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

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with five weighing stations. At four of these, random

sample checks are made with the machine operators

performing the weighing. The fifth line has a Garvens

check weigher attached. The reasons for such a distri-

bution are as follows.

0078 At four of the lines with random sample weighings,

rolled-out, ready-made pastry is produced. On the

basis of the adjustment message of the system (in

grams), the machine operators set the pastry thickness

on the machines, or they correct it if necessary. Al-

though this information is received in grams and not

in correction values in millimeters of pastry thickness,

the machine control functions completely satisfactor-

ily thanks to the experience of the operators.

0079In contrast to earlier generations of control

methods, the system has the great advantage that it

supplies adjustment messages in absolute values and

decisions no longer have to be made on the basis of a

mean value alone.

0080At the fifth line, always the same product, unrolled

pastry, is produced and packaged in large quantities.

The criteria listed earlier are therefore applicable here

and a check weigher is used.

0081Leisi produces one or more batches daily for a

major customer. The system thus supplies the sum-

maries in the form of batch statistics. If necessary,

these can be passed on to the customer.

0082In addition to the statutory requirements which the

SQC52 system in operation with Leisi fulfills, it also

offers attractive prospects from the economic effi-

ciency standpoint. Quite apart from the savings in

material owing to optimum fill quantities, it greatly

rationalizes control operations. The data of approxi-

mately 50 articles are permanently stored. After every

product change at a filling station, the control system

is thus immediately ready for operation. If the pack-

aging of a product is changed, only the new tare value

must be entered. This is performed simply by over-

writing the old value.

See also: Cleaning Procedures in the Factory: Overall

Approach; Quality Assurance and Quality Control

Weight Maintenance See Slimming: Slimming Diets; Metabolic Conseqences of Slimming Diets and

Weight Maintenance

Whales See Marine Foods: Production and Uses of Marine Algae; Edible Animals Found in the Sea; Marine

Mammals as Meat Sources

fig0009 Figure 9 SQC61 evaluations. Reproduced from Weighing,Ency-

clopaedia of Food Science, Food Technology and Nutrition, Macrae

R, Robinson RK and Sadler MJ (eds), 1993, Academic Press.

WEIGHING 6129

WHEAT

Contents

The Crop

Grain Structure of Wheat and Wheat-based Products

The Crop

S T Grundas, Dobrzanski Institute of Agrophysics,

Polish Academy of Sciences, Lubin, Poland

Introduction

0001 For 10 000 years, wheat (Triticum) has been an object

of particular interest, owing to its specific taste and

nutritional value, as well as its ease of cultivation and

storage. Archeological evidence indicates that primi-

tive unleavened bread, baked on heated stones, was

first made in the Neolithic era. The early Egyptians

were developers of bread and the use of the oven and

developed baking into one of the first large-scale food

production industries. Nowadays, wheat constitutes

about one-third of the global production of cereals,

and its yearly production in the mid-1990s reached

600 10

tonnes. Wheat has a predominant role in

the grain trade and is utilized as food (67%), feed

(20%), seed (7%), and industrial products (6%).

Wheat meal used for human consumption provides

20% of all the energy consumed by the human popu-

lation. It is consumed mainly as bread.

0002 This article provides information on the following:

the global distribution of wheat; its varieties and

market classes; the morphology and anatomy of the

spikelet and grain; its chemical and nutritional com-

position; grading, handling, storage; wheat process-

ing and end uses; the role of wheat gluten proteins.

Distribution, Varieties, and Market

Classes of Wheat

Distribution

0003 There are over 20 species of wheat, differing in their

basic number of chromosomes (diplo-, tetra-, and

hexaploid), and several thousand varieties. The most

economically significant species are the ordinary

wheat Triticum aestivum sp. vulgare (hexaploid)

and the hard wheat T. durum (tetraploid). The global

area of wheat cultivation covers a total of about

240 10

ha, and approximately 90% of that is

occupied by T. aestivum, which has the greatest

number of crop-yielding varieties of starchy grains.

