1 of 52© boardworks ltd 2006. 2 of 52© boardworks ltd 2006

1 of 52 © Boardworks Ltd 2006


What is in food?

How can chemistry be used to understand food and cooking?


How is cooking chemistry?

The reactions that take place when food is cooked make it easier to digest.

Cooking is a type of chemistry. During cooking, irreversible chemical reactions occur and new products are formed.

Other chemical reactions can spoil food and make it unsafe to eat.

are exposed to the air.

Cooking also kills microbes that can be found in food.

Apples react with oxygen and turn brown when they


What molecules are foods made of?

There are three main types of food molecules.

Proteins are chains of different amino acids.

Fats are made up of lipids. A lipid has a structure of three fatty acid molecules and a glycerol molecule.

Carbohydrates are chains of repeating molecules of glucose and other sugars.

Food also contains vitamins and minerals, which areneeded in small amounts for a healthy body.


Why do eggs look different cooked?

Changing the shape of the protein also changes its properties. The protein becomes easier to digest and more useful to the cells of the human body.

Eggs are a protein food and so are made up of amino acid chains.

When eggs are cooked they become firmer. This is because cooking eggs changes the shape of the amino acid chains. This is called denaturing.

Meat is also made up of amino acids and reacts to cooking in a similar way.


What happens when dried pasta is cooked?

Pasta is made up of starch granules. When it is cooked in boiling water, the starch granules absorb water and the pasta becomes soft and edible. It is now rehydrated.

Freshly-made pasta contains water, which can make it go off, and so it must be eaten soon after it is made.

Milk, fruit, vegetables, meat, soups and sauces can all be dehydrated tostop them from spoiling.

To preserve pasta, the water content is removed by leaving it in a hot environment. It becomes dehydrated.


preservatives and antioxidants

emulsifiers and stabilizers

What are additives?

Traditionally, herbs and spices have been added to food to improve its flavour.

Lemon juice (citric acid), salt and vinegar have also been used to help food last longer.

Today, a wide range of natural and artificial ingredients are used in small quantities to enhance or preserve food. These are called additives. The main groups of additives are: flavourings

colourings.


Types of additives


Types of additives – activity


What is an emulsion?

Oils and water are insoluble in each other and do not naturally mix. These liquids are immiscible.

Milk, salad dressings and paint are all examples of emulsions.

Fine droplets of oil become dispersed through out the water, This give the emulsion a thick and creamy texture.

Salad dressings often have to be shaken before use because the ingredients have separated.

Adding oil to water in a particular way forms an emulsion.

What could be used to prevent the ingredients separating?


Making an emulsion


What stops emulsions from separating?

Emulsifiers have a hydrophilic (‘water loving’) part and a hydrophobic (‘water hating’) part.

Mayonnaise is an emulsion. Unlike salad dressings it does not separate when it is left to stand. Why is this?

Mayonnaise is made using egg yolk. This contain lecithin, which is a natural emulsifier.

Natural and artificial emulsifiers are used to stop oil and water separating in emulsions.

water

oil

emulsifier


Uses of additives


Using additives


What are E-numbers?

Food labels often contain E-numbers. Nearly all additives, including natural products like citric acid, have E-numbers.

However, not everyone agrees that these additives are safe. Some additives with E-numbers that are used in the UK are banned in other countries. For example, the food colouring E104 (quinoline yellow) is banned in Australia and the USA.

E-numbers are often blamed for health problems, including hyperactivity in children, but what exactly are they?

The ‘E’ stands for ‘European Community’. To be given an E-number, additives are tested to make sure they meet safety requirements set by the European Community.


What goes into food?

natural – from nature

natural identical – chemically the same as products from nature but made in a laboratory

artificial – man-made and not found in nature.

Many food companies claim to have no artificial additives, but what exactly do they mean?

Additives can be classified into one of three groups:

Food labelled as containing no artificial additives may contain synthetically produced natural identical additives.

Some additives that are banned in the UK are used abroad. How can food be tested to make sure it does not containthese additives?


Using chromatography


What are plant oils?

First the plant material is crushed to make a paste. The paste is then pressed to remove water and other impurities. Oils obtained in this way are often labelled “virgin” or “cold pressed”.

