Food Chemistry

Food chemistry is the study of the substances that make up food and the chemical changes that occur when food is grown, stored, processed, cooked, digested, and used by the body.

Foods contain thousands of different chemical compounds. Many are organic compounds based on carbon.

Important groups include:

• carbohydrates — sugars, starches and fibre
• lipids — fats and oils
• proteins
• vitamins
• organic acids
• pigments
• flavour and aroma compounds

Food also contains important inorganic substances, especially:

• water
• minerals
• salts

Understanding food chemistry helps explain why bread browns, eggs become firm when heated, oil does not mix with water, fruit changes colour after cutting, and foods provide different nutrients.

Food Is Made of Chemicals

Everything we eat is made from chemicals.

An apple, for example, contains:

• water
• sugars
• fibre
• organic acids
• vitamins
• minerals
• pigments
• flavour compounds
• proteins
• small amounts of lipids

The word chemical does not mean artificial or dangerous.

Glucose is a chemical.

Water is a chemical.

Vitamin C is a chemical.

Proteins are chemicals.

Food chemistry examines these substances scientifically.

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Organic Chemistry and Food

Organic chemistry is particularly important because many nutrients are carbon compounds.

Functional groups studied in organic chemistry appear throughout food molecules.

For example:

–OH groups occur extensively in sugars.

–COOH occurs in fatty acids, amino acids and many food acids.

–NH₂ occurs in amino acids.

–COO– ester linkages occur in fats and oils.

C=C bonds occur in unsaturated fatty acids.

Therefore, the organic chemistry studied earlier helps explain the chemistry of food.

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The Major Nutrients

Four particularly important groups of organic compounds in nutrition are:

These nutrients have very different molecular structures.

Their structures help determine how they behave during:

• cooking
• digestion
• storage
• metabolism

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Carbohydrates in Food

Carbohydrates contain mainly:

carbon, hydrogen and oxygen

Important dietary carbohydrates include:

• glucose
• fructose
• sucrose
• lactose
• starch
• dietary fibre

Carbohydrates are abundant in foods such as:

• bread
• rice
• pasta
• potatoes
• cereals
• fruit
• vegetables
• sugar

Sugars

Simple sugars include:

glucose

fructose

Glucose and fructose have the same molecular formula:

C₆H₁₂O₆

but different structures.

This demonstrates an important principle:

same molecular formula does not necessarily mean same molecular structure

Different structures can produce different chemical and physical properties.

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Sucrose

Common table sugar is:

sucrose

Sucrose is a disaccharide formed from two monosaccharides:

glucose + fructose

During digestion, sucrose can be hydrolysed into its smaller sugar components.

Sucrose occurs naturally in plants and is particularly abundant in:

• sugar cane
• sugar beet

It is also added to many manufactured foods.

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Starch

Starch is a polysaccharide made from many glucose units.

Plants use starch for:

energy storage

Foods rich in starch include:

• potatoes
• rice
• wheat
• corn
• bread
• pasta

During digestion:

starch → smaller carbohydrates → glucose

Enzymes help catalyse these reactions.

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Dietary Fibre

Dietary fibre includes carbohydrate materials that human digestive enzymes cannot completely break down.

An important example is:

cellulose

Cellulose occurs in plant cell walls.

Although humans cannot digest cellulose into glucose efficiently, fibre contributes to healthy digestive function.

This demonstrates that:

not every carbohydrate has the same nutritional role.

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Carbohydrates and Energy

Glucose can be used during cellular respiration.

A simplified equation is:

glucose + oxygen → carbon dioxide + water + energy

Symbolically:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

Some of this released energy is transferred into ATP.

Therefore:

food → glucose → cellular respiration → usable cellular energy

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Lipids in Food

Lipids include:

• fats
• oils
• phospholipids
• sterol-related molecules

Dietary lipids occur in foods such as:

• oils
• butter
• nuts
• seeds
• avocados
• dairy products
• eggs
• meat
• oily fish

Lipids are particularly important as a concentrated source of stored chemical energy.

Triglycerides

Many dietary fats and oils consist mainly of:

triglycerides

A triglyceride is constructed from:

one glycerol + three fatty acids

The molecules are connected through:

ester linkages

This directly connects food chemistry with our previous study of esters.

