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

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during milling. In many countries the addition of

these nutrients is mandatory. Vitamins of the B com-

plex, including niacin, riboflavin, thiamin, and folic

acid are the most important additives in white flours.

Niacin can be determined by absorbance at 400 nm

after reaction with cyanogen bromide. Riboflavin,

thiamin, and folic acid are normally determined by

spectrophotometric/fluorometric or microbiological

methods.

0034 The ratio of ash in wheat bran relative to the endo-

sperm is approximately 20:1. Consequently, removal

of the bran during milling also depletes the mineral

content of the flour. Efforts to replenish essential

minerals include the addition of calcium in the form

of creta praeparata (calcium carbonate) and iron salts.

Calcium content in flour can be determined volumet-

rically by ethylenediaminetetraacetic acid (EDTA)

titration. Iron is determined colorimetrically.

Physical Dough and End-Product Tests

0035 Physical dough tests are commonly carried out as part

of flour analysis. They provide information on the

viscoelastic properties of wheat flour dough which is

closely related to flour functionality. The most widely

used instrumentation includes the Brabender farino-

graph and extensograph, the mixograph, and the

Tripette & Renaud (Chopin) alveograph.

0036 The farinograph, a torque-recording mixer, is the

most commonly used instrument. It measures the

mixing properties of a flour-water dough system and

provides information on the mixing time required to

reach peak torque prior to dough breakdown (dough

development time) and on the stability of the dough

to overmixing (mixing tolerance index and stability).

The instrument also provides an indication of water

absorption potential since addition of water is

adjusted until the peak torque during mixing reaches

a defined value (500 Brabender units). This informa-

tion is used extensively (usually in combination with

protein content and flour ash) to meet bakery specifi-

cations for pan bread flours as well as a wide variety

of other products (hearth breads, flat breads, steamed

breads, noodles, chapattis). Flours with long dough

development times (> 4 min) and long stability times

(> 12 min) are considered as strong. Flours with

development times of 2–4 min and stability times

of approximately 4–8 min are considered to be of

medium strength and those with shorter development

times and stability times are considered as weak.

Examples of each are shown in Figure 2.

0037 The mixograph is also a torque-recording mixer

that provides information on dough mixing time re-

quirements and dough tolerance to overmixing. It is

used extensively in the USA for flour strength classifi-

cation. The increased use of personal computers (PCs)

in laboratories has resulted in development of soft-

ware which assists in the interpretation of these

(farinograph and mixograph) dynamometer-powered

instruments.

0038The extensograph provides a method of measuring

the stretching properties of a flour–water–salt dough

which has been mixed to defined conditions in the

farinograph. The load-extension curve (extenso-

gram) provides a measure of the maximum height

Stability

DDT

500

510

Stability

DDT

500

510

Stability

DDT

500

510

(a)

(b)

(c)

fig0002Figure 2 Farinograms of flours showing (a) strong, (b)

medium, and (c) weak physical dough properties. Dough devel-

opment time (DDT) and stabilities measured in minutes are

shown as indicated. Reproduced from Flour, Encyclopaedia

of Food Science, Food Technology and Nutrition, Macrae R,

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

2548 FLOUR/Analysis of Wheat Flours

(resistance of dough to stretching), extensibility

(length of dough at rupture during stretching), and

area of the curve (energy required to stretch dough to

breaking point). This method is used to assess flour

strength and viscoelastic balance for bread produc-

tion. The instrument has also been used to estimate

the oxidation requirements of bread flours. Due to

the large sample requirement (300 g flour) and the

long time required to run the test, the extensograph

is not so commonly used as it was previously in

quality control applications.

0039 The alveograph, like the extensograph, is used to

measure the stretching properties of a flour–water–

salt dough. Ingredients are mixed in the instrument’s

mixing chamber, extruded and cut into rounded disks

which are clamped into a chamber through which air

is pumped, resulting in the stretching of a dough

‘bubble’ until rupture occurs. The maximum pressure

required to stretch the dough and the length (time

required to rupture the dough) are obtained directly,

while the W value (related to energy required to

stretch the dough to rupture) and G (swelling index)

are calculated from the curve. These values, especially

the W value, are commonly used in specifications for

‘French-style’ hearth breads in Europe, the Middle

East, and South and Central America. Alveograph

parameters are also being used increasingly in soft

wheat flour specifications (for cakes, cookies,

biscuits, etc.).

0040 An alveograph parameter which is receiving

increasing attention is the ratio of the peak height

to the length of the alveogram (the P/L ratio). It is

related to the W value, in that, while a given W value

can arrive by different combinations of P or L, the P/

L ratio gives a better picture of the shape of the

alveogram. A P/L ratio of about 1.0 is preferred for

the baking of raised breads. Weak, extensible doughs,

suitable for cake and cookie production, have P/L

ratios of about 0.2, while P/L ratios of 2 or higher

indicate that the dough is inclined to be ‘bucky,’ and

lacks the desired degree of extensibility.

0041 Detailed information on these instruments is

provided in handbooks published by the American

Association of Cereal Chemists.

