Minerals:Major and Trace

Page 123 - 140

By: Mohammed Sabah

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What are minerals?What are minerals?

• Regulate body processesRegulate body processes• Give structure to things in the bodyGive structure to things in the body• No calories (energy)No calories (energy)• Cannot be destroyed by heatCannot be destroyed by heat

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Categories of mineralsCategories of minerals

• Major minerals - potassium - sodium - calcium -magnesium - chloride - sulfate - phosphate - and bicarbonate.

• Major minerals - potassium - sodium - calcium -magnesium - chloride - sulfate - phosphate - and bicarbonate.

• Trace minerals– Chromium– Copper– Flouride– Iodine– Iron– Manganese– Selenium– Zinc

• Trace minerals– Chromium– Copper– Flouride– Iodine– Iron– Manganese– Selenium– Zinc

More than 60 elements may be present in foods. It is customary to divide the minerals into two groups, the major salt components and the trace elements

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The major salt components include potassium, sodium, calcium, magnesium, chloride, sulfate, phosphate, and bicarbonate.

Trace elements are all others and are usually present in amounts below 50 parts per million (ppm).

The trace elements can be divided into the following three groups: 1. essential nutritive elements, whichinclude Fe, Cu, I, Co, Mn, Zn, Cr, Ni,Si, F, Mo, and Se.

2. nonnutritive, nontoxic elements, includingAl, B, and Sn

3. nonnutritive, toxic elements, includingHg, Pb, As, Cd, and Sb

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The minerals in foods are usually determined by ashing. This destroys the organic compounds and leaves the minerals behind. However, determined in this way, the ash does not include the nitrogen contained in proteins and is in several other respects different from the real mineral content.

Organic anions disappear during incineration, and metals are changed to their oxides. Carbonates in ash may be the result of decomposition of organic material.

The phosphorus and sulfur of proteins and the phosphorus of lipids are also part of ash. Some of the trace elements and some salts may be lost by volatilization during the ashing.

Sodium chloride will be lost from the ash if the incineration temperature is over 600ºC. Clearly, when we compare data on mineral composition of foods, we must pay great attention to the methods of analysis used. 5

Minerals in Milk

The normal levels of the major mineral constituents of cow's milk are listed in Table 5-1. These are average values; there is a considerable natural variation in the levels of these constituents.

The ash content of milk is relatively constant at bout 0.7 percent

A number of factors influence the variations in salt composition, such as feed, season, breed and individuality of the cow, stage of lactation, and udder infections.

An important difference between milk and blood plasma is the relative levels of sodium and potassium. Blood plasma contains 330 mg/100 mL of sodium and only 20 mg/100 mL of potassium.

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In contrast, the potassium level in milk is about three times as high as that of sodium. Some of the mineral salts of milk are present at levels exceeding their solubility and therefore occur in the colloidal form. Colloidal particles in milk contain calcium, magnesium, phosphate, and citrate. These colloidal particles precipitate with the curd when milk is coagulated with renin.

When milk is heated, calcium and phosphate change from the soluble to the colloidal phase. Changes in pH result in profound changes of all of the salt equilibria in milk.

Decreasing the pH results in changing calcium and phosphate from the colloidal to the soluble form. At pH 5.2, all of the calcium and phosphate of milk becomes soluble

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Minerals in Meat The major mineral constituents of meat are listed in Table 5-4.

Sodium, potassium, and phosphorus are present in relatively high amounts. Muscle tissue contains much more potassium than sodium.

Meat also contains considerably more magnesium than calcium.

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Wheat flour with high ash content is darker in color; generally, the lower the ash content, the whiter the flour.

Minerals in Plant Products

Plants generally have a higher content of potassium than of sodium. The major minerals in wheat are listed in Table 5-5 and include potassium, phosphorus, calcium, magnesium, and sulfur.

Sodium in wheat is present at a level of only about 80 ppm and is considered a trace element in this case.

