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

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tbl0004 Table 4 Composition of cellulosic materials (g per 100 g of dry matter)

Cellulose Lignin Hemicellulose Pectin Starch Free sugars

Vegetables

Leafy

Broccoli 7.2 0.26 24 1.7 15

Brussels sprouts 9.04 2.1 26 8.7 18

Cabbage 8.9 4.3 26 4.3 47.3

Cauliflower 13.4 Tr 13 5.0 29

Lettuce 20.6 Tr 9.2 0 17

Legumes

Beans, haricot 5.3 0.9 22.0 51.3

Beans, runner 17 3 21 2.9 39.6

Peas 14 2 36 66 6.9

Root

Carrot 12.9 Tr 19 0.9 24.8

Turnip 11 Tr 23 Tr 47.7

Fruiting vegetables

Pepper 3.5 Tr 10 Tr 34.2

Tomato 9.1 5.3 11 Tr 46.4

Tuber

Potato 1.2 Tr 9.2 84.6 1.5

Fruits

Apples 2.9 Tr 5.8 2.3 1.8 63.9

Apricots

15 3.3 0 56.6

Banana 1.3 0.93 3.83 10.4 55.8

Blackberries

44 1.9 0 34.1

Cherries, sweet 1.2 0.3 4.5 0.4 0 65.4

Grapefruit 0.6 0.9 4.9 0 67.7

Lemons

35 3.4 0 21.1

Oranges

14 3.3 0 59.6

Peaches 1.8 5.1 12.2 3.3 0 74

Pears 4.2 2.7 8.2 Tr 63.5

Pineapples

7.64 0.25 0 74.1

Strawberries 3.6 8.4 10 3.5 Tr 61.8

Seeds

Barley 5.3 64.1

Corn

2.4 71.8 1.9

Grain sorghum

2.7 2.5 70.2 1.4

Oats

11.9 60.6

Peanut

2.8 2.5 4.0 4.7

Wheat

2.1 74

Agricultural residues

Barley straw 44 7 27

Cottonseed hulls 59 13 15

Oat straw 41 11 16

Rice straw 33 7 26

Sorghum straw 31 11 30

Sugarcane bagasse 40 13 29

Wheat straw 39 10 36

Trees

Hardwood

Aspen 53.3 16.3 26.2

White birch 41.0 18.9 36.2

Red maple 44.1 24.0 29.2

Softwood

Balsam fir 44.8 29.4 23.6

Jack pine 41.6 28.6 25.6

White spruce 44.8 27.1 26.1

Bast fibers

Flax 71.2 2.2 18.6 2.0

Leaf fibers

Manila hemp 70.2 5.7 21.8 0.6

Seed fibers

Crude cotton 95.3 0 0 1.0

1006 CELLULOSE

(50 g l

1

oxalic acid dihydrate, 700 ml l

1

95% etha-

nol, 50 ml l

1

12 M HCl), which is then removed by

filtration. The filter contents are washed with ethanol

and acetone. The crucible is dried at 100



C for 8 h.

The crucible contains cellulose and insoluble ash. The

crucible may be placed in a 500



C oven for 3 h; the

weight loss corresponds to the cellulose content.

0042 A simpler approach to removing the lignin from the

ADF has been described by C.S. Edwards. The ADF is

soaked in activated trigol (i.e. 6.3 ml of 32% hydro-

chloric acid dissolved in 1 l of pure triethylene glycol)

in a 121



C autoclave for 60 min. The sample is then

washed with 95% ethanol and acetone. The residue

contains cellulose and insoluble ash.

0043 Other gravimetric methods Cross and Bevan cellu-

lose is the lignocellulose portion remaining after

removing hemicellulose with two boilings in NaOH

and removing lignin with chlorine and bleach.

0044 Monoethanolamine cellulose is the lignocellulose

portion remaining after monoethanolamine treat-

ment, chlorination, and bleaching.

0045 Norman–Jenkins cellulose is the lignocellulose por-

tion remaining after sodium sulfite boiling, bleaching,

and acid treatment.

0046 a-Cellulose is the cellulose fraction insoluble in

room temperature 17.5% sodium hydroxide wash

water (DP > 90).

0047 b-Cellulose is the cellulose fraction in the alkaline

wash water that precipitates upon neutralization

(15 < DP < 90).

0048 g-Cellulose is the cellulose fraction soluble in the

neutralized alkaline wash water (DP < 15).

0049 Holocellulose is the residue that remains after lig-

nocellulose is defatted with hot, azeotropic benzene/

ethanol and delignified with hot chlorous acid

(HClO

). Holocellulose contains the cellulose and

hemicellulose of the original plant material.

Colorimetric Method

0050 Hexosan assays may be used to measure cellulose, the

dominant hexose polymer in starch-free plant mater-

ials (other than softwoods). Holtzapple describes an

assay in which the hexosan sample is placed in a

sealed test tube with 1530 g l

1

sulfuric acid and

20 g l

1

chromotropic acid, and boiled for 1 h. Hexose

C6 degrades to form formaldehyde, which reacts with

the chromotropic acid to form a purple compound

that is measured spectrophotometrically. There is

minor interference by pentosans that may be reduced

by lowering the chromotropic acid concentration to

1gl

1

and shortening the reaction time to 20 min.