0042 Small-scale end-product tests are regularly carried

out in laboratories to assess flour performance. These

tests vary widely depending on the product and the

local, regional, or national preference of the con-

sumer. A discussion of this topic is beyond the scope

of this article.

Health-related Tests

0043 Six categories of toxic substances may affect wheat

and wheat flour. These include pesticide residues;

molds and mycotoxins, (the toxic metabolites of

molds); toxic trace elements; foreign substances such

as filth; radionuclides and microorganisms. Of all the

types of pesticides that may be used in the production

and storage of grain, which include mainly insecti-

cides, herbicides, fungicides, and plant growth regu-

lators, compounds used just prior to harvest and

postharvest chemicals such as those used for fumiga-

tion and grain protection are the major risks for

residues in wheat and flour. The presence of myco-

toxins in wheat is associated with high levels of fungi

which in turn are usually attributed to growing and

harvesting conditions favorable to mold growth and

poor storage conditions. The presence of unaccept-

able levels of toxic elements such as mercury, lead,

arsenic, and cadmium in wheat may be due to a

combination of factors which include the use of

agricultural chemicals containing these substances,

environmental contamination of soil, inherent variety

characteristics, and natural soil conditions.

0044The presence of filth such as insect parts and eggs,

excreta from insects and rodents, and rodent hairs in

wheat and flour is usually the result of poor house-

keeping, failure to maintain proper sanitary condi-

tions in grain storage areas and mills, and ineffective

grain cleaning. Radionuclide contamination of grain

is possible from fallout resulting from nuclear acci-

dents such as the Chernobyl incident in 1986. The

presence of undesirable microorganisms at harmful

levels in wheat and flour is also a matter of poor

sanitation practices and poor grain or flour storage

conditions.

0045Quality assurance of wheat moving into food chan-

nels to insure the absence of harmful levels of toxic

substances is an ongoing process. It involves screening

and control measures to identify contaminated par-

cels so that they can be removed from food channels

and monitoring measures to confirm the absence of

objectionable levels of toxic substances from com-

mercial shipments. Insuring the safety of flour with

respect to toxic substances is generally the responsi-

bility of government health agencies and is usually

accomplished through ongoing monitoring of prod-

ucts. Flour testing by mills and end users is carried out

to insure that sanitary conditions are maintained and

to meet specific requirements by processors.

0046Tests for pesticide residues, mycotoxins (especially

from Fusarium spp.) and toxic elements are sensitive

to parts per million or parts per billion levels. The

analytical technique followed for determination of

pesticide residues and mycotoxins will depend greatly

on the requirements for sensitivity, selectivity, rapid-

ity, and economy. For highly accurate and sensitive

work, procedures using gas chromatography, high-

performance liquid chromatography and mass

FLOUR/Analysis of Wheat Flours 2549

spectroscopy are usually followed for determination

of pesticide residues and mycotoxins, whereas for

toxic elements, atomic absorption spectroscopy is

most often employed. Other procedures, involving

the use of thin-layer chromatography, column chro-

matography and enzyme-linked immunosorbent

assay (ELISA) test kits are also appropriate for

many applications.

0047 Tests for microorganisms in flour normally involve

the extraction of the sample with sterile buffer,

adding an aliquot of the extract at several dilutions

to agar containing appropriate nutrients, and counting

colonies after a specified growth period under fixed

conditions. Controlled growing conditions and select-

ive media can be used to aid the detection of specific

organisms. Colony appearance, biochemical activity,

and staining techniques are used in the identification

process. Some of the more common tests include

those for nonspecific aerobic microorganisms (stand-

ard plate counts for bacteria plus molds and yeasts),

coliforms, fecal coliforms, Salmonella, Staphylo-

coccus, Bacillus cereus and B. subtilis (the cause of

ropiness in bread).

0048 Insects and filth (including insect fragments and

eggs, insect and rodent excrement) present in wheat

are normally removed during the cleaning process

prior to milling. However, insects and eggs present

in the interior of the wheat kernel may not be re-

moved by this process. Tests for filth are therefore

carried out to measure the amount of insect material

derived from the wheat and, more importantly, to

insure that proper sanitary conditions are maintained

in the processing plant. Flour specifications from sec-

ondary users may also require verification. The first

step in identifying the presence of insects and filth

involves visual inspection. Flour can also be exam-

ined directly by microscopy. To obtain more accurate

results, filth is analyzed by several methods, involving

wetting and digestion of the flour with pancreatic

enzyme solutions or boiling 5% hydrochloric acid,

sieving and filtering, followed by examination of the

filter paper by microscopy.

See also: Ascorbic Acid: Properties and Determination;

Spectroscopy: Near-infrared; Starch: Structure,

Properties, and Determination; Wheat: Grain Structure of

Wheat and Wheat-based Products

Further Reading

American Association of Cereal Chemists (2000) Approved

Methods of the American Association of Cereal Chem-

ists, 10th edn. St Paul, MN: The Association.

International Association for Cereal Science and Tech-

nology (1998) ICC Standards; Standard Methods of the

International Association for Cereal Science and Tech-

nology (ICC). Vienna: ICC.

Pomeranz Y (1988) Wheat: Chemistry and Technology, 3rd

edn., vols I and II. St Paul, MN: American Association of

Cereal Chemists.

