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  • Imagine if you felt ill every time you drank milk. People who are lactose intolerant have exactly this problem, and biotechnology is finding ways to help them.

    Lactose is milk sugar

    Lactose is a sugar that occurs naturally in milk and milk products. It’s a disaccharide – a large sugar made up of two smaller sugar units, called glucose and galactose.

    When you drink milk, lactose is broken down in your gut by an enzyme called lactase, and your body absorbs the smaller sugar units.

    Lactose intolerance

    Lactose intolerance is an inability to digest milk and milk products, and it is caused by a lack of the lactase enzyme. Without this enzyme, lactose is not broken down and stays in the gut, where it becomes food for gut bacteria.

    Recent estimates state that 65% of the world’s population are unable to digest the milk sugar lactose. If you can digest milk, this is due to a genetic mutation in your DNA that first arose 12,000–10,000 years ago.

    Symptoms of lactose intolerance

    Lactose intolerance can cause nausea, stomach cramps, bloating and/or diarrhoea. The amount of milk that causes this reaction can vary from person to person.

    Lactose intolerance is much milder than a milk allergy. Even small amounts of milk can be life-threatening for someone with a milk allergy.

    Treating lactose intolerance

    People who are lactose intolerant can avoid dairy products or reduce the amount of dairy products they eat. They could also use milk substitutes, like soy milk or rice milk or buy lactose-free milk.

    Biotechnology solutions to lactose intolerance

    There are several biotechnology solutions available for people with lactose intolerance:

    • Dairy products with less lactose: Adding bacteria to milk during processing can reduce the amount of lactose in the end products. For example, yoghurts and cheeses like blue vein, Parmesan and Edam only have small amounts of lactose due to the action of bacteria.
    • Making lactose-free milk: You can buy lactase in order to make your own lactose-free milk. Pretreating milk with lactase enzyme breaks down the lactose into glucose and galactose. After 24 hours in the fridge, the lactose content of milk will be reduced by about 70%. The lactase enzyme is obtained from a type of yeast called Kluyveromyces. Yeast lactase works at a neutral pH (6.5–7), so once it reaches the acid conditions of your stomach, it no longer breaks down lactose.
    • Buying lactose-free milk: Lactose-free and lactose-reduced milk, cream, ice cream and yoghurt are available in New Zealand supermarkets. Pretreatment with lactase is used to make these products. Lactose-free products are often sweeter and are smoother because they contain the single unit sugars glucose and galactose, which are more soluble.
    • Boosting your lactase: Lactase enzymes are available in tablet form for people to take before they eat dairy products. The enzyme is extracted from Aspergillus fungi. The enzyme, called β-galactosidase, has a similar action to human lactase. This enzyme works in acidic conditions in the stomach (pH 3–6), so it’s taken before eating. Lactase tablets are available in New Zealand.

    Related content

    Find out more about genes and lactose intolerance and a genetic test for lactose intolerance.

    Activity idea

    Lactose intolerance – investigate the effect of the digestive enzyme lactase on a sugar found in milk called lactose. The digestive system condition known as lactose intolerance will also be looked at.

      Published 3 September 2009 Referencing Hub articles
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