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

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World War II in Hawaii, Leucaena leaf meal was used

in both pig and poultry rations as a substitute for

alfalfa meal. Provided that the levels that were fed

were less than 10% there were no ill effects. Finally,

ruminants can modify the spectrum of their rumen

microflora to convert mimosine to 3,4-dihydroxypyr-

ididine, which appears to have no biological activity.

0060 With regard to Lathyrus sativus consumption,

three approaches have been taken to reduce the prob-

lems associated with its consumption. In India, the

crop has been banned. However, it apparently has a

pleasant flavor and is a common adulterant of red

gram (pigeon pea dhal). There is some suggestion that

since the ban, the total area sown to the crop has

increased. Therefore, the two following methods of

dealing with the problem would appear to have a

greater potential.

0061 As with many other legume species that contain

ANFs, they can be removed by traditional processing

methods such as soaking, boiling, and fermentation.

The major problem is that often in times of famine, it

is not only food that is in short supply. Reduced

amounts of wood for cooking often mean that food

is cooked for less time, and the ANFs are therefore

not destroyed to the same extent. At the same time,

because of the drought resistance of the mother

plant, it may become the only grain legume that is

available, so the total amount consumed, and thus the

dose of ODAP, is increased.

0062 In Bangladesh, Lathyrus sativus is the most import-

ant single pulse crop and is grown on about

82 000 ha. To this end, plant breeders in Bangladesh,

in association with workers from Belgium and

Canada, have selected lines of Lathyrus with low

levels of ODAP. The aim is to produce cultivars that

are safe to eat with no, or a reduced, requirement for

processing.

Trypsin Inhibitors

0063 Trypsin inhibitors that inhibit the activity of the

enzymes trypsin and chymotrypsin in the gut, thus

preventing protein digestion, are found in many

plant species. These species include a range of grain

legumes such as common bean (Phaseolus vulgaris),

cowpea (Vigna unguiculata), Lima bean (Phaseolus

lunatus), peanut (Arachis hypogaea), peas (Pisum

sativum), soybean (Glycine max) and winged bean

(Psophocarpus tetragonolobus). However, they are

also found in cereals such as wheat (Triticum aesti-

vum) and barley (Hordeum vulgare), potatoes (Sola-

num tuberosum), and a number of species in the

genus Cucurbita. Because of the extensive use of soy-

bean meal in monogastric feeding, the trypsin inhibi-

tors associated with this plant species have been

studied most extensively. (See Trypsin Inhibitors.)

0064When monogastric animals are fed rations, which

contain large amounts of raw soybean meal, there is

poor growth, poor hair and feather production, and

digestive disturbances. However, there is recent evi-

dence to suggest that consumption of food containing

trypsin inhibitors may have a role in combating breast

cancer in humans.

0065Compounds responsible There are many plant-

derived trypsin inhibitors. Most of these inhibitors

differ in their specificity. Many can inhibit one or

two enzymes. Different forms of inhibitor may be

present in the same seed, and most of the inhibitors

can inhibit trypsin, but they may also inhibit chymo-

trypsin. However, in legume seed, the two most im-

portant inhibitor families are the Kunitz trypsin

inhibitor family and the Bowman–Birk trypsin inhibi-

tor family.

0066The Kunitz inhibitor family was the first family to

be isolated. It is a peptide comprising 181 amino

acids containing two disulfide bridges with a mole-

cular weight of about 21 000 Da. As this inhibitor

inhibits trypsin stoichiometrically to form a stable

complex, it is known as a single-headed inhibitor.

It primarily inhibits trypsin, but it can weakly inhibit

chymotrypsin. It is inactivated by heat and by gastric

juices.

0067The Bowman–Birk inhibitor family is widely dis-

tributed in legume seed. It is a smaller peptide

molecule and contains 71 amino acids. It contains a

high level of cystine and has seven disulfide bridges.

The molecular weight is about 8 000 Da. It is a

double-headed molecule and inhibits both trypsin

and chymotrypsin at two different binding sites.

Bowman–Birk inhibitors are resistant to gastric juices

and to proteolytic enzymes. There is also a suggestion

that they may be resistant to breakdown by heat.

0068Symptoms Animal response to trypsin inhibitors in

the diet varies with animal species. In chicks, rats,

and mice, the inhibitors cause pancreatic hypertrophy

and increased pancreatic secretion. However, they

do not have these effects on pigs, dogs, or preruminant

calves. Most monogastrics have reduced growth

when fed on rations with high levels of raw soybean

meal. Protein digestibility may be reduced, and

dietary protein is excreted in the feces. There is also

reduced nitrogen and sulfur absorption. One of the

effects of the inactivation of digestive enzymes in

the intestine is the stimulation of trypsin and chymo-

trypsinsecretionfromthepancreas,whichcancreatean

increased demand for the sulfur amino acids methio-

nine and cystine. In turn, this leads to increased

endogenous loss of both nitrogen and sulfur.