Dietary Importance

D A T Southgate, Norwich, Norfolk, UK

Background

0001Flour is defined in most dictionaries as a term used for

the ground material from cereal grains and related

materials. In the context of Western Europe and most

of North America, it most often implies the ground

material from wheat, although the flour from other

cereals, notably rye, maize, and rice, seeds of noncer-

eals such as buckwheat, sorghum, and millets, and

legumes such as soya bean are also sources of flours

widely used in human nutrition. This article will

focus most attention on the flours from wheat and

only comment briefly on the nutritional contribution

of the other flours.

0002The nutritional importance of flours derives first

from a source of many nutrients and, second, from

the many different types of foods that can be prepared

that include flours of one kind or another as ingredi-

ents. The cultivation of cereals and the recognition

that, when ground, they provide the basis of a wide

range of foods from breads, where they are the major

ingredients, to foods such as soups and gruel’s, where

they can be major or minor components, formed a

key stage in the development of human civilization in

the Middle East.

0003Mature cereal grains, as harvested from the plant,

are hard and rather indigestible, unless they are

steamed or soaked in water. Grinding or pounding

the grain breaks the hard external coat and makes

them more acceptable as foods. There is good archeo-

logical evidence for the development of grinding, ini-

tially between hand-operated stones, ‘querns,’ and

later between mechanically operated millstones, and

since the late nineteenth century between steel rollers

to produce flours that greatly extended the range of

foods in which cereals could be used.

Structure of the Cereal Grains

0004While the different cereal grains differ in detail in their

structure, the principal components are common

across all cereals and indeed most seeds. There is a

2550 FLOUR/Dietary Importance

toughened outer seed coat, which includes the wall of

the ovary in the grass flower.

0005 In the wheat grain, these bran layers amount

to about 8% of the grain weight. The seed contains

the embryo or germ, which accounts for 2.5% of the

wheat grain. The bulk of the grain is the endosperm,

which contains the food reserve for the germinating

grain. The cells of the endosperm have thin walls and

are packed with starch grains as the reserve carbohy-

drate. Legume seeds also contain lipid as the energy

reserve.

0006 In the wheat grain, the endosperm accounts for

about 82% of the grain. In the wheat grain, there is

distinct layer of cells with thickened walls lying be-

tween the endosperm and the bran. This aleurone

layer is rich in protein and B-vitamins, and contains

most of the lipid in the grain. Grinding the grain

breaks the endospermal cell wall and liberates the

starch, which is the major component of cereal flours.

In wheat, the rotating action of the millstones and

rollers has the effect of separating the branny layer as

a flake, which can be separated very easily from the

edospermal material. The structure of the rye grain is

similar, but in barley and rice, the outer layers are

fused with the seed coat, and separation requires a

different method. The other major cereal, maize, has

a very tough coat that separates during pounding.

Production of Flours

0007 Once the cereal has been ground, the ground material

is usually fractionated to produce a range of types

of flour. The initial grinding between conventional

millstones produces wholemeal flour from which

the different types of flour based primarily on the

proportion of the whole grain present in the flour

can be produced by sieving. Wholemeal wheat flour

conventionally contains 98% of the starting grain

(there is an allowance for cleaning the grain) and is

said to have an extraction rate of 100%. Sieving

removes progressively more of the branny and germ

materials from the flour leading to flours of lower

extraction rates where the proportion of endosperm

is higher. Low-extraction flours are very fine and

white, and are used in the production of some types

of cakes. Bread-making flours have typical extraction

rates of around 72%.

0008 Roller milling initially separates the branny layers

as a flake, and the particle size of the remaining grain

material is progressively reduced to produce different

streams of flours with different proportions of

endosperm. The different types of flour and nominal

extraction rates are formed by combining the differ-

ent streams. Rye flours can be produced in similar

ways, but most flours in use tend to be of the higher

extraction rates. Corn flours are produced by sieving

the ground cereal and, in many parts of the world, are

consumed as high-extraction pounded flours. Corn-

flour is a very fine endospermal fraction.

0009Barley and rice grains have a different structure

in that the outer layers of the seed coats are fused

to the grain and cannot be removed by conven-

tional milling. These grains are usually processed by

blocking or ‘pearling’ the grain, in which the outer

coats are removed with abrasive discs that grind away

the outer layers to leave a grain that is made up

mainly of endosperm. This is traditionally made into

flour by pounding, although both barley and

rice flours form minor proportions of the total use

of these cereals.

0010Oats have a highly silicified seed coat and are typ-

ically prepared by steaming and rolling to produce

groats rather than flours similar to wheat. The com-

position of some important flours is given in Table 1.

Proximate Composition

Carbohydrates

0011Carbohydrates form the major constituent of all

flours, and starch is the major carbohydrate present.

