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 lactoseintolerant.
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
Symptoms of lactose-intolerance
abdominal pain
abdominal bloating
(The undigested lactose passes into the large intestine, where
native bacterial populations start to digest it, producing gas as a
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 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.
Pectinase is used to
produce and clarify
fruit juices.
Enzymes are used
in brewing to
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
• 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

Lactose intolerance - Kent Science Resource Centre