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

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mill to improve the flour color. One of the most

commonly used bleaching agents is benzoylperoxide.

Chlorine is another agent that is added as a gas

mainly to soft wheat flour, where another objective

is to control the flour pH level (Table 3).

0051 Enzymatic activity To compensate for any natural

deficiency of enzymes to convert starch to maltose,

usually malted barley flour or enzymes are added.

The treatment is approximately 0.25%, depending

on the strength of the malt and the requirements of

the flour treated.

Heat Treatment

0052 Heat treatment of flour is used to change its physical

and rheological properties. The heat reduces the elas-

ticity and even denatures the gluten. The starch can be

gelatinized and enzymatic activity reduced or elimin-

ated. The heat also causes a reduction in the bacterial

count of flour. In terms of amylograph values, a flour

viscosity of about 300 Brabender units (BU) could

be effected by heat treatment and reach 800 BU.

The new characteristics improve the water-holding

capacity of the treated flour. The heat-treated flour

is used for special end uses such as soups, sausage

filling material, infant foods, and other food and

nonfood products.

New Developments and Their Effect on

Product Characteristics

Debranning of Wheat Before Milling

0053 The newly applied process of debranning the wheat

outer layers from the kernels before milling yields

products that are different from those produced by a

conventional mill, in terms of quality and nutritional

values. The finely adjusted debranning machine

action on the wheat kernel allows the miller to

remove by abrasion individually each of the seven

bran layers before grinding the endosperm to flour.

From the outer to inner layer, these are: cuticle, epi-

carp, endocarp, testa, nucellar layer, and aleurone

layer. Each is significantly different in characteristics

from the other. While the nutritous aleurone layer is

high in protein content (28%), the epidermis, epicarp,

and endocarp have a very high level of insoluble

dietary fiber.

0054As mentioned earlier, the process of sprouting

softens the wheat kernel, and accordingly, when

milled on a conventional milling system, the bran is

pulverized somewhat more than sound wheat, and

the ash increases as a result of the fine bran particles.

Wheat debranning before milling removes most of the

kernel layers that contain high levels of a-amylase

such that the resulting flours have a reduced enzym-

atic activity and are more suitable for bread-baking

purposes.

See also: Air Classification: Uses in the Food Industry;

Bread: Dough Mixing and Testing Operations; Flour:

Roller Milling Operations; Analysis of Wheat Flours;

Dietary Importance; Milling: Principles of Milling; Types

of Mill and Their Uses; Starch: Structure, Properties, and

Determination; Wheat: Grain Structure of Wheat and

Wheat-based Products

Further Reading

Canadian International Grains Institute (1993) Grain &

Oilseeds Handling, Marketing, Processing. 4th edn,

vol. II.

Code of Federal Regulations (1991) Whole Wheat Flour.

No. 21, Part 137. Washington, DC: Food and Drug

Administration.

tbl0003 Table 3 Additives to wheat flour

Flour additive Physicalstate Rate (p.p.m.) Effect Maximumlevel (p.p.m.)

Nutritional additives

Thiamin Premix 4.4–7.7 Prevents beriberi Regulations

Riboflavin Premix 3.7–4.8 Eye and mouth tissue health Regulations

Niacin Premix 35–64 Prevents pellagra Regulations

Iron Premix 29–43 Forms hemoglobin Regulations

Folic acid Premix 1–2 Prevents birth defects Regulations

Calcium Powder 2116 Counter phytic acid Optional

Flour-improving additives

Potassium bromate Powder 10–20 Oxidation 50 p.p.m.

Azodicarbonamide Powder 2–20 Aging 45 p.p.m.

Chlorine Gas 1000–1400 Bleach/age As required

Benzoyl peroxide Powder 50 Bleach 150 p.p.m.

Ascorbic acid Powder 70 Mix-time reduction 200 p.p.m.

L-Cysteine (hydrochloride) Powder 30 Mix-time reduction 90 p.p.m.

Fungal a-amylase Powder 30 Diastatic supplement As required

4004 MILLING/Characteristics of Milled Products

Code of Federal Regulations (1996) Food and Drugs Stand-

ards of Identity. Parts 100–169, Sections 137.300 and

137.320. Revised 1 April 1996. Washington, DC: Food

and Drug Administration.

Current Good Manufacturing Practices (1986) Federal

Food and Drug Administration, Food, Drug, and Cos-

metics, Act Sections 402(a)(3) and 402(a)(4). Washing-

ton, DC: Federal Food and Drug Administration.