The various fractions resulting from the milling process have quite different ash contents. The ash content of flour is considered to be related to quality, and the degree of extraction of wheat in milling can be judged from the ash content of the flour.

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Interactions with Other Food Components

The behavior of minerals is often influenced by the presence of other food constituents.

The recent interest in the beneficial effect of dietary fiber has led to studies of the role fiber plays in the absorption of minerals. The mineral absorption is decreased by fiber.

A study of the behavior of iron, zinc, and calcium showed that interactions occur with phytate, which is present in fiber. Phytates can form insoluble complexes with iron and zinc and may interfere with the absorption of calcium by causing formation of fiber-bound calcium in the intestines.

When a mineral binds to phytic acid, it becomes insoluble, precipitates and will be nonabsorbable in the intestines. This process can therefore contribute to mineral deficiencies in people whose diets rely on these foods for their mineral intake

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Iron bioavailability may be increased in the presence of meat. This is the so-called meat factor.

The exact mechanism of this effect is not known, but it has been suggested that amino acids or polypeptides that result from digestion are able to chelate nonheme iron. These complexes would facilitate the absorption of iron.

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What Processing Does to Sodium and Potassium Contents of Foods

Milk (whole)

Unprocessed

Peach pie

Processed

Canned,cream corn

Instantpudding

Oat cereal

Fresh peaches

Milks

Chipped beef

Vegetables

Fresh corn

Meats

Roast beef

Fruits

Rolled oats

Grains

SodiumPotassium

Key:

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ASH ANALYSIS• “Ash = inorganic residue remaining after either

ignition or complete oxidation of organic matter in a foodstuff”– dry ashing (proximate analysis)• whole grain, cereals and dried vegetables

– wet ashing (oxidation, preparation for elemental analysis)• meat and meat products

– microwave (low temperature ashing)• volatile elements

• Ash content of fresh food is rarely >5%13

Small sample for ashing requires very careful preparation in order to be representative.

Food materials should be dried before ashing if greater than 15% moisture.

High fat & moisture foods (meat products) or high in sugar (syrups) will swell and splatter or foam resulting in loss of sample if not pre-prepared by evaporating on steam bath or with infrared lamp or gently over Bunsen flame.

Dry ashing - suitable for most foods.

Wet ashing (oxidation) - for samples of high fat content for preparation for elemental analysis.

Plasma (low temperature ashing) - to preserve volatile elements for later elemental analysis.

Important when selecting ashing method to consider if any elements of interest may be lost through volatilisation

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Wet ashing• Wet oxidising of organic substances• Place 1g dried sample of food in H2SO4 & HNO3

• Heated to 200C on hot plate in fume-hood’ brown-yellow fume will evolve– sample should become colourless

• Cool and transfer oxidised food solution to 50 mL volumetric flask

• Make to volume with ultra pure water• Follow wash down procedure for fume-hood

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Contamination• Grinding with steel grinders• Old glassware can contaminate samples for

micro-elemental analysis– glass is acid washed & triple rinsed with ultra

pure water

• Solvents including water may contain high amounts of minerals– need pure reagents high in cost– run reagent blank

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Elemental Analysis

Step 1: AshingStep 2: Solubilize ash in Conc. HCl - boil and evaporate solution to dryness.Step 3: Re-dissolve residue in 0.5 N HCl.Step 4: Concentration or dilute as desiredStep 5: Determination of individual components.

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METHODS FOR DETERMINING MINERAL CONSTITUENTS

1.Spectrometric Methods

2. Emission Spectroscopy - Flame Photometry Method

3. Atomic Absorption Spectrometry

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1- Spectrophotometric Method:Formation of colored complex with some ligand.

Example: Fe++ (Ferrous Ion) with 1.10 phenanthroline (orthophenanthrolines).

A pair of unshared electrons can coordinate certain metallic ions to give complexes. In the case of ferrous ion, the orthophenanthroline complex is quite stable and is intensely red in color. The complex is sometimes called Ferroin.