Finally, the inhibitors can stimulate the release of

PLANT ANTINUTRITIONAL FACTORS/Characteristics 4585

cholecystokinin into the blood stream, which further

increases pancreatic secretion.

0069 A number of factors can modify the effect of tryp-

sin inhibitors in the diet. These include the animal

species, the age of the animal, other ANFs present in

the diet, and the type and level of protein in the diet. It

appears that human trypsins are not inactivated by

either family of the soybean trypsins.

0070 Minimization of problems As with many other

ANFs, the level of trypsin inhibitors can be reduced

by moist heat treatments. Loss of activity is associated

with temperature, duration of heat treatment, mois-

ture conditions, and particle size. Up to 95% of activ-

ity can be destroyed by heating at 100



C for 15 min.

Autoclaving for 15–30 min has also been shown to

destroy most trypsin inhibitor activity in a range of

grain legume species. However, the results are not

universally applicable. In the industrial production

of soybean oil and meal, the heating caused during

the process substantially reduces the level of trypsin

inhibitor activity.

0071 Plant breeders have been able to show that there is

considerable variation in the level of inhibitor activity

among genotypes of the same legume species. Re-

cently, in peas, breeders have produced isogenic

lines that differed only in their level of seed trypsin

inhibitor. Similarly, there are also inhibitor-free lines

of soybean. Thus, the breeding of plants with reduced

levels of trypsin inhibitors in their seed is possible.

However, as with a number of other ANFs, it is not

clear what role the inhibitors serve in the possible

protection of the plant. Until this is resolved, given

that they are mainly rendered inactive by the process-

ing of the seed, it may be better to leave the inhibitors

in the seed.

Conclusions

0072 It appears that our ancestors, and people in many

societies in the developing world today, have been

well aware of the ANFs that are present in the plant

material eaten. They have long established methods

of reducing the risks involved by one or more of

the processes of soaking, testa removal, heating, fer-

menting, germinating, or protein extraction to pro-

duce isolates. However, these systems do not always

work, and in many developing countries, the prob-

lems of already-poor nutrition are exacerbated by the

presence of ANFs in the diet.

0073 In the developed countries, in recent years, there

has been a swing away from meat-based diets to-

wards the consumption of more legume seed. A result

has been an increased number of cases reported where

people have become ill after eating legume seed that

had not been fully processed. It has been suggested

that this is because the need to remove the ANFs is no

longer common knowledge.

0074In the processing of some plant materials to pro-

duce products like Canola or soybean oil, the heat

that is produced during crushing and milling may be

sufficient to render the resulting press cake safe to

feed to nonruminants, including humans. Industrial

producers prefer to use products that require as little

extra processing as possible. To try to meet this

demand, plant breeders have been actively trying to

reduce the levels of ANFs in plant products. However,

the downside is that this often renders plants more

susceptible to attack by birds, insects, and fungi while

they are growing, and to increased depredations of

stored products by insects, particularly weevils.

0075It is possible that, if the controversy over the use of

GM-modified plants for human food can be resolved,

plant breeders could remove the ANFs from food

plants. The partial protection that the ANFs currently

provide could be obtained by the insertion of one or a

few specific genes.

See also: Bioavailability of Nutrients; Carbohydrates:

Classification and Properties; Galactose;

Glucosinolates; Goitrogens and Antithyroid

Compounds; Heat Treatment: Chemical and

Microbiological Changes; Legumes: Legumes in the Diet;

Phytic Acid: Nutritional Impact; Hemagglutinins

(Haemagglutinins); Plant Antinutritional Factors:

Detoxification; Sucrose: Properties and Determination;

Tannins and Polyphenols; Trypsin Inhibitors

Further Reading

Bruneton J (1999) Toxic Plants Dangerous to Humans

and Animals. Paris: E

ditions TEC & DOC.

Cheeke PR (1998) Natural Toxicants in Feeds, Forages

and Poisonous Plants, 2nd edn. Danville: Interstate

Publishers.

D’Mello JPF, Duffus CM and Duffus JH (eds) (1991) Toxic

Substances in Crop Plants. Cambridge: Royal Society of

Chemistry.

Huisman J (1990) Antinutritional Effects of Legume Seeds

in Piglets, Rats and Chickens. PhD thesis, Wageningen

Agricultural University, The Netherlands.

Jansman AJM, Hill GD, Huisman J and Poel AFB van

der (eds) (1998) Recent advances of research in anti-

nutritional factors in legume seeds and rapeseed. In:

Proceedings of the 3rd International Workshop on ‘Anti-

nutritional Factors in Legume Seed and Rapeseed’.