Evers T and McRitchie F (2000) Ash who needs it? World

Grain 18(6): 56–63.

Farrand EA (1972) The influence of particle size and starch

damage on the characteristics of bread flours. The

Bakers Digest, February, 22–26.

Gruber FJ (1964) Getting the most from a bread score.

American Society of Bakery Engineers Bulletin 174.

September, 702–708.

Manser J (1985) Feinheitsgrad von Durum-Mahlerzeugnis-

sen aus der Sicht der Teigwarenindustrie. Getreide Mehl

& Brot 39(4): 117–123.

Panter A (1988) Divide milling of Canadian spring wheat

flour. Association of Operative Millers Technical Bul-

letin December: 5347–5353.

Posner ES (1991) Wheat and flour ash as a measure of

millability. Cereal Foods World 36(8): 626–629.

Posner ES (2000) Wheat. In: Kulp K and Ponte JG, Jr. (eds)

Handbook of Cereal Science and Technology. New

York: Marcel Dekker.

Posner ES and Hibbs AN (1997) Wheat Flour Milling.

St. Paul, MN: American Association of Cereal Chemists.

Pyler EJ (1982) Baking Science and Technology. Chicago,

IL: Siebel.

Mincing See Meat: Sausages and Comminuted Products

MINERALS – DIETARY IMPORTANCE

J H Freeland-Graves, The University of Texas at

Austin, Austin, TX, USA

P J Trotter, Augustana College, Rock Island, Illinois,

USA

Introduction

0001 Minerals are of critical importance in the diet even

though they comprise only 4–6% of the human

body. Major (macro-) minerals are those required in

amounts greater than 100 mg day

1

and represent 1%

or less of body weight (Figure 1). These include cal-

cium, phosphorus, magnesium, sulfur, potassium,

chloride, and sodium (Table 1). Trace (micro-)

minerals are essential in much smaller amounts, less

than 100 mg day

1

, and make up less than 0.01% of

body weight. Essential trace elements are chromium,

copper, fluoride, iodine, iron, manganese, silicon, and

zinc (Table 2). Ultratrace minerals are a subcategory

of trace minerals that are required in amounts less

than 50 ng g

1

in the diets of animals. These include

arsenic, boron, molybdenum, nickel, selenium, and

vanadium (Table 3). Other inorganic elements which

may contribute to biological processes, but which

have not been established as essential, are barium,

bromine, cadmium, lead, lithium, and tin. Nonnutri-

tive metals such as aluminum, bismuth, gallium, gold,

mercury, and silver may also be present in small

amounts in foods. These metals have no known func-

tion and may contaminate wholesome food and create

toxic symptoms. (See Heavy Metal Toxicology; Trace

Elements; Refer to individual minerals.)

Food Sources

0002A mineral is an inorganic homogeneous substance.

When food is burned, the organic portions oxidize;

the ashes remaining are minerals. The ash can be ana-

lyzed to determine the specific quantity and type of

minerals present. The level of some minerals, such as

iodine and selenium, in foods is particularly dependent

upon the amount of the mineral in the soil of the region

where the food is produced. Avariety of common food

sources of minerals are listed in Tables 1–3.

0003The natural occurrence of minerals in food is not

always desirable. In vegetable oils, miniscule amounts

of iron and copper contribute to the development of

rancidity. Sequestrants, such as ethylenediaminetetra-

acetic acid, are added to render them ineffective.

Other foods are enriched by the addition of minerals.

Some examples are the addition of iodine to salt, iron

to flour and bread, calcium to orange juice, and iron

and other minerals to breakfast cereals. (See Food

Fortification.)

MINERALS – DIETARY IMPORTANCE 4005

fig0001 Figure 1 A portion of the periodic table of elements. Elements thought to be essential are shaded; fluoride may be beneficial rather

than essential.

tbl0001 Table 1 Food sources, physiological functions, deficiency symptoms, and requirement of major minerals

Mineral Foodsource Physiological functions Deficiencysymptoms Toxicity symptoms Requirements

Calcium Milk, cheese,

yogurt, turnip,

greens

Bone calcification, blood

clotting, muscle

contraction, nerve

transmission

Rickets, osteoporosis,

osteomalacia, tetany

Hypercalcemia, kidney

stones, constipation,

depression, confusion

UL 2.5 g day

1a

1000 mg

Chloride Salt, processed

foods

Electrolyte in fluid balance,

gastric acidity, acid–

base balance

Hypochloremic metabolic

alkalosis, hypotension

Hypertension (in

conjunction with excess

sodium)