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Fatty Acids

Fatty acids contain:

• a long hydrocarbon chain
• a carboxyl group, –COOH

They can be:

saturated

or:

unsaturated

A saturated fatty acid contains no carbon-carbon double bonds in its carbon chain.

An unsaturated fatty acid contains one or more:

C=C

bonds.

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Saturated and Unsaturated Fats

Saturated fatty acid chains can often pack together relatively closely.

Many fats rich in saturated fatty acids are therefore solid or semi-solid at room temperature.

Many naturally occurring unsaturated fatty acids contain cis C=C bonds, which introduce bends or "kinks" into their chains.

These bends make close packing more difficult.

Many oils rich in unsaturated fatty acids are therefore liquid at room temperature.

The pattern is not absolute, but it demonstrates:

molecular structure → intermolecular interactions → physical properties

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Why Oil and Water Separate

Water is:

polar

The long hydrocarbon regions of many lipid molecules are:

non-polar

Polar water molecules interact strongly with one another, while non-polar lipid molecules do not interact favourably with water.

Therefore:

oil and water separate

This can be summarized by the useful idea:

"like dissolves like."

Polar substances tend to interact well with other polar substances.

Non-polar substances tend to interact well with other non-polar substances.

Emulsions

Although oil and water normally separate, they can sometimes be mixed into an:

emulsion

An emulsion is a mixture in which droplets of one liquid are dispersed through another liquid.

Examples include:

• mayonnaise
• salad dressings
• cream
• some sauces

An emulsifier helps stabilize the mixture.

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Lecithin and Mayonnaise

Egg yolk contains molecules including lecithin, a mixture rich in phospholipids that can act as emulsifiers.

These molecules contain regions that interact differently with water and lipids.

They help stabilize tiny oil droplets throughout the water-containing mixture.

This is why egg yolk is useful when making mayonnaise.

Food chemistry explains what appears to be a simple cooking technique.

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Proteins in Food

Proteins are constructed from:

amino acids

Dietary protein is found in foods such as:

• meat
• fish
• eggs
• milk
• cheese
• beans
• lentils
• soy
• nuts
• seeds

Proteins contain mainly:

C, H, O and N

and some also contain:

S

Amino Acids and Proteins

A typical amino acid contains:

–NH₂

and:

–COOH

Amino acids join through:

peptide bonds

to form polypeptide chains.

These chains fold into specific three-dimensional shapes.

Therefore:

amino acids → polypeptides → proteins

The shape of a protein strongly influences its properties.

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What Happens When an Egg Is Cooked?

Raw egg white contains proteins dissolved and dispersed in water.

When heated, protein molecules gain energy.

Some interactions maintaining their folded structures are disrupted.

The proteins unfold.

This is called:

denaturation

The unfolded protein molecules can then interact with one another and form a network.

The transparent egg white becomes:

opaque and firm

This is a chemical and structural transformation of the proteins.

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Protein Denaturation

Proteins can be denatured by conditions such as:

• heat
• extreme pH
• some chemicals
• mechanical treatment in certain systems

Denaturation changes the protein's three-dimensional structure.

Importantly:

denaturation does not normally mean that all peptide bonds have been broken.

The amino-acid sequence usually remains largely intact while the protein's folding changes.

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Cooking Meat

Heating meat causes several chemical and physical changes.

Proteins:

• denature
• change shape
• interact differently
• may lose water

Connective tissue can also change during prolonged cooking.

At the surface, sufficiently high temperatures can produce browning reactions that create new flavours and aromas.

Cooking is therefore a combination of:

heat transfer + physical changes + chemical reactions

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The Maillard Reaction

One of the most important reactions in cooking is the:

Maillard reaction

It involves reactions between certain:

amino compounds and reducing sugars

during heating.

It contributes to the colour and flavour of foods such as:

• toasted bread
• roasted coffee
• grilled meat
• baked cookies
• roasted potatoes

Why Browning Creates New Flavours

The Maillard reaction is not one single simple reaction.

It involves a complex series of reactions producing many new molecules.

Some contribute:

• brown colour
• roasted aromas
• nutty flavours
• savoury flavours

This is why:

bread and toast

do not taste identical.

Heating has produced new compounds.

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Caramelization

Caramelization is another type of food browning.

It involves chemical changes in:

sugars

when they are strongly heated.

Caramelization can produce:

• brown colours
• characteristic aromas
• new flavours

It occurs in foods such as:

• caramel
• heated sugar
• some baked goods

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Maillard Reaction vs. Caramelization

These processes are related to browning but are not the same.