In the unprocessed endosperm, the starch is contained

within starch granules, which survive into the flours,

although some starch granules are broken during

milling. Most cereals contain the two forms of starch,

amylopectin and amylose; amylopectin is usually the

major component forming 75–82% of the total

starch, but waxy maize contains virtually pure amy-

lopectin, and there are also high-amylose maizes con-

taining around 70% amylose, which gives them

special physical properties that are important for use

in some types of products.

tbl0001Table 1 Composition of some different flours (per 100 g)

Cereal Water Protein Fat Carbo-

hydrate

NSP

Wheat 14.0 12.7 2.2 63.9 9.0 Wholemeal,

mixed grist

Rye 15.0 8.2 2.0 75.9 11.7 Wholemeal

Barley 11.7 10.6 2.1 64.0 14.9 Wholemeal

Maize 12.0 9.2 3.9 73.7 4.4 Wholemeal

Rice 11.6 6.4 0.8 80.1 na Low extraction

Oatmeal 8.9 12.4 8.7 72.6 6.8 Wholemeal

Soya 7.0 36.8 23.5 23.5 10.7 Full fat

Nonstarch polysaccharides.

Based on a number of sources. See Southgate DAT (1999) Cereals and

cereals products. In: Garrow JS, James WPT and Ralph A (eds.) Human

Nutrition and Dietetics, 10th edn, pp. 333–347. Edinburgh: Churchill

Livingstone.

na, not available

FLOUR/Dietary Importance 2551

0012 Small amounts of free sugars are present in most

flours, in wheat; sucrose is the major sugar, with

traces of glucose and fructose. Maltose at low levels

may be present, but high maltose levels are usually

evidence of grains beginning to germinate at the time

of harvest, which makes them less suitable for many

processes.

Nonstarch Polysaccharides

(Dietary Fiber)

0013 The outer seed coats of the cereal grains contain

plant cell wall material (dietary fiber), and cereals

are of major nutritional importance in the provision

of dietary fiber in the diet. The amounts of the

nonstarch polysaccharides (NSP), which are the

major components of plant cell wall material, depend

on the extraction rate of the flour. Wholegrain

flours contain the highest amounts, and the

amount present falls as the extraction rate decreases.

Table 2 illustrates the effects of extraction on the

composition of wheat flours. The nonstarch

polysaccharides of wholemeal wheat and rye are

rich in the noncellulosic polysaccharides; of these,

arabinogalactans have water-binding properties

that are important for the physical characteristic of

flours. Low-extraction flours contain mainly the cell

walls from the endosperm, which are rich in cellulose.

The noncarbohydrate lignin is also present in many

seed coats; this makes the NSP from the higher ex-

traction flours less digestible to the intestinal micro-

flora of the large bowel and may be nutritionally

important for increasing fecal bulk. The NSP from

barley and oats are rich in b-glucans, which are water-

soluble, giving viscous colloidal solutions that are

nutritionally important in the products of these two

cereals.

Lipids

0014Most of the lipid in the cereal grains is located in the

germ, and small amounts are transferred to the endo-

sperm component during milling. Oats are distinctive

in this respect because they contain higher levels of

lipid. The cereal lipids are typically unsaturated.

Proteins

0015Cereal grains contain a range of proteins, the

amounts and types present varying with the variety,

which determines the suitability of the flours for

use in products. Wheats are classified into a number

of types according to the amounts of types of protein

present. North American and central European

wheats contain higher levels of protein and are

said to be ‘strong’; these provide the flours that are

most suitable for bread-making. British wheats tend

to have lower protein contents and are ‘weak’ and less

suitable for bread-making, although the mechanical

development of the dough in the Chorleywood

Process enables high proportions to be used in the

mixed grists used in bread-making. ‘Hard’ wheats

contain higher amounts of protein and differ from

‘soft’ wheats in their capacity to produce high-

extraction and free-flowing flours. Wheats for

bread-making are preferably hard and strong. Soft

wheats are used in the production of biscuits and

other products.

0016One important group of proteins in many cereals,

especially wheat and rye, are the glutens. The glutens

are insoluble proteins rich in sulfur amino acids,

and they have the property of producing three-

dimensional networks within the dough trapping

the carbon dioxide formed by fermentation with the

yeast; these are responsible for the formation of

the characteristic texture of breads, which is a major

factor in the nutritional importance in flours,

especially in wheat-producing countries. Rye flours

also contain a gluten that yields a less well-developed

crumb structure. Rye breads tend to be more solid

than wheat breads, and wheat/rye mixtures are espe-

cially important nutritionally in northern Europe.

Barley does not produce breads in this sense and are

more equivalent to cake-like structures as do oat

flours.

0017The glutens are also nutritionally significant in

being responsible for the intestinal lesions in ‘gluten-

sensitive enteropathy’ and ‘celiac disease.’ The amino

acid composition of cereal proteins is reasonably bal-

anced, but lysine is one of the limiting amino acids

that is partially destroyed in baking. Maize proteins

are low in tryptophan, and pellagra has been ob-

served in maize-consuming populations.

tbl0002 Table 2 Effects of extraction on the composition of wheat flours

(per 100 g)

Flour,

(extraction rate)

Water Protein Fat Carbo-

hydrates

NSP

Energy

(kJ)

Wholemeal

(100%)

14.0 12.7 2.2 63.9 9.0 1318

Brown

(85%)

14.0 12.6 1.8 68.5 6.4 1377

Bread-making

(72%)

14.0 11.5 1.4 75.3 3.1 1451

Patent

(45%)

14.1 10.8 1.3 79.2 na 1480

Available carbohydrates sum of sugar and starches.

