食品化学第2章 water 水(partly).ppt

第二章水 chapter2 water 水的结构 Water Structure 水与溶质的相互作用 interrelation between water and Solutions 水分的存在状态 State of water in food 水分活度 Water activity 分子流动性和食品稳定性 Molecular mobility & Food stability Food Chemistry Water is essential About 65% of the adult body is made up of water Lack of water can cause death more quickly than lack of any other nutrient Humans require 7-11 cups per day. One cup is 240 ml. H 2O Food Chemistry Water content of food Food water content (%) Fruits and vegetables 90-99 Fruits juices 80-89 Beef and dairy 10-60 Crackers and cereals 1-9 Food Chemistry some phenomenon about food Free flowing — Agglomerated (结块 Texture Changes Crispy/crunchy — soft Food Chemistry Functions of water Carries nutrients and wastes 营养成分和废物载体 Maintains structure of molecules 生物大分子构象的稳定剂 Participates in chemical reaction 反应剂和反应介质 Acts as a solvent for nutrients 溶剂 As lubricant , plasticizer and cushions 润滑剂、增塑剂和缓冲剂 Maintain blood volume Food Chemistry Water Molecular Structure 水的分子结构 H 2 O, hydrogen bonding between water molecules, covalent boning within the molecule positive charge negative charge Polar molecules Food Chemistry Water Molecular Structure Tetrahedral Structure of Water 水分子是四面体结构 The OH bonds are highly polarized - OH 具有较强的极性 Strong H-bonds (~10% of covalent bond) 可以形成强的氢键(~10% 共价键) Each water molecule can hydrogen bond hydrogen bond to two neighbors allowing the formation of an extensive 3D structure 每个水分子可以与两个相邻水分子形成 3D 结构 Food Chemistry 水的超分子结构 Supramolecular Structure of Water Water is highly hydrogen bonded (only about 15% of H-bonds break on melting ice) The bonds form and break dynamically Strong affinity (吸引力) of water for itself High specific heat (to warm water must break some H-bonds) Water Ice Food Chemistry 液态水的结构不稳定,并不是单纯由氢键形成四面体形状,而是通过“ H- 桥”形成短暂的多边形结构; 水分子的排列是动态的; 水中的氢键可被溶于其中的盐及具有亲水/疏水