Maillard Reaction

Typically involves:

reducing sugars + amino compounds

Caramelization

Primarily involves:

sugars

Therefore, not all food browning should simply be called caramelization.

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Starch Gelatinization

When starch is heated in water, starch granules can absorb water and swell.

This process is called:

gelatinization

The mixture becomes thicker.

This occurs when preparing foods such as:

• sauces
• gravy
• custard-like starch mixtures
• some soups

This is another example of molecular changes producing visible changes in food texture.

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Why Pasta and Rice Change When Cooked

Rice and pasta contain large amounts of starch.

During cooking:

• water enters the food
• starch granules absorb water
• heating changes starch organization
• the texture softens

Protein changes can also contribute, especially in wheat-based foods.

Cooking therefore changes both:

molecular structure and macroscopic texture.

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Baking Bread

Bread-making involves several areas of chemistry.

Yeast can ferment sugars.

A simplified reaction is:

glucose → ethanol + carbon dioxide

The carbon dioxide forms bubbles that help dough rise.

During baking:

• gases expand
• proteins change structure
• starch gelatinizes
• water evaporates
• crust browning occurs
• new flavour compounds form

A loaf of bread is essentially a complex chemistry experiment.

Fermentation

Microorganisms can perform chemical reactions that transform food.

Yeast can convert sugars into:

ethanol + carbon dioxide

Other microorganisms can produce organic acids.

Fermentation is important in foods including:

• bread
• yogurt
• cheese
• fermented vegetables

Different microorganisms and conditions produce different chemical products.

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Acids in Food

Foods contain many organic acids.

Examples include:

citric acid — common in citrus fruits

acetic acid — characteristic acid in vinegar

lactic acid — associated with fermented dairy and other fermented foods

malic acid — found in many fruits

tartaric acid — found naturally in grapes and some other fruits

These acids contribute to:

• taste
• pH
• preservation
• chemical reactions during processing

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Vitamin C

Vitamin C, or ascorbic acid, is an organic compound important in human nutrition.

It is found in foods including:

• citrus fruits
• peppers
• berries
• broccoli
• kiwi fruit

Vitamin C is water-soluble.

The body requires it for processes including collagen synthesis and normal physiological function.

Vitamins

Vitamins are organic compounds required in relatively small quantities for normal biological functions.

They do not all have the same chemical structure or function.

Some are:

water-soluble

while others are:

fat-soluble

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Water-Soluble Vitamins

The major water-soluble vitamin groups are:

• vitamin C
• B vitamins

Their molecular structures allow substantial interaction with water.

Because of their water solubility, some can be lost into cooking water.

Their stability also varies, and heat, oxygen, light, and storage conditions can affect some vitamins.

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Fat-Soluble Vitamins

The main fat-soluble vitamins are:

A, D, E and K

Their structures contain substantial non-polar regions.

They are absorbed and transported in association with dietary lipids.

This provides another example of:

molecular structure → solubility → biological behaviour

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Minerals Are Not Vitamins

A common mistake is to call minerals vitamins.

Minerals such as:

• calcium
• iron
• magnesium
• potassium
• zinc

are:

inorganic nutrients

Vitamins are:

organic compounds

Both are important, but they are chemically different.

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Food Processing

Food processing includes physical and chemical treatments used to prepare, preserve, modify, or package food.

Examples include:

• heating
• freezing
• drying
• fermentation
• pasteurization
• milling
• mixing
• emulsification

Processing can improve:

• safety
• storage life
• texture
• flavour
• convenience

It can also change nutrient composition.

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Food Preservation

Food can spoil because of:

• microbial growth
• enzyme activity
• oxidation
• chemical reactions

Preservation methods attempt to slow or prevent these processes.

Examples include:

refrigeration — slows many reactions and microbial growth

freezing — greatly slows many biological and chemical processes

drying — reduces available water

acidification — lowers pH

heating — can destroy many microorganisms and deactivate enzymes

packaging — can reduce exposure to oxygen, moisture or microorganisms

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Oxidation in Food

Food molecules can react with oxygen.

This can produce unwanted changes.

For example, oxidation can contribute to:

• rancidity in fats
• pigment changes
• flavour changes
• nutrient loss

Antioxidants can slow some oxidation processes.

