Functional and chemical properties of food

Welcome to Food Science!

Ever wondered why an egg turns from clear goo to a solid white? Or why bread turns brown and crunchy in the toaster? That’s not just cooking—it’s science! In this chapter, we are going to look at the functional and chemical properties of food. Basically, we are looking at how ingredients "behave" when we prep and cook them.

Don't worry if some of the scientific words look a bit scary at first. We’ll break them down with simple examples you see in the kitchen every day!

1. Proteins: The Shape-Shifters

Proteins are like long, tangled balls of string. When we cook them or add acid, they change their shape and texture.

Protein Denaturation

Denaturation is when the long protein chains "unravel" and change shape. This happens because of heat (cooking an egg), acid (adding lemon juice to milk), or agitation (whisking an egg white).

Protein Coagulation

Once those protein chains have unraveled, they start to bump into each other and "clump" together. This is called coagulation. The protein traps water between the clumps, changing the food from a liquid to a solid.

Example: Think of a raw egg. It’s runny. When you fry it, the proteins denature (unravel) and then coagulate (clump together) to make the solid white part.

Gluten Formation

Gluten is a protein found in wheat flour. It only forms when you add water and knead (work) the dough.

Memory Aid: Think of gluten like a stretchy net. It gives bread its "chew" and holds in the bubbles of gas so the bread can rise.

Foam Formation

When you whisk egg whites, you are trapping air. The protein denatures and stretches around the air bubbles to create a foam. If you over-whisk it, the protein "net" breaks and the foam collapses!

Quick Review:
• Denaturation: Proteins unravel.
• Coagulation: Proteins clump together (solidify).
• Gluten: The "stretchy net" in bread.
• Foam: Air trapped in a protein structure.

2. Carbohydrates: The Magic of Starch and Sugar

Carbohydrates like flour and sugar react in very specific ways when heated.

Gelatinisation

This is how we thicken sauces! Starch granules (like in flour or cornflour) are put into a liquid and heated.

Step-by-step:
1. At \(60^{\circ}C\), the starch granules start to absorb liquid and swell.
2. At \(80^{\circ}C\), they get so full that they burst, releasing starch into the liquid.
3. At \(100^{\circ}C\) (boiling), the sauce reaches its thickest point. This is called gelatinisation.

Dextrinisation

This happens when dry heat is applied to starchy foods. The starch molecules break down into smaller molecules called dextrins. This makes the food turn brown and taste sweeter.

Example: Toasting a piece of bread is the perfect example of dextrinisation.

Caramelisation

This is specifically for sugar. When sugar is heated, it melts and turns into a brown, syrupy liquid. This adds a sweet, nutty flavor and a dark color.

Top Tip: Be careful! Caramelised sugar goes from "delicious" to "burnt and bitter" very quickly!

Key Takeaway: Gelatinisation thickens, Dextrinisation browns starch, and Caramelisation browns sugar.

3. Fats and Oils: The Texture Makers

Fats don't just add flavor; they change the physical structure of our bakes.

Shortening

When you "rub" fat into flour (like making shortcrust pastry), the fat coats the flour particles. This creates a waterproof barrier that prevents long gluten chains from forming. The result is a short, crumbly texture.

Aeration

When you cream butter and sugar together for a cake, the sugar crystals trap tiny bubbles of air in the fat. This makes the final cake light and fluffy.

Plasticity

This is the ability of a fat to soften and spread. Some fats (like margarine) have high plasticity, meaning they are easy to spread even when cold. This is because they are made of a mix of different triglycerides that melt at different temperatures.

Emulsification

Oil and water don't usually mix—they separate. An emulsion is when we use an emulsifier (like lecithin found in egg yolks) to join them together.

Example: Mayonnaise is an emulsion of oil and vinegar held together by egg yolk.

Did you know? Without emulsifiers, your salad dressing would always have a layer of oil floating on top!

4. Fruit and Vegetables: Enzymes and Air

Enzymic Browning

Have you ever sliced an apple and seen it turn brown? That is enzymic browning. When the fruit is cut, the inside is exposed to oxygen. Enzymes (biological catalysts) in the fruit speed up a reaction with the oxygen that turns the fruit brown.

How to stop it:
• Acid: Squeeze lemon juice on the fruit (the acid stops the enzyme).
• Blanching: Putting veg in boiling water briefly destroys the enzymes.
• Water: Keep sliced potatoes in a bowl of water to keep the air away.

Oxidation

This is when foods lose nutrients (especially Vitamin C) because they are exposed to air. This is why we should cook vegetables quickly in a small amount of water to keep the vitamins inside.

5. Raising Agents: Making it Rise

Raising agents add gas into a mixture to make it light and airy.

Chemical Raising Agents

These produce carbon dioxide (\(CO_2\)) gas when heated.

• Bicarbonate of Soda: Needs moisture and heat. It can leave a "soapy" taste, so it's often used in strong flavors like gingerbread.
• Baking Powder: This is a mix of bicarb (an alkali) and cream of tartar (an acid). It reacts to create gas without the soapy taste.

Mechanical Raising Agents

This is using "elbow grease" or a whisk!
• Whisking: Trapping air in eggs.
• Folding: Gently mixing to keep the air you already trapped inside.
• Sieving: Air is trapped between the flour particles as they fall.

Steam

When a very liquid batter (like Yorkshire puddings or Choux pastry) is put into a very hot oven, the water turns to steam. The steam forces the mixture up, making it rise.

Biological Raising Agents (Yeast)

Yeast is a living organism. It eats sugar and, through fermentation, releases \(CO_2\) gas and alcohol. This is what makes bread dough grow in size (proving).

Common Mistake to Avoid: Don't use boiling water with yeast! It’s a living thing—boiling water will kill it, and your bread won't rise.

Summary Quick-Check

1. Proteins: Denature (unravel) and Coagulate (clump).
2. Starch: Gelatinisation (thickens with liquid/heat).
3. Sugar: Caramelisation (browns/melts).
4. Fats: Shortening (crumbly) and Aeration (fluffy).
5. Raising Agents: Can be Chemical (powder), Mechanical (whisking), Steam, or Biological (yeast).