Module 2 Minerals

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Module 2Minerals

• Food Chemistry 2
• ND Food Technology

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Table of Contents

• Introduction
• Major minerals
• Trace elements
• Metal uptake in canned foods

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1. Introduction

• Minerals may be present in food as
• Inorganic salt
• Organic salt
• Combined with organic materials (e.g. phosphorus
  combined with phosphoproteins, metals combined
  with enzymes)
• Can be over 60 elements present in food
• Divide minerals into groups

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1. Introduction
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1. Introduction

• Mineral content determinned by incineration
  (ashing) in muffle oven/microwave furnace
• To destroy organic compounds, leaving minerals
  behind

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1. Introduction

• Different methods temperatures of incineration
  give different results
• Organic anions disappear
• Metals changed to their oxides
• Carbonates may be result of decomposition of
  organic material
• Some trace elements salts may be lost by
  volatilisation
• Sodium chloride lost if incineration tempgt600C
• Abundance of certain element (e.g. in soil) ?
  increase level of mineral in plant/animal
• Enrichment of minerals (e.g. murcury in fish)

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2. Major minerals

• Monovalent minerals present in food as soluble
  salts in ionized form (e.g. in apple cations
  Na, K anions Cl-, S-)
• Polyvalent minerals present in form of
  equilibrium between ionic, dissolved, nonionic,
  colloidal (e.g. milk, meat)
• Metals also in form of chelates
• Metal complexes formed by 2/more covalent bonds
  between a ligand metal cation
• A ligand is a group bonded to a central atom in a
  complex (capable to donate electron pairs to
  metal ion)
• Ligand functions as Lewis base metal functions
  as Lewis acid

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2. Major minerals

• Chelate stability
• More stable when ligand is more basic
• Depends on nature of metal ion (elecronegativity)
• Decreases with decrease in pH
• Formation of chelates can be ring systems (e.g.
  chloropyll 6-membered ring)
• Metals can form chelates with donor atoms (N, O,
  P, S) or donor groups (NH2, COOH, CO)
• Examples of chelates in food
• Hemoglobin, myoglobin, VitB12, calcium caseinate

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2. Major minerals

• Sodium concerns
• NB for flavour acceptability of food
• Concerns about sodium cause human hypertension
• Recommended daily intake 0.5g, but humans use a
  lot more
• Suggested replace salt with mixture of sodium
  chloride potassium chloride
• Mineral absorption decreased by fiber
• Phytate (in fiber) forms insoluble complexes with
  Fe Zn ? interfere with absorption of Ca by
  causing formation of fiber-bound Ca in intestines

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2. Major minerals

• Minerals in milk
• Depends on feed, season, breed, stage of
  lactation, udder infections
• Mineral content constant at 0.7
• Milk contains much more potassium than blood
  plasma
• Some minerals in milk present at levels beyond
  solubility thus in colloidal form (e.g. Ca, Mg,
  phosphate, citrate)
• Coloidal minerals removed by
• Precipitation with curd when milk is coagulated
  with rennin
• ultrafiltration

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2. Major minerals

• Minerals in meat
• Mainly sodium (in extracellular fluid of muscle)
  potassium, phosphorus, magnesium (intracellular
  fluid)
• Nonsoluble minarals associated with proteins
• Leaner meat ? higher mineral content
• Drip loss ? sodium mostly lost
• Processing does not reduce mineral content of meat

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2. Major minerals

• Cured meats may have increased sodium, because
  cured in brine (sodium chloride/potassium
  nitrite)
• Ionic equilibria NB in water-binding capacity of
  meat
• Normal pH (5.5) of rigor is close to iso-electric
  point of actomyosin
• Thus net charge on protein at minimum water
  binding also at minimum
• Addition of acid/base ? cleavage of slat
  cross-linkages ? electrostatic repulsion
  increases ? loosens protein network ? more water
  can be taken up
• Addition of salts (sodium chloride to meat
  increases water-holding capacity

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2. Major minerals

• Struvite
• Or magnesium-ammonium-phosphate
  Mg(NH4)PO46H2O
• Usually mistaken for broken pieces of glass in
  canned seafood
• Mg of seawater ammonia forms struvite by the
  effect of heat on fish muscle protein

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2. Major minerals

• Minerals in plants
• Potassium, sodium (only trace element),
  phosphorus, Ca, Mg, sulfur
• Minerals in wheat all concentrated in bran/areas
  close to bran coat
• Ash content in flour related to quality (the
  higher the ash content, the darker the colour)
• High grade patent flour (pure endosperm)
  0.3-0.35 ash, wholewheat meal 1.35-1.8 ash
• Also influenced by rainfall, soil conditions,
  fertilizers
• Soybeans
• 5 ash mostly potassium phosphorus
• Phosphorus in form of phytic acid
• Phytates NB effect on protein solubility
  interfere with absorption of Ca in diet

