Lactases

Lactases are enzymes that catalyze the hydrolysis of lactose, the disaccharide sugar found in milk, into its constituent monosaccharides, glucose and galactose. In humans and other mammals, lactase activity is primarily associated with lactase-phlorizin hydrolase (LPH), a membrane-bound enzyme expressed on the brush-border membrane of enterocytes in the small intestine. The enzyme acts on lactose during digestion, enabling absorption of the resulting sugars.

In humans, lactase expression is developmentally regulated. Most mammals show a decline in lactase production after weaning. A notable minority, due to genetic variants in regulatory regions of the LCT gene, retain high lactase expression into adulthood, a trait known as lactase persistence. The geographic distribution of lactase persistence varies widely and has been shaped by historical patterns of dairy consumption.

Lactase deficiency leads to lactose intolerance when undigested lactose reaches the colon, where it can cause bloating, diarrhea, and abdominal pain. Diagnosis can involve hydrogen breath testing or genetic testing. Management includes reduced lactose intake or use of lactase enzyme supplements; some individuals tolerate certain dairy products as lactose content is low or well metabolized.

Industrially, microbial lactases are widely produced for commercial use. Enzymes derived from yeasts or molds (for example, Kluyveromyces spp. or Aspergillus spp.) are employed to manufacture lactose-free dairy products and to convert lactose to glucose and galactose, improving digestibility and sweetness. Lactase enzymes also find applications in dairy processing and the production of prebiotic sugars.