Nonstarch polysaccharides.

na, not available.

2552 FLOUR/Dietary Importance

Vitamins

0018 Cereals are good sources of some B-vitamins and poor

sources of vitamin C and lipid-soluble vitamins. The

vitamins are concentrated in the germ and the outer

layers of the grain. Milling and the separation of the

endosperm from the germ and bran lead to fraction-

ation of the vitamins so that the concentrations are

much lower in low-extraction white flours (Table 3).

Inorganic Nutrients

0019 Flours, in common with most foods derived from

plants, are rich in potassium and low in sodium.

The production of self-raising flours increases the

amounts of sodium and calcium, depending on the

type of raising agent. Cereal flours are also good

sources of phosphorus and reasonable sources of

magnesium. Calcium levels are modest, and signifi-

cant levels of iron and zinc are present. The inorganic

nutrients are concentrated in the outer branny layers

and in the germ, so that milling of the grain leads to

the fractionation of the nutrients, and low extraction

flours have much lower levels than the wholegrain

flours. Table 4 illustrates the effects of extraction on

some inorganic nutrients in wheat flours. The phos-

phorus in cereals is mainly present in phytic acid

(m-inositol hexaphosphate), which is nutritionally

important because it forms insoluble compounds

with calcium, iron, and zinc, and thus reduces their

bioavailability by preventing absorption in the small

intestine.

Fortification with Inorganic Nutrients

0020At the start of World War II in 1939, the UK author-

ities were concerned that the supply of dairy products

might be reduced by enemy action and that the pro-

portion of cereal products in the diet would have to

increase. The extraction rate of flours would also

have to be increased to divert more cereal imports to

human foods. These changes in the diet would accen-

tuate the effects of phytic acid on the calcium in the

diet. Regulations were introduced to implement for-

tification of all wheat flours, other than wholemeal,

with calcium. After the war, there was a delay in

returning to the low-extraction (white) flours for

bread-making, but in 1953, when the regulations

were relaxed, it was decided that the flour should be

fortified with iron, thiamin, and niacin to maintain

the concentrations of these nutrients at the levels they

had been in the higher-extraction flours used in war

time and the immediate postwar period. Although the

primary nutritional reasons for fortification of wheat

flours have largely disappeared, the fortification con-

tinues in the UK so that the calcium, iron, thiamin,

and niacin levels in the UK flours are higher than

those in most other countries.

0021Fortification with other nutrients has been con-

sidered recently in the UK. These include vitamin D

in flours used primarily by immigrant communities in

order to counteract the increase in the incidence of

rickets in those communities. However this fortifica-

tion was never introduced because of the difficulty in

restricting the fortified flours to those for whom it

was intended. Fortification with folic acid has been

proposed as a prophylactic measure for reducing the

incidence of neural-tube defects. The latter fortifica-

tion is being implemented in the USA.

Losses of Nutrients on Storage of Flours

0022Provided the moisture content is below 15 g per

100 g, the nutrients in flours are relatively stable at

cool ambient temperatures. Losses due to infestation

with mites can occur on prolonged storage, especially

at higher temperatures. The lipids in flours slowly

oxidize at ambient temperatures, and rancidity can

develop in wholemeal flours, which therefore have

shelf-lives of about 3 months compared with about

9 months from brown flours and 2–3 years for white

flours in paper bags.

tbl0003 Table 3 Effects of extraction rate on the B-vitamins in flours

unfortified wheat flours (per 100 g)

Grade

(extractionrate)

Thiamin

(mg)

Riboflavin

(mg)

Niacin

(mg)

Vitamin B

(mg)

Folates

(mg)

Wholemeal,

100%

0.47 0.09 5.7 0.50 57

Brown, 85% 0.30 0.07 1.7 0.30 51

Bread-making,

72%

0.10 0.03 0.7 0.15 31

Patent, 45% 0.10 0.02 0.7 na na

na, not available.

Various sources modified from Southgate DAT (1999) Cereals and cereals

products. In: Garrow JS, James WPT and Ralph A (eds.) Human Nutrition

and Dietetics, 10th edn, pp. 333–347. Edinburgh: Churchill Livingstone.

tbl0004 Table 4 Effects of extraction rate on the inorganic constituents

in wheat flours (mg per 100 g)

Grade K Ca Mg P Fe

Wholemeal 360 35 140 340 4.0

Brown 280 20 110 270 2.5

Bread-making 130 15 36 130 1.5

Patent 100 15 19 89 1

Fortification increases the calcium values by about 120 mg and iron by

about 0.7 mg. Modified from Southgate DAT (1999) Cereals and cereals

products. In: Garrow JS, James WPT and Ralph A (eds.) Human Nutrition

and Dietetics, 10th edn, pp. 333–347. Edinburgh: Churchill Livingstone.