Wageningen, July 1998. Wageningen: Wageningen Pers.

Liener IE (ed.) (1980) Toxic Constituents of Plant Food-

stuffs. New York: Academic Press.

Nartey F (1977) Manihot esculenta (Cassava): Cyanogen-

esis, Ultrastructure and Seed Germination. DSc thesis,

University of Copenhagen, Denmark.

4586 PLANT ANTINUTRITIONAL FACTORS/Characteristics

Raffauf RF (1996) Plant Alkaloids: A Guide to their

Discovery and Distribution. New York: Food Products

Press.

Roberts MF and Wink M (1998) Alkaloids: Biochemistry,

Ecology, and Medicinal Applications. New York:

Plenum Publishing.

Shahidi F (ed.) (1997) Antinutrients and phytochemicals in

food. In: ACS Symposium Series 662. Washington, DC:

American Chemical Society.

Waller GR and Nowacki EK (1978) Alkaloid Biology and

Metabolism in Plants. Newyork: Plenum Press.

Wink M (ed.) (1999a) Biochemistry of plant secondary

metabolism. In: Annual Plant Reviews, vol. 2. Sheffield:

Sheffield Academic Press.

Wink M (ed.) (1999b) Functions of plant secondary metab-

olites and their exploitation in biotechnology. In: Annual

Plant Reviews, vol. 3. Sheffield: Sheffield Academic

Press.

Detoxification

I E Liener, University of Minnesota, St. Paul,

MN, USA

Introduction

0001 Proteins of plant origin, particularly oil seeds and

legumes, provide a valuable source of protein for

humans and animals, despite the fact that they con-

tain substances that can adversely affect the nutri-

tional quality of the protein (Table 1). Fortunately,

in many cases, these substances are heat-labile and

can be readily eliminated or inactivated by the heat

treatment involved in domestic cooking and commer-

cial processing, or by treatment with chemicals. In

other cases, potential toxicants remain innocuous

until they are acted upon by enzymes of endogenous

origin. Paradoxically, advantage can sometimes be

taken of the action of these enzymes to detoxify

certain plants employing such traditional modes of

food preparation as germination or fermentation.

Protease Inhibitors

0002Proteins capable of inhibiting mammalian digestive

enzymes, such as trypsin and chymotrypsin, are widely

distributed in nature and have been shown to retard the

growth of animals by virtue of their ability to interfere

with the digestion of dietary protein. The animal tends

to adapt to this situation by stimulating the secretory

activity of the pancreas as well as its size. In extreme

cases, such as the long-term ingestion of these inhibi-

tors, the pancreas may exhibit precancerous lesions.

0003Because of its economic importance, the soya bean,

which is very rich in protease inhibitors, has received

the most attention with respect to the means whereby

these inhibitors can be inactivated. Because they

are proteins, they can be denatured by heat treat-

ment, and this is accompanied by a loss in inhibitory

activity. In general, destruction by heat treatment is a

function of the temperature, duration of heating, par-

ticle size, and moisture content, conditions that are

carefully controlled in order to minimize thermal

damage to the nutritive value of the protein, which

may occur if excessive heat is applied. An example of

the relationship between the destruction of the tryp-

sin inhibitor and the concomitant improvement in the

nutritional value of the protein in shown in Figure 1.

It is reassuring to note that most commercially

available soybean products intended for human con-

sumption such as tofu, soy protein isolates and con-

centrates, and textured meat analogs have received

sufficient heat treatment to reduce the trypsin inhibi-

tor activity to nontoxic levels.

0004Although the treatment of soya beans and other

legumes by boiling in water or exposure to live

steam (sometimes referred to as ‘toasting’) are the

most commonly employed methods for inactivating

the trypsin inhibitor, other modes of heat treatment or

processing have proved to be equally effective. These

tbl0001 Table 1 Examples of naturally occurring toxicants of plant origin, their distribution and physiological effects

Toxicant Distribution Physiological effect

Protease inhibitors Most legumes Impaired growth, enlarged pancreas

Lectins Most legumes Impaired growth

Goitrogens Cabbage family Hyperthyroidism

Cyanogens Lima beans, cassava Respiratory failure

Phytate Most plants Interference with mineral availability

Tannins Most legumes Interference with protein digestion

Oligosaccharides Most legumes Flatulence

Mimosine Leucaena Goiter

b-N-oxalyl-a,b-diamino-propionic acid Lathyrus sativus Lathyrism

PLANT ANTINUTRITIONAL FACTORS/Detoxification 4587

include dry roasting, microwave cooking, g irradi-

ation and infrared radiation.

0005 Traditional methods of preparing various foods

derived from beans generally result in products

that are quite low in protease inhibitor activity.