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Why Cut Fruit Turns Brown

When some fruits are cut, cells are damaged.

Enzymes and other compounds that were previously separated can come into contact with oxygen.

This can lead to:

enzymatic browning

Apples, bananas, pears, and avocados can show this effect.

Acidic conditions, lower temperatures, or reduced oxygen exposure can slow browning in some foods.

Rancidity

Fats and oils can undergo chemical changes during storage.

Oxidation of lipids can produce compounds with undesirable:

• smells
• flavours

This deterioration is associated with:

rancidity

Factors that can accelerate lipid oxidation include:

• oxygen
• light
• heat
• some metal ions

This is why storage conditions matter.

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Antioxidants

An antioxidant is a substance that can help slow certain oxidation processes.

Antioxidants are used naturally or as food additives to help protect:

• flavours
• colours
• nutrients
• fats and oils

Some vitamins can also participate in antioxidant chemistry.

However, the term "antioxidant" does not automatically mean that consuming very large amounts of a substance provides additional health benefits.

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Food Additives

A food additive is a substance added for a technological purpose.

Examples include:

• preservatives
• antioxidants
• colours
• flavourings
• emulsifiers
• stabilizers
• thickeners
• acidity regulators
• sweeteners

Additives have different chemical structures and functions.

Their presence does not automatically mean a food is unsafe.

Food safety depends on the identity, amount, exposure, and evidence concerning the substance.

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Reading an Ingredient List

Ingredient lists can provide useful chemical information.

Suppose a product lists:

wheat flour, sugar, vegetable oil, milk powder, citric acid, lecithin, flavouring

Organic chemistry can help interpret these ingredients.

Sugar → carbohydrate

Vegetable oil → mainly lipids

Milk powder → contains proteins, carbohydrates and lipids

Citric acid → organic acid

Lecithin → phospholipid-rich emulsifier

Flavouring → may contain various organic compounds

An ingredient list therefore contains considerable chemical information.

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Ingredient Order

In many food-labelling systems, ingredients are listed according to their amount by mass, generally from greatest to least at the time of manufacture, although exact labelling rules vary by jurisdiction.

Therefore, ingredients near the beginning usually make up a larger proportion of the product than ingredients near the end.

This can help consumers interpret what a food contains.

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Nutrition Information

Nutrition labels commonly provide information about:

• energy
• protein
• carbohydrates
• sugars
• fat
• saturated fat
• sodium

Depending on the jurisdiction, they may also list:

• fibre
• vitamins
• minerals
• other nutrients

When comparing foods, it is important to check whether values refer to:

per serving

or:

per 100 g / 100 mL

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"Sugar" Is Not One Chemical

The term sugar can refer to several carbohydrates.

Examples include:

• glucose
• fructose
• sucrose
• lactose
• maltose

These molecules have different structures.

Therefore, a food label containing terms such as glucose syrup, fructose, sucrose, or lactose is describing different carbohydrate ingredients.

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"Fat" Is Also Chemically Diverse

Dietary fat is not one single molecule.

Food lipids can contain many different fatty acids.

The proportions of:

• saturated fatty acids
• monounsaturated fatty acids
• polyunsaturated fatty acids

vary among foods.

Therefore, two foods with the same total amount of fat can have different lipid compositions.

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Food Chemistry and Nutrition

Chemistry helps us understand nutrition, but nutrition cannot usually be reduced to a single molecule.

Health effects depend on factors such as:

• overall dietary pattern
• quantities consumed
• nutrient balance
• energy intake
• individual biological needs
• preparation methods

For example, glucose is essential to metabolism, but this does not mean unlimited intake of added sugars is desirable.

Similarly, lipids perform essential biological functions, but different types and amounts matter.

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Energy Density

Different nutrients provide different amounts of energy.

Approximately:

carbohydrate: 4 kcal/g

protein: 4 kcal/g

fat: 9 kcal/g

This explains why fat is a particularly concentrated energy source.

It also explains why organisms can store substantial energy in relatively small masses of lipid.

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Protein and Nutrition

Dietary proteins provide amino acids.

The body can use these amino acids to produce:

• enzymes
• structural proteins
• transport proteins
• antibodies
• receptors
• many other molecules

Some amino acids must be obtained in sufficient quantities from the diet.

These are called:

essential amino acids

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Food Chemistry and Digestion

Digestion involves chemical reactions that break large molecules into smaller molecules.

