Lactase

Lactase () is an enzyme produced by many organisms. It is located in the brush border of the small intestine of humans and other mammals. It is essential to the complete digestion of whole milk; it breaks down lactose, a sugar which gives milk its sweetness. People who have deficiency of lactase, and consume dairy products, may experience the symptoms of lactose intolerance. Lactase can be purchased as a food supplement, and is added to milk to produce "lactose-free" milk products. Lactase is an enzyme that some people are unable to produce in their small intestine. Technology to produce lactose-free milk, ice cream, and yogurt was developed by the USDA Agricultural Research Service in 1985. This technology is used to add lactase to milk, thereby hydrolyzing the lactose naturally found in milk, leaving it slightly sweet but digestible by everyone. Without lactase, lactose intolerant people pass the lactose undigested to the colon where bacteria break it down, creating carbon dioxide and that leads to bloating and flatulence. Lactase supplements are sometimes used to treat lactose intolerance. Lactase produced commercially can be extracted both from yeasts such as Kluyveromyces fragilis and Kluyveromyces lactis and from molds, such as Aspergillus niger and Aspergillus oryzae. Its primary commercial use, in supplements and products such as those from Lacteeze and Lactaid, is to break down lactose in milk to make it suitable for people with lactose intolerance. The U.S. Food and Drug Administration has not independently evaluated these products. Lactase (or a similar form of β-galactosidase) is also used to screen for blue white colonies in the multiple cloning sites of various plasmid vectors in Escherichia coli or other bacteria. The optimum temperature for human lactase is about 37 °C and the optimum pH is 6. In metabolism, the β-glycosidic bond in D-lactose is hydrolyzed to form D-galactose and D-glucose, which can be absorbed through the intestinal walls and into the bloodstream.