There are numerous varieties of T. durum cultivated

in continental climate zones and covering approxi-

mately 10% of the total area.

0004The geography of wheat cultivation is illustrated in

Figure 1. The areas of wheat cultivation are mainly

found in the northern hemisphere. Wheat is grown

both as a winter and as a spring cereal in the moderate

climate zones, and in the tropical regions in low lands

and uplands alike. The distribution of wheat over the

various parts of the world is related to the numerous

species and varieties, and to their adaptability to

particular environments.

0005Wheat harvesting is a continuous process around

the world and every month is a period of harvest in

one of the wheat-growing regions.

Wheat Varieties and Marked Classes

0006Five marked classes of wheat are distinguished: Hard

and Soft Red Winter (HRW and SRW), Hard Red

Spring (HRS), durum (Durum), and White, which is

classified in the following subclasses: Hard and Soft

Winter (HWW and SWW), and Hard and Soft Spring

(HWS and SWS).

0007Although variety is an important factor affecting

quality, wheats are seldom classified on the basis of a

single variety. In practice, we adopt the classification

of wheat according to its class. Each class consists

fig0001Figure 1 Main wheat-growing regions in the world; the north-

ern and southern distribution boundaries are marked with a

broken line. From Grzesiuk S and Kulka K (1988) Biology of

Cereal Kernels. Warsaw: Polish Scientific Ed. (in Polish) with

permission.

6130 WHEAT/The Crop

of a group of varieties of similar characteristics for

specific purposes.

000 8 As an example, in Canada a model HRS wheat

is the Marquis variety, for years now replaced in

production by varieties genetically similar, but more

valuable economically, such as Neepawa, Manitou,

and Thatcher. Out of Amber classes (CWAD1 and

CWAD2) T. durum wheats, representative varieties

are Kyle and Plenty. Wheat varieties grown in USA

are genetically similar to those grown in Canada. In

Argentina, approximately 97% of the area of wheat

cultivation is taken up by winter wheat similar in its

value to the HRS class. In Australia, the primary crop

is winter wheat, class ASW (see Grading below), of

hard and soft white grain, genetically similar to the

Argentinean wheat. In Europe, and especially in

France and Germany, the high level of agriculture

resulted in these two countries having virtually the

highest grain yield per unit of area of cultivation.

Recently, ‘clubs’ have been set up by wheat producers

who achieve yields of 10–15t ha

1

. In this region the

dominant type are wheats of the SRW class. The EU

countries have dozens of high-yield varieties of very

good grain quality. In Mediterranean countries such

as Italy and Spain some T. durum is grown. East

European countries grow mainly red winter wheats,

some of which have very good baking qualities. In the

countries of the Commonwealth of Independent

States (CIS) both spring and winter, red and white

wheats are grown, as well as some durum wheats.

The CIS has the largest area of wheat cultivation in

the world. The leading varieties in terms of yield

and grain quality are winter wheats Bezostaya 1 and

Mironovskaya 808, and the spring wheat Saratovs-

kaya 29.

Morphology and Anatomy of Spikelet and

Grain

Spikelet

0009 The central part of the ear or spike is a waveform

rachis, composed of a number of short nodes and

internodes (Figure 2a). Spikelets grow at the nodes,

constituting modified shoots (Figure 2b). Two

glumes, located at the base of each spikelet, are

shorter than the rest of lemmas in florets. In floret

the grain is enclosed between two pales (the palea,

from the inside, and the lemma, from the outside).

Ordinary wheats which have fusiform spikes are

awned or awnless, and easily threshed.

Grain

0010 The dorsal side (the same side as the germ) of the

wheat grain can be oval, ovate, or elliptical, with a

cluster of long or short brush hairs at the apex, and an

oval or circular embryo at the bottom. Wheat kernels

have a longitudinal crease or a deep groove the length

of the ventral side (opposite the germ). The shape of

the groove is a characteristic feature of some species

and varieties.