Carbohydrates

polysaccharides → smaller sugars → monosaccharides

Proteins

proteins → peptides → amino acids

Lipids

Many dietary lipids are broken into smaller components that can be absorbed and processed.

Many digestive reactions involve:

hydrolysis

Water participates in breaking chemical bonds.

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Enzymes in Digestion

Digestive enzymes act as biological catalysts.

Examples include:

amylases — act on starch

proteases — act on proteins

lipases — act on lipids

Enzymes speed up chemical reactions without being permanently consumed.

Their specific three-dimensional structures allow them to interact with particular substrates.

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Cooking and Digestibility

Cooking can change the digestibility of some foods.

For example:

• starch gelatinization can make starch more accessible to digestive enzymes
• protein denaturation can make some protein structures more accessible
• plant cell structures can soften

However, excessive processing or heating can also reduce levels of some heat-sensitive nutrients.

Cooking therefore produces both useful and sometimes undesirable chemical changes.

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Structure → Properties → Food Function

Food chemistry repeatedly demonstrates the relationship:

STRUCTURE → PROPERTIES → FUNCTION

Glucose

Many –OH groups
→ polar
→ water-soluble
→ easily transported in aqueous biological fluids

Triglycerides

Large hydrocarbon-rich structures
→ largely hydrophobic
→ concentrated energy storage

Proteins

Specific amino-acid sequences
→ specific three-dimensional shapes
→ specific biological functions

Phospholipids

Hydrophilic region + hydrophobic region
→ self-assembly in water
→ cell membranes and useful emulsifying behaviour

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Worked Example: Breakfast Chemistry

Consider a breakfast containing:

• toast
• egg
• butter
• orange

Toast

Contains substantial:

carbohydrate

Browning can involve:

Maillard reactions

Egg

Contains significant:

protein and lipid

Heating causes:

protein denaturation

Butter

Contains substantial:

lipid

particularly triglycerides.

Orange

Contains:

• water
• sugars
• organic acids
• fibre
• vitamin C

A simple breakfast therefore contains a wide variety of organic chemistry.

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Worked Example: Mayonnaise

Why can mayonnaise contain both oil and water without immediately separating?

It is an:

emulsion

Egg yolk provides emulsifying substances such as phospholipids.

Their molecular structures contain regions that can interact with:

• water
• lipids

This helps stabilize dispersed oil droplets.

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Worked Example: Apple Browning

An apple is cut and left exposed to air.

Observation:

the cut surface becomes brown

Why?

Cutting damages cells and allows enzymes and substrates to interact in the presence of oxygen.

This produces:

enzymatic browning

Cooling, acidic conditions, or reducing oxygen exposure can slow the process.

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Worked Example: Egg White

Raw egg white is heated.

Observation:

clear liquid → opaque solid

Why?

Heat causes proteins to:

denature and form new interactions

The proteins form a network that changes the texture and appearance.

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Worked Example: Nutrition Label

A food provides per serving:

Carbohydrate: 25 g

Protein: 6 g

Fat: 10 g

Approximate energy contribution:

Carbohydrate:

25 × 4 = 100 kcal

Protein:

6 × 4 = 24 kcal

Fat:

10 × 9 = 90 kcal

Approximate total:

100 + 24 + 90 = 214 kcal

This is an approximation because real food labels and energy calculations can involve additional factors.

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Common Mistakes

Thinking "Chemical" Means Dangerous

All food consists of chemicals.

Thinking Organic Means Healthy

In chemistry, organic describes carbon-based chemistry. It does not automatically mean nutritious or healthy.

Thinking All Carbohydrates Are the Same

Glucose, sucrose, starch, glycogen and cellulose have different structures and functions.

Thinking All Fats Are Identical

Food lipids contain different fatty acids and molecular compositions.

Thinking Oil Contains No Fat

Oil is largely lipid and is nutritionally classified as fat.

Thinking Proteins Are Only Important for Muscles

Proteins also form enzymes, antibodies, receptors, transport proteins and many cellular structures.

Thinking Vitamins Provide Large Amounts of Energy

Vitamins support biological processes but are not major energy-providing nutrients like carbohydrates and fats.

Confusing Vitamins and Minerals

Vitamins are organic compounds.

Minerals are inorganic nutrients.

Thinking Browning Is Always Burning

Browning can involve reactions such as the Maillard reaction, caramelization, or enzymatic browning.

