脂肪-科普123

脂肪

杂烩百科2023-02-02 15:54:02百科

脂肪(fat)

源自动植物的不挥发、不溶於水而油腻的物质。在化学构造上，动物油和植物油（参阅oil）是相同的，主要由甘油三酯（甘油和脂肪酸反应生成的酯）组成，只有在溶点和物理状态（固体或液体）有所不同，全视脂肪酸的饱和情况和碳链的长度而定。甘油酯可能只含有少量脂肪酸，也可能多至一百种（在乳脂肪中）。几乎所有的天然脂肪和油由2碳单位构成，而且仅含碳原子数为偶数的脂肪酸。天然脂肪如玉米油除了甘油三酯之外，还含有少量化合物，其中包括磷脂、植物类固醇、维生素A、维生素E、蜡、类胡萝卜素等，以及许多其他的成分（包括这些东西的分解产物）。在食物中，脂肪来自成熟的种子和水果（玉米、花生、油橄榄和鳄梨），也来自动物的肉、蛋和奶。脂肪的每一单位重量的热量两倍於蛋白质和碳水化合物的。在食物中脂肪的消化（通常部分）是由脂来进行，被分解的产物从肠子进入血液，脂肪即以肉眼看不见的小滴随血液运至使用地点或贮藏地点。脂肪容易因水解而被分解（主要化为丙三醇和脂肪酸），这是应用在许多工业上的第一步骤。

English version：

fat

Any organic compound of plant or animal origin that is not volatile, does not dissolve in water, and is oily or greasy. Chemically, fats from animals and from vegetables (oils) are identical, consisting mainly of triglycerides (esters of glycerol with fatty acids); the differences are in the melting temperature and physical state (solid or liquid) of each, which depends on the saturation of the fatty acids and the length of the carbon chain. The glycerides may have only a few component fatty acids or as many as 100 (in butterfat). Almost all natural fats and oils are constructed from two-carbon units and thus contain only fatty acids with an even number of carbon atoms. Natural fats such as corn oil have small amounts of compounds besides triglycerides, including phospholipids, plant steroids, tocopherols (vitamin E), vitamin A, waxes, carotenoids, and many others, including decomposition products of these. Fats in foods come from ripe seeds and fruits (corn, peanuts, olives, avocados) and from animal sources (meat, eggs, milk). They contain more than twice as much energy (calories) per unit of weight as proteins and carbohydrates. Digestion of fats in foods, often partial, is done by enzymes called lipases. The breakdown products are absorbed from the intestines into the blood, which carries microscopic fat droplets reconstituted from digested fats or synthesized in cells to sites of storage or use. Fats are readily broken down, primarily into glycerol and fatty acids, by hydrolysis, a first step for many of their numerous industrial uses. See also lipid.