0011The grain structure is presented in Figure 2c. The

grain coat is made up of the fruit and the seed coat,

adhering directly to the aleurone layer. The pericarp

(fruit coat) consists of several layers of translucent

cells, strongly lignified, elongated in shape and

encrusted with mineral substances, and of a layer of

perpendicular and tubular cells. The seed coat con-

sists of a compact cell layer and pigment strand,

providing the grain with its characteristic coloring,

and a hyaline layer.

0012The aleurone layer, made up of large thick-walled

cells filled with functional proteins and nutritional

components, encloses the endosperm, and disappears

around the embryo.

0013The endosperm consists of large, thin-walled cells,

filled mainly with starch and protein. In the subaleur-

one area, especially on the dorsal side of the grain, the

dominant cells are elongated in the direction of the

endosperm center. Cells within the endosperm are less

regular in shape. Starch grains are enclosed in the thin

layer of adherent protein and located within a protein

matrix which fills the individual cells of the endo-

sperm to varying degrees. The highest protein content

is observed in the cells of the subaleurone layer of the

endosperm. The closer to the center of the grain, the

lower the protein content.

Chemical and Nutritional Composition of

Wheat Grain

Chemical Composition

0014The chemical composition of wheat grain and of its

anatomical parts (Table 1) is determined by genetic

and ecological (climate, soil, tillage) factors, and by

the physical and chemical effects acting on the grain

during its storage and processing.

0015The primary quantitative component of wheat

grain is starch. Cereal grains store energy in the

form of starch. The starchy endosperm varies in

composition from its outer portion, just beneath the

aleurone layer, to its center. The amount of starch

contained in wheat grain varies but is generally be-

tween 60 and 70% of the weight of the grain. Starch

is basically polymers of glucose. Chemically, at least

two types of polymers are distinguishable: amylose,

an essentially linear polymer, and amylopectin, which

is highly branched. The ratio of amylose to amylo-

pectin is relatively constant, at about 23 + 3%

WHEAT/The Crop 6131

amylose. Wheat endosperm has two types and sizes of

starch granules: the large (25–40 mm) lenticular and

small (5–10 mm) spherical granules. Apart from

starch, the grain and especially the grain coat, the

aleurone and the embryo, contain other carbohy-

drates, such as cellulose, hemicelluloses (pentosans),

and sugars. Pentosans, although their content in

endosperm is low (2–3%), form the basic structure

of endosperm cell walls. Of particular interest is the

concept that pentosans could, depending on their

water-absorbing capacity (which is 10 times their

mass), represent ‘moisture pumps’ that to a certain

extent regulate moisture levels in different flour com-

ponents after their hydration in the dough-making

process.

0016Proteins are among the basic nutritional compon-

ents of grain, and their quantity and quality deter-

mine the applicability of the grain and its products

for particular purposes. The total protein content is

determined on the basis of the nitrogen multiplied by

factors of 5.7.

0017The protein substances of wheat are divided,

in relation to their solubility, into the following

subgroups: (1) albumins, in water; (2) globulins, in

Spike

(ear)

Spikelet

Rachis

(a)

Awn (not always present)

Palea

Lemma

Grain

Glume

}

Pales

Rachilla

(b)

Brush

Starchy

endosperm

Crease

region

Attachment

region

Grain coat

Aleurone layer

Embryo

(c)

fig0002 Figure 2 Structure of the spike (ear), spikelet, and grain: (a) spikelets arranged alternately on the main axis or rachis; (b) a mature

spikelet; (c) grain structure.

6132 WHEAT/The Crop

10% sodium chloride; (3) prolamins, in 70% ethanol;

(4) glutelins, in dilute alkaline or acid solutions.

