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Fennema's Food Chemistry · Chapter 9 · Minerals

Minerals

Eaten ≠ absorbed: it's all chemistry

Major vs traceBioavailabilityEnhancers/inhibitors6 minigames inside

Popeye ate spinach for iron… really?

Spinach contains iron — but its oxalate and phytate lock the iron up, so absorption is dismally low.
A high content doesn't mean it's available. What matters: is it soluble in the gut, and what binds it?

9.1 Introduction

What are minerals?

Minerals = the inorganic elements in food other than C, H, O, N. About 25 are essential to life.

C/H/O/N make up ~99% of atoms in living systems; minerals are minor but pivotal.
They drive hundreds of enzyme reactions, bone/teeth, oxygen transport, nerve signaling.
Excess can be toxic — the safe range is wide thanks to homeostasis.

Two classes

Major：Ca · P · Mg · Na · K · Cl

Trace：Fe · Zn · I · Se · Cu · Cr · Mn · F

By concentration in tissue — not importance.

Classification

Major vs trace: different amounts, equal importance

~90 elements occur naturally; ~25 are essential to humans/animals (shaded in the periodic table).

Ca·P

Major minerals

Need >100 mg/day: Ca, P, Mg, Na, K, Cl. Build bone, balance fluids.

Fe·Zn

Trace elements

Need mg–µg/day: Fe, Zn, I, Se, Cu, Mn, F. Mostly enzyme cofactors.

Pb·Hg

Non-essential/toxic

Pb, Hg, Cd: not nutrients; enter food as contaminants; tightly monitored.

🎮 MINIGAME · CLASSIFY#1

Major mineral or trace element?

Click the button on each row.

Calcium (Ca)

Iron (Fe)

Sodium (Na)

Iodine (I)

Phosphorus (P)

Selenium (Se)

🎉 Done! Major (Ca·P·Mg·Na·K·Cl) needed >100 mg/day; trace (Fe·Zn·I·Se…) needed in tiny amounts — but deficiency still causes disease.

9.2 Principles

Mineral chemistry: solubility, acid/base, chelation

Solubility

Absorption starts with solubility. Na⁺/K⁺/Cl⁻ exist as free ions, highly soluble; most others are complexes/chelates.

Acid/Base

Metal cations are Lewis acids (accept electron pairs), coordinating Lewis bases like H₂O. Fe³⁺ → octahedral [Fe(H₂O)₆]³⁺.

Chelation

Multidentate ligands grip the metal. Can solubilize (ferric citrate) or precipitate/lock (calcium oxalate, insoluble).

Same iron: FeCl₃ in water → precipitates as ferric hydroxide (unavailable); but ferric citrate stays soluble → chelation decides its fate.

Table 9.2

Essential minerals: function, deficiency, sources (Table 9.2)

Mineral	Function	Deficiency	Sources
Calcium	Bone/teeth, clotting, nerve signaling	Osteoporosis, hypertension	Dairy, tofu, leafy greens
Iron	O₂ transport (hemoglobin), energy	Anemia (widespread), fatigue	Red meat, beans, fortified foods
Zinc	Metalloenzyme cofactor, gene expression	Growth retardation, poor healing	Red meat, shellfish, wheat germ
Iodine	Thyroid hormone synthesis	Goiter, cretinism	Iodized salt, seaweed, seafood
Selenium	Antioxidant (in peroxidases)	Keshan disease (myocarditis)	Cereals from Se-rich soils, meat
Sodium	Extracellular fluid, BP, transport	Rare; excess → hypertension	Processed foods (added salt)

Click headers to sort. Note many minerals are harmful in excess too — the safe range is wide but maintained by homeostasis.

🎮 MINIGAME · MATCH#2

Match each mineral to its deficiency

Click a mineral, then its deficiency.

Mineral

Deficiency

🎉 All matched! Deficiencies like iodine→goiter are exactly why public-health programs iodize salt and fortify flour with iron.

9.3.3 Bioavailability

Bioavailability: eaten ≠ absorbed

Bioavailability = the fraction actually absorbed and utilized after ingestion.

Huge range: from <1% for some iron to >90% for sodium/potassium.
The key is solubility in the small intestine — insoluble forms can't reach the brush border.
So a label's "content" often misstates how much you can actually absorb.

Five factors

Chemical form (heme > nonheme Fe)
Food ligands (phytate, oxalate, fiber)
Redox (vit C reduces iron)
Mineral–mineral (Ca↓Fe, Fe↓Zn)
Physiology (pregnancy ↑ Fe)

Table 9.5

Enhancers vs inhibitors of iron

✅ Enhancers

Vitamin C (ascorbic acid): reduces Fe³⁺ → more absorbable Fe²⁺, forms soluble chelate
Meat factor: meat/poultry/fish boost iron absorbed in the same meal
Organic acids: citric, lactic — soluble chelates

⛔ Inhibitors

Phytate (IP6): storage P in grains/legumes; chelates Ca, Fe, Zn → antinutrient
Oxalate: spinach etc.; strongly inhibits calcium
Polyphenols/tannins: tea, coffee; inhibit nonheme iron
Mineral competition: high Ca↓Fe, high Fe↓Zn

🎮 MINIGAME · MCQ#3

Why does a glass of orange juice boost iron absorption from plant foods?