Confusing Maillard Browning with Caramelization

Maillard reactions involve amino compounds and reducing sugars.

Caramelization primarily involves sugars.

Thinking Cooking Only Produces Physical Changes

Cooking can produce both physical and chemical changes.

Thinking Denaturation Breaks Proteins Completely into Amino Acids

Denaturation mainly changes protein folding.

Thinking Oil and Water Separate Because Oil Is Heavier

Their separation is primarily related to differences in polarity and intermolecular interactions; density determines which layer sits above the other.

Assuming Every Food Additive Is Harmful

Food additives have different purposes and safety profiles. Their effects depend on the particular substance and exposure.

Judging a Food from One Nutrient

Overall nutrition depends on the complete diet and quantities consumed.

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Key Terms

Food chemistry — The study of the chemical composition, properties and transformations of foods.

Nutrient — A substance required or used by the body for energy, growth, repair or regulation.

Carbohydrate — A class of organic compounds including sugars, starches and fibre.

Monosaccharide — A simple sugar such as glucose or fructose.

Disaccharide — A carbohydrate composed of two monosaccharide units.

Polysaccharide — A carbohydrate composed of many linked monosaccharide units.

Glucose — An important monosaccharide used in cellular respiration.

Fructose — A monosaccharide found naturally in many foods.

Sucrose — A disaccharide composed of glucose and fructose.

Starch — A glucose-storage polysaccharide in plants.

Cellulose — A structural polysaccharide in plant cell walls and an important component of dietary fibre.

Dietary fibre — Food components, largely from plants, that resist digestion by human digestive enzymes.

Lipid — A diverse group of largely hydrophobic organic compounds including fats and oils.

Triglyceride — A lipid formed from glycerol and three fatty acids.

Fatty acid — An organic molecule containing a hydrocarbon chain and carboxyl group.

Saturated fatty acid — A fatty acid containing no C=C bonds in its hydrocarbon chain.

Unsaturated fatty acid — A fatty acid containing one or more C=C bonds.

Protein — A biological macromolecule composed of amino-acid residues.

Amino acid — A building block of proteins containing amino and carboxyl functional groups.

Peptide bond — The linkage connecting amino-acid residues in proteins.

Vitamin — An organic compound required in relatively small quantities for normal physiological function.

Mineral — An inorganic nutrient required by the body.

Denaturation — A change in a protein's three-dimensional structure.

Maillard reaction — A complex set of browning reactions involving reducing sugars and amino compounds during heating.

Caramelization — Chemical transformations of sugars caused by strong heating.

Gelatinization — Changes occurring when starch granules absorb water and swell during heating.

Fermentation — Chemical transformation of substances by microorganisms or their enzymes.

Emulsion — A mixture in which droplets of one liquid are dispersed through another immiscible liquid.

Emulsifier — A substance that helps stabilize an emulsion.

Lecithin — A mixture rich in phospholipids commonly used for emulsifying properties.

Oxidation — A chemical process involving loss of electrons or an increase in oxidation state, often involving oxygen in food deterioration.

Rancidity — Deterioration of fats or oils producing undesirable flavours or odours.

Antioxidant — A substance capable of slowing certain oxidation processes.

Food additive — A substance added to food for a technological purpose.

Preservative — A substance or process used to help slow food deterioration.

Enzymatic browning — Enzyme-catalysed browning that can occur when cut plant tissues are exposed to oxygen.

Hydrolysis — A chemical reaction in which water participates in breaking a bond.

Enzyme — A biological catalyst.

Energy density — The amount of energy provided per unit mass of food.