These substances form groups of particles of similar

physicochemical and structural properties but, occur-

ring in various grain tissues, they differ from one

another in amino acid composition (Table 2). The

proteins of the starchy endosperm contain small

quantities of lysine, a considerable amount of glu-

tamic acid, and some prolines. The proteins of the

embryo and the aleurone layer of the endosperm are

characterized by a relatively high content of leucine,

lysine, and aspartic acid.

001 8 Fats are the third important component of wheat

grain. Their highest contents are observed in the

embryo and the aleurone layer (Table 1). A high

content of fats in cereal products can result in their

rapid spoilage. Carotenoids, found mostly in an

embryo and in the aleurone layer, belong in a group

of fats which are of practical importance. They have a

considerable nutritional value, as they constitute the

basis for the formation of vitamin A in humans and

animals. They have a yellow or pale orange coloring,

which determines the typical creamy look of wheat

flour. Whitening flour by chemical processing results

in a decrease in its nutritional value through the

oxidation of the carotenoids.

001 9 The ash formed in the course of burning grain or

flour originates from inorganic compounds and

organic substances (Table 1). The highest content of

mineral substances is found in the aleurone layer and

in the grain coat, and the lowest in the endosperm.

Nutritional Composition of Grain and its Products

0020 The nutritional value of wheat is determined by the

technological properties of the grain (good milling

and baking characteristics) and the nutritional qual-

ities of its products, in combination with taste and

digestibility.

002 1 The nutritional components of the grain provide

energy and ‘building materials,’ and play a regulatory

role. Primary components providing energy are

sugars and fats and, less frequently, proteins. Com-

ponents providing building materials are mainly

proteins and minerals, while those performing a regu-

latory function include vitamins and minerals. The

energy values of the major chemical components of

grain and its products are presented in Table 3.

0022The nutritional value is also determined by the

content of endogenous amino acid (lysine, methio-

nine, tryptophan), the levels of which are relatively

low in wheat. For this reason, an admixture of milk

or soya flour to wheat flour improves the quality

of bread or other bakery products. A typical day’s

healthy diet would include 55% or more of daily

calories from complex carbohydrates, such as cereal

grains. Eating six or more servings of bread, pasta,

tbl0001 Table 1 Main chemical components in particular parts of the wheat grain

Content of chemicalcomponents (% db)

Chemical components Whole grain Grain coat withaleuronelayer Embryo Endosperm

Proteins 10–17 23–33 36–42 9–14

Carbohydrates

Starch 60–70 0 0 78–84

Sugars 3.0–6.0 3.0–5.0 22–28 3.0–4.0

Pentosans 6.0–9.5 30–40 9–11 2.5–3.0

Cellulose 2.5–3.3 12–20 3–5 0.13–0.18

Fats 2.0–2.5 7.0–8.5 12–16 0.5–0.7

Minerals 1.4–2.3 9–11 5–6 0.3–0.5

Data from various sources, selection by author. db, dry-weight bases.

tbl0002Table 2 Amino acid content in proteins from various parts of

the wheat grain

Amino acid content (g per100 g)

Amino acid Endosperm Embryo Aleurone layer

Lysine 1.7 8.4 4.6

Histidine 2.3 4.0 4.0

Arginine 3.5

Aspartic acid 3.3 6.4 8.0

Threonine 2.7 2.6 3.1

Glutamic acid 39.3 8.4 16.4

Proline 14.7 3.5 3.9

Glycine 7.3

Alanine 3.5 6.4 5.1

Cystine 1.0 1.8

Valine 4.3 4.0 5.4

Methionine 1.9 1.5 1.5

Isoleucine 4.1 2.5 3.1

Phenylalanine 6.0 2.0 4.0

Tyrosine 3.9 1.5 3.0

Leucine 7.6 4.5 6.0

Tryptophan 2.0 1.7 4.0

Data from Grzesiuk S and Kulka K (1988) Biology of Cereal Kernels.