750 mg

Magnesium Spices, nuts, coffee,

cocoa, vegetables

Cellular metabolism,

muscle relaxation, nerve

transmission

Nervous disorders, muscle

weakness, tetany,

arrhythmia,

hypertension

Diarrhea, UL 350 mg

nonfood magnesium per

day

310–420 mg

Phosphorus Cheese, meats,

peanuts, soft

drinks

Bone calcification, energy

release, membrane

structure, acid–base

balance

Fatigue, anorexia, bone

demineralization,

muscle weakness

Metastatic calcification and

skeletal porosity (in

animals) UL 4 g day

1a

700 mg

Potassium Fresh foods,

molasses, milk,

legumes,

bananas

Electrolyte in fluid balance,

nerve transmission,

muscle contraction,

blood pressure

Weakness, anorexia,

cardiac arrhythmia,

irrational behavior

Muscle weakness and

paralysis, cardiac

arrhythmia or arrest

2000 mg

Sodium Salt, cured meats,

processed foods

Electrolyte in fluid balance,

membrane potential of

cells, active transport,

blood pressure

Hyponatremia, nausea,

anorexia, weakness,

confusion, convulsions

Edema, hypertension,

congestive heart failure

in elderly

500 mg

Sulfur Meat, fish, eggs,

cheese, legumes

Energy transfer

(constituent of sulfur-

containing amino acids,

insulin and some

vitamins)

Unknown Depressed growth

(animals)

Tolerable upper intake level (UL) recommended for adults from the Institute of Medicine (1999): see Further Reading.

Daily recommendation for an adult man from the Institute of Medicine (1999): see Further Reading.

Daily recommendation for an adult man from the National Research Council (1989): see Further Reading.

4006 MINERALS – DIETARY IMPORTANCE

Bioavailability

0004 The total amount of a mineral in a food does not

necessarily reflect the amount that is available for

absorption into the body. The presence of dietary

fibers and mineral-binding ligands, such as phytates

and oxalates, may substantially diminish the bioavail-

ability of minerals. Phytates are abundant in bran,

whole grains, and oil-seed legumes; oxalates are

found in dark-green leafy vegetables, such as spinach.

Diets rich in these compounds, found in strict vege-

tarian diets, may have the potential to affect mineral

status adversely. (See Bioavailability of Nutrients;

Vegetarian Diets.)

0005 Polyphenolic compounds, formerly called tannins,

are other dietary components that bind minerals. In

tea, large concentrations of polyphenolic compounds

can reduce the absorption of iron in a meal by as

much as 87%. (See Tannins and Polyphenols.)

0006The amount of available mineral in a food may be

further reduced by the large quantities of other min-

erals. For instance, the amount of oral manganese

absorbed may be greatly decreased by the concomitant

ingestion of calcium (Figure 2). Phosphates are known

to diminish the absorption of zinc. Food sources that

are high in fiber, phytates, oxalates, polyphenolic com-

pounds, and other minerals should therefore be used in

moderation in order to insure optimal mineral ad-

equacy of the diet. (See Dietary Fiber: Effects of Fiber

on Absorption; Phytic Acid: Nutritional Impact.)

0007In contrast, some dietary factors improve the

bioavailability of minerals. Ascorbic acid, sugars,

and amino acids enhance the absorption of iron and

amino acids; citrate, phosphate, gluconate, and high

tbl0002 Table 2 Food sources, physiological functions, deficiency symptoms, and requirement of essential trace minerals

Mineral Food sources Physiological functions Deficiency symptoms Toxicity symptoms Requirements