There is also some interference with lignin, so the

most accurate results are obtained with holocellulose,

rather than the original lignocellulose. (See Spectros-

copy: Visible Spectroscopy and Colorimetry.)

Chromatographic Method

0051The cellulose content can be estimated from the

glucose composition, because cellulose is the main

source of glucose in plant materials (assuming free

sugars and starch are not present). (See Chromatog-

raphy: Principles.)

See also: Chromatography: Principles; Dietary Fiber:

Properties and Sources; Fructose; Hemicelluloses;

Lignin; Protein: Chemistry; Spectroscopy: Visible

Spectroscopy and Colorimetry; Sucrose: Properties and

Determination

Further Reading

Atalla RH (1987) The Structures of Cellulose. ACS Sympo-

sium Series, No. 340. Washington, DC: American

Chemical Society.

Bogan RT, Kuo CM and Brewer RJ (1979) Cellulose deriva-

tives, esters. In: Kirk–Othmer Encyclopedia of Chemical

Technology, 3rd edn., vol. 5, New York: Wiley.

Edwards CS (1973) Determination of lignin and cellulose in

forages by extraction with triethylene glycol. Journal of

the Science of Food and Agriculture 24: 381–388.

Fengel D (1970) Ultrastructural behavior of cell wall poly-

saccharides. Tappi 53(3): 497–503.

Goering HK and Van Soest PJ (1970) Forage Fiber Analysis.

Agricultural Handbook, No. 379, Jacket No. 387–598.

Washington, DC: US Department of Agriculture.

Greminger GK (1979) Kirk–Othmer Encyclopedia of Chem-

ical Technology, 3rd edn., vol. 5. New York: Wiley.

Holtzapple MT and Humphrey AE (1983) Determination

of soluble and insoluble glucose oligomers with chromo-

tropic acid. Analytical Chemistry 55: 584–585.

Jayne G (1971) Cellulose and cellulose derivatives. In:

Bikales NM and Segal L (eds) High Polymers, 2nd

edn., vol. V, part IV. New York: Wiley Interscience.

Plunguian M (1943) Cellulose Chemistry. New York:

Chemical Publishing.

Southgate DAT (1976) Determination of Food Carbohy-

drates. London: Applied Science.

Turbank AF, Durso DF, Battista OA et al. (1979) Cellulose.

In: Kirk–Othmer Encyclopedia of Chemical Technology,

3rd edn., vol. 5. New York: Wiley.

Tr, trace.

From Southgate DAT (1976) Determination of Food Carbohydrates, pp. 91–93. London: Applied Science.

From Zaborsky OR (1981) CRC Handbook of Biosolar Resources, vol. II. Boca Raton, FL: CRC Press.

From Marsden WL (1986) CRC Critical Reviews in Biotechnology, vol. 3, issue 3, p. 235. Boca Raton, FL: CRC Press.

From Timell TE (1957) Carbohydrate composition of ten North American species of wood. TA P P I 40: 568.

From Turbank AF, Durso DF, Battista OA et al. (1979) Cellulose In: Kirk^Othmer Encyclopedia of Chemical Technology, 3rd edn., vol. 5. New York: Wiley.

CELLULOSE 1007

CEREALS

Contents

Contribution to the Diet

Bulk Storage of Grain

Handling of Grain for Storage

Breakfast Cereals

Dietary Importance

Contribution to the Diet

C MacEvilly, Food Safety Promotion Board, Cork,

Ireland

Background

0001 Cereals are grown for their highly nutritious edible

seeds which are often referred to as grains. They

remain the staple food in most diets, even given

their decline in importance as a country becomes

more affluent. Current nutritional advice highlights

the benefits of cereal foods as a source of complex

carbohydrates and as foods that should replace some

of the energy currently provided by fat in the diet.

0002 Cereals supply a variety of nutrients and other food

components like phytochemicals. Although cereals

make an important contribution to the diet, they

cannot alone support life because they are lacking in

vitamins A, D, and C and iodine, for example. Also

cereal proteins are deficient in certain amino acids,

notably lysine. Refined cereal products and unrefined

cereals have certain advantages and disadvantages.

With refinement, some nutrients and fiber are

removed, but the body is better able to make use of

certain nutrients. The role of fortified cereals as a

means of increasing levels of specific vitamins has

been recognized. This chapter will discuss the role

that cereal plays in both in the developed and

developing world and the implications that the type

of cereal has on the diet.

Cereals as a Global Food Source

0003The world has over 50 000 edible plants and just three

of them – rice, maize, and wheat – supply 60% of the

world’s food energy intake. Table 1 presents an over-

view of world cereal production for 1999.

0004Rice feeds almost half of humanity. Per capita rice

consumption has generally remained stable, or risen

slightly since the 1960s. However, it has declined in

recent years in many of the wealthier rice-consuming

countries, such as Japan, the Republic of Korea, and

Thailand, because rising incomes have enabled people

to eat a more varied diet.

0005Although there are over 10 000 species in the Gra-

mineae (cereal) family, few have been widely intro-

duced into cultivation over the past 2000 years.