FLOUR/Dietary Importance 2553

Nutritional Contributions of Flours

0023 The major nutritional contributions of flours to the

human diet lie in the wide range of products in which

flours are components. The range of products derived

from flours in the UK diet, for example, is very large,

ranging from breads and biscuits where flour is the

primary ingredient, to its use in the preparation of

pastry for meat, fish, vegetable, and fruit dishes, pizza

bases, and pasta. Flours are used as thickening con-

stituents in soups and many other dishes.

0024 This widespread use means that flours are an

important source of energy in the diet. Their contri-

bution to protein intake is also significant because

the proportion of protein to energy approaches

many dietary recommendations. Although the con-

ventional approach is to view cereals as energy

sources alone, it is important to recognize that the

current dietary recommendation for the proportion

of energy from starchy carbohydrates in the diet

could not be met without the contributions from

flour. High-extraction cereal flours and the products

made from them are significant sources of nonstarch

polysaccharides.

See also: Bread: Dietary Importance; Celiac (Coeliac)

Disease; Cereals: Contribution to the Diet; Dietary

Importance; Cobalamins: Properties and Determination;

Physiology; Milling: Principles of Milling; Riboflavin:

Properties and Determination; Physiology; Starch:

Structure, Properties, and Determination; Thiamin:

Properties and Determination; Physiology; Vitamin B

Properties and Determination; Physiology

Further Reading

Department of Health and Social Security (1981) Nutri-

tional Aspects of Bread and Flour. Report on the Panel

on Bread and Flour of the Committee on Medical

Aspects of Food Policy. Reports on Health and Social

Subjects No. 23. London: HMSO.

FAO/WHO (1998) Carbohydrates in Human Nutrition.

Report of a Joint FAO/WHO Expert Consultation.

Rome: FAO.

Food Standards Agency (2001) McCance and Widdowson’s

The Composition of Foods, 6th edn.

Holland B, Unwin ID and Buss DH (1988) Cereals and

Cereal Products. Nottingham, UK: Royal Society of

Chemistry and Ministry of Agriculture Fisheries and

Food.

Holland B, Welch AA, Unwin ID et al. (1991) McCance and

Widdowson’s The Composition of Foods, 5th edn. Cam-

bridge: Royal Society of Chemistry and Ministry of

Agriculture Fisheries and Food.

Kent NL (1983) Technology of Cereals, 3rd edn. Oxford:

Pergamon Press.

Southgate DAT (1999) Cereals and cereals products. In:

Garrow JS, James WPT and Ralph A (eds) Human Nu-

trition and Dietetics, 10th edn, pp. 333–347. Edinburgh:

Churchill Livingstone.

Flow See Rheological Properties of Food Materials; Sensory Evaluation: Sensory Characteristics of Human

Foods; Food Acceptability and Sensory Evaluation; Practical Considerations; Sensory Difference Testing; Sensory

Rating and Scoring Methods; Descriptive Analysis; Appearance; Texture; Aroma; Taste

Fluidized-bed Drying See Drying: Theory of Air-drying; Drying Using Natural Radiation; Fluidized-bed

Drying; Spray Drying; Dielectric and Osmotic Drying; Physical and Structural Changes; Chemical Changes;

Hygiene; Equipment Used in Drying Foods

Fluorescence Spectroscopy See Spectroscopy: Overview; Infrared and Raman; Near-infrared;

Fluorescence; Atomic Emission and Absorption; Nuclear Magnetic Resonance; Visible Spectroscopy and

Colorimetry

2554 FLOUR/Dietary Importance

FLUORIDE

A Hardisson, M I Rodrı

guez and A Burgos,

University of La Laguna, Canary Islands, Quebec,

Spain

Background

0001 Fluorine is the most electronegative of all the known

chemical elements and the most reactive. Its chemical

characteristics make it one of most physiologically

active ions. The interest in this element undoubtedly

comes from the observations made in the 1980s of the

toxic and therapeutic effects of fluorine, especially on

teeth. In high doses, it can cause disorders in enamel

formation, leading to mottled teeth or dental fluor-

osis, and in relatively small doses, it can reduce the

prevalence of dental caries by over 50%. Dental

caries are frequently suffered by the population,

even in the most developed countries, and fluorides

remain the best remedy. In fact, it has been shown

that there is a correlation between communities that

have consumed water containing moderate levels of

fluoride (around 1.5 mg l

1

) and lower rates of dental

caries. However, the relationship between consuming

water containing high levels of fluoride ions and

fluorosis has also been confirmed. Fluorosis is a dis-

ease that is characterized by ‘mottled teeth,’ and high

intakes of fluoride are probably related to the appear-

ance of kidney problems, leading to decalcification of

the bones due to the flouride-sequestering quantities

of Ca

2þ

that are essential for the correct develop-

ment of the bones. Fluorine is a component of water

that, according to the WHO, should be present in

concentrations of around 1 mg l

1

to prevent dental

caries, but if these levels exceed 1.5 mg l

1

, toxic

effects start to appear, making the margin between

essential and toxic levels very slim indeed.

Sources

0002 The body’s main source of fluorine is undoubtedly

drinking water, as this is the cheapest and most effi-

cient way of providing it, and fluoride plays an im-

portant role in human health. There are also traces of

fluorine in almost all food products. The fluoride

content in food is of great importance, as it can have

both beneficial and prejudicial effects on our health

when added to the quantities supplied by fluoride-

treated water and toothpaste.