Chromium Mushrooms, yeast,

prunes, nuts

Glucose metabolism,

enhanced insulin

sensitivity, nucleic acid

stability

Glucose intolerance,

neuropathy, elevated

serum insulin and lipids

Cancer (hexavalent form) 35 mg

Copper Nuts, shellfish, liver,

raisins, grains,

chocolate

Iron utilization, nervous

system, pigmentation,

immune defense,

neovascularization

Neutropenia, anemia,

decreased pigmentation,

neurological, skeletal,

cardiovascular, and

cartilage abnormalities

Gastrointestinal discomfort

(> 5 mg day

1

), liver

damage, weakness,

nausea

900 mg

Fluoride

Fluoridated water,

seafood, tea

Precipitates calcium and

phosphorus in bone and

teeth

Increased dental caries Mottled tooth enamel, joint

stiffness UL 10 mg day

1c

3.0 mg

Iodine Saltwater fish,

iodized salt,

bakery goods

Thyroid hormones in basal

metabolism

Goiter, stunted growth,

mental retardation,

myxedema, cretinism,

hypothyroidism

Goiter, hypothyroidism 150 mg

Iron Liver, meats,

molasses,

prunes, nuts

Hemoglobin and

myoglobin formation for

oxygen transport,

cellular oxidation

Anemia, poor body

temperature regulation,

impaired psychomotor/

intellectual performance

Liver damage, diabetes,

increased risk of heart

disease due to lipid

oxidation

8mg

Manganese Tea, nuts, oatmeal,

bran, pineapple

Cartilage and bone equity,

brain function, lipid and

carbohydrate

metabolism

Rash, nervous disorders,

hypocholesterolemia,

skeletal/mitochondrial

abnormalities

Brain or neurological

disorders resembling

Parkinson’s disease,

schizophrenia

2.3 mg

Silicon Pectin, grains, beer,

cereals

Bone calcification and

cartilage formation,

growth

Depressed growth and

skeletal development

(chick)

Kidney stones; generally

nontoxic

40 mg

Zinc Meats, shellfish,

liver, legumes

Reproduction, growth, skin

integrity, wound healing,

taste acuity, immune

response

Impaired sexual

development/growth,

skin lesions, hair loss,

anorexia, behavioral

disturbances

Poor immune response,

lower high-density

lipoprotein-cholesterol,

copper deficiency

(chronic > 0.50 mg

day

1

)

11 mg

Daily recommendations or usual dietary intakes for an adult male from the Institute of Medicine (2001) Dietary Reference Intakes for Vitamin A, Vitamin K,

Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press.

May be beneficial rather than essential.

Tolerable upper intake level (UL) recommended for adults from the Institute of Medicine (1999) Dietary Reference Intakes for Calcium, Phosphorus,

Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press.

Daily recommendation for an adult male from the Institute of Medicine (1999) Dietary Reference Intakes for Calcium, Phosphorus, Magnesium,Vitamin D, and

Fluoride. Washington, DC: National Academy Press.

18 mg for adult female.

MINERALS – DIETARY IMPORTANCE 4007

dietary protein increase the absorption of copper. The

milk sugar lactose increases the absorption of calcium

by approximately 30%.

Requirements

000 8 The amount of a mineral required in the diet for

optimal health and prevention of chronic disease is

the basis for new dietary recommendations, dietary

reference intakes (DRIs), that have been formulated in

the USA in conjunction with the reference nutrient

intakes (RNIs) from Canada. These have been set for

major minerals (calcium,magnesium,and phosphorus)

and trace elements (chromium, copper, fluoride,

iodine, iron, manganese, molybdenum, selenium, and

zinc). The DRIs consist of four standards:

0009Estimated average requirements (EAR), based on

the median of a population;

0010Recommended dietary allowances (RDA),

designed to meet nutrient needs of almost all

(97.5%) healthy individuals;

0011Adequate intakes (AI) for minerals with insuffi-

cient data to establish an EAR;

0012Tolerable upper intake levels (UL) based on the max-

imum intake per day that appears to be safe for an

individual over a long period of time (Figure 2).

0013No recommendations are made for other trace and

ultratrace elements that participate in biological pro-

cesses because of a lack of research.

0014In the UK, dietary reference values have been sug-

gested for six minerals (calcium, phosphorus, magne-

sium, sodium, potassium, and chloride), and for

five trace elements (iron, zinc, copper, iodine, and

selenium). ‘Safe’ intakes have been set for molyb-

denum, manganese, chromium, and fluoride. (See

Dietary Reference Values.)