Warsaw: Polish Scientific Ed. (in Polish).

WHEAT/The Crop 6133

and cereal grains each day is the right choice for an

overall healthy lifestyle.

0023 Wheat grain is relatively low in vitamins; only the

B-group vitamins are present in any notable quan-

tities. The B-group vitamins as a component of

wheat grain are presented in Table 4. Likewise, fat,

the content of which is low in wheat flour, plays no

significant role in the nutritional value of wheat flour

and its products.

Grain Grading, Handling, and Storage

Grading

0024 The grading of wheat grain involves the isolation

and valuation of grain portions based on the

physical and chemical properties of the grain. The

scope of wheat grain grading in use is related to

the state and development of agricultural knowledge,

as well as to the level of organization of the local

cereal market (pricing polices, grain-purchasing

system).

0025 The systems of wheat grain grading include the

following groups of grain properties:

0026 Stable properties, related to genetic properties,

such as grain size and coloring, protein content,

and sedimentation factors.

0027 Variable properties, subject to change as a result of

drying, cleaning, sorting, and transport (moisture

content, contamination, damage to grain), related

to climatic conditions (bulk density).

0028 Permanent faults and defects, such as stale smell,

fermented smell, foreign smell, or faults that can

be rectified, e.g., washing grain contaminated with

soil or foreign matter.

0029 The stability properties are primary properties, and

it is on their basis that the market classes are distin-

guished. This is the most important group of proper-

ties characterizing the market grades of wheats in

international trading.

0030The variable properties are secondary properties,

although also important from the viewpoint of grain

quality. The group of variable properties, system-

atized into several ranges in terms of values, consti-

tutes grain grades, which are identical for all the

market classes and varieties. The quality grading of

wheat grain sometimes includes an assessment of

mechanical damage, which occurs wherever grain

is subjected to the destructive action of internal or

external forces.

0031The results of research carried out using X-ray

methods showed significant differences in grain endo-

sperm cracks between common wheat varieties. It

was stated that natural wetting of dry grain (below

15% of moisture content) during rainfall in field

conditions is one of the main reasons for its cracking.

Considering the results of endosperm cracks which

can appear before harvest in some climatic regions of

wheat production, special attention should be paid

not only to proper combined adjustment but also to

the state of natural continuity of endosperm tissue

and to genetic features of the variety. The suscepti-

bility of wheat to mechanical damage is determined

by genetic factors (hard and soft grains), environmen-

tal effects (climatic condition during the preharvest

period), and by the conditions of grain storage (exces-

sive humidity). The combination and selection of

these properties determine the unification of grain

material in terms of quality.

0032The permanent faults and defects are excluded in

grain grading, as their character disqualifies grain

from food usage. Defined faults which can be recti-

fied constitute special grades of defective quality.

0033The standards of wheat valuation have been estab-

lished by Canada and the USA. These countries have

a system of wheat grading with classes based on the

varietal properties as expressed by the vegetation

period (spring and winter wheats), grain coloring

(red, white) and hardness (hard, soft). In recent

years, an extra class, Utility, has been added to the

grading system, and it is made up of certain genetically

tbl0003 Table 3 Energy value of some grades of flour and wheat

bakery products

Product Energy value (kJper100 g)

Theoretical Actual

Wholemeal flour (97% type 1888) 1575 1400

Bread-making flour (80% type 850) 1533 1365

Patent flour (type 500) 1512 1386

Semolina 1533 1407

Graham bread 1071 945

White bread 1050 1010

Rolls (popular types) 1050 1030

Data from various sources, selected by the author.

tbl0004Table 4 The B-group vitamins located in endosperm of wheat

grain and recommended daily intake for adults

B-groupvitamins Content in endosperm

(%)

Daily intake for adults

(mg)

Thiamin 3 2.0–3.0

Riboflavin 32 2.0–2.5

Pyridoxine 6 1.5–2.0

Niacin 12 15.0–20.0

Pantothenic acid 43 10.0–11.0

Data from Pomeranz Y (1988) Wheat: Chemistry and Technology, vol. II. St

Paul, Minnesota, USA: American Association of Cereal Chemists, and

other sources, selected by the author.