0003 Man is naturally exposed to fluorides due to the

increasing industrial use of these compounds, the

increased use of fluoride toothpastes by the general

population, and the treatment of water with fluoride

as a fundamental weapon in the arsenal against caries

in certain communities. Apart from water, there are

other natural sources of fluorine to be found in the

animal and vegetable worlds (tea is rich in fluorides);

the atmosphere and even some medicines and cosmet-

ics are occasional sources.

Dietary Intake

0004The level of fluorine in water is often used as a criter-

ion to establish whether or not a population’s diet is

deficient in this element. However, in order to accur-

ately determine fluoride intake, the contribution from

food, both liquid and solid, the air, occasionally con-

taminated with fluoride either from industry or of

volcanic origin, and the widely consumed products

that have been treated with fluoride to fight caries

should also be taken into consideration. The main

tissues that are known to take up fluorine are

bone and dental enamel, and uptake is proportional

to total intake. Dietary recommendations are be-

tween 1.5 and 4 mg per person per day for adults,

between 0.1 and 1 mg per person per day for the first

year of life, between 0.5 and 1.5 mg per person per

day for the next two years, and up to 2.5 mg per

person per day for 12-year-old children.

Dental Caries

0005More than a decade passed after the discovery of the

relationship between fluoride and endemic chronic

dental fluorosis, before the beneficial influence of

fluoride on the prevalence of caries was established.

This discovery was the fruit of many years of research

on dental fluorosis.

0006Later studies have shown that the addition of fluor-

ide to the drinking water in areas of low natural

concentrations is a practical and efficient method of

reducing the incidence of dental caries. The recom-

mendations approved by health organizations, there-

fore, suggest fluoride concentrations of between 0.7

and 1.2 mg l

1

, depending on the average local tem-

perature. Dental health has also improved in recent

years, even in areas with low concentrations of fluor-

ide in drinking water. This is probably due to in-

creased intakes of fluoride from other sources, such

as food processed with fluoride-enriched water,

external applications of fluorine by orthodontists,

fluoride supplements, and even unintentional intake

of fluoride-treated toothpaste.

FLUORIDE 2555

Content in Waters and Liquid Food

Products

0007 The fact that fluoride is an element that has a benefi-

cial effect on human health in certain dosages, but can

become toxic to man in slightly higher concentrations,

highlights the need for an exhaustive evaluation of the

total quantity of fluoride consumed by a person in a

specific community in a given geographic area. This

quantity is affected both by community habits and by

climate conditions, fundamentally by average tem-

peratures (especially important in areas in which the

public water supply has been treated with fluoride).

Methodology

0008 One of the problems to be considered is the choice of

the most suitable method for determining fluoride

contents. The most widely used techniques include:

gravimetry (precipitation as PbFCl, precipitation as

calcium fluoride) and volumetry (determining the sol-

uble fluoride and the combined fluoride), indirect

colorimetry (SPADNS method, quercetin–zirconium

system (III), zirconium–alizarin red system, zirco-

nium–chromium cyanine system, zirconium–alizarin

sulfonate system), direct colorimetry, potentiometric

methods (based on the use of a selective fluoride ion

electrode), and spectrofluorimetric methods. In some

cases, especially for complex matrices, prior separ-

ation of fluorides may be necessary. The most

widely used methods of separation include fluorine

distillation, ion exchange, HF microdiffusion, and

interference ion precipitation.

Water

0009 Fluoride in drinking water is commonly the main

source of total fluoride intake. The intake of



from drinking water will depend fundamentally

on: (1) the concentration of F



in the water, (2) the

age of the person, (3) weather conditions (tempera-

ture), and (4) eating habits. Table 1 shows typical

average fluoride concentration in drinking waters

obtained in different geographic areas and at

different times. Although the contents are variable

in general, there are some waters in India that have

a high fluoride content, similar to the levels of the

north Tenerife (Spain) water supply in the health

district of Icod de los Vinos. Based on the average

concentration intervals and an average water con-

sumption of 2 l per day, the fluoride intake would be

between 5 and 11.1 mg of fluoride per liter per person

per day, which exceeds dietary recommendations and

explains the fact that this is an area with a high degree

of dental fluorosis.

0010Table 2 shows the average concentration in the

most commonly consumed domestic and foreign min-

eral waters in Spain, at different times in the same

geographic area (the island of Tenerife). Some of these

concentration values are above the recommended

level of 1 mg l

1

, but none is above the maximum

ceiling of 1.5 mg l

1

Wine

0011Small concentrations of fluoride can be found natur-

ally in wine, but these quantities do not generally

exceed the maximum limit of 1 mg l

1

recommended

by the International Vine and Wine Bureau. In fact,

the fluoride contents found in most research work

done in this field are between 0.1 and 0.9 mg of

fluoride per liter. The natural fluoride content of

wine, therefore, cannot be classified as unhealthy in

normal circumstances. The fluoride gets into the wine

from the fluoride contained in the irrigation water, so

tbl0001 Table 1 Average fluoride content in drinking waters of different geographic areas