0015Recommendations for minerals are more difficult

to define than other nutrients as minerals can be

Mn onl

Plasma (nmol l

−1

)

Mn + CaMn + PMn + CuMn + Zn

fig00 02 Figure 2 Plasmauptakeofmanganeseasaffectedbyoral

loadsofmanganese(Mn),calcium(Ca),phosphorus(P),copper

(Cu),andZinc(Zn).Areasunderthecurveforresponseofplasma

manganesewhenthefollowingwasadministered:40mgMn,

40mgMnplus800mgCa,40mgMnplus800mgP,40mgMn

plus2mgCu,and40mgMnplus50mgZn.

tbl0003 Table 3 Foodsources,physiologicalfunctions,deficiencysymptoms,andrequirementofessentialultratraceminerals

MineralFoodsourcesPhysiologicalfunctionsDeficiencysymptomsToxicitysymptomsRequirement

a,b

ArsenicFish,meat,poultryTaurineandpolyamine

metabolism

Depressedgrowth,

reproductive

abnormalities,sudden

death(animals),

nervousdisorders

Dermatosis,low

hematopoiesis,sensory

disturbances,skin

cancer

2–29 mg

BoronMilkanddairy

products,fruits,

nuts,vegetables

Energyutilization,

development/

maintenanceofbone

Elevatedurinarycalcium,

aggravatedarthritis

(humans),poorbone

development(chicks)

Nausea,anorexia,weight

loss,decreasedsexual

activityandspermcount

1mg

MolybdenumLegumes,cereals,

leafygreen

vegetables

Sulfur,pyrimidine,and

purinemetabolism

Lowuricacid,tachycardia,

tachypnea(humans),

kidneystones(sheep)

Gout45 mg

NickelOatmeal,legumes,

peas,nuts,

chocolate

Productionofhormones,

membraneproperties,

oxidation/reduction

Lowbloodglucose,

abnormalbonegrowth,

poorironabsorption,

alteredcalcium

metabolism

Nasalandlungcancers,

asthma,contact

dermatitis,poorstress

andimmuneresponse

<100 mg

SeleniumMeats,fish,grainsAntioxidant,thyroid

hormonemetabolism,

capillaryintegrity

Cardiomyopathy,liver

damage,birthdefects

(wildfowl)

Skinlesions,brittlehair,

nails,andhooves

(animals)UL400 mg

55 mg

VanadiumParsley,black

pepper,

mushroom,dill,

shellfish

IodinemetabolismReducedgrowth,poor

bonegrowth,impaired

reproduction(animals),

poorfeathers(chicks)

Greentongue,intestinal

upset,dehydration,

breathingdifficulty

6–18 mg

DailyrecommendationsorusualdietaryintakesforadultsfromtheInstituteofMedicine(2001)DietaryReferenceIntakesforVitaminA,VitaminK,Arsenic,

Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon,Vanadium, and Zinc. Washington, DC: National Academy Press.

NutrientinformationfromtheAmericanSocietyofNutritionalSciences:www.nutrition.org(2000).

UL, upper intake level.

4008 MINERALS – DIETARY IMPORTANCE

both essential and toxic. The safe range of intake is

somewhere between levels known to produce a defi-

ciency and those that result in toxicity with continued

exposure (Figure 3). Some minerals, such as zinc and

copper, have a relatively large difference between the

adequate and toxic doses, whereas others, such as

iron and selenium, have a fairly narrow window of

optimal intakes.

0016 It should be emphasized that the recommendations

mentioned above are for healthy persons as they

consume their usual diets. The values may not be

applicable to individuals receiving parenteral solutions,

those with inborn errors that may influence absorption,

transport, utilization, storage, or excretion, and during

conditions of malnutrition, disease, and increased

demand (pregnancy, lactation, growth, stress, injury).

Physiological Importance of Minerals

0017 Minerals serve structural, catalytic, and regulatory

functions in the body. The major minerals serve as

structural components of tissues and function in

cellular and basal metabolism, as well as water and

acid–base balance (Table 1). Three of the major min-

erals – sodium, potassium and chloride – are called

electrolytes. Although the functions of the trace and

ultratrace minerals vary considerably, as shown in

Tables 2 and 3, these minerals are primarily catalytic.

These function as cofactors for enzymes or essential

components of important biomolecules. For example,

copper, manganese, and zinc are important com-

ponents of enzymes, zinc is a component of some

transcription factors (DNA-binding proteins) that

regulate gene function, iron is an essential component

of the heme portion of hemoglobin, iodine is an inte-

gral part of thyroid hormones, and cobalt is a necessary

element in vitamin B

(cobalamin). (See Coenzymes.)

0018 It should be emphasized that the presence of a min-

eral in the body is not proof of essentiality. Metals that

are toxic may enter the body via contaminated foods

and nonfoods, inhalation of fumes, and absorption

through the skin. They remain in the body since there

is no mechanism for excretion. For example, strontium

may be found in bones as a result of drinking contamin-

ated milk; mercury may be deposited in the brain after

inhalation of vapors; and lead may be present in the

brain following ingestion of lead-containing paint.