Cereals constitute the ‘starchy staples’ in the human

tbl0001 Table 1 World cereal production – forecast for 2000 (million tonnes)

Wheat Coarse grains Rice (paddy) Total

1999 2000 1999 2000 1999 2000 1999 2000

Asia 260.1 251.2 218.1 190 553.1 540.4 1031.2 981.6

Africa 14.9 13.5 76.1 79.1 17.7 17.5 108.7 110.1

Central America 3.1 3.4 28.7 28.7 2.3 2.4 34.1 34.5

South America 19.7 18.6 58.6 61.7 21.1 20.1 99.5 100.4

North America 89.5 86.7 290.5 305.6 9.3 8.7 389.3 401.0

Europe 178.3 188.2 202.4 194.8 3.2 3.1 383.9 386.2

Oceania 24.3 20.3 8.9 9.9 1.4 1.1 34.6 31.2

World 589.8 581.8 883.4 869.7 608.2 593.4 2081.4 2044.9

406

397

1880

1848

Developing countries 276.6 268.4 369.3 345.2 582.1 568.1 1228.0 1181.8

Developed countries 313.2 313.3 514.1 524.4 26.1 25.3 853.4 863.1

From FAO/GIEWS Food Outlook no. 5, p. 4, with permission.

Rice in milled terms.

Including rice in milled terms.

1008 CEREALS/Contribution to the Diet

diet and as such are the primary source of dietary

carbohydrate throughout the world. The contribu-

tion of these crops to the diet varies from continent

to continent, and even among countries within con-

tinents. The consumption of starchy staples through-

out the world has changed over the last three decades.

Figure 1 shows the world picture of dietary patterns,

with countries highlighted according to the starchy

staple providing the highest proportion of energy. As

can be seen, large parts of the world depend on wheat

and rice, with more selected areas dependent on

maize, sorghum, and millet.

0006 The distribution of the production, and to a great

extent the importance, of the different cereals is in

part due to the climatic constraints on the growth of

the different species. Wheat production is limited to

temperate zones; rye has a wider northern range and

can be grown in the Arctic circle, and rice can be

grown in standing water in tropical and subtropical

climates and less commonly on dry uplands. Barley

and oats have a similar range to wheat, although oats

thrive on poorer soils. Maize and millets are major

crops in the tropics and subtropics; much is also

grown in temperate climates where it is also import-

ant as animal feed.

0007 As a food, cereals have many benefits and there are

several reasons why cereals have become the staple

food of mankind. They do not deteriorate easily if

kept dry, they are easily stored and transported, they

are cheap to produce, and they have a high nutrient

density. (See Wheat: The Crop; Rice; Barley; Oats;

Maize; Rye; Millets.)

The Nutritional Composition

0008In westernized countries approximately 50% of the

food energy available is derived from cereals and in

the developing world it provides two-thirds of energy

and protein. Cereals provide 1400–1600 kJ per 100 g

whole cereal. The nutritional composition of the main

types of cereal grains and some products is shown

in Table 2. Cereal grains contain, on average, 75%

carbohydrate, 10–15% protein, 2% fat, and 10–15%

water.

Cereals as an Energy and Protein Source

0009Cereals are classified as ‘carbohydrate foods’ and

although this is compositionally correct, such a clas-

sification does not take into consideration the import-

ance of the proteins present in cereals. They constitute

a rich source of both nonstarch polysaccharides (diet-

ary fiber) and starch, which together comprise 70–

77% of the grain. Protein accounts for 6–15% and

the limiting amino acid is lysine, although maize is

additionally low in tryptophan. Protein quality is

highest in the outer layers of the endosperm (a starchy

Dietary patterns

Dietary patterns, 1989-91

Other symbols

Dietary energy supply per caput less than 2700 Calories (1992-94)

Data not available

Water bodies

Source: FAO, UNFPA

123456

1 - Rice

2 - Maize

3 - Wheat

4 - Milk, meat, wheat

5 - Millet, sorghum

6 - Roots and tubers including:

Cassava, Yarns, Taro, Plantain

fig0001 Figure 1 Dietary patterns.

CEREALS/Contribution to the Diet 1009

core with a protein matrix) and in the germ (the

grain’s embryonic root and shoot) because that is

where the lysine-rich albumins and globulins (salt-

soluble proteins) are located and as a result are

more affected by processing.

0010 Gluten is the major protein in wheat and rye. The

special properties of this protein make it particularly

important in breadmaking; isolated gluten is also

used as a method for assessing suitability of cereal

proteins in gluten intolerance (celiac disease), which

will be discussed later. Oryzenin is the major protein

in rice. Table 3 shows the role of cereals in the supply

of dietary energy and protein in various countries.

0011 The data are presented as food supply statistics

(sometimes referred to as food balance sheets or

food disappearance statistics). This type of popula-

tion level data is relatively easy to collect compared

with information based on the dietary records of

individuals, which requires meticulous attention to

detail. However, there are also important drawbacks:

data exist only for basic commodities, they cannot

show patterns in different sectors of the population,

and they substantially overestimate the amounts of

food actually eaten as they do not take into account

wastage, for example.