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3. Trace elements

• Present in all foods from
• uptake from soil (absorption through roots),
• feed (e.g. milk),
• contamination from processing (metal pickup from
  packaging/equipment, nickel in milk from
  stainless steel tanks)
• Industrial air pollution, fertilizers, chemicals,
  sewage sludge (nitrogen phosphate)
• Abundance depends on abundance in environment
• Very high concentrations may lead to sclerosis
  cancer
• Aluminium (used in packaging, utensils, food
  additives) may cause Alzheimers disease

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3.1. Cobalt

• Only metal containing VitB12 Marmite!
• In corn, legumes, cereals
• Human requirement small, no deficiencies

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3.2. Copper

• Present in foods as part of enzymes (e.g.
  polyphenolases)
• Powerful prooxidant catalises oxidation of
  unsaturated fats, oils ascorbic acid

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3.3. Iron

• Component of heme pigment enzymes
• Iron deficiencies in population disappearance
  of iron equipment in processing plants
• In animal liver well absorbed, veg eggs not
  well absorbed
• Absorption depends on form
• Ferrous sulphate well absorbed, but will
  discolour/oxidize food to which its added
• Elemental iron well absorbed not change food
  (added to enrich flour)
• The meat factor amino acids from digestion can
  chelate nonheme iron ? the complexes formed can
  facilitate absorption of iron

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3.4. Zinc

• 2nd most NB mineral for humans
• Stimulates activity of enzymes promote biochem.
  reactions in body, helps heal wounds, sense of
  taste smell
• Abundant - deficiencies unknown
• In beans, nuts, whole grains, dairy products
• Zinc poisoning acid foods (fruit juice) stored
  in galvanized containers ? zinc dissolves

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3.4. Manganese

• In wide range of foods, but not easily absorbed
• High concentration in germ and bran of wheat
• Associated with activation of some enzymes
• Maintains blood sugar levels

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3.5. Molybdenum

• Plays role in enzymes (e.g. aldehide oxidase,
  sulfite oxidase, xanthine oxidase)
• In cereal grains, leafy veg (rich in
  chlorophyll), animal organs
• Contents in food varies

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3.6. Selenium

• Bound to organic molecules (bound to proteins in
  milk)
• Protects against liver necrosis, works as
  antioxidant (protects against cancer)
• Most active form is selenite
• Volatile can be lost during processing
• In nuts (Brazil nuts), tuna, grains

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3.7. Flourine

• plays a role in the development and health of
  bones and teeth
• In veg (spinach), milk, fish, flouridated tap
  water

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3.8. Iodine

• High levels in fish shellfish
• NB for functioning of thyroid gland - deficiency
  leads to goiter

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3.8. Nickel

• Legumes, nuts, cocoa, shellfish, hydrogenated
  fats (mostly plants)

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3.9. chromium

• In wheat (flour)
• Refining processing lead to loss in chromium,
  but can also leach into food product from
  stainless steel equipment
• Needed for sugar metabolism maintain blood
  sugar level
• Dietery intake suboptimal in most people can
  lead to nutritional problems

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3.10. Silicon

• High in foods from plant origin (unrefined
  grains, cereal products, root crops)
• Required, along with VitC, for collagen
  formation, prevention of osteoporosis

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4. Metal uptake in canned foods

• Canned foods take up minerals from container
• Tin iron from the tin plate
• Tin and lead from the solder
• In acid foods canned in the absence on O2, tin
  forms the anode of the tin-iron couple ? tin goes
  slowly in solution ? protect product for 2 years
  or longer
• Rapid detinning
• When iron forms the anode ? in presence of
  oxidizing agents dissolution of tin is
  accelerated ? after all tin is in solution, H2
  forms ? can swells ? can becomes a springer
• Spinach, greenbeans, tomato, veg soups, fruit
  juices

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4. Metal uptake in canned foods

• Sulfide staining (in pork, fish, peas)
• When food contains sulphur containing amino acids
  (cysteine, methionine)
• Upon heating ? reduction ? sulfide ions form ?
  react with tin iron ? SnS FeS ? sulfide stain
  
• Type of tin plate size of crystals in tin
  coating effects corrosion resistance
• Tin can preserve light colour of food (wax beans)
• Iron can darken food
• Black compound of iron (dissolved from can)
  rutin (flavonol extracted from the food) in
  all-green asparagus
• Black colour forms after iron is oxidized to the
  ferric state