Oils can be made by crushing the seeds, beans and nuts of some plants, including olives and sunflowers.

Plant oils are types of fat and can provide the body with energy. They are also good sources of vitamins.

Distillation and chemical processes can also be used to make plant oils. Oils obtained in this way are often labelled “refined”.


Using plant oils


Chemistry of fats and oils


What are the differences between fats?

Saturated fats contain no carbon-to-carbon double bonds. The straight fatty acids chains pack closely together.

Unsaturated fats contain at least one carbon-to-carbon double bond. This bends the fatty acid chains and they cannot pack closely together.

Saturated fats are less healthy than unsaturated fats because the dense packing makes them harder for the body to digest.


Testing for double bonds


How is margarine made?

Some of the carbon-to-carbon double bonds in the plant oils are broken and extra hydrogen atoms are added. This hardens the oil to make it a solid at room temperature.

Margarine was originally made using buttermilk, a waste product from making butter.

Most modern margarines are made from plant oils. The oil is heated and hydrogen is pumped through it. This is called hydrogenation.

Nickel is used as a catalyst for this reaction. It is filtered out before the margarine is packaged and sold.

Not all the carbon-to-carbon double bonds are broken. This means that margarines still contain unsaturated fats. The oil is partially hydrogenated.


The history of margarine


What are trans fats?

Trans fats can be formed by the partial hydrogenation of plant oils.

Partially hydrogenated oils were used to make margarine. Today, most margarines are made using other methods and contain less trans fat.

However, partially hydrogenated plant oils are commonly used in food products, such as biscuits and ready meals.

Trans fats are a type of fat that the body finds difficult to break down. These molecules can block the arteries of the heart.

Medical organisations in the UK have campaigned to get trans fats clearly labelled on food. Some supermarkets are now removing trans fats from their own-brand foods.


Some research has shown that EFAs can help lower blood pressure and decrease the risk of blood clots.

What are essential fatty acids?

Essential fatty acids (EFAs) can be found in plant oils. They are needed by the body but it cannot produce them.

There are two main types of EFAs: omega-3 – found in flax seeds (linseed),

pumpkin seeds, walnuts and oily fish

omega-6 – found in corn, sunflower and soya oil

It is easy to get enough omega-6 because corn and soya oil are often added to processed food.

However, most people eat fewer foods containing omega-3.


Plant oils activity


How do you make bread?

Although bread comes in many forms it is made from three main ingredients: water, grains and leavener (also called raising agents).

Leaveners are used to make bread and cakes rise. Baking powder and yeast are commonly used raising agents.

More than 12 billion sandwiches are eaten in the UK each year.

Bread is a basic food used all over the world.

99% of households in the UK eat bread.

About 9 million large loaves of bread are sold in the UK a day.


How does baking powder make cakes rise?

Baking powder contains sodium hydrogencarbonate. When this is heated during cooking it breaks down into sodium carbonate, carbon dioxide and water.

This is a thermal decomposition reaction. Other hydrogencarbonates and carbonates react to heat in this way.

It is the carbon dioxide gas that makes cakes rise.

heatsodium

hydrogencarbonatesodium

carbonatecarbon dioxide water+ +

2NaHCO3 Na2CO3 CO2 H2O+ +


What makes bread rise?

Yeast is a type of fungus used to make bread rise. Bread is usually made from wheat flour. As yeast digests the carbohydrates in flour it produces carbon dioxide.

Making bread from yeast is an aerobic reaction, which means it needs oxygen. Once the yeast has been added, the uncooked dough is left to rise.

Cooked bread has a spongy texture. Small holes can be seen when bread is sliced. These were formed by carbon dioxide.


How is alcohol made?

Adding yeast to sugars under anaerobic (without oxygen) conditions produces alcohol and carbon dioxide. This is called fermentation.

Alcoholic drinks have been made for thousands of years.

yeastsugar

solution alcoholcarbon dioxide+

C6H12O6 2C2H5OH 2CO2 +

Wine and cider are made from fruit.

Beer and spirits are made from cereals.


Health and social issues of alcohol


Is food naturally safe?