Lipids

0012In themselves, cereals are low-fat foods, their

endogenous fats making only a very minor contribu-

tion to total intake and being overshadowed by the

amount and composition of the fats used in the

cooking and preparation of the cereal foods com-

monly consumed. Although lipids comprise only

about 1.5–7% of cereal grains, some lipid compon-

ents appear to have special properties that contribute

to added health benefits. Most (approximately 80%)

of the lipid in cereals is present as triglycerides (fatty

acids esterified in a glycerol backbone). Linoleic

(C18:2) acid is the major unsaturated fatty acid in

cereals except brown rice, which contains more oleic

acid (C18:1). Palmitic acid (C16:0) is the major sat-

urated fatty acid in cereals and, except in barley, is

present in lower concentrations than linoleic and

oleic acids. However, cereals also contain a broad

class of unsaponifiable lipid material (about 2–10%

of the total) that includes tocols, carotenoids, sterols,

and high-molecular-weight alcohol. Tocols and caro-

tenoids have antioxidant properties and sterols have

been extensively studied for their role in the reduction

of blood cholesterol levels.

Mineral Elements and Vitamins

0013Whole grains are a good source of thiamin and pro-

vide significant amounts of many other B vitamins.

However, factors affecting the bioavailability of these

vitamins from grain products are still under investi-

gation. The germ is rich in vitamin E; however, vita-

min E is not stable to light, heat, and air, so almost all

processing methods will adversely affect its concen-

tration. As grains mature, the niacin they contain

becomes progressively more bound to indigestible

components of the seeds. Cereal grains are deficient

in vitamin A, C, and D. The ascorbic acid that is

customarily added to white flour to improve its

baking properties has no nutritional significance. In

addition, low levels of vitamins D and K are found in

the lipids of most cereals. Recent results from the

National Food Survey in the UK suggest that fortified

cereals provide almost 32% of the average intake of

folic acid.

tbl0002 Table 2 Composition of cereals, grains, and some products

Product Water

(%)

Protein

(%)

Fat

(%)

Carbohydrates

(%)

Energy

value

(kJper

10 0 g)

Wheat 14 12.7 2.2 63.9 1318

Flour (plain) 14 9.4 1.3 77.7 1450

Bran 8.3 14.1 5.5 26.8 872

Germ 11.7 26.7 9.2 (44.7) 1276

Bread

(white sliced)

40.4 7.6 1.3 46.8 926

Raw macaroni 9.7 12.0 1.8 75.8 1483

Rye (grain and

wholemeal)

15 8.2 2.0 75.9 1428

Rice (raw white) 11.4 7.3 3.6 85.8 1630

Oatmeal 8.2 11.2 9.2 66.0 1567

Data from Holland B, Welch AA, Unwin ID, Buss DH, Paul AA and

Southgate DA (1991) The Composition of Foods, 5th edn. London: Royal

Society of Chemistry and MAFF.

tbl0003 Table 3 Consumption of cereal grains (1998) and their

contribution to the estimated intake of dietary energy and

protein in selected countries

Country Total consumptionof cereals

(kgper person per year)

Energy Protein

Argentina 127.1 926 24.4

Australia 90.2 724 24.3

Chile 135.8 1102 29.6

China 186.6 1623 35.5

Denmark 112.4 875 26.8

Finland 104.6 842 26.0

Germany 96.9 764 23.2

Greece 149.9 1056 33.3

India 168.4 1545 36.5

Iran 174.7 1446 40.1

Nigeria 157.2 1320 34.9

Spain 102.9 758 23.5

UK 85.0 656 21.3

US 118.8 885 26.1

Yugoslavia 112.5 872 25.0

From FAO Food Balance Sheets 1994–1998. Rome: FAO.

1010 CEREALS/Contribution to the Diet

0014 Cereals consist of about 1.5–2.5% of minerals.

This includes minerals such as potassium, phos-

phorus, magnesium, iron, and zinc. Selenium enters

the food chain via plants, which obtain it from soil.

Wide international variations in intakes have been

observed, in part because of wide differences in selen-

ium soil content and differences in selenium bioavail-

ability from different foods. In 1997, 12.2% of total

selenium intakes in the UK were obtained from breads

and 10% from cereals. A wide variability exists in the

levels of selenium present in grain and cereal products.

Among the cereal grains, rice contains the highest

levels (10–13 mg 100 g

1

) while recent analysis of

levels in bread (6–9 mg 100 g

1

) suggest that levels

have decreased over the last 20 years and are signifi-

cantly lower than selenium levels in US bread samples

(32–44 mg 100 g

1

). This is because wheat is a good

source of selenium in North America, as the wheat is

grown in soils rich in selenium. In Europe, although

bread and cereals make a significant contribution to

selenium intake, due to frequency of consumption

(22% of total selenium in the UK), European wheat

is not a good source of selenium because of the low

bioavailability of selenium from European soils.

Wheat is not a good natural source of iron in Europe

but many cereals are fortified with iron.

0015 The differences in selenium intake between the USA

and Europe are reflected in serum and whole-blood

selenium concentrations. Although serum values of

100 mgl

1

are the suggested level required for optimal

enzyme activity, current levels in the EU appear to be

below this level with mean serum selenium levels in

seven European countries calculated as 79 mgl

1

0016 Mineral composition of grains can be affected by

genetic factors, as well as environmental ones, such as

soil composition, crop fertilization practices, and

climatic conditions. The values reported for any

grain can vary over a wide range. Refer to individual

vitamins and minerals.