✔ Correct: vitamin C is a strong reductant — it converts poorly-absorbed Fe³⁺ to Fe²⁺ and chelates iron, protecting it from phytate/oxalate. Hence the classic 'plant iron + vitamin C' pairing. It does little for other minerals, which aren't readily reduced.

🎮 MINIGAME · CLASSIFY#4

Does this factor enhance or inhibit iron absorption?

Click the button on each row.

Vitamin C

Phytate

Meat factor

Tea tannins/polyphenols

Citric acid

Oxalate

🎉 Done! Rule of thumb: reductants, organic acids and meat help iron; phytate, oxalate, tannins block it. To boost iron: add vitamin C, skip strong tea.

Iron bioavailability (representative)

Heme vs non-heme iron: very different absorption

Iron comes in two forms with very different fates:

Heme iron (meat/hemoglobin): absorbed as an intact porphyrin, largely shielded from inhibitors.
Non-heme iron (plant/fortified): ionic, solubility is everything — vitamin C rescues it, phytate ruins it.

Vegetarian iron strategy: non-heme iron + vitamin C, avoid strong tea / high phytate.

Representative values: heme iron (meat) is well and stably absorbed; non-heme (plant) is low and swings with vitamin C (↑) and phytate (↓).

🎮 MINIGAME · CALC#5

A fortified cereal serving has 5 mg iron at 18% bioavailability. How much iron (mg) is actually absorbed?

absorbed = intake × bioavailability.

✔ Correct: absorbed = intake × bioavailability = 5 mg × 0.18 = 0.9 mg. This is why 'content' ≠ 'absorbed' — and 18% is actually decent; much non-heme iron is lower.

✗ Try again: absorbed = 5 × 0.18 ≈ 0.9 mg.

9.4.1 Ash

Ash: burning the minerals out

High ash ≈ more minerals, but says nothing about which or how available — that needs element-specific analysis plus bioavailability.

550°C

Ashing

Incinerate at ~500–550°C; organic matter burns off, the residue (ash) = total minerals.

近似

Proximate analysis

Ash is one of the six proximate-analysis fractions (moisture/ash/protein/fat/fiber/carb).

AAS

Element-specific

AAS and ICP precisely quantify individual elements.

9.4.4 / 9.5 Fortification & function

Fortification & function: minerals at work in food

🧂

Iodized salt

Salt iodization — one of the great public-health wins; slashed goiter.

Iron/zinc fortification

Flour & cereals fortified with Fe/Zn to fight widespread anemia.

Calcium: gelling

Ca²⁺ cross-links pectin/soy protein → tofu, jams, LM-pectin gels.

PO₄

Phosphates

Buffering, leavening (baking powder), emulsifying salts (processed cheese).

NaCl

Salt (NaCl)

Flavor, preservation (lowers a_w), controls protein function.

Fe·Cu

Fe/Cu: catalysis

Transition metals catalyze lipid oxidation & discoloration — agents of deterioration.

9.3.6 Heavy-metal toxicity

Heavy metals: not nutrients — toxicants

These have no nutritional role and enter food as contaminants. The job of food chemistry/regulation is to monitor and reduce exposure.

Lead (Pb)

Children's learning/behavior, anemia, kidney damage. From Pb-soldered cans, leaded gas, glazes.

Mercury (Hg)

Methylmercury biomagnifies in long-lived predatory fish; numbness, vision/hearing loss, kidney damage.

Cadmium (Cd)

Kidney damage, bone disease, cancer. From crops on Cd-contaminated soils.

🎮 MINIGAME · MCQ#6

Which toxic heavy metal accumulates especially in long-lived predatory fish (as methylmercury)?

✔ Correct: mercury. Methylmercury biomagnifies up the food chain, peaking in tuna, swordfish and shark — which is why pregnant women are advised to limit these fish.

Applied strategy

Want more iron from a meal? Three levers

You're eating plant (non-heme) iron — how to absorb more of it?

↓

① Add a reductant

Pair vitamin C

Orange, tomato, peppers — reduce Fe³⁺ to Fe²⁺.

② Use the meat factor

Add some meat/fish

A little meat/poultry/fish lifts overall absorption.

③ Avoid inhibitors

Cut phytate & strong tea

Soak/ferment to cut phytate; skip strong tea/coffee at meals.

Content is the surface; absorption is the truth

The mineral story is a tug-of-war of solubility and chelation: whoever keeps the mineral soluble and absorbable wins. Master this chemistry and you can explain why spinach is poor for iron, and why we iodize salt.

~25

essential minerals

<1–90%

bioavailability range

vitC↑/phytate↓

non-heme iron

550°C

ashing

Self-check: can I separate major/trace, name 3 enhancers & 3 inhibitors of iron, and explain what ash measures?