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Measure the intensity of emitted radiation

2- Emission Spectroscopy - Flame Photometry Method

3- Atomic Absorption spectroscopyAtomic Absorption spectroscopy involves the study of the absorption of radiant energy by neutral atoms in the gaseous state.

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Analysis of specific minerals

• Flame photometry and atomic absorbtion spectroscopy

• EDTA complexation titration• Redox reactions• Precipitation titration• Colorimetric methods• Ion selective electrodes

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EDTA complexometric titration

Fennema, 1996 p.625

• Formation of stable complexes of metal ions with ethylenediamine.tetraacetic acid (EDTA)– except alkali metals (Na)

• Via the presence of donor oxygen and nitrogen atoms EDTA is able to form six, five member chelate rings

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Water hardness - EDTA titration

• Adjust water sample pH to 10 by adding buffer solution (NH4OH + Na2EDTA + MgCl2) and Calmagite indicator solution

• Titrate with 0.01 EDTA to a blue endpoint• This method is suitable to assess Ca in ashed

fruits and vegetables

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• Add magnesium salt and enough EDTA to bind all magnesium.

• In buffer solution the Ca replaces the Mg bound to the EDTA.

• The free magnesium binds to Calmagite,– pink magnesium Calmagite complex persists until

all Ca in the sample has been titrated with the EDTA.

• Excess EDTA removes Mg from Clamagite and produces a blue endpoint

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Minerals in a 60-kilogram (132-pound) Human Body

TRACE MINERALSThere are more than a dozen trace minerals,although only six are shown here.

Amount (g)

MAJOR MINERALSThe major minerals are those present in amountslarger than 5 g (a teaspoon). A pound is about454 g; thus only calcium and phosphorus appearin amounts larger than a pound.

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Sodium• fluid volume regulator, electrolyte balancer• source– mostly in processed foods

• deficiency– must be replaced with water if blood sodium

drops• toxicity– edema and hypertension

• diet moderate in sodium is recommended

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Chloride

• essential nutrient• fluid and electrolyte balance• abundant in foods (especially processed)– part of sodium chloride

• rarely lacking• dehydration due to water deficiency

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Potassium• maintaining fluid and electrolyte balance– affects homeostasis, such as a steady heartbeat

• found in both plant and animal cells– less found in processed foods

• deficiency– hypertension– most common electrolyte imbalance– muscle weakness

• toxicity– rare from food– over consumption of supplements

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Calcium• most abundant mineral in body• bone structure, calcium bank• found primarily in milk and milk products• deficiency– limits mass & density• growing years• age related

– silent, no signals

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Label

Key:

Fruits

Milk and milk products

Legumes, nuts, seeds

Meats

Best sources per kcalorie

Breads and cereals

Vegetables

CALCIUMAs in the riboflavin figure, milk and milk products (white)dominate the calcium figure. Most people need at least threeselections from the milk group to meet recommendations.a Values based on products containing added calcium salts;the calcium in 1⁄2 c soybeans is about 1⁄3 as much as in1⁄2 c tofu. b If bones are discarded, calcium declines dramatically.

Food Serving size (kcalories)Milligrams

AI formen

19–50

AI formen51+

AI forwomen19–50

AI forwomen

51+

Calcium in Selected Foods 30

Phosphorus

• 2nd most abundant• energy metabolism, transport lipids, cell

membranes• foods rich in protein, supply phosphorus

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Key:

Fruits

Milk and milk products

Legumes, nuts, seeds

Meats

Best sources per kcalorie

Breads and cereals

Vegetables

PHOSPHORUSProtein-rich sources, such asmilk (white), meats (red), andlegumes (brown), provideabundant phosphorus as well.