Complex Carbohydrates and Dietary Fiber

0017 Cereals are composed of up to 85% (dwb; dry weight

basis) of complex carbohydrates. These are defined

by their sugar residues and the linkages between

them. Cereals also contain cellulose, b-glucans and

dietary fiber. Fiber is the sum of the plant polysac-

charides plus lignin that is not digested by enzymes in

the intestine. Cereals are a unique source of dietary

fiber and in countries where whole-grain products,

such as wholemeal bread, are popular, cereal products

may contribute more than 40% of the average dietary

fiber intake (data taken from the UK National Diet

and Nutrition Survey).

0018 Fiber has two forms – soluble and insoluble. Although

to some extent their function overlaps, they do have

different effects on the body and so it is important to

eat a variety of high-fiber foods to get both types.

0019Both types of fiber – soluble and insoluble – can

help with weight control. In the stomach, they absorb

water and some delay the emptying of the stomach,

instigating a feeling of fullness.

0020Insoluble fibers found in wheat bran, whole-grain

breads, and cereals hold water in the colon, thus increas-

ing bulk which stimulates the muscles of the digestive

tract so that they retain their health and tone. The toned

muscles can move waste product more easily through

the colon for excretion. This helps prevent constipation,

hemorrhoids, and diverticulosis.

0021Soluble fibers found in oat bran are credited with

reducing the risk of heart and artery disease – athero-

sclerosis – by lowering the level of cholesterol in the

blood. It appears that the products of bacterial diges-

tion of soluble fiber in the colon are absorbed into the

body and may inhibit the body’s production of chol-

esterol as well as enhancing the clearance of choles-

terol from the blood. Blood cholesterol levels may

also decrease if food sources of soluble fiber are

used as part of a low-fat, low-cholesterol diet. Certain

fibers also bind to cholesterol compounds in the gut

and carry them out of the body so that the whole-

body content of cholesterol is lowered.

0022In January 1997, the US Food and Drug Adminis-

tration (FDA) allowed the first food-specific health

claim for a whole-grain cereal, oats. That regulation

was amended in February 1998 to include soluble

fiber from psyllium seed husks. In the USA, foods

containing whole oats or psyllium seed husks as

ingredients can now make a health claim linking

consumption with a reduced risk of coronary heart

disease when they are part of a diet low in saturated

fat and cholesterol. The FDA acknowledged that sol-

uble fiber from sources other than oats and psyllium

probably also affects blood lipids and reduces the risk

of heart disease, but that the sources would need to be

considered on a case-by-case basis.

0023Soluble fibers also improve the body’s handling of

glucose, even in people with diabetes, perhaps by

slowing down the digestion or absorption rate of

carbohydrates. Blood glucose levels therefore stay

moderate, helping to prevent symptoms of diabetes

such as hypoglycemia.

Phytochemicals

0024During the last decade, data from experimental and

epidemiological studies have been accumulated

showing that grains contain a large variety of poten-

tially health-promoting substances called ‘plant

chemicals’ or ‘phytochemicals.’ The explosion of

new information related to the exciting approach of

CEREALS/Contribution to the Diet 1011

phytochemicals is certainly only a prelude to their

inclusion in our daily diet.

0025 Because foods are complex mixtures of various

phytochemicals, studying them is a difficult task.

A major group of phytochemicals in foods are the

phenolic compounds, which include plant flavonoids

like catechins. In cereals, flavonoids are present in

small quantities only. Barley contains measurable

amounts of catechins and some di- and trimer pro-

cyanidins. Work mainly in experimental animals

and in vitro has suggested that flavonoids possess

numerous biochemical and pharmacological qual-

ities, including anticarcinogenic, antiinflammatory,

and antiallergic properties.

0026 Other phytochemicals found in cereals include

phytoestrogens such as lignans, isoflavones, and

coumestans. The precursors of these compounds are

found in fiber-rich unrefined grain products and

cereals. Lignans are potent antioxidants and exert

anticancer effects in experimental studies. Lignan

contents vary greatly between cereals. The amounts

in cereals are low compared to that in linseed and

high compared to those in vegetables. However, since

the consumption of cereals is considerable, high

amounts of lignans and other bioactive phyto-

chemicals are provided in the daily diet.

0027 Further nutritive antioxidants present in cereals are

small amounts of carotenoids, tocopherols, and toco-

trienols, especially in the lipid-rich germ. Grains are a

unique group in that they contain more tocotrienols

than other food products. Tocotrienols possess

vitamin E activity.

Fortification

0028 No one cereal can provide adequate amounts of all

nutrients to meet the nutritional requirements of a

child or adult. Because of the stable nature of cereal

products, their contributions to the diet of the popu-

lations of the world’s nations are frequently perceived

by governments as an important means of insuring

adequate nutritive standards, not only through their

natural composition but also through the addition

of nutrients from other sources. Various terms are

applied to such additions, including restoration,

fortification, and enrichment.

0029 The nutritional quality of sorghum and millets,

especially the former, is poor. Therefore attempts

have been made to fortify these cereals to make

nutritionally superior and acceptable products. Cost,

availability of ingredients, and marketability must be

taken into consideration if fortification is to be imple-

mented successfully on a sustained basis. In the UK,

bread and breakfast cereals are currently voluntarily

fortified with folic acid and this in part may explain

the importance of cereal sources to the folic acid

intake of populations. Other vitamins and minerals

that are currently fortified include thiamin, iron, ribo-

flavin, niacin, and calcium. In the USA, mandatory

fortification was enforced on 1 January 1998.

