Lactose is naturally present in milk and the amount of lactose varies between dairy products. For example, yoghurt and buttermilk contain less lactose than milk and hard cheeses contain hardly any lactose. Lactose can also be present in small amounts in products in which milk, milk powder or certain components of milk have been processed, such as chocolate products, coffee creamers and cake.
Lactose in milk and milk products
Lactose or milk sugar is a disaccharide which consists of a glucose molecule and a galactose molecule. Lactose is only found in milk from mammals (1). Mother’s milk contains on average 7.0 g lactose per 100 g; cow’s milk contains an average of 4.7 g lactose per 100 g (2). Fermented cow’s milk products contain less lactose than milk as a result of the addition of bacteria strains which split lactose into glucose and galactose during the preparation process (1). Yoghurt contains between 4 – 4.7g lactose per 100 g and the amount varies between semi-skimmed and full-fat yoghurt. Hard cheeses such as cheddar and gouda contain hardly any lactose. (2) During the cheese-making process most of the lactose is removed during the process of washing and separating the curd. The remaining lactose is broken down by lactic acid bacteria during the maturing process. Hard cheeses, which have matured for at least 4 weeks, contain less than 0.1% lactose.
Characteristics of lactose
Lactose differs from other carbohydrates in three main ways:
- Lactose is less cariogenic (causing caries) than other carbohydrates such as sucrose and glucose. A reason for this may be that the production of acids from lactose is a relatively slow process (1) and milk as a whole is not acidic (pH = 6.6) and can therefore neutralise acidity in the mouth.
- Lactose has a lower glycemic index than glucose because lactose is not always fully digested in the small intestine. Galactose (produced from the breakdown of lactose into glucose and galactose) contributes to the rise in blood sugar level only after it has been converted into glucose in the liver. These characteristics of lactose result in blood sugar levels rising less quickly than with glucose and sucrose. (1)
- The sweetness of lactose is about one third lower than that of sucrose. For this reason lactose is used as the carbohydrate in infant formula milks. (1)
- Schaafsma, G. (2008). Lactose and lactose derivatives as bioactive ingredients in human nutrition. International Dairy Journal, 2008, Vol. 18: 458-465.
- McCance and Widdowson’s The Composition of Foods, Seventh summary edition. Cambridge: Royal Society of Chemistry.