脂类Lipids脂类Lipids.doc

脂类Lipids What is lipid? Lipids are broadly defined as hydrophobic or amphiphilic organic molecules Approximately 95% of food lipids fall into a group called triacylglycerides (all three glycerol -OH groups are replaced). Other important lipids are phospholipids (e.g. emulsifying agents such as lecithin) and sterols (e.g cholesterol). Lipids can be liquid at room temperature, such as soybean oil, or solid, such as margarine (人造黄油), shortening, lard. Triacylglycerides The nature and properties of lipids are related to the type of fatty acids present. Fatty acids from plants and animals are different - affecting both their physical and chemical properties。 Diacylglycerides DAG Monoacylglycerides MAG Physical Properties of fats Saturated fats Have high proportion of saturated fatty acids such as myristic acid肉豆蔻的 and palmitic acid棕榈酸 Usually are solid at room temperature. Usually are found in animal foods-beef, pork, lamb, milk, cheese; exceptions are coconut and palm oil. Are thought to increase the level of cholesterol in blood. Properties of Fat Polyunsaturated fats Have high proportion of polyunsaturated fatty acids such as linoleic, linolenic acid (from plants)and arachidonic acids (from animals) Usually are liquid at room temperature. Usually come from plants- soy, corn, safflower, exception is fish Are thought to decrease the cholesterol level in blood. Monounsaturated fats Are found in olive oil and peanut oil (oleic is the most common MUFA) Are thought to have a neutral effect on blood cholesterol Fats function in the Body In our body, lipids or fats (fatty acids) have several essential and important functions. Fats Structural element in membranes are essential parts of cell walls and membrane of cell and organs. store and release energy - when metabolized fats release more energy than any other food constituent. i.e. 2.25x more than protein. Immune recognition insulate the body and protect body and organs such as kidneys from damage. are