华南理工大学：《食品分析》课程PPT教学课件（Food Analysis）Chapter 3 Water Activity

Measurement of water content and water activity

Measurement of water content and water activity

Contents 1.Introduction 2.Structure of water 3.Categories of water in food 4.Water-solute interaction 5.Measurement of water content 6.Water activity 7.Measurement of water activity

Contents 1.Introduction 2. Structure of water 3.Categories of water in food 4. Water-solute interaction 5. Measurement of water content 6. Water activity 7. Measurement of water activity

Introduction

Introduction

We live by the grace of water National Geographic Special Edition,Nov.1993 Water is H2O,hydrogen two parts,oxygen one,but there is also a third thing,that makes it water and nobody knows what it is. D H Lawrence (1885-1930) 'We may ask why all trees and bushes or at least most of them -unfold a flower in a five-sided pattern,with five petals.Some botanist might well examine the sap of plants to see if any difference there corresponds to the shapes of their flowers. Johannes Keplar

We live by the grace of water “ Water is H2O, hydrogen two parts, oxygen one, but there is also a third thing, that makes it water and nobody knows what it is.” D H Lawrence (1885-1930) “We may ask why all trees and bushes – or at least most of them –unfold a flower in a five-sided pattern, with five petals.Some botanist might well examine the sap of plants to see if any difference there corresponds to the shapes of their flowers.” Johannes Keplar National Geographic Special Edition, Nov. 1993

水遁道 细胞膜 离子地道 图！通过细胞壁的分子通道 细胞和外部世界（包括其它细胞）之间的分离壁是远离不渗透壳的。相反， 它是为不同的通道所贯通的。许多这样的通道专门为特殊的离子或分子所使用 而且不允许其它类型的物质通过。图左为水通道，图右是离子通道

图! 通过细胞壁的分子通道 细胞和外部世界（包括其它细胞）之间的分离壁是远离不渗透壳的。相反， 它是为不同的通道所贯通的。许多这样的通道专门为特殊的离子或分子所使用 而且不允许其它类型的物质通过。图左为水通道，图右是离子通道

Natural landscape

Natural landscape

Water vapor Water Ice

Water vapor Water Ice

Water(moisture)is the predominant constituent in many foods Content and distribution of water have great effects on the structure,external appearance, surface,quality,flavor of food,and microbial sensibility on food. Different food have their own water content which can reflect its characteristic.For example,garden stuff,75%-95%;meat,50%- 80%;bread,35%-45%;cereal,10-15%;milk power,4%;

Water(moisture) is the predominant constituent in many foods Content and distribution of water have great effects on the structure, external appearance, surface, quality, flavor of food, and microbial sensibility on food. Different food have their own water content which can reflect its characteristic. For example, garden stuff ,75%-95%; meat, 50%- 80%; bread, 35%-45%；cereal, 10-15%;milk power, 4%;

Structure of water 水和水的结构：Structure of water and ice 化合水： Constitutional water 多层水：Multilayer water 邻近水：Vicinal water 水分活度：Water activity 分子的移动性：Molecular mobility 疏水水合：Hydrophobic hydration 疏水相互作用：Hydrophobic interaction

Structure of water 水和冰的结构：Structure of water and ice 化合水: Constitutional water 多层水: Multilayer water 邻近水: Vicinal water 水分活度: Water activity 分子的移动性：Molecular mobility 疏水水合：Hydrophobic hydration 疏水相互作用：Hydrophobic interaction

Structure H2O 104.5 3 冰中水分子的四面体形排列情况

Structure