0030Wheat flour and other common cereal products are

very suitable vehicles for fortification because there

are virtually no major population subgroups which

would not be able to use cereal grains and because

cereals are consumed by all socioeconomic sub-

groups. In the UK and Canada, the addition of nutri-

ents to flour, where addition is required, is made at

the flour mill. In the USA enrichment is permitted

either at the mill or at the bakery. In most developing

countries refined cereal products are not vitamin-

enriched, but 10 nations are currently adding iron to

wheat or maize flours and many other countries are

considering doing so.

0031For any supplementation initative to succeed it is

necessary that the added nutrient is physiologically

available; it does not create an imbalance of essential

nutrients, e.g., by competing for absorption with

another nutrient; it does not adversely affect the

acceptability of the product; and there is reasonable

assurance that intakes will not become excessive. (See

Food Fortification.)

Effects of Processing and Cooking

0032Changes resulting from cooking are complex: in only

a few cases, such as boiled rice and pasta, are cereal

products cooked substantially on their own. More

frequently they are included in a recipe, so that differ-

ences between the raw cereal ingredient and the final

product reflect not only changes due to cooking but

also to dilution and interaction with other ingredients.

0033In general, fiber, protein, vitamin, and mineral con-

centrations in cereals decrease from the outer layer to

the inner part of the seed, with the decline being

steeper in some cereals than others. For that reason,

and because of the removal of the aleurone (outer)

fraction of the cereal, milling results in large losses of

many nutrients. When wheat is milled to white flour,

the niacin content drops to about 20% of its original

level, thiamin to 27%, and riboflavin to 19%. After

milling of wheat to white flour and then bleaching,

almost 98% of vitamin E is lost.

0034Many cereal-based foods are subjected to heat pro-

cessing in baking, frying, and extrusion cooking, and

these have effects on more labile vitamins. In pro-

cesses involving boiling the losses are of the order of

40% for most of the B-group vitamins; losses of

folates are slightly higher at around 50%. In baking

the losses are generally lower except for the folates.

The losses during the more vigorous conditions of

1012 CEREALS/Contribution to the Diet

extrusion cooking are still of the same order, primar-

ily because the cooking times are generally shorter

than with more conventional cooking procedures.

0035 Probably the most significant enzymic changes that

occur during processing are those involved in the

conversion of starch into sugars and the subsequent

fermentation mediated by microorganisms, convert-

ing sugars to alcohol or lactic acid. Another import-

ant example is the reduction in phytate content

during fermentation and the proving of bread doughs.

Negative Attributes

0036 In spite of the fact that cereals are among the safest

and most important foodstuffs, there are some anti-

nutritious aspects of their composition (some of these

affect only a small proportion of consumers). There

are hazards associated with their storage and hand-

ling also.

0037 The negative nutritional attributes of phytate

derive from the fact that it forms insoluble complexes

with minerals such as calcium and iron, possibly

reducing their bioavailability and leading to failure

of their absorption in the gut of animals and humans

and thus to mineral deficiencies. The reduced bio-

availability of minerals depends upon several factors,

including the nutritional status of the consumer, con-

centration of minerals and phytate in the foodstuff

(and the diet as a whole), ability of endogeneous

carriers in the intestinal mucosa to absorb essential

minerals bound to phytate and other dietary sub-

stances, and the digestion or hydrolysis of phytate

by phytase during processing and in the intestine.

0038 Tannins are phenolic compounds of the flavonoid

group and are also considered to have negative attri-

butes. It is alleged that they reduce protein digestibil-

ity through phenol–protein complexing. There is also

no doubt that they and their derivatives can adversely

affect flavor and color, thus reducing palatability.

Tannins in seeds are concentrated in their outer

layers, therefore milling to remove the bran and

testa is an effective means of reducing the tannin

content. However, because nutrient content and pro-

tein quality tend to decrease from the outer to the

inner regions of cereal grains, tannin reduction by

milling is achieved at the expense of nutrient loss.

0039 Adverse effects on health can arise from the con-

sumption of cereals contaminated by toxic sub-

stances. At least 25% of the world’s crops may be

affected by mycotoxins, even small quantities of

which can potentially harm humans. These are toxic

secondary metabolites produced by fungi. Aflatoxins,

often found in wheat and rice, as well as corn, are

some of the most potent naturally occurring carcino-

gens. (See Mycotoxins: Classifications.)

0040Celiac disease is a permanent condition, requiring a

lifelong strict gluten-free diet, and is the main form of

wheat intolerance. Older literature suggests that

celiac disease has a prevalence of around one case in

1500 people in the UK. However, the advent of sensi-

tive serological screening tests has allowed studies

which suggest that the true prevalence may be higher,

both in the UK (although a population-based

study has yet to be conducted) and abroad. Studies

in Italy, the USA, and The Netherlands have sug-

gested that one in 300 of the general population in

these countries may be gluten-sensitive. Classically,

celiac disease inflicts many ‘‘negative attributes’’ on

its sufferers, including diarrhea, weight loss, and

anemia. However, these may be absent and many

individuals may suffer from mild or nonspecific

symptoms, which may be ignored for many years.

Delayed diagnosis can result in osteoporosis, infertil-

ity, or even cancer. The condition is triggered by the

ingestion of wheat, rye, and barley. Oats are probably

safe for consumption by gluten-sensitive individuals.

