脂肪酸(fatty acid)
一种有机化合物，为植物、动物和微生物类脂化合物中的重要成分。一般由一条偶数碳原子的直链组成，整个长链上及其一端都有氢原子，另一端有一个羧基（-COOH），所以是一种羧酸。若分子内的碳－碳键均为单键，则称为饱和脂肪酸。若有双键或三键则称为不饱和脂肪酸，并具有较强的反应性。少数脂肪酸具有支链，也有一些具环状结构（如前列腺素）。脂肪酸在自然界不以游离状态存在，而通常与甘油化合形成甘油三酯。分布最广的脂肪酸是油酸，在某些植物油（如橄榄、棕榈、花生、向日葵籽的油）中含量很高，人类脂肪含近一半油酸。许多动物不能合成某些脂肪酸而需从食物中摄取。
English version：
fatty acid
Organic compound that is an important component of lipids in plants, animals, and microorganisms. Fatty acids are carboxylic acids with a long hydrocarbon chain, usually straight, as the fourth substituent group on the carboxyl (&singlehorzbond;COOH) group (see functional group) that makes the molecule an acid. If the carbon-to-carbon bonds (see bonding) in that chain are all single, the fatty acid is saturated; artificial saturation is called hydrogenation. A fatty acid with one double bond is monounsaturated; one with more is polyunsaturated. These are more reactive chemically. Most unsaturated fats are liquid at room temperature, so food manufacturers hydrogenate them to make them solid (see margarine). A high level of saturated fatty acids in the diet raises blood cholesterol levels. A few fatty acids have branched chains. Others (e.g., prostaglandins) contain ring structures. Fatty acids in nature are always combined, usually with glycerol as triglycerides in fats. Oleic acid (unsaturated, with 18 carbon atoms) is almost half of human fat and is abundant in such oils as olive, palm, and peanut. Most animals, including mammals, cannot synthesize some unsaturated “essential” fatty acids; humans need linoleic, linolenic, and arachidonic acids in their diet.