For example, tofu comprises mainly protein that

has been precipitated from a hot-water extract of

soya beans with calcium–magnesium salts, and

soya milk is simply a hot-water extract of soya

beans that may have been clarified by filtration.

In both cases, the boiling or steaming of the soya

beans prior to extraction with water serves to

inactivate the inhibitors. The same holds true for

fermented preparations of soya beans and other

legumes such as tempeh, miso, and natto in which

the beans have been subjected to boiling prior to the

fermentation step.

0006 The trypsin inhibitors are protein molecules whose

activity is retained only if the disulfide bonds of

the cystine residues remain intact. Thus, cleavage of

these disulfide bridges by treatment of soya beans

with reducing agents (cysteine, N-acetylcysteine,

mercaptoethanol, or reduced glutathione) or with

sodium metasulfite causes inactivation of the in-

hibitors.

0007 A search for varieties of soybeans that might be

devoid of trypsin inhibitors has led to the indentifica-

tion of a cultivar that has only about half of the

inhibitory activity of most commercial varieties

of soya beans. This is due to the absence of the

Kunitz trypsin inhibitor, the Bowman–Birk inhibitor,

presumably accounting for the remainder of the

activity. This particular variety of soya bean has

the economic advantage of requiring less heat than

conventional soya beans in order to produce a

product of comparable nutritional value for animal

feeding. (See Plant Antinutritional Factors: Charac-

teristics.)

Lectins

0008Paralleling the distribution of protease inhibitors

present in oil seeds and legumes is a class of proteins

referred to as ‘lectins’. These are proteins that

exhibit the unique property of being able to bind to

specific sugars that are part of the structure of

so-called glycoproteins. Their antinutritional effect

lies in the fact that, by binding to the glycoproteins

located on the surface of the cells lining the small

intestines, they interfere with the absorption of nutri-

ents; the result is a failure in growth and eventual

death.

0009The toxic effects of the lectins can be effectively

eliminated by heat treatment, essentially under the

same conditions as those that inactivate the protease

inhibitors. However, there are documented cases

where beans that have been eaten raw or only

partially cooked have led to serious outbreaks of

100

0 2 4 6 10 20

Minutes at 100

⬚C

3.1

2.7

2.3

1.9

1.5

Protein efficiency ratio (PER)

Trypsin inhibitor (TI) activity (TIU mg

−1

)

(TI)

(PER)

fig0001 Figure 1 Effect of heat treatment on the trypsin inhibitor (TI) activity and protein efficiency (PER) of soya beans. PER¼gain in weight

(g)/protein intake (g). Courtesy of Academic Press, New York.

4588 PLANT ANTINUTRITIONAL FACTORS/Detoxification

gastrointestinal illness. For example, bean-containing

stews and casseroles, when cooked in a slow cooker

where a relatively low temperature is maintained for

a long period of time, retain sufficiently high levels of

lectin to cause illness.

0010 With the availability of the soya bean variant

devoid of the Kunitz trypsin inhibitor (see above) as

well as one that was found to be free of the lectin, it

became possible to compare the relative contribution

of these two antinutritional factors to the poor nutri-

tive value of raw soya beans. In comparison with

conventional raw soya beans, a greater improvement

in the growth performance of chicks was noted for

the Kunitz inhibitor-free soya beans than that

obtained with the lectin-free soya beans. These results

may be taken to indicate that the Kunitz trypsin

inhibitor is a more important antinutritional factor

than the lectins. It is important to note, however, that

heat treatment is necessary for the inactivation of

both of these factors in order to achieve a maximum

nutritive value.

Goitrogens

0011 Goiter-causing agents in the form of glycosides (also

referred to as ‘glucosinolates’) are found in members

of the cabbage family, which includes not only cab-

bage but also broccoli, Brussels sprouts, cauliflower,

turnips, rapeseed, and mustard seed. These com-

pounds are biologically inactive as long as they

remain bound to glucose ((1) Figure 2), but an

enzyme, myrosinase, present in the same plant, serves

to release the active goitrogenic principle, goitrin ((2)

Figure 2). The glucosinolates found in the cabbage

family appear to pose little risk to human health since

the enzyme responsible for the release of goitrin is

inactivated by household cooking. The glucosinolates

may also be removed to a great extent by leaching out

into the cooking water. The common usage of rape-

seed meal in the feeding of livestock may prove to be

toxic unless it has been treated with moist heat. Alter-

native methods of detoxification of rapeseed may

involve prior extraction of the glucosinolates with

water or acetone or by decomposition with iron

salts or soda ash. These procedures, however, do not

preclude the possibility that some goitrin produced

enzymatically prior to processing may still remain in

the meal. A more effective means of detoxification is

one in which an aqueous slurry of the meal is deliber-

ately allowed to undergo autolysis, which serves to

liberate virtually all of the goitrin; the latter is then

removed by extraction with water or acetone. Lactic

acid fermentation or treatment with a specific fungus

(Geotrichum candidum) has also been reported to

be an effective means for the biological destruction

of the glucosinolates in rapeseed meal. The immobil-

ization of myrosinase on a solid matrix offers a

promising approach for the hydrolysis of the glucosi-

nolates, provided the goitrogenic end products are

subsequently removed by extraction, as described

above. (See Plant Antinutritional Factors: Character-

istics.)

