amaranth grain flour has been tested as a com-

ponent of high-quality protein foods and as a drink in

blends with milk and other grain flours. The product

possibilities are numerous, but very few have been

commercialized. A total of 60 cereal grain foods

containing small amounts of amaranth are marketed

in the Americas. In Mexico, eight different amaranth

grain flours are marketed, with the most popular

product being alegria, a mixture of popped amaranth

with sugar. Product and market development will be

crucial to amaranth’s growth in the food chain.

See also: Amino Acids: Properties and Occurrence;

Cereals: Contribution to the Diet; Fatty Acids: Properties;

Protein: Food Sources