0019The standard criteria of essentiality are as follows:

(1) a deficiency or conditioned deficiency state is

induced and prevented or cured by a mineral; (2) the

mineral is required as a structural component by body

tissues, regulators, or is a dietary essential; (3) bio-

logical fluids maintain a certain concentration of the

mineral as a component electrolyte; and/or (4) a

molecular process uses the mineral as a cofactor.

For the ultratrace elements, another criteria for essen-

tiality may be that (5) a deficiency state creates a

suboptimal biological function, which can be circum-

vented or revoked by the addition of a usual dietary

level of the mineral. (See Coenzymes.)

Minerals and their Interactions

0020Minerals act as cofactors in biochemical reactions

since they have the ability to form stable chelates with

nitrogen donor ligands in amino acids, peptides, and

proteins. They can stabilize the structure and change

the conformation (which may influence function), bind

substrates or cofactors, activate an enzyme–substrate

complex, and influence the enzyme’s affinity for a

substrate by the specificity of the metallic ion.

0021Binding to proteins can be beneficial as it limits the

amount of free ions available. When some minerals

(such as arsenic, chromium, copper, iron, nickel) are

consumed in excess they may bind to DNA in a cross-

link manner. This type of cross-link binding may

create a dysfunctional or mutated DNA that may

play a role in carcinogenesis (initiating cancer).

Excess free ions of iron, for example, may stimulate

the formation of free radicals which attack lipids or

the free ions may bind to DNA in cells. Mutations in

DNA may be related to the association between

excess iron and colon cancer.

0022Some minerals, such as the cupric ion, bind

strongly to proteins, and are not freed by dialysis. In

contrast, zinc undergoes nonenzymatic chelation.

Zinc ions are known to bind covalently with the

nitrogen from the imidazole moiety of histidine and,

possibly, glutamate. The binding of copper and zinc

to metallothionein, a protein involved in the homeo-

stasis of these minerals, confers resistance against the

enzymatic degradation of this protein. Metallothio-

nein chelates copper and zinc via the sulfhydryl

groups (—SH) of its cysteine moieties. The affinity

of this protein for copper is 105 times greater than for

EAR

Deficiency

Toxicity

RDA

Safe range of intake

Dietary intake

fig0003 Figure 3 Dietary recommendations for minerals are located

within a continuum between deficiency and toxicity. EAR, Esti-

mated average requirements; RDA, recommended dietary allow-

ances; UL, upper intake level.

MINERALS – DIETARY IMPORTANCE 4009

zinc. (See Protein: Interactions and Reactions In-

volved in Food Processing.)

0023 In calcium binding, coordination primarily involves

oxygen atoms. A main-chain carbonyl (—COO—)

is one ligand and each oxygen is the carboxyl group

(—COOH) of glutamyl and aspartyl residues. Iron

in nonheme proteins, such as transferrin, invariably

binds to the sulfhydryl group of a cysteine residue or

inorganic sulfur. In heme proteins, one ligand is the

nitrogen of imidazole in histidine. A sulfhydryl group

is a ligand for copper, zinc, cadmium, mercury, and

other heavy metals. Some proteins have double metal

sites (e.g., aspartate, glutamate) so that different

metallic ions can have a site in common.

Mineral–Mineral Interactions

0024 Minerals interact with each other according to their

physicochemical properties, i.e., valence shell elec-

tronic structure, ionic radius, coordination number

and geometric configuration, redox potential, spin

transition state, and ligand exchange. Minerals with

similarities in some of these properties can be predicted

to develop antagonistic relationships. For example,

both divalent iron and trivalent cobalt have a d

elec-

tronic configuration (six electrons of the d orbital),

divalent copper (0.81) and divalent iron (0.83) have

similar ionic radii, and vanadate and chromate

have similar 3d-4s configurations. Thus antagonistic

relationships can be predicted between iron and cobalt,

copper and iron, and vanadate and chromate.

0025 A calcium–phosphorus interaction occurs in the

body when levels of serum calcium decline. Parathy-

roid hormone is secreted, which decreases the renal

reabsorption and urinary excretion of phosphorus,

resulting in lower serum phosphorus. This hormone

also induces the active form of vitamin D which

increases intestinal calcium absorption and renal

phosphorus reabsorption, resulting in higher serum

levels of calcium and phosphorus. This feedback

mechanism maintains a homeostatic control of the

serum levels of these minerals. During low dietary

intake of calcium, zinc supplementation has an

inhibitory effect. (See Cholecalciferol: Physiology.)