Cyanogens

0012Many plants are potentially toxic because they con-

tain glycosides, principally linamarin ((3) Figure 3),

from which hydrogen cyanide may be released by the

action of an endogenous enzyme, linamarinase, when

the plant tissue is macerated. Among the cyanogenic

O−glucose

Linamarin

(3)

Linamarinase

O + Glucose + HCN

Acetone

fig0003Figure 3 Structure of the major cyanogen present in lima

beans. Enzymatic hydrolysis of linamarin (3) releases acetone,

glucose and hydrogen cyanide.

CH CH

N OSO

−

glucose

Progoitrin

Spontaneous

cyclization

CH S

(5-vin

loxazolidine-2-thione)

CH CH

NCS

+ Glucose + HSO

−

Myrosinase

(1)

(2)

Goitrin

fig0002 Figure 2 Structure of one of the goitrogenic compounds pre-

sent in the cabbage family. Progoitrin (1) is biologically inactive,

but, upon hydrolysis by the enzyme myrosinase, the active

principle goitrin (2) is released.

PLANT ANTINUTRITIONAL FACTORS/Detoxification 4589

plants most likely to be consumed by humans are the

lima bean and cassava. Although some tropical

varieities of the lima bean may contain toxic levels

of cyanide, those varieties consumed in the USA and

Europe generally have levels of cyanide below the

dosage known to be toxic to humans. Cassava is a

staple food item in the tropics and often contains

toxic levels of cyanide unless properly processed.

The traditional method of preparing cassava involves

the removal of the peel, which is particularly rich in

linamarin, followed by a thorough washing of the

pulp with running water. A further reduction in tox-

icity is achieved by the application of heat (boiling,

roasting, or sun drying), which serves to inactivate

linamarinase and to volatilize any hydrogen cyanide

that may have been produced. The cyanide content of

casava can also be reduced by a lactic acid fermenta-

tion to produce a native Nigerian dish called gari. The

hydrogen cyanide released by the enzymes elaborated

by the fermenting agent is then eliminated by frying.

The use of an exogenous source of linamarinase de-

rived from one of several species of fungi and bacteria

has also been proposed for enhancing the detoxifi-

cation of gari. An appreciable degree of detoxifica-

tion of cassava pulp for use in the feeding of livestock

can be achieved by ensilage.

Phytate

0013 Phytic acid ((4) Figure 4) or its salt, phytate, is inositol

combined with six phosphate groups and is a

common constituent of most plants. Its antinutri-

tional effect lies in the fact that it forms a chelate

with metal ions such as calcium, magnesium, zinc,

and iron to form poorly soluble compounds that are

not readily absorbed from the intestine, thus inter-

fering with the bioavailability of these essential

minerals. The ability of phytate to bind metal ions is

lost when the phosphate groups are removed by hy-

drolysis through the action of phytase. Heat alone is

relatively ineffective in reducing the phytate content

of plant materials, but the phytate content can be

reduced by taking advantage of the endogenous

phytase that accompanies the phytate in separate

compartments of the plant tissue. For example, by

the simple expedient of allowing ground soya beans

to undergo autolysis under conditions that are opti-

mal for phytase activity, one can obtain a significant

reduction in phytate content. An exogenous source of

phytase is commercially available as a feed additive to

livestock and poultry diets. This not only serves to

eliminate the mineral binding ability of the phytate

that may be present from other plant ingredients of

the diet, but also makes more phosphate available to

the animal.

0014Traditional fermented dishes derived from such

plants as soya beans, cassava, rice, maize, cowpeas,

or yams have reduced levels of phytate, presumably

due to the action of phytase produced by various

molds, bacteria or yeasts involved in the fermenta-

tion. Even the use of yeast in breadmaking serves to

reduce the phytate content of wheat flour. The ger-

mination of mature seeds of various legumes results in

a great increase in phytase activity with a concomi-

tant reduction in phytate. Other techniques for re-

moving phytate such as ultrafiltration and ion

exchange chromatography have been proposed, but

these are unlikely to replace the simpler methods

already described. (See Phytic Acid: Properties and

Determination; Nutritional Impact.)

