food analysis(食品分析)20.ppt

Determination of carbohydrates Contents Introduction Definition Classification Structure of carbohydrates Distribution of carbohydrates in food Function of carbohydrates in food processing Determination of carbohydrates Introduction Definition Chemically, carbohydrates are organic molecules in which carbon, hydrogen and oxygen bond together in the ratio: Cx(H2O)y where x and y are whole numbers that differ depending on the specific carbohydrate to which we are referring 多羟基醛或者酮及其衍生物和缩合物 Carbohydrates are the main energy source for the human body. Carbohydrates are the most abundant class of organic compounds found in living organisms. Classification（从组成上分） Simple Sugars Monosaccharides:不能再被水解的多羟基醛或者酮，是碳水化合物的基本单位。如葡萄糖、果糖、半乳糖等。 Complex Carbohydrates Oligosaccharides ：2～10个单糖分子缩合而成，水解后生成单糖。 如蔗糖、麦芽糖、乳糖等。 Polysaccharides：由许多单糖分子缩合而成，如淀粉、纤维素、果胶等。 Monosaccharides Two of the most common monosaccharides are glucose and fructose. Both glucose and fructose have the same chemical formula (C6H12O6) however they have different structures as seen below Disaccharides have two sugar units bonded together. For example, common table sugar is sucrose a disaccharide that consists of a glucose unit bonded to a fructose unit:? Lactose maltose Complex Carbohydrates Definition polymers of the simple sugars.? long chains of simple sugar units bonded together ，often referred to as polysaccharides).? Several polysaccharides Starch Cellulose pectin amylose Cellulose Characteristic of monosaccharides Fructose can also act as a reducing sugar, even though it has a ketone group instead of an aldehyde group. Under basic conditions, the fructose molecules can, essentially, have the location of the carbonyl bond switched to convert them into a glucose molecule. This occurs in a number of steps involving removing hydrogens from the #1-C and its oxygen and moving them to the #2-C and its oxygen. any mon