(See Food Intolerance: Types; Food Allergies.)

0041In conclusion, cereals are important sources of

many nutrients, but they are limited in others. In the

past few years, a steady stream of exciting new devel-

opments in cereal nutrition has flowed from scientists

to consumers. Sometimes data seem contradictory

but gradually the physiological benefits of cereal-

rich diets are becoming clearer and indications are

good that more health benefits of grains and grain

components will soon be revealed.

See also: Barley; Food Fortification; Food Intolerance:

Types; Food Allergies; Maize; Millets; Mycotoxins:

Classifications; Oats; Rice; Rye; Wheat: The Crop

Further Reading

Andlauer W and Furst P (1998) Antioxidative power of

phytochemicals with special reference to cereals. Cereal

Foods World 43: 356–360.

British Nutrition Foundation (BNF) (1994) Briefing Paper.

Starchy Foods in the Diet. London: British Nutrition

Foundation.

British Nutrition Foundation (BNF) (1999) Briefing Paper.

Nutrition and Food Processing. London: British Nutri-

tion Foundation.

British Nutrition Foundation (BNF) (2001) Briefing Paper.

Selenium and Health. London: British Nutrition Foun-

dation.

British Nutrition Foundation (BNF) (2002) Task Force

Report. Health Effects of Plant Derived Foods and

Drinks. London: British Nutrition Foundation.

Blackwood AD, Salter J, Dettmar PW and Chaplin MF

(2000) Dietary fibre, physicochemical properties and

their relationship to health. Journal of the Royal Society

for Promotion of Health 120: 242–247.

CEREALS/Contribution to the Diet 1013

Carl Hoseney R (1994) Principles of Cereal Science and

Technology, 2nd edn. Minnesota: American Association

of Cereal Chemists.

FAO/GIEWS Food Outlook No 5, November 2000, page 4.

FAO/WHO Experts consultation. Carbohydrates in human

nutrition, 2nd edn. (1998) FAO. Food and Nutrition

Paper. Rome: FAO.

Garrow JS, James WPT and Ralph A (2000) Human Nutri-

tion and Dietetics, 10th edn, pp. 333–348. London:

Churchill Livingstone.

Henry RJ and Kettlewell PS (1996) Cereal Grain Quality.

London: Chapman and Hall.

Holland B, Welch AA, Unwin ID, Buss DH, Paul AA and

Southgate DA (1991) The Composition of Foods,5thedn.

London: Royal Society of Chemistry and MAFF.

Kent NL and Evers AD (1994) Technology of Cereals and

Introduction for Students of Food Science and Agricul-

ture, 4th edn. Oxford: Pergamon.

Kulp K and Ponte JG (2000) Handbook of Cereal Science

and Technology, 2nd edn. New York: Marcel Dekker.

Ministry of Agriculture, Fisheries and Food (1997) Total

Diet Study – Aluminium, Arsenic, Cadmium,

Chromium, Copper, Lead, Mercury, Nickel, Selenium,

Tin and Zinc. Food Surveillance Information Sheet

no. 191. (http://archive.food.gov.uk/maff/archive/food/

infsheet/1999/no191/191tds.htm)

Ministry of Agriculture, Fisheries and Food (2000)

National Food Survey. London: The Stationery Office.

Bulk Storage of Grain

D Richard-Molard, INRA, Nantes, France

Introduction

0001 At the beginning of the 21st century, world produc-

tion of cereal grains is about 1600 million tonnes.

This represents by far the greatest production of

staple food material, the second most important

source, i.e., tuber-producing crops, being far behind,

with a total production of less than 100 million

tonnes of edible dry matter. A simple arithmetic cal-

culation shows that cereal crops will be able to pro-

vide more than the 1.3 kg of bread or rice per day for

all of the 6000 million world population, provided

that postharvest losses are minimized.

0002 Whatever the political problems and ethnic questions,

two essential facts must be taken into account: cereals

(mainly wheat and maize) are produced in excess in only

a limited number of countries, and only during limited

periods in the year. Good and safe storage would allow

consumption to be delayed and grain to be exported

anywhere throughout the year and is, therefore, of pri-

mary economic, political, and social importance.

Existing Losses of Cereal Crops

0003It is difficult, if not impossible, to calculate accurately

the postharvest losses resulting from poor storage

conditions and inadequate practices. However, in

1976 it was estimated that losses of grain could rep-

resent a commercial value up to US$4000 million.

0004Food and Agriculture Organization (FAO) reports

generally indicate that percentage losses remain at

rather low levels in industrialized countries, probably

never more than 1 or 2%, whereas they can reach

very high levels, maybe 50% or even more, in coun-

tries where climatic conditions are unfavorable and

modern storage equipment is lacking. It is important,

however, to realize that, in developed countries,

low percentage levels of loss involve enormous quan-

tities of grain, leading to problems of significant

economical importance. By contrast, high levels of

losses in developing areas apply in most cases to

only limited quantities of stored cereals, raising

questions of vital importance only for the populations

concerned.

0005It must also be emphasized that losses in grain

quality can occur without significant losses of dry

matter, e.g., decreases of nutritional value, losses

of vitamins or essential fatty acids, appearance of

toxicity, off-flavors or discolorations due to micro-

biological activity and insect pest infestation. The

assessment of such hidden losses remains impossible

at the present time.