Tannins

0015Oilseeds and legumes contain appreciable levels of

polyphenol compounds, broadly referred to as

‘tannins’ ((5) Figure 5). The negative nutritional

effects of tannins are diverse and incompletely under-

stood, but the major effect is to interfere with the

digestibility of dietary protein. This may be due to

the binding of the tannins to the protein to form

substrates that are resistant to digestive enzymes or

to a direct binding to these enzymes themselves.

0016Since tannins are located primarily in the seed coat

of dry seeds, the physical removal of the seed coat by

dehulling or milling markedly reduces the tannin con-

tent with a resultant improvement in the nutritional

quality of the protein. Soaking in water or salt solu-

tion prior to household cooking also causes a signifi-

cant reduction in tannin, provided the cooking broth

is discarded. Treatment with a variety of chemicals

such as ammonia, hydrogen peroxide, formaldehyde,

polyethylene glycol, or polyvinylpyrrolidone has also

proved to be an effective means for reducing the

OPO

Phytic acid (4)

fig0004 Figure 4 Structure of phytic acid (4). Enzymatic removal of the

phosphate groups by phytase serves to eliminate its metal-

binding property.

4590 PLANT ANTINUTRITIONAL FACTORS/Detoxification

tannin content of plant sources of protein. Germin-

ation leads to more than a 50% loss in tannins in

legumes such as the chick pea, green gram, mung

bean, and black gram, presumably due to the action

of polyphenol oxidase of endogenous origin. (See

Tannins and Polyphenols.)

Flatulence-producing Factors

0017 One of the important factors limiting the use of

legumes in the human diet is the production of intes-

tinal gas (flatulence), which is generally attributed to

the inability of the gut enzymes to hydrolyze the

a-1,6-galactosidic linkages of such oligosaccharides

as raffinose, stachyose and verbascose ((6), (7) and (8)

respectively Figure 6). In their unhydrolyzed forms,

these oligosaccharides become metabolized by the

microflora of the large intestine into carbon dioxide,

hydrogen, and methane, gases that are responsible for

the characteristic features of flatulence, namely

nausea, cramps, diarrhea, and the social discomfort

associated with the release of rectal gases. Advantage

may be taken of the endogenous galactosidases pre-

sent in the plant tissue by allowing a slurry of the raw

ground beans to undergo autolysis under suitable

conditions or by treatment with an exogenous source

of these enzymes derived from molds or bacteria.

Such traditional dishes as tofu and tempeh, which

have undergone fermentation by microorganisms,

likewise have little flatus activity. Protein isolates

from which these oligosaccharides have been

eliminated during the course of their isolation are

essentially devoid of the offending oligosaccharides.

Preparations of galactosidases from microbial sources

that have been immobilized as continuous flow react-

ors or in the form of a hollow-fiber dialyzer have also

been employed for removing flatulence-producing

factors.

Saponins

0018Saponins comprise a large family of structurally re-

lated compounds containing a steroid or triterpenoid

aglycone (sapogenin) linked to one or more oligosac-

charide moieties. Despite the fact that saponins are

widely distributed in the plant kingdom, only a small

number of such plants are actually toxic to mammals.

It has long been recognized, however, that saponins,

such as the glycoside of medicagenic acid ((9)

Figure 7), which is found in alfalfa, is considered to

have an adverse effect on the productive performance

of nonruminant animals such as swine and poultry.

(5)

fig0005 Figure 5 Structure of condensed tannin (5), which, by forming a

complex with dietary protein, interferes with the digestion of

protein.

HOH

Sucrose

Raffinose (6)

Stachyose (7)

Verbacose (8)

fig0006 Figure 6 Structure of the oligosaccharides (6, 7, and 8) responsible for flatulence. In the absence of enzymes in the small intestine of

humans that are capable of hydrolyzing a-1,6-galactosidic likages, these compounds are metabolized by the microflora of the gut into

gaseous end products.

PLANT ANTINUTRITIONAL FACTORS/Detoxification 4591

The negative effect of the saponins can be reversed,

however, by the inclusion of dietary cholesterol,

which interferes with the absorption of saponins by

forming an insoluble complex with saponins. By the

same token, dietary saponins may exert a positive

effect by reducing cholesterol levels in the tissue and

serum of experimental animals. (See Saponins.)

Mimosine

0019 Leucaena leucephela is a tropical legume used pri-

marily as a forage crop for feeding livestock, but its

use is limited by the fact that it contains an unusual

amino acid, mimosine ((10) Figure 8). This com-

pound has an adverse effect on the growth of rumin-

ants because bacteria can convert mimosine to 3,4-

dihydroxypyridine ((11) Figure 8) which acts as a

goitrogenic agent. In Hawaii, ruminants can convert

greater amounts of the Leucaena before it becomes

toxic than ruminants in Australia because of the pres-

ence of bacteria in the rumen capable of detoxifying

mimosine. In fact, when Australian ruminants were

inoculated with these organisms, they became more

resistant to the toxic effects of mimosine.