Geographic area Analytic method Meanconcentration

(mgl

1

)

Ye a r

Portugal (Ribeira

o Prieto) Ion-selective electrode 0.1–1 1990

India (Visakhapatnam) Ion-selective electrode 0.31–8.35 1997

Spain (Basque Country) Ion-selective electrode A

lava: <0.05–11.12 1984

Guipu

zcoa: <0.05–0.26

Vizcaya: <0.05–0.45

Spain (La Rioja) Ion-selective electrode 0.22–1.1 1986

Spain (Tenerife) Colorimetry 6% < 1.5 1985

SPADNS and ion-selective electrode 64% 0.5–1.5

20% <0.5

Spain (Tenerife) Ion-selective electrode 3.90 1988

Spain (Tenerife) Ion-selective electrode 4.22 2001

Kenya Ion-selective electrode 0.28 1995

Poland Ion-selective electrode 1.2 1996

Spain (Soria) Ion-selective electrode 0.2 1999

2556 FLUORIDE

when it is found in higher concentrations, one can

assume that there has been some form of contamin-

ation, either natural (soil or water that is excessively

rich in fluoride) or accidental, with two main sources.

The first source would be the use of cement vats for

making the wine and/or for storing the wine; the

second source of contamination would come from

the direct addition of fluoride-enriched compounds

like antiseptics or antifermentation agents. Although

their use is banned in many countries, they are still

used, because it is known that, even when diluted to

between 1:400 and 1:5000, fluoride still presents a

marked antiseptic action.

0012 Another source that must be added to the two main

sources is the increasing use of kryolite (sodium fluor-

oaluminate) in the USA as an insecticide to control

certain pests that affect the vineyards. This new

source of pollution raises the fluoride content in the

wine produced from these grapes to 3 mg of fluoride

per liter, which, in principle, makes it necessary to

review wines that were not initially considered to have

a high fluoride content. On this subject, mention must

be made of the wine fluorosis discovered in Barcelona

in 1965. A joint study by the Departments of Medical

Pathology, Bromatology and Toxicology of the Uni-

versity of Barcelona demonstrated that the etiology of

some periostitis deformans was the consequence

of consuming wine with high fluoride concentrations.

Situations of this kind require not only a high intake

of fluoride, but also the nutritional deficits typically

exhibited by alcoholics, making it more probable

that consumers of wines containing added fluorides

will suffer from this kind of disease. As fluoride has

a marked preference for bone, it causes alterations

in the skeleton, as well as inhibiting some impor-

tant enzymes (phosphoenolpiruvase, phosphotases,

esterases, and even the cytochrome oxidase system).

0013According to several results (Table 3), the fluorine

contents of wines of different vintages studied exceed

neither the established limit of 1 mg l

1

nor the rec-

ommended daily intake.

Beers, Soft Drinks, and Juices

0014Table 4 gives the fluoride contents in the most popu-

lar beers and soft drinks. These results indicate that

the fluoride content found comes mainly from the

water used in the manufacturing process. According

to the literature, the F



content in beers is low, around

0.3–0.8 mg l

1

, unlike wine, which can reach 6–

8mgl

1

, due to the reasons mentioned in the section

on wine; because it is stored in cement vats, and

because of the use of compounds with added fluoride

like antiseptics and antifermenting agents. With

regard to soft drinks, the drinks made from

carbonated water have the highest fluoride content

(1.05 mg l

1

), although they do not reach the permit-

ted maximum of 1.5 mg l

1

. Bottled natural fruit

juice, however, has a lower content.

Milk and Derivatives

0015Milk and dairy products are consumed universally.

Their importance in our diet has been accepted for

thousands of years. Table 4 lists literature data on the

fluoride content in milks and derivatives. The values

detected in dairy products are below 0.4 mg kg

1

, the

recommended ceiling for formula for children, so

tbl0002 Table 2 Average fluoride concentration in bottled waters consumed in Spain of different origins

Geographic area Analyticalmethod Mean concentration

(mgl

1

)

Ye a r

Spain (Mainland) Ion-selective electrode 1.77 1976

Spain (Tenerife) Ion-selective electrode 0.66 1989

Spain (Tenerife) Ion-selective electrode 1.47 1990

Spain (Tenerife) Ion-selective electrode 1.1 1995

Spain (Tenerife) Ion-selective electrode 1.09 2001

tbl0003 Table 3 Average fluoride concentration in wines from different areas of Spain

Geographic area Analyticalmethod Mean concentration

(mgl

1

)

Ye a r

Spain (Mainland) Ion-selective electrode 0.83 1971

Spain (Mainland) Ion-selective electrode 0.13 1979

Spain (Jerez) Ion-selective electrode 0.31 1983

Spain (Mainland) Ion-selective electrode 0.28 1988

Spain (Tenerife) Ion-selective electrode 0.20 1990

Spain (Mainland) Ion-selective electrode 0.25 1990

Spain (Tenerife) Ion-selective electrode 0.20 1996

Spain (Tenerife) Ion-selective electrode 0.24 2000

FLUORIDE 2557