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Lactase (EC 3.2.1.108) is an enzyme produced by many organisms and is essential to the complete digestion of whole milk. It breaks down the sugar lactose into its component parts, galactose and glucose. Lactase is found in the brush border of the small intestine of humans and other mammals.
The lactose operon (lac operon) is an operon required for the transport and metabolism of lactose in E. coli and many other enteric bacteria.Although glucose is the preferred carbon source for most enteric bacteria, the lac operon allows for the effective digestion of lactose when glucose is not available through the activity of β-galactosidase. [1]
The correlation between lactase persistence frequencies and latitude in 33 populations in Europe was found to be positive and significant, while the correlation between lactase persistence and longitude was not, suggesting that high levels of lactose assimilation were indeed useful in areas of low sunlight in northern Europe. [50]
Lactose is a disaccharide composite of two simple sugars, glucose and galactose. Bovine milk averages 4.8% anhydrous lactose, which amounts to about 50% of the total solids of skimmed milk. Levels of lactose are dependent upon the type of milk as other carbohydrates can be present at higher concentrations than lactose in milks. [90]
Many adult humans lack the lactase enzyme, which has the same function as β-galactosidase, so they are not able to properly digest dairy products. β-Galactose is used in such dairy products as yogurt, sour cream, and some cheeses which are treated with the enzyme to break down any lactose before human consumption. In recent years, β ...
When lactose intolerance is due to secondary lactase deficiency, treatment of the underlying disease may allow lactase activity to return to normal levels. [6] In people with celiac disease, lactose intolerance normally reverts or improves several months after starting a gluten-free diet , but temporary dietary restriction of lactose may be needed.
The capability to produce lactic acid is one of the reasons why L. lactis is one of the most important microorganisms in the dairy industry. [5] Based on its history in food fermentation, L. lactis has generally recognized as safe (GRAS) status, [6] [7] with few case reports of it being an opportunistic pathogen. [8] [9] [10]
Lactose is not added directly to many foods, because its solubility is less than that of other sugars commonly used in food. Infant formula is a notable exception, where the addition of lactose is necessary to match the composition of human milk. [citation needed] Lactose is not fermented by most yeast during brewing, which may be used to ...