0026 Magnesium also affects parathyroid hormone

secretion and competes with calcium for intestinal

absorption. At the cellular level, calcium transport by

the sarcoplasmic reticulum is a magnesium-dependent

process. When dietary magnesium is high, intestinal

absorption of phosphorus is inhibited. It has been ob-

served that both calcium and magnesium negatively

influence fluoride uptake at the intestine.

0027 Diets high in zinc have been shown to be detrimen-

tal to the status of both iron and copper. Excessive

zinc results in iron-deficiency anemia via a direct

effect on absorption. The opposite is true, i.e., high

dietary iron reduces zinc absorption. The antagonism

between zinc and copper is being exploited in the

treatment of Wilson’s disease, a genetic disease in

which copper abnormally accumulates in the liver.

The administration of 75 mg zinc day

1

blocks the

intestinal absorption of copper and returns copper

balance to normal quantities.

0028Iron-deficiency anemia is also produced by excessive

quantities of manganese. During periods of low man-

ganese intake, the absorption of iron greatly increases.

(See Anemia (Anaemia): Iron-deficiency Anemia.)

0029The significant interactions that can occur when

excessive amounts of minerals are ingested suggest

that mineral supplements be avoided under usual

circumstances. High-dose supplements of one min-

eral can upset the delicate balance of other minerals

in the body. Consumption of a varied, nutrient-dense

diet is a better choice than supplements for achieving

optimal mineral status.

Influence of Minerals on Food Processing

and Food Quality

0030Minerals have the potential to affect the color,

texture, flavor, pH, and nutritive value of foods and

are often used as food additives.

Color

0031The brilliant colors of fruits and vegetables are due to

a variety of plant pigments. Chlorophyll pigments,

which contribute blue-green, yellow-green, and

gray-green colors, react with both zinc and copper

to produce a bright green color. The color change

occurs when these minerals replace the central

magnesium atom in the chlorophyll molecule. (See

Chlorophyl; Colorants (Colourants): Properties and

Determination of Natural Pigments.)

0032Anthocyanins are red and blue pigments which

turn red with acid, blue with an alkali, and are some-

times colorless with prolonged heating. When foods

containing anthocyanins are processed in tin (actually

tin-coated) cans, the tin must be lacquered to prevent

the anthocyanins from forming greenish-blue pig-

ments. A greenish-blue color is also created when

rusted tin pans are used for fruit pies. Contact of a

fruit filling, such as blueberry or raspberry, with the

tin and iron salts may cause it to discolor.

0033Anthoxanthins (flavones) are pigments that are

clear and white in acid, yellow in alkali, and pink

with prolonged heating. Tin and aluminum react

with these pigments and change the color to a bright

yellow. This is illustrated by the bright-yellow

cooking water produced when onions are cooked in

an aluminum pan. When anthoxanthins react with

4010 MINERALS – DIETARY IMPORTANCE

iron and copper, blue-black and reddish-brown colors

appear, as seen in onions fried in such pans.

0034 Sulfur prevents the darkening of foods which

occurs when melanin is formed. This brown-black

pigment is created via enzymatic browning in the

presence of oxygen. Dried fruits, such as apricots

and golden raisins, which might turn an unappetizing

brown when drying, can be dipped in a sulfur solution

or exposed to sulfur fumes to prevent discoloration.

Pineapple juice is used as a dipping solution for cut

fresh fruits, such as bananas, because its high sulfur

content retards color changes. Cut lettuce for salad

bars was once sprayed or dipped in a sulfite solution

to retard browning, but this practice has been banned

since over 100 people had allergic reactions (includ-

ing one death) in response to the sulfur.

0035 Chloride salts, such as chlorine dioxide and nitro-

syl chloride, and chlorine are used to accelerate the

natural aging and bleaching of flour.

Texture

0036 When canned vegetables and fruits are cooked during

processing, the tissue softens as cementing pectic sub-

stances in the cell walls of plant tissue degrade. This

softening can be counteracted by the addition of cal-

cium ions in the form of calcium hydroxide and cal-

cium pectate. The calcium salts react with the pectic

substances to form a firm material. Calcium salts are

often added to canned tomatoes as a firming agent.

The presence of phytates in vegetables, such as peas,

decreases the firming effect of the calcium ions due to

formation of a calcium–phytate complex.