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Key Takeaways

• Food chemistry studies the substances in foods and how they change.
• Foods contain both organic and inorganic substances.
• Major organic nutrients include carbohydrates, lipids, proteins and vitamins.
• Water and minerals are important inorganic components of food.
• Carbohydrates contain mainly carbon, hydrogen and oxygen.
• Sugars, starch and fibre are carbohydrates.
• Glucose is an important source of energy for cellular respiration.
• Starch is a plant energy-storage polysaccharide.
• Cellulose contributes to dietary fibre.
• Lipids include fats and oils.
• Triglycerides contain glycerol and three fatty acids.
• Triglycerides contain ester linkages.
• Saturated fatty acids contain no C=C bonds in their carbon chains.
• Unsaturated fatty acids contain one or more C=C bonds.
• Molecular structure influences whether fats are solid or liquid.
• Lipids are largely hydrophobic.
• Oil and water separate because of differences in polarity and intermolecular interactions.
• Emulsifiers can help stabilize mixtures of oil and water.
• Proteins are made from amino acids.
• Heating can cause protein denaturation.
• Cooking an egg is a familiar example of protein denaturation.
• The Maillard reaction contributes to browning and flavour development.
• Maillard chemistry involves amino compounds and reducing sugars.
• Caramelization involves chemical changes in sugars.
• Starch gelatinization contributes to thickening and texture changes.
• Fermentation uses microorganisms to transform food chemicals.
• Vitamins are organic compounds needed in relatively small quantities.
• Vitamins B and C are water-soluble.
• Vitamins A, D, E and K are fat-soluble.
• Minerals are not vitamins.
• Food processing can improve safety, storage, flavour and texture.
• Oxidation can contribute to food deterioration.
• Lipid oxidation can contribute to rancidity.
• Enzymatic browning occurs in many cut fruits.
• Antioxidants can slow some oxidation processes.
• Ingredient lists contain useful chemical information.
• Food additives perform specific technological functions.
• Digestion involves chemical reactions including hydrolysis.
• Carbohydrates provide about 4 kcal/g.
• Proteins provide about 4 kcal/g.
• Fats provide about 9 kcal/g.
• Food chemistry helps connect organic chemistry with nutrition, biology and everyday life.

The major relationship throughout this topic is:

MOLECULAR STRUCTURE → CHEMICAL PROPERTIES → FOOD BEHAVIOUR → NUTRITIONAL/BIOLOGICAL FUNCTION

And everyday cooking provides many examples:

egg + heat → protein denaturation

bread + heat → Maillard browning

starch + water + heat → gelatinization

sugar + strong heat → caramelization

oil + water + emulsifier → stable emulsion

Check Your Understanding

1. What is food chemistry?

2. Name four major groups of organic compounds found in foods.

3. Why is carbon important in food chemistry?

4. Give three examples of carbohydrates found in food.

5. What is the molecular formula of glucose?

6. Distinguish between a monosaccharide and a polysaccharide.

7. What is the biological role of starch in plants?

8. Why is cellulose considered dietary fibre for humans?

9. What type of molecules make up most fats and oils?

10. What components form a triglyceride?

11. What type of linkage occurs in triglycerides?

12. Distinguish between saturated and unsaturated fatty acids.

13. Why are many unsaturated oils liquid at room temperature?

14. Why do oil and water normally separate?

15. What is an emulsion?

16. What is the role of an emulsifier?

17. Why can egg yolk help stabilize mayonnaise?

18. What are proteins made from?

19. What happens to many proteins when heated?

20. Explain why egg white becomes firm when cooked.

21. What is the Maillard reaction?

22. How does caramelization differ from the Maillard reaction?

23. What is starch gelatinization?

24. Explain the role of yeast in bread making.

25. Distinguish between water-soluble and fat-soluble vitamins.

26. Why are minerals not classified as vitamins?

27. What is enzymatic browning?

28. What is rancidity?

29. What does an antioxidant do?

30. Challenge: A student prepares a meal containing pasta, grilled chicken, mayonnaise, and sliced apple.

a. Identify the major carbohydrate source.
b. Explain what happens to starch while the pasta cooks.
c. Identify an important biomolecule in the chicken.
d. Explain what happens to chicken proteins during heating.
e. Explain why browning can develop on the surface of the chicken.
f. Name the reaction that contributes to this browning.
g. Identify the two broad types of reactant involved in that reaction.
h. Explain why mayonnaise contains both oil and water without immediately separating.
i. Define an emulsion.
j. Explain the role of an emulsifier.
k. Identify a substance in egg yolk that can help emulsification.
l. Explain why lipid molecules do not normally mix readily with water.
m. Identify the major type of lipid present in many food oils.
n. Describe the basic structure of a triglyceride.
o. Explain the difference between saturated and unsaturated fatty acids.
p. Explain why the cut apple may become brown.
q. Name this type of browning.
r. Suggest one condition that could slow the apple's browning.
s. Explain how organic chemistry helps us understand all four foods.
t. Use one example from the meal to demonstrate:

structure → chemical properties → food behaviour → biological or nutritional function.