0006In every situation it is of primary importance to

have the best understanding of local environmental,

economic, climatic, and ethnic conditions, and appre-

ciation of possible causes of grain deterioration

during storage, in order to minimize losses.

0007Some basic questions still lack satisfactory tech-

nical or economic answers but, usually, it can be

said that postharvest losses are mostly due to lack of

adequate training of the people who handle and store

the grain. Most significant losses generally result

from insect infestation or from the growth of micro-

organisms. To a lesser extent, biochemical changes in

the grain itself can also be important.

0008The causes and extent of grain losses may differ

widely from one place to another. They depend on

many parameters but three major environmental

factors determine the extent of damage in a given

situation: the water content of the grain, the mean

temperature of the bulk, and the duration of storage.

Of these factors, water is by far the most important

and also the most interesting because it can be

managed; whereas it is very difficult to control tem-

perature in practice. (See Storage Stability: Mechan-

isms of Degradation; Parameters Affecting Storage

Stability.)

1014 CEREALS/Bulk Storage of Grain

Main Biological Causes of Losses

0009 Unless cereal grains are sufficiently dry at harvest,

they must be considered as perishable biological

products that will be damaged by microorganisms

or insects, depending on the environmental condi-

tions. Surprisingly, the major role played by micro-

organisms, and particularly by molds, has only been

recognized recently, but it is now understood that

artificial drying of moist grains after harvest is essen-

tial for the avoidance of mold growth during storage,

rather than for the prevention of development of

insects or biochemical changes in the kernel itself.

(See Spoilage: Molds in Spoilage.)

0010 Respiration of the grain itself is a secondary phe-

nomenon in most situations, when germination is not

taking place. Respiration of the germ seems to remain

more or less constant and at a very low level, compat-

ible with seed conservation, whatever the hydration

or the gaseous environmental conditions.

0011 To initiate germination of the grain, very large

moisture contents, higher than 70–80% (wet basis),

i.e., sufficient for the full hydration of the grain, are

necessary. When much moisture migration occurs in

metallic bins, intense condensation is produced, gen-

erally on the roof of silos, and grain sprouting at the

top of farm silos or in railway wagons frequently

occurs. (See Water Activity: Effect on Food Stability.)

Role of Microorganisms in Grains

0012 The microorganisms which make up the microflora

of cereal grain and their products are now well

known in regard to their ecological requirements

and the damages they are able to produce during

storage.

0013 As soon as the relative humidity in equilibrium

with the grain is sufficient for the growth of micro-

organisms (with freely available oxygen), the greater

the humidity and temperature, the more intense and

rapid the activity of microorganisms (Table 1). Fortu-

nately, there exists an absolute hydration limit below

which microbial activity cannot take place. Expressed

in terms of relative humidity of the air in equilibrium

with the stored grain, this absolute limit is about 65%

for all cereal species of interest for humans. It corres-

ponds to a moisture content of about 13% (wet basis)

for wheat at 25



C. Below this limit, nothing of im-

portance can occur in the kernel for many years, with

the exception of possible weak evolution of the lipids,

as explained below. Above this hydration limit, which

is in fact very low, some mold species belonging to the

genera Aspergillus, Eurotium (Figure 1) and Monas-

cus, among others, can develop. With the extraordin-

ary physiological ability to grow in extremely dry

conditions, these molds invariably do develop unless

additional barriers such as cooling, antifungal agents,

or modified atmospheres are utilized. Such molds

contaminate cereal grains all over the world, but it

must be emphasized that the growth of these so-called

xerotolerant or xerophilic species is very slow, and

usually not accompanied by mycotoxin formation or

significant deterioration of nutritional value. For

their growth, molds utilize lipids and carbohydrates

from the grain (as do humans) and produce carbon

dioxide, water, and heat in exchange, following the

simplified scheme shown in eqn (1).

Grain components þ oxygen from air

þ H

O þ energy þ heat ð1Þ

0014The main consequence is a local increase in relative

humidity and temperature and it is generally accepted,

but not easily demonstrated, that this progressively

allows the growth of molds with greater water require-

ments, such as Penicillium spp., other Aspergillus spp.,

or even Fusarium spp. These kinds of molds are able to

destroy the grains and to produce extremely dangerous

mycotoxins, such as the hepatotoxic aflatoxin B

or the

immunosuppressive T

toxin. (See Mycotoxins:Occur-

rence and Determination.)

0015In practice, chiefly for economic reasons, grains are

most often stored at moisture contents around

15–16% (wet basis); this allows storage without vis-

ible molding for some months, as shown in Table 1,

tbl0001 Table 1 Microorganisms able to grow and approximate safe storage periods for various moisture contents of wheat

Moisture (% wet basis) ERH (%) Microorganisms Safe storage period

12 50 None Indefinite

14 65 Aspergillus glaucus Years

15 68 A. candidus, Penicillium spp. Years

16 75 A. ochraceus, most penicillia Year

17 77 Most storage fungi Months

18 80 Some yeasts, some lactic bacteria Month

20 85 Most yeasts, most fungi (Fusarium spp.) Week

30 95 Most fermentative bacteria Days

ERH, Equilibrium relative humidity. Data mainly from the cited literature.

CEREALS/Bulk Storage of Grain 1015