Fermentation occurs when the lactose in dairy products breaks down.
Fermentation is the anaerobic, energy-producing decomposition of organic substances by bacteria, yeast, or other microorganisms. Milk sugar, better known as lactose, imparts a characteristic sweetness to dairy products. It is chemically a disaccharide consisting of two chemically joined monosaccharides, glucose and galactose. The fermentation of lactose, depending on the microorganism involved, can produce different products, but the most common among them is lactic acid, a viscous acid with the chemical formula CH 3 CH (OH) COOH. Fermentation can be used to remove lactose from foods, which is beneficial for those who are lactose intolerant; lactose fermentation should not be confused with lactic acid fermentation.
Lactose intolerance is currently very rare among people of central or northern European descent.
The mechanisms of lactose fermentation are less known than one might anticipate. This may be due, in part, to an assumption and theory proposed by the much respected biochemist Emil Fischer, that lactose yeast fermentation begins first with the cleavage of the disaccharide into its substituent sugars; this assumption remained largely unchallenged for decades. There is now evidence that this assumption may not be true. Indeed, in the case of bacterial lactose fermentation in the gut, the mechanistic pathway varies along with the choice of bacteria. Most of these pathway mechanisms are complex and multi-step: see the cited references for more details.
Lactose intolerance means that the small intestine cannot absorb lactose, so it passes into the colon, where it is fermented by bacteria.
Lactose intolerance results from a deficiency of the enzyme lactase, normally found in the duodenum or the first part of the small intestine. As it cannot be absorbed directly by the small intestine, any remaining lactose travels to the colon, where it is fermented by certain bacteria. The result is large amounts of gas, causing painful cramps, bloating and diarrhea for the patient. One way to deal with the difficulty is to eat foods that are naturally low in lactose or from which the lactose has been removed. Another way to deal with this is to add β-galactosidase enzyme supplements to the diet – produced from the Aspergillus fungus.
Health researchers estimate that about 50 million Americans are lactose intolerant.
Milk-based products are rich in lactic acid and casein protein. The fermentation of lactose into lactic acid increases the acidity of the food; the acid combines with the casein, and the two coagulate and precipitate. The precipitate is then removed from the milk and the derived dairy product is low in – or free of – lactose. Alternatively, there are soy, rice, almond and other plant-based, dairy-like food substitutes. Non-dairy foods that contain lactose include processed meats, some sauces, chips and dips. Intolerance is usually not absolute; patients can usually consume at least some lactose, so their diet can include at least some of the lactose-containing foods without the need for supplements.