6134 WHEAT/The Crop

similar varieties of winter and spring wheat. Wheat

grading in the USA additionally provides, in the

subclasses, for the proportion of vitreous grains, and

it is simplified, compared to the Canadian system,

by using identical grades for all classes and subclasses.

The system also includes an additional grade, called

Sample Grade, samples of which do not conform

to established requirements of the basic-quality

grades.

0034 Argentina uses a system of bread wheat division

into subclasses in relation to the grain type (hard,

semihard, and soft), and into grades. Australia has

developed a grading system for white-grain wheats.

The grading is based on the health requirements,

cleanliness and bulk density established for the basic

class called Australian Standard Wheat (ASW). Grain

of lower quality than that of ASW is classified as

General Purpose, or as Feed grain.

0035 Wheat grading in the CIS is based on principles

similar to those followed in the USA, with the distinc-

tion that classes are replaced here by types, and sub-

classes by subtypes, primarily designed to take into

consideration the proportions of vitreous grains.

Some European countries (e.g., France, Germany)

use a grading system based on the protein content,

bulk density, and sedimentation factor. With only

slight differences in the appearance of many varieties,

and with the possibility of grain quality reduction as a

result of environmental effects, grades have been de-

veloped to include, in addition, the contamination of

the grain and the falling number.

0036 Other countries, in which wheat is grown or only

imported, also use specific standards for the evalu-

ation of the quality of wheat grain and its products.

Most frequently such systems are modifications of the

systems presented above.

0037 In relation to grading, the following definitions are

applied:

0038 Hard wheat is wheat which, as a result of variety

or breeding in combination with environmental

factors during growth, has a vitreous endosperm

generally considered an advantage for the produc-

tion of bread-making flours.

0039 Soft wheat is wheat which, as a result of variety or

breeding in combination with environmental

factors during growth, has a white opaque endo-

sperm generally considered more suitable for the

production of cake and biscuit flours.

Handling

0040 Grain handling includes harvesting, segregation,

cleaning, and sometimes, drying. Preliminary segre-

gation takes place during combine harvesting of the

grain which, depending on its moisture content and

level of contamination, is then additionally cleaned

and dried.

0041With the use of various means of grain transport,

both internal (in the grain-cleaning machinery and for

grain loading and off-loading) as well as external

(road, rail, or sea transport), loads of wheat grain of

initially determined grades are sometimes subject to

mechanical damage, which considerably reduces their

technological value.

0042Grain stockpiling is a concentric process in which

the grain is gradually moved from the farm to the

world market. That movement passes the following

stages: farm silos, local, regional, and terminal stor-

age elevators (the latter frequently located at

harbors). At every stage, grain is subjected to classifi-

cation – from highly detailed to more general grading,

improvement (drying, cleaning, sorting, and deinfes-

tation, if required), and grouping of supplies into

larger batches of constant quality. Isolated fractions

of undersize grain and lower-grade wheat are sold on

the local market. With depressed demand, the con-

centric movement may end at the local market. In

case of oversupply it proceeds into the regional or

the national markets. With grain exports, the concen-

tric movement may flow out of the national borders

and continue worldwide.

Storage

0043The principal factors affecting the intensity of the

process of grain respiration, and therefore also the

extent of quantitative losses to the mass of the grain

in storage, are the following: grain moisture content,

temperature, and grain condition relative to its his-

tory. Grain respiration is more intensive in soft grain

than in hard grain. If grain moisture content is rela-

tively low (below 14% weight basis, wb), and the

bulk of grain of that moisture is homogenous, such

grain can be stored for several years without signifi-

cant losses. However, if proper air temperature and

humidity conditions are not observed in the storage

area, the increasing humidity resulting from the pro-

cess of grain respiration may lead to the phenomenon

of spontaneous heating of the grain, which excludes

its use for human consumption.

