tailieunhanh - The Encyclopedia Of Nutrition And Good Health - L

Bách khoa toàn thư - Dinh dưỡng và sức khỏe tốt - Vần L | L label See FOOD LABELING. labile Refers to the chemical alteration of molecules often leading to the loss of biological function. Cells are composed of a huge array of molecules ranging from ultra-stable very simple minerals like sodium chloride to complex molecules assembled from carbon atoms organic compounds . Very large molecules macromolecules such as proteins and nucleic acids like DNA and RNA are among the most complex organic molecules in the body. Macromolecules are hundreds to many thousands of times larger than simple sugar molecules. Such huge molecules tend to be fragile They are easily altered with heat cooking or by acidic or alkaline conditions. Certain nutrients are labile as well Dissolved vitamin c is readily oxidized by air while excessive cooking destroys the B complex vitamins thiamin and folic acid. Baking dough at high temperatures can destroy the essential amino acid lysine in wheat protein. Polyunsaturated fatty acids major constituents of fats and oils are readily oxidized when exposed to air light and heat fat rancidity decomposition is the culmination of this process. internal processes can destroy biomolecules as well. Certain hormone-like derivatives of essential FATTY ACIDS PROSTAGLANDINS and LEUKOTRIENES are exceedingly labile and break down in a matter of seconds. The chemical currency of the cells atp survives only minutes in cells before being broken down hydrolyzed . See also free radicals. lactalbumin The major protein of whey which is the soluble protein fraction remaining after milk has curdled. Untreated cow s milk contains 20 percent lactalbumin and 80 percent casein. Lactalbu min occurs in two forms alpha-lactalbumin and beta-lactalbumin. Alpha-lactalbumin is a constituent of lactose synthetase the enzyme that synthesizes lactose milk sugar . In a milk allergy the immune system recognizes as foreign a milk protein such as lactalbumin. it will mount an allergic response when exposed to this food constituent. See also .