Lactase (or β-galactosidase) is the enzyme involved in the hydrolysis of lactose to galactose and glucose. Lactase produced commercially can be extracted from yeast fungi such as Kluyveromyces fragilis. Its primary commercial use is to break down lactose in milk to make it suitable for people with lactose intolerance. Lactase is also used in the manufacture of ice cream. Because glucose and galactose are sweeter than lactose, lactase produces a more pleasant taste. Lactose also crystallises at the low temperatures of ice cream; however, its constituent products stay liquid and contribute to a smoother texture. Lactase is used in the conversion of whey into syrup and is also used as a sweetener in many products. Lactose is what is known as a compound sugar, because it is made by joining two simpler sugars: glucose and galactose. Glucose is the body's most important chemical, the energy source for every molecular activity. Most of what we eat is turned into glucose. That's the whole function of digestion. (Even the galactose is swiftly converted into more glucose.)
Lactase is the enzyme in the small intestine that digests lactose (the naturally occurring sugar in milk). Although milk is called "nature’s most perfect food," my many, it contains in its unaltered or unfermented state a substance which is indigestible by most people. Lactose is the natural sweetener in milk. Lactose requires the presence of lactase, an enzyme produced in the small intestine, in order to be reduced to the usable form of sugar, glucose. In the absence of lactase, "sweet" milk may, though it doesn’t always, precipitate symptoms of digestive tract distress, cramps, flatulence, and/or diarrhea. A few children and many people after childhood do not produce sufficient lactase, resulting in impaired ability to digest milk. These people are lactose intolerant and often suffer from symptoms including cramps, gas, and diarrhea.
Lactase has an optimum temperature of about 48 °C for its activity and an optimum pH of 6.5.
The molecular basis of human lactase persistence/non persistence polymorphism is being investigated. Lactase is a small intestinal enzyme which hydrolyses lactose, the main carbohydrate in milk. In many humans lactase activity declines after weaning whilst in others lactase persists into adulthood. This difference is genetically determined. Lactase persistence, as this is called, allows satisfactory digestion of significant quantities of fresh milk and is common in Northern Europeans and certain African and Arabian normadic tribes. Lactase non-persistence, in which lactase is not present in adults, is responsible for adult-type hypolactasia, a condition which results in diarrhoea, flatulence and meteorism when significant quantities of fresh milk are drunk.
Lactose is present at concentrations of about 4.7% (w/v) in milk and the whey (supernatant) left after the coagulation stage of cheese-making. Its presence in milk makes it unsuitable for the majority of the world's adult population, particularly in those areas which have traditionally not had a dairy industry. Real lactose tolerance is confined mainly to peoples whose origins lie in Northern Europe or the Indian subcontinent and is due to 'lactase persistence'; the young of all mammals clearly are able to digest milk but in most cases this ability reduces after weaning. Of the Thai, Chinese and Black American populations, 97%, 90% and 73% respectively, are reported to be lactose intolerant, whereas 84% and 96% of the US White and Swedish populations, respectively, are tolerant. Additionally, and only very rarely some individuals suffer from inborn metabolic lactose intolerance or lactase deficiency, both of which may be noticed at birth. The need for low-lactose milk is particularly important in food-aid programmes as severe tissue dehydration, diarrhoea and even death may result from feeding lactose containing milk to lactose-intolerant children and adults suffering from protein-calorie malnutrition. In all these cases, hydrolysis of the lactose to glucose and galactose would prevent the (severe) digestive problems. Lactases are now used in the production of ice cream and sweetened flavoured and condensed milks. When added to milk or liquid whey (2000 U kg-1) and left for about a day at 5°C about 50% of the lactose is hydrolysed, giving a sweeter product which will not crystallise if condensed or frozen. This method enables otherwise-wasted whey to replace some or all of the skim milk powder used in traditional ice cream recipes. It also improves the 'scoopability' and creaminess of the product. Smaller amounts of lactase may be added to long-life sterilised milk to produce a relatively inexpensive lactose-reduced product (e.g. 20 U kg-1, 20°C, 1 month of storage). Generally, however, lactase usage has not reached its full potential, as present enzymes are relatively expensive and can only be used at low temperatures.
Deficiency of intestinal beta galactosidase activity causing intolerance to milk-containing foods which presents clinically as abdominal cramps, diarrhoea and bloating. Diagnosis today is made by a positive lactose H2 breath test but if contrast studies are done, the addition of lactose to the barium produces barium dilution, bowel dilatation and rapid transit.