DAIRY TECHNOLOGY: MILK COMPOSITION
Diagram
Lactose-free milk and regular milk side by side
Lactose-free milk
Regular milk with the enzyme lactase added: the lactose is already split into glucose and galactose.
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Regular milk
Milk as it comes: its lactose is whole, and the drinker must digest it.
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The core difference
Lactose. Lactose-free milk has its lactose broken down before drinking; regular milk does not.
Figure 1: Lactose-free milk compared with regular milk. Drawn in our own style from Miller, Jarvis and McBean, Handbook of Dairy Foods and Nutrition, 3rd ed., 2006, chapter on lactose digestion.
Introduction
Lactose-free milk and regular milk look and pour the same, and their protein, fat and calcium are the same. The difference is one sugar, already broken down.
The core difference is lactose. Regular milk holds lactose, the milk sugar, which the body must split with its own enzyme, lactase. Lactose-free milk has lactase added in the factory, so the lactose is already split into glucose and galactose before the milk reaches the glass. People who lack lactase can then drink it without discomfort.
Quick comparison
Table 1: Lactose-Free Milk compared with Regular Milk
| Aspect | Lactose-Free Milk | Regular Milk |
|---|---|---|
| Lactose | Nearly zero, already split by added lactase | About 4.5 to 5 percent lactose, whole |
| How it is made | Lactase enzyme added to milk, then held to split the lactose | Milk pasteurized and packed, no enzyme added |
| Taste | Slightly sweeter, glucose and galactose taste sweeter than lactose | Normal milk taste, less sweet |
| Protein | Same as regular milk | Same as lactose-free milk |
| Fat and calcium | Same as regular milk | Same as lactose-free milk |
| Calories | Same as regular milk | Same as lactose-free milk |
| Digestion | Easy for people who lack lactase | Needs the drinker’s own lactase to split the lactose |
| Who it suits | People with lactose intolerance or lactose maldigestion | People who make enough lactase |
| Shelf life | Similar, sometimes a little longer | Standard, days to 2 weeks when cold |
| Price | Higher, the enzyme and extra step add cost | Lower, the standard milk |
Scientific explanation
Definition
Lactose-free milk is milk treated with the enzyme lactase, which splits its lactose into glucose and galactose, so that almost no lactose remains.
Regular milk is milk with its lactose whole, as it comes from the animal, needing the drinker’s own lactase to digest it.
Working principle
Lactase splits lactose by hydrolysis: it adds a water molecule across the lactose and breaks it into two simpler sugars, glucose and galactose.
People with lactose intolerance make too little lactase in the gut, so whole lactose reaches the colon, where bacteria ferment it and make gas and discomfort. Splitting the lactose in advance removes that step, so the milk is digested without trouble.
Apparatus
A tank where lactase is added to the milk and held at the right temperature, plus the normal pasteurizer and filler.
In the laboratory, lactose is measured by an enzymatic test or by chromatography to check that the splitting is complete.
Measurement procedure
Add lactase to the milk, hold it at the set temperature until the lactose is split, then pasteurize or UHT treat the milk and pack it.
The books give no single standard procedure that names this pair, so the steps above are the standard industrial method for making lactose-free milk. Check the result by measuring the lactose left in the milk.
Factors affecting readings
The amount of lactase, the temperature and the holding time decide how completely the lactose is split.
The milk must be handled cleanly: the enzyme step adds time, and any contamination in that time can spoil the milk. Storage temperature decides the shelf life, as for regular milk.
Formulas and calculations
Lactose hydrolysis is a chemical equation, not a calculation: C12H22O11 + H2O gives C6H12O6 + C6H12O6. One molecule of lactose plus one molecule of water gives one molecule of glucose and one molecule of galactose.
Worked example: milk with 5.0 percent lactose holds 50 g of lactose per litre. Splitting it fully gives about 25 g of glucose and 25 g of galactose per litre, because the two sugars have the same weight. The total sugar stays about the same, but the milk tastes sweeter, because glucose and galactose taste sweeter than lactose.
Industrial applications
- Lactose-free milk: drinking milk for people with lactose intolerance.
- Lactose-free milk: tea, coffee and cooking for people who cannot digest lactose.
- Regular milk: drinking milk for people who make enough lactase.
- Regular milk: cheese, yoghurt and cultured products, where lactose feeds the cultures.
- Both: the base for flavoured milks and milk drinks.
Advantages and limitations
- Lactose-free milk advantage: people with lactose intolerance can drink it without discomfort.
- Lactose-free milk limitation: slightly sweeter taste, higher price, and it is not needed by people who digest lactose well.
- Regular milk advantage: normal taste and lower price, and its lactose feeds the cultures in yoghurt and cheese.
- Regular milk limitation: people who lack lactase get gas, bloating and discomfort from its lactose.
FAQ
Is lactose-free milk dairy free?
No. It is real milk with the same protein, fat and calcium. Only the lactose has been split. People with milk protein allergy cannot drink it.
Why does lactose-free milk taste sweeter?
Its lactose is split into glucose and galactose, which taste sweeter than lactose, even though the total sugar is the same.
Can I cook with lactose-free milk?
Yes, in the same way as regular milk. It behaves the same in tea, coffee, sauces and baking.
What is the difference between lactose intolerance and milk allergy?
Lactose intolerance is a lack of the enzyme lactase, so lactose is not digested. Milk allergy is an immune reaction to milk protein, usually casein or whey. Lactose-free milk helps the first, not the second.
Does lactose-free milk have the same calcium?
Yes. The enzyme only splits the lactose. Protein, fat, calcium and vitamins are unchanged.
References and further reading
- Miller, Jarvis and McBean, Handbook of Dairy Foods and Nutrition, 3rd ed., 2006, chapter on lactose digestion (Google Books page read)
- FTN books on disk: Chemistry of Milk, Dairy Chemistry and Biochemistry, Market Milk (agrimoon dairy series).