0037 In commercial baking, the texture and baking qual-

ity of bread dough are improved by the use of bro-

mates and iodates which act as oxidizing agents. If the

dough must wait for the oven, gas that is evolving

may be lost before cooking and the baked goods

will lose their characteristic light texture. To prevent

the loss of gas, baking powders have been specially

formulated to produce two reactions. In sodium

aluminum sulfate–phosphate powder, monocalcium

phosphate reacts first when moistened at room tem-

perature to create a smooth, light batter; then sodium

aluminum sulfate reacts when it is solubilized by hot

water. In sodium acid pyrophosphate (SAPP)-baking

powder, a pyrophosphate replaces the monocalcium

phosphate because it has a slower reaction rate. An

even slower reaction rate is seen with sodium acid

aluminum phosphate (SALP) powder that contains

sodium aluminum phosphate. SALP powder is used

in cakes because it retains carbon dioxide until the

gluten strands coagulate, thus preventing formation

of tunnels. (See Bread: Chemistry of Baking.)

0038 Mineral salts are also used as anticaking agents and

flow conditioners for powdered foods that have a

tendency to cake or form lumps, such as salt, confec-

tioner’s sugar, and baking powder. Some compounds

used are tricalcium phosphate, silicon dioxide, cal-

cium silicate, aluminum stearate, ferric ammonium

citrate, and monocalcium phosphate.

Flavor and pH

0039The intensity of flavor and tartness in sherbets, car-

bonated beverages, and fruit drinks is enhanced by

the addition of potassium citrate and phosphoric

acid. The correct proportion of acidity and alkalinity

is critical in controlling the correct flavor, texture,

and keeping quality of several dairy products. Buffer-

ing agents such as sodium bicarbonate, calcium car-

bonate, hydrogen chloride, sodium citrate, sodium

hydroxide, and calcium oxide may be used to control

pH. (See pH – Principles and Measurement.)

Safety and Quality of Foods

0040Sulfur dioxide and sulfites are added to foods because

of their ability to act as antioxidants, and to fermenting

alcoholic beverages because it is more toxic to bacteria

and molds than to yeast. Wine can have an exception-

ally high sulfur concentration, as much as 200 mg per

0.5 l. This level far exceeds the acceptable daily intake

of 0.7 mg kg

1

. In the USA, all foods containing detect-

able levels of 10 mgg

1

sulfite or more are labeled. (See

Antioxidants: Synthetic Antioxidants.)

0041Mold inhibitors, such as calcium and sodium

propionate, monocalcium phosphate and sodium dia-

cetate, are added to baked goods. These prevent ropi-

ness in bread and increase the shelf-life. (See Spoilage:

Molds in Spoilage.)

0042Sequestrants or chelating agents are added to foods

to bind metals, such as calcium, iron, and copper.

When the metals bound to the chelator are no longer

in an ionized form, oxidative changes such as stale-

ness, rancidity, and off-flavors are prevented from

developing. These compounds are important in fruit

juices, canned seafood, milk, and salad dressings.

They are also used to clarify wine and other beverages

of minerals.

0043The presence of minerals in foods may influence

the cooking or processing time. Calcium ions, for

example, have a firming effect, which prolongs the

length of the cooking time. This may occur when hard

water is used since it naturally contains calcium salts.

If a long cooking period is desired for flavor develop-

ment, as in preparing baked beans, calcium, as well as

acids, can be added. In home cooking, molasses is

used since it contains high concentrations of calcium

as well as aconitic acid.

0044The use of soft water in food processing, however,

may not always be desirable. In the formulation of

MINERALS – DIETARY IMPORTANCE 4011

low-sodium foods, soft water derived from a water

softener should be avoided because it may contain as

much as 50 mg of sodium dl

1

. Sodium is also added

when foods are brined, as in preparing pickles or

preventing the discoloration of vegetables. When

meats are processed according to kosher laws, large

amounts of sodium are added as the blood is removed

by salting.

See also: Anemia (Anaemia): Iron-deficiency Anemia;

Antioxidants: Synthetic Antioxidants; Bioavailability of

Nutrients; Cholecalciferol: Physiology; Coenzymes;

Colorants (Colourants): Properties and Determination of

Natural Pigments; Dietary Fiber: Effects of Fiber on

Absorption; Dietary Reference Values; Food

Fortification; Functional Foods; Heavy Metal

Toxicology; Protein: Interactions and Reactions

Involved in Food Processing; Spoilage: Molds in

Spoilage; Trace Elements; Vegetarian Diets