《食品化学与分析 Food Chemistry and Analysis》课程PPT教学课件（英文版）Water

WATER Water Functions Important component of food. 1. Universal solvent (salt, vitamins, sugar, gases, pigment) 2. Capable of ionizing (H3O+ , OH- ) 3. Affects the texture 4. Chemical reactions (hydrolysis of protein = n amino acids) 5. Stabilizing the colloids by hydration 6. Necessary for micro-organisms growth

WATER Water Functions Important component of food. 1. Universal solvent (salt, vitamins, sugar, gases, pigment) 2. Capable of ionizing (H3O+ , OH- ) 3. Affects the texture 4. Chemical reactions (hydrolysis of protein = n amino acids) 5. Stabilizing the colloids by hydration 6. Necessary for micro-organisms growth

Hydrogen Bond The bond is formed due to the affinity of electro-positive hydrogen atoms for electro-negative atoms such as O. Binding energy of hydrogen bond is about 10% of covalent bond. H-bond strength = 10 Kcal/mol. H + d O - d H + d H + d H + d H + d O - d O - d H + d H + d H + d O - d

Hydrogen Bond The bond is formed due to the affinity of electro-positive hydrogen atoms for electro-negative atoms such as O. Binding energy of hydrogen bond is about 10% of covalent bond. H-bond strength = 10 Kcal/mol. H + d O - d H + d H + d H + d H + d O - d O - d H + d H + d H + d O - d

THE EFFECTS OF HYDROGEN BONDS OF WATER H2S 34 -86 -16 H2O 18 0 100 Compounds MW MP(C) BP(C) CH4 16 -184 -164

THE EFFECTS OF HYDROGEN BONDS OF WATER H2S 34 -86 -16 H2O 18 0 100 Compounds MW MP(C) BP(C) CH4 16 -184 -164

Water is a good dissolving solvent - Why? 1. Physical action of dispersion of solute molecule due to the high￾activity of water molecules at the surface of the solute. 2. The high di-electric constant of water (80x that of vacuum) diminishes the effectiveness of attractive forces that tend to hold the solute molecules together. 3. Hydration of the solute by a chemical complex such as the "hydrogen bond

Water is a good dissolving solvent - Why? 1. Physical action of dispersion of solute molecule due to the high￾activity of water molecules at the surface of the solute. 2. The high di-electric constant of water (80x that of vacuum) diminishes the effectiveness of attractive forces that tend to hold the solute molecules together. 3. Hydration of the solute by a chemical complex such as the "hydrogen bond

H +d H+d H+d H +d O -d O -d O -d H +d H +d O -d H+d H+d O -d H +d H +d H +d H +d O -d H+d H+d O -d H+d H+d O -d Dissolving of ions by high di-electric constants of water F = Q1 x Q2 / DR2 EFFECTS OF DIELECTRIC CONSTANTS ON SOLUBILITY

H +d H+d H+d H +d O -d O -d O -d H +d H +d O -d H+d H+d O -d H +d H +d H +d H +d O -d H+d H+d O -d H+d H+d O -d Dissolving of ions by high di-electric constants of water F = Q1 x Q2 / DR2 EFFECTS OF DIELECTRIC CONSTANTS ON SOLUBILITY

DIELECTRIC CONSTANT The Capacity of Condenser of a Material D= The Capacity of Condenser of Vacuum Condition The forces of electrostatic attraction tending to recombine charges of opposite sign are given by Coulomb's Law. F = Q1 x Q2 / DR2 where: Q1 , Q2 are magnitude of charges R= Distance between charges D = Dielectric constant of the medium separating charges

DIELECTRIC CONSTANT The Capacity of Condenser of a Material D= The Capacity of Condenser of Vacuum Condition The forces of electrostatic attraction tending to recombine charges of opposite sign are given by Coulomb's Law. F = Q1 x Q2 / DR2 where: Q1 , Q2 are magnitude of charges R= Distance between charges D = Dielectric constant of the medium separating charges

KINDS OF WATER - DEGREE OF WATER BINDNESS Monolayer Water is bound in food - restricted in its movement due to charges, hydrogen bond, physical entrapment. Hard to remove from food. Never be able to remove water completely. Multilayer Water - additional layer of water around food particle. Not as hard to remove as the monolayer. Mobile or Free Water - consisted with ideal solution

KINDS OF WATER - DEGREE OF WATER BINDNESS Monolayer Water is bound in food - restricted in its movement due to charges, hydrogen bond, physical entrapment. Hard to remove from food. Never be able to remove water completely. Multilayer Water - additional layer of water around food particle. Not as hard to remove as the monolayer. Mobile or Free Water - consisted with ideal solution

REACTION RATES IN FOOD AS A FUNCTION OF WATER ACTIVITY

REACTION RATES IN FOOD AS A FUNCTION OF WATER ACTIVITY

MOISTURE ANALYSIS WHY DO WE NEED MOISTURE ANALYSIS? 1. Material balance 2. Meeting the standards of product 3. Product stability (prevent deterioration, mold, bacteria, insect damage) 4. Express the composition on Dry Weight Basis 5. Economic importance (H2O is cheap)

MOISTURE ANALYSIS WHY DO WE NEED MOISTURE ANALYSIS? 1. Material balance 2. Meeting the standards of product 3. Product stability (prevent deterioration, mold, bacteria, insect damage) 4. Express the composition on Dry Weight Basis 5. Economic importance (H2O is cheap)

WATER DETERMINATION METHODS 1. Drying methods 2. Distillation method 3. Chemical methods 4. Spectrometry methods As a general rule in all analyses, choose the fastest simple convenient method which will give results within the desired range of accuracy - savings on time, labor costs, will quickly cover capital expenditure

WATER DETERMINATION METHODS 1. Drying methods 2. Distillation method 3. Chemical methods 4. Spectrometry methods As a general rule in all analyses, choose the fastest simple convenient method which will give results within the desired range of accuracy - savings on time, labor costs, will quickly cover capital expenditure