0044In some wheat-growing regions, e.g., in the Scandi-

navian countries, wheat grain is relatively moist

during harvesting and has to be dried to maintain

its level of quality. Drying must be performed at

specific levels of temperature and humidity of the

drying air. Exceeding the required temperature

may lead to the loss in the baking value of the flour.

To avoid damaging grain meant for baking purposes,

its temperature should not exceed 35



C at moisture

contents above 20% wb. There is a general view that

the so-called ‘critical moisture content’ (14% wb), at

WHEAT/The Crop 6135

which changes related to fungal growth are at a min-

imum and the grain remains in an abiotic condition,

can be maintained by air with a relative humidity of

less than 70%.

Wheat Processing and End Uses

Processing

0045 Grain for processing must be of a satisfactory tech-

nological quality, and is subjected to a process of

preparation for milling. The process of preparation

consists of sorting, decontamination, and grain

surface cleaning. Most frequent is the process of dry

cleaning, using the following equipment: winnowers,

aspirators, dry stone separators, pearling mills,

brushers, or wet brushing machines. An important

measure in the process of grain preparation is the

conditioning which brings the grain to the most fa-

vorable condition from the viewpoint of the grain

milling quality and the flour baking value. This

process strengthens the grain coat and facilitates

the diminution of the endosperm, but usually elimin-

ates the aleurone layer because it is tightly bound to

the grain coat. The aleurone layer contains most

of cereals’ active anticancer compounds. Therefore,

whole grain products are recommended. The

embryo, on the other hand, owing to its high fat

content, easily flakes off after passing between

smooth-bore cylinders.

0046 The milling of the wheat grain, understood as a

process of grain diminution down to the level of

flour, is realized currently in rather complex and

highly mechanized processing plants, equipped with

special machines for grain cleaning, grinding, and

sorting.

0047 One-time diminution of grain into a product of a

specific particle size, so-called simple grinding, is used

when grinding wheat grain for wholemeal flour. In

graded flour production, the grain and the products

of its diminution go through a process of repeat

grinding, and such grinding is known as complex

grinding.

0048 Extraction is the ratio of the mass of flour obtained

as a result of milling to the initial grain mass. The

level of flour extraction is related to its degree of

‘whiteness.’ Flours obtained from mealy wheats, at

the same level of extraction, is always brighter than

flour from vitreous wheats. Fine flour, of fine granu-

lation, is lighter than flour of the same extraction but

of coarser granulation. Flours of fine and uniform

granulation improve the process of dough formation.

With increasing level of extraction, the baking value

of the flour from soft wheat grain decreases. Flours of

higher extraction have higher protein contents, and

also contain more cellulose, vitamin B, and mineral

substances such as phosphorus, iron, calcium, mag-

nesium, zinc, and copper, but have a lower content of

starch. More starchy flours, i.e., those of lower pro-

tein and cellulose content, are made of pure grits and

fine-ground, while the highest content of cellulose

and ash characterize flours made from the final

milling passages. Sometimes, during the process of

milling, wheat germs of high nutritional value but

short storage life are isolated.

End Uses

0049Wheat is used in baking, primarily to make white

bread and numerous other bakery products. Al-

though wheat is consumed in many forms, including

noodles, gruels, cooked cereals, and ready-to-eat

cereals, bread has established itself worldwide as a

major convenient and delicious food, especially when

made according to regional preferences for flat

breads, French bread (baguette), Italian breads,

Vienna bread, white and variety pan breads, Polish

bread specialties, and many other ethnic varieties. A

specific form of bread, known in the countries of the

Far East, especially in China, is steamed bread.

