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Fennema's Food Chemistry · Chapter 1 · Introduction

Introduction to
Food Chemistry

Every moment of food is a chemical reaction

What is food chemistryA brief historyDeterioration reactions4 minigames inside
After three days on the shelf…
A cut apple browns, oil turns rancid, greens go yellow, meat develops off-flavors.
Every "spoilage" is, at heart, a chemical reaction. Food chemistry is about reading and controlling them.
1.1 Definition

What is food chemistry?

Food science studies the physical, chemical and biological properties of foods; food chemistry focuses on their composition and the chemical changes they undergo during handling, processing and storage.

  • Its subjects are biological tissues that are dead or dying — post-mortem muscle, post-harvest fruits and vegetables.
  • Unlike biologists (who study how life is sustained), food chemists study what happens after tissue leaves the living state.

The core question

What is food made of? How do those components change during processing and storage? And how can we control them to keep food safe, nutritious and palatable?

🎮 MINIGAME · MCQ#1
What do food chemists primarily study?
✔ Correct: food chemistry deals with the composition and chemical change of dead/dying tissue (post-mortem muscle, post-harvest produce). Microbial flora belongs to food microbiology; additives are only one small part.
1.2 History

A brief history: chemists who saw into food

1780s

Scheele

Isolated lactose, citric, malic acids and glycerol — first pure compounds from plant/animal matter.

1780s

Lavoisier

Wrote fermentation as a balanced equation; founded combustion analysis. Father of modern chemistry.

1820s

Chevreul

Studied animal fat; named stearic & oleic acids — pioneer of fatty-acid research.

1847

Liebig

Published the first book on food chemistry; classified foods as nitrogenous / non-nitrogenous.

1820

Accum

His treatise exposed rampant 19th-c. adulteration, spurring analytical chemistry.

1906

Wiley → Pure Food & Drug Act

Hanneberg/Stohmann devised proximate analysis; Wiley drove the first U.S. food law.

🎮 MINIGAME · MATCH#2
Match each chemist to their contribution
Click a left item, then its match on the right.
Chemist
Contribution
🎉 All matched! From isolating components → quantitative analysis → exposing fraud & legislation, food chemistry grew from curiosity into a science that guards the food supply.
Book map

The six major chemical components of food

The whole book unpacks these six classes — and the interactions between them.

H₂O

Water

Most abundant; governs texture & stability (Ch.2).

CHO

Carbohydrates

Sweetness, browning, thickening & gelling (Ch.3).

Lipid

Lipids

Energy, mouthfeel, oxidative rancidity (Ch.4).

Prot

Proteins

Structure, enzymes, emulsifying/foaming (Ch.5–6).

Vit

Vitamins

Micro but essential; easily lost in processing (Ch.8).

Min

Minerals

Catalytic, structural and nutritional roles.

1.3 Approach

The four-step analytical approach

Safety comes first — e.g. "commercial sterility" of low-acid canned foods means eliminating Clostridium botulinum spores.

①

Define quality attributes

Ask: which attributes make this food safe & high-quality?

②

Identify key reactions

Which chemical/biochemical reactions affect quality & safety?

③

Integrate the two

Understand how reactions drive attributes — build cause & effect.

④

Apply to real situations

Apply to real formulation, processing & storage problems.

Table 1.1

Quality attributes — and how they degrade

AttributePossible alteration
TextureLoss of solubility / water-holding; toughening or softening
FlavorRancidity (hydrolytic/oxidative), cooked/off-flavors
ColorDarkening, bleaching (or desirable browning)
Nutritive valueLoss/degradation or altered bioavailability of nutrients
SafetyGeneration of toxins — or inactivation of toxins

Click a header to sort. To consumers, most changes — except nutrition & safety — are readily evident.

🎮 MINIGAME · CLASSIFY#3
Which quality attribute does each change affect?
Click the matching attribute button on each row.
Lipid oxidation → rancid off-flavor
Cut apple browns at the surface
Protein denatures; solubility drops
Vitamin C lost during cooking
Mold produces aflatoxin
🎉 Done! For any food problem, first ask which attribute changed, then trace which reaction caused it — that's the Table 1.1 × Table 1.2 logic.
Table 1.2

The major families of deterioration reactions

  • Non-enzymic browning (Maillard): baked & IM foods
  • Enzymic browning: cut fruits & vegetables
  • Oxidation: lipid off-flavors, vitamin loss, pigment fading
  • Hydrolysis: lipids, proteins, carbohydrates, pigments
  • Metal interactions: anthocyanin complexing, Mg loss from chlorophyll, catalysis
  • Lipid isomerization / cyclization / polymerization: frying-oil decay
  • Protein denaturation: egg-white coagulation, enzyme inactivation
  • Protein cross-linking: nutritive loss in alkali processing
  • Polysaccharide synthesis & degradation: post-harvest plants
  • Glycolytic changes: post-mortem animal / post-harvest plant tissue
Key: carbonyl compounds (from lipid oxidation & carbohydrate degradation) are the hub of many deteriorations — driving browning, off-flavors and nutrient loss.
1.3.1 Real situations

What controls the rate? Temperature, pH, water activity

Deterioration is a chain: primary → secondary events → attribute change.

Arrhenius: k = A·e−ΔE/RT — rate climbs exponentially with temperature.
  • Temperature T: broadest effect (deviates near freezing).
  • pH: small shifts can change quality a lot.
  • Water activity a_w: most reactions slow as a_w drops — lipid oxidation is the exception.

Schematic: relative rate vs water activity a_w (classic food stability map). Lipid oxidation rises at low a_w.

🎮 MINIGAME · MCQ#4
Most deterioration slows as a_w drops — but one accelerates at low a_w. Which?
✔ Correct: lipid oxidation. At very low a_w the protective role of water (diluting radicals, hydrating metal catalysts) is lost, so oxidation speeds up; other reactions slow as a_w drops, while browning peaks at intermediate a_w (~0.6–0.7).
Table 1.4

Factors that govern stability

Product factors

  • Chemical properties of constituents (incl. catalysts)
  • Oxygen content
  • pH
  • Water activity a_w
  • Glass-transition T_g & water content W_g

Environmental factors

  • Temperature T, time t
  • Atmosphere (O₂, humidity)
  • Chemical/physical/biological treatments imposed
  • Light exposure
  • Contamination, physical abuse
1.4 Societal role

The societal role of food chemists

📣

Why engage

High training → high responsibility; if you stay silent, less-qualified voices prevail.

🧪

Counter chemophobia

Use evidence against the 'additives = poison' myth; help the public judge soundly.

🌐

Web credibility

Teach students to weigh sources — peer-reviewed science vs marketing/agenda.

⚖️

Inform debates

GMOs, organic vs conventional, cloned animals — need an objective expert voice.

Methodology

Faced with a food-deterioration problem — where to start?

First observe: which quality attribute changed?
↓
① Visible / tasted

Pin the attribute

Texture? Flavor? Color? (Table 1.1)

② Trace reactions

Find primary events

Which reaction class caused it? (Tables 1.2–1.3)

③ Control conditions

Adjust factors

T, pH, a_w, O₂, light… (Table 1.4)

Understand food, and you can control it

This chapter gave you an analytical map: attribute → reaction → factor. Every later chapter is that same map applied to a different component.

Ch.2
Water & Ice
Ch.3–4
Carbs · Lipids
Ch.5–6
Proteins · Enzymes
Ch.8
Vitamins

Self-check: can I name 5 quality attributes, 5 reaction classes, and the key factors that control them?