Some types of mushrooms, like the death cap, contain poisonous chemicals. Even when cooked they can be deadly. It can be dangerous to pick and eat mushrooms growing in the wild.

Humans cannot digest the starch found in the cell walls of potatoes. Cooking changes the structure of the starch molecules, making it possible to digest.

Food can naturally contain harmful chemicals and microbes. Some of these can be killed by cooking but some cannot.

Nuts contain a chemical that can trigger an allergic reaction in some people. The chemical is not destroyed by cooking.


Can cooking food make it harmful?

Acrylamide causes cancer in animals, so this discovery was very worrying.

In 2002, scientists found high levels of acrylamide in cooked starchy foods.

Cooking starchy foods at high temperatures can cause arclyamide to form.

Further research suggested that the levels of acrylamide in an average diet would not increase the risk of cancer. This is

Studies have found high levels of acrylamide in chips, crisps, breakfast cereals and crisp breads.

a controversial topic and research is ongoing.


How else can food become unsafe?

Artificial additives are synthetically made and are not based on natural ingredients. They have been linked to hyperactivity, skin problems and asthma.

Microbes and fungus can form on food when it is stored. Mould on nuts can produce cancer-causing aflatoxins.

Barbecues can be a high-risk area for food poisoning. Food can appear crispy and brown on the outside but that does not mean it is cooked properly. It is always best to check the middle of the food before eating it.


Wheel of Misfortune: food risk game


What are food chains?

The food chain is a series of steps that takes food from the environment to our plates.

When most people lived in the countryside, growing and making their own food, the food chain was very simple.

meat from several farms.

additives from a laboratory

Today, the food chain is more complicated.

vegetables from around the world

Travelling from the factory where it was made to the shop adds yet another step to the chain.

For example, a typical ready meal might contain:


How do we know if food is safe?

The Food Standards Agency (FSA) is a UK independent government department, set up by Parliament in 2000.

It aims to:

improve food law

decrease illness from food

make food labelling clearer

encourage healthy eating

raise industry standards.

There are local, national and European laws to help prevent harmful food entering the food chain.


How can food risks be studied?

Most research works by controlling all the factors in the experiment. Is it possible to control the diet of a human?

It many take many years for side effects to show in humans. How long should new ingredients be tested for?

It can be hard for scientist to prove or disprove that there is a risk of consuming a food. Can you think of any problems of testing ingredients on humans?

Recent studies have suggested that combinations of additives might cause health problems. Should scientists

Genetics means that some people are more likely to react to substances than others. On how many people should an ingredient be tested before it is declared safe?

test foods as a whole or the individual chemicals?


Food safety


True or false activity


Glossary (1/3)

additive – A natural or artificial substance added in small quantities to enhance or preserve food.

antioxidant – An additive that stops the chemicals in food reacting with oxygen spoiling.

artificial – An additive that is man-made and not found in nature.

colouring – An additive used to make food more colourful and visually appealing.

denature – A change in the physical shape of proteins.emulsifier – Additive used to stop the ingredients in an

emulsion separating. E-number – A code number for an additive that has met

the European Community safety standards.


Glossary (2/3)

essential fatty acid – A type of fat that is required by the body but that it cannot produce.

fermentation – The conversion of sugar to alcohol and carbon dioxide by yeast in the absence of oxygen.

flavouring – An additive used to improve the taste of food.monounsaturated – Fats containing one carbon to

carbon double bond. Usually liquid at room temperature. natural identical – An additive that is chemically the

same as a product from nature but made in a laboratory. plant oil – An oil that can be produced from the nuts,

seeds or beans of a plant. polyunsaturated – Fats containing two or more carbon-

to-carbon double bonds. Usually a liquid at room temperature.


Glossary (3/3)

preservative – An additive used to keep food edible for longer.

saturated – Fats containing no carbon-to-carbon double bonds. They are usually solid at room temperature.

sodium hydrocarbonate – Compound used in baking to make cakes rise.

stabilizer – An additive used to maintain the texture of food.

thermal decomposition – The breakdown of a compound into two or more simpler products by heating.

trans fat – A type of fat produced during the manufacture of margarine that cannot be broken down by the body.

yeast – A fungus used in baking bread and brewing alcohol.


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Multiple-choice quiz