0050Soft wheat flour (of generally low extraction and

protein content) is used mostly to make cakes, wafers,

and dough that is used for cooked products (noodles

and some types of pasta) and for special cakes and

cookies made with butter and sugar.

0051Pasta and noodles are wheat-based products that

are formed from a dough but are not leavened. It is

generally believed that the ideal raw material for

pasta is semolina from durum wheat. Durums are

usually amber in color; they are high in carotenoid

pigments. When durum wheat is expensive, common

hard wheat farina (purified middlings from hard

wheat) is often blended with durum or used by itself

to produce pasta. In general, the hard-wheat farina

produces good pasta except that it does not have the

yellow color and is not as resistant to overcooking as

that produced from semolina.

0052Generally, we can say that the baker converts the

flour produced by the miller from wheat grown by

the producer into delicious basic foods favored by the

consumer and capable of being eaten with every meal,

by every ethnic and age group every day of the year,

regardless of economic level, from the cradle to the

grave.

Role of Wheat Gluten Proteins

0053Gluten is a highly molecular complex of proteins –

gliadins and glutenins – together with other compon-

ents of the endosperm cells. Gladins and glutenins are

typical storage proteins of wheat. Glutenins, as a

6136 WHEAT/The Crop

group of wheat proteins, are heterogeneous, and can

be separated, using electrophoresis, into over a dozen

fractions of different molecular weights. An appro-

priate percentage of high-molecular fractions in

wheat flour is responsible for the baking value of

the flour.

0054 Gluten, as a specific and unique substance formed

in the dough obtained from ordinary wheat flour, is

characterized by physical properties such as cohesion,

elasticity, and considerable stretchability. In bakery

applications, the basic characteristics of gluten are its

high water absorption (it can even triple its mass),

and its ability to form viscoelastic films which play a

direct part in the proving of the dough. The properties

of film-forming are also used in the production of

other foodstuffs, such as the glazing of sausage and

meat pa

0055 Among the different environmental factors

affecting grain quality, temperature fluctuation

during grain filling is seen to be the most important

factor. Most of the studies have examined the effect

of extreme temperatures on dough properties. Daily

mean temperatures up to 30



C during grain filling

generally increased dough strength, while tempera-

tures above 30



C produced weaker dough.

0056 In terms of nutritional value, gluten is at the

bottom of the scale, owing to its low content of lysine,

methionine, and tryptophan, but in combination with

other proteins, e.g., with soya, it displays a higher

nutritional value than each of the proteins by itself.

One of the reasons for the increasingly frequent add-

ition of gluten to wheat flour is the fact that new

wheat varieties, grown under intensive cultivation

conditions and providing high crop yield, produce

protein of lower value.

0057 Gluten cannot be considered as a natural substance

occurring in wheat. It is a form given to protein

components as a result of modifying measures applied

during the extraction of flour for dough-making with

the result that certain proteins can expand in a water

medium or in a weak solution of sodium chloride, in

combination with mechanical activity. No correlation

has been ascertained between the amount of gluten

washed out, and its quantitative characteristics.

Proteins are considered to be a particularly labile

(reactive) system of chemical compounds in the

grain, and hence the yield of gluten – adopted as a

basis for the qualitative evaluation of grain material –

depends on the character and rate of interaction

taking place within the material under analysis. Stud-

ies confirm the technological effects of protein–water,

protein–mineral substance, protein–carbohydrate, or

protein–lipid interactions. Each of these types of

interactions may have a positive or a negative effect

under specific conditions. Contemporary baking

technology uses a complex system of dough kneading

whereby, apart from the addition of water, various

substances which react easily with gluten proteins are

introduced. For these reasons, countries experiencing

a need for standardization of flour and dough quality

have developed numerous instrumental methods to

support or supplant the determination of gluten yield.

See also: Bread: Dietary Importance; Cereals:

Contribution to the Diet; Bulk Storage of Grain; Handling

of Grain for Storage; Wheat: Grain Structure of Wheat and

Wheat-based Products