RDAfor

adults

Food Serving size (kcalories)Milligrams

Phosphorus in Selected Foods32

Magnesium

• minute amount, but critical– energy metabolism, catalyst, ATP production

• critical to heart function• ingestion of hard water may reduce incidence

of heart disease• toxicity is rare, but can be fatal

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Magnesium in Selected Foods

Key:

Fruits

Milk and milk products

Legumes, nuts, seeds

Meats

Best sources per kcalorie

Breads and cereals

Vegetables

MAGNESIUMLegumes (brown) are a richsource of magnesium.

RDA forwomen19-31

RDA formen19-30

Food Serving size (kcalories)Milligrams

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Sulfur

• sulfur is not used by the body– found in thiamin and several amino acids

• high sulfur content in– skin, hair, nails

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Trace Minerals• iron• zinc• iodine• selenium• copper• manganese• fluoride• chromium• molybdenum

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The trace elements can be divided into the following three groups:1.essential nutritive elements, which include Fe, Cu, I, Co, Mn, Zn, Cr, Ni, Si, F, Mo, and Se.

2. nonnutritive, nontoxic elements, including Al, B, and Sn.

3. nonnutritive, toxic elements, including Hg, Pb, As, Cd, and Sb

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Trace Minerals

• small amounts found in the body• small amounts needed• deficiency can be fatal, excess can be deadly– TM are active in all body systems

• content is dependent on soil and water composition and processing

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Iron• essential nutrient• mostly found in – hemoglobin • carrier of oxygen

– myoglobin • protein in muscles, making oxygen available

• iron balance is critical• deficiency– fatigue and anemia–

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Iron

• red meats, fish, poultry, eggs, legumes are good sources

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Iron in Selected Foods

Key:

Fruits

Milk and milk products

Legumes, nuts, seeds

Meats

Best sources per kcalorie

Breads and cereals

Vegetables

IRONMeats (red), legumes (brown),and some vegetables (green)make the greatest contributionsof iron to the diet.

RDA forwomen

51+

RDA forwomen19–50

RDAfor

men

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Zinc

• cofactor for many enzymes affecting growth and digestion

• deficiency– growth retardation– sexual immaturity– impaired immune response

• protein containing foods are a good source of zinc

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Zinc in Selected Foods

Label

Key:

Fruits

Milk and milk products

Legumes, nuts, seeds

Meats

Best sources per kcalorie

Breads and cereals

Vegetables

ZINCMeat, fish, and poultry (red) areconcentrated sources of zinc.Milk (white) and legumes(brown) contain some zinc.

RDAfor

women

RDAfor

men

Micrograms RAEFood Serving size (kcalories)

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Iodine• converted to iodide in GI tract• essential component of thyroid hormone– regulates temperature, reproduction, growth, cell

production• deficiency– goiter: enlarged thyroid gland– cretinism• during pregnancy• irreversible mental and physical retardation

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Iodine• world’s ocean and iodized salt are best

sources

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Selenium

• essential antioxidant nutrient• deficiency associated with heart disease• seafood, meats, whole grains, vegetables– dependent on soil content

• toxicity– loss and brittleness of hair and nails

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Copper

• important player in several enzyme reactions• deficiency is rare• food sources are legumes, whole grains, nuts,

shellfish, seeds

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Manganese

• cofactor for many enzymes that metabolize carbs, lipids and amino acids

• deficiency is rare• too much can affect the nervous system• found in nuts, whole grains, leafy veggies

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Fluoride• presence makes – bones stronger– teeth more resistant to

tooth decay• fluoridated water is

best source– most bottled water is

lacking• too much can damage

teeth

Key:< 49%

50% – 74%> 75%

U.S. Population with Access to Fluoridated Water through Public Water

Systems

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Chromium

• essential nutrient involved in carb and lipid metabolism– maintains glucose homeostasis

• deficiency– creates diabetic like symptoms

• sources include liver, whole grains, yeast

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Molybdenum

• cofactor for many enzymes• found in legumes, cereals, organ meat

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Contaminant Minerals

• heavy metals– lead– mercury– cadmium

• enter food through water, soil, air pollution• interfere with nutrients• bioaccumulation

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Remember to eat foods, not nutrients

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