What is the difference between this milk and ordinary milk? What is lactose? Lactose is a type of sugar found in milk.

Who drinks lactose-free milk? People who are lactose-intolerant. This means they can’t digest lactose! Why not?

Milk digestion The cells lining the small intestine produce an enzyme called lactase Lactase enzyme breaks down lactose into two simpler sugars called glucose and galactose. These are then absorbed into the blood stream. People with lactose-intolerance have a deficiency of this lactase enzyme.

Symptoms of lactose-intolerance abdominal pain abdominal bloating gas diarrhoea nausea (The undigested lactose passes into the large intestine, where native bacterial populations start to digest it, producing gas as a by-product)

Producing lactose-free milk Manufacturers of lactose-free milk simply add the enzyme lactase to the milk. What does this do to the milk? The lactase enzyme breaks down the lactose in the milk into glucose and galactose. These simpler sugars can be absorbed directly into the bloodstream. This milk therefore poses no issues for lactose-intolerant people.

What is immobilised lactase? Firstly – a quick recap on enzymes Write down 5 things you know about enzymes!

Enzymes Enzymes are protein molecules which accelerate the chemical reactions in living cells. Enzymes are specific to one chemical reaction. Enzymes are not used up in chemical reactions and so can be used over and over again. Enzymes are greatly affected by temperature and pH. Enzyme activity increases with temperature, up to a point. Above certain temperatures enzymes are denatured and will no longer work.

The lock and key theory

Enzymes are widely used in industry. Protease enzymes are used in 'biological' washing powders to speed up the breakdown of proteins in stains like blood and egg. Enzymes are used in brewing to increase productivity Pectinase is used to produce and clarify fruit juices.

What are immobilised enzymes? As enzymes are not changed during chemical reactions, it is cost-effective to use them more than once.  However, if the enzymes are in solution with the reactants and/or products it is difficult to separate them.  If the enzyme can be attached to a solid support, they can be used again after the products have been removed The term "immobilized" means unable to move or stationary.  And that is exactly what an immobilized enzyme is:  an enzyme that is physically attached to a solid support over which a substrate is passed and converted to product.

Why use immobilised enzymes? Enzymes can be easily removed from the product and then re-used. Product is not contaminated with the enzyme  (especially useful in the food and pharmaceutical industries) Immobilised enzymes have greater thermal stability. This allows higher temperatures to be used, which increases the rate of reaction. The reaction can be stopped rapidly by removing the enzyme from the reaction solution.

You are now going to investigate the use of immobilised lactase to produce lactose-free milk