Lathyrism

0020Human consumption of the legume chickling vetch

(Lathyrus sativus) causes a neurological condition

known as ‘lathyrism,’ a disease that is common in

India and Bangladesh. The causative factor of

this disease has been identified as b-N-oxalyl-

a,b-diaminopropionic acid ((12) Figure 9), but over

90% of this toxin can be eliminated by the simple

expedient of soaking the seeds overnight in an excess

of water followed by steaming, roasting, or sun

drying.

COOH

GLU

GLUGLU

(9)

fig0007 Figure 7 Structure of medicagenic acid (9), a saponin that is present in alfalfa and is responsible for toxic effects in livestock.

NOCH

CH COOH

Mimosine

NHO

3,4-Dihydroxypyridine

(10)(11)

fig0008 Figure 8 Structure of minosine (10) and its goitrogenic metabolite, 3,4-dihydroxypyridine (11).

C COOH

CH NH

COOH

(12)

fig0009Figure 9 The structure of b-N-oxalyl-a,b-diaminopropionic (12),

the causative factor of lathyrism in humans.

4592 PLANT ANTINUTRITIONAL FACTORS/Detoxification

See also: Glucosinolates; Phospholipids: Properties

and Occurrence; Phytic Acid: Properties and

Determination; Nutritional Impact; Saponins; Soy (Soya)

Beans: Properties and Analysis; Dietary Importance;

Tannins and Polyphenols; Plant Antinutritional

Factors: Characteristics

Further Reading

Cheeke PR (ed.) (1989) Toxicants of Plant Origin, vols.

I–IV. Boca Raton, FL: CRC Press.

Douglas MW, Parsons CM and Hymowitz T (1999) Nutri-

tional evaluation of lectin-free soybeans for poultry.

Poultry Science 78: 91–95.

Jones RJ and Megarrity RG (1986) Successful transfer of

DHP degrading bacteria from Hawaiian goats to Aus-

tralian ruminants to overcome the toxicity of Leucaena.

Australian Veterinary Research Journal 63: 259–261.

Legras JL, Jory M, Arnaud A and Galzy P (1990) Detoxifi-

cation of cassava pulp using Brevibacterium sp. R312.

Applied Microbiology and Biotechnology 33: 529–533.

Liener IE (ed.) (1980) Toxic Constituents of Plant Food-

stuffs, 2nd edn. New York: Academic Press.

Liener IE (1987) Detoxifying enzymes. In: King RD,

Cheetham PSJ (eds) Food Biotechnology, pp. 249–271,

vol. 1. London: Elsevier.

Liener IE (1989) Control of antinutritional and toxic

factors in oilseeds and legumes. In: Lucas EW, Erikson

DR and Nip W-K (eds) Food Uses of Whole Oil and

Protein Seeds, pp. 249–271. Champaign, IL: American

Oil Chemists Society.

Liener IE (1997) Plant lectins: properties, nutritional sig-

nificance, and function. In: Shahidi F (ed.) Antinutrients

and Phytochemicals in Food, ACS Symposium Series

662, pp. 31–43. Washington, DC, American Chemical

Society.

Majak W (1992) Mammalian metabolism of toxic glyco-

sides from plants. Journal of Toxicology 11: 1–40.

Marfo EK, Simpson BK, Idou JS and Oke OL (1990) Effect

of local food processing on phytate levels in cassava,

cocoyam, maize, sorghum, rice, cowpea and soybean.

Journal of Agricultural and Food Chemistry 38: 1580–

1585.

Moneam NMA (1990) Effect of presoaking on faba bean

enzyme inhibitors and polyphenols after cooking. Jour-

nal of Agricultural and Food Chemistry 36: 1479–1482.

Sessa DJ and Ghoutous PE (1987) Chemical inactivation of

soybean trypsin inhibitors. Journal of American Oil

Chemists Society 64: 1682–1687.

Watson D (ed.) (1998) Natural Toxicants in Food. Boca

Raton, FL: CRC Press.

PLANT DESIGN

Contents

Basic Principles

Designing for Hygienic Operation

Process Control and Automation

Basic Principles

H L M Lelieveld and G J Curiel, Unilever Research

and Development Vlaardingen, Vlaardingen,

The Netherlands

Background

0001 If a plant is not of a proper hygienic design, it will be

difficult to clean, and if not clean, the inactivation

of microorganisms can be extremely difficult. After

inadequate cleaning, harmful microorganisms may

grow and affect product quality and safety. This

chapter summarizes the basic principles of hygienic

plant design to control the microbiological quality

and safety of the final product.

0002Raw materials usually contain microorganisms.

When given time and the right environment, they can

grow out and increase to very high numbers. In food-

processing equipment, the temperature and availabil-

ity of nutrients are often ideal for the growth of many

types of microorganisms. Consequently, when given

enough time, such as in areas where the product is

stagnant or residing for a long time for any other

reason, microorganisms will cause problems. Product

that is free from (viable) microorganisms may become

recontaminated by microorganisms in the environ-

ment (air, people, insects, and other pests), by the

processing and packaging equipment and by the pack-

aging materials. Equipment must be hygienically

PLANT DESIGN/Basic Principles 4593

designed and fabricated, installed in a sufficiently hy-

gienic environment, and be operated by staff who con-

sistently observe the critical hygiene rules that apply.

Requirements for Hygienic Food Plants

Location and Buildings Exterior

0003 Preferably, food plants should not be located near

areas where levels of microorganisms, insects, or

rodents can be exceptionally high. Therefore, a food

plant should not be near a sewage treatment plant or

in the middle of an animal farm area. Also, although

decorative, there should be no trees, bushes, and

plants near the factory. Such flora attracts insects

and birds, which are sources of all kinds of patho-

genic microorganisms. Also, there should be no

breeding places for insects, so there should be

no decorative ponds and generally no stagnant water

at all in the vicinity. To avoid attracting insects, exter-

nal lighting should never be mounted to, or near to,

the wall of the plant. If positioned at a suitable dis-

tance, illumination will be adequate while insects

move away from the plant. The outer walls of factor-

ies should not provide landing or breeding places for

birds or other animals. The lower part of the walls

must be rodent-resistant. Also, walls should be deep

enough to prevent rodents from digging tunnels

underneath to gain access to the plant. Measures

must be taken to prevent animals gaining access to

any area between the ceiling and roof. Roofs should

not retain water (breeding of insects and bacteria) and

thus slope such that draining is adequate. Doors

must be self-closing; windows and doors that are

opened infrequently, including emergency exits,

should be such that there is little space between

door and frame.

Layout

0004 As the requirements for raw materials differ from

those applying to intermediate or final products, the

design of food plants should start with defining the

hygiene requirements for the product in the subse-

quent stages of the production process. Based on

that inventory, the layout of the plant should be

decided, taking into account the various flows: of

product, packing material, people, and air. Air, unless

freed from microorganisms, should always move

away from the exposed final product. Primary packing

materials should be clean (complying with the micro-

biological requirements for the product to be packed).

Neither people nor any material should move from the

raw materials area to the finished exposed product

area unless measures have been taken to prevent the

carryover of microbial contamination. To protect

microbiologically sensitive products, high-care areas

may be needed. The entrance to such an area should

have facilities for (compulsory) change of footwear

and coats. All areas should have well-designed and

well-maintained handwash facilities.

0005It is essential too, that, if the layout is correct, staff

do not nullify the effect of correct measures by not

knowing or not following the rules. For example, one

is easily tempted to open doors and windows on a hot

summer day, thereby completely destroying the air-

flows needed to prevent product contamination.

Also, if possible and unobserved, people are likely to

take ‘shortcuts’ to move from one place to another

and thereby entering high-care areas from raw mater-

ial areas. It is part of correct plant design to ensure

that the rules are correct and sensible and that every-

body is aware of their importance – and perhaps of

the sanctions in case of breach: the health of con-

sumers and the reputation of the factory are at stake.

Construction

0006Floors Floors are one of the great challenges: on the

one hand, for obvious reasons, they should not be

slippery. On the other hand, because they must be

cleaned, floors must be smooth. In the case of dry

floors, the problem is relatively easy to control, but

any spilled liquid (water or product) may present an

occupational hazard. The hazard selfevidently is re-

lated to both floor and footwear, and their interaction

must be taken into account. Clearly, a ‘dry-floor

policy’ will help to reduce both hygiene and occupa-

tional problems. Smooth concrete floors are accept-

able for reception and many raw material storage

areas. In areas where product is not protected,

ceramic tiles or seamless mortar resin floors are

preferred. In high-care areas, often, seamless resin

floors are the best choice. Floors must have rounded

corners where the floor meets the wall and should

slope approximately 2% towards drains or gutters.

0007Walls Walls should be smooth and cleanable and

should be covered by ceramic tiles or a good-quality

coating or paint. If sandwich panels are used, all sides

should comply with the chemical resistance required.

It is important that all seams are reliably sealed. In

some cases, seams can be sealed by welding with the

parent material. In other cases, and where walls meet

the floor, sealants should be used. Also, anything

mounted to the wall should be sealed all around to

prevent access to insects and dirt. The surface of

choice should be strong enough to meet factory con-

ditions, and repairs to any damage should be carried

out within a short time. Where walls separate various

hygiene areas, care must be taken that any holes for

service lines are properly sealed.

4594 PLANT DESIGN/Basic Principles