WATER

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

2. 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. + d H - d + d O H - d + O d H + d + H d H - d - O d O + d + H + d d H H

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

4. Water is a good dissolving solvent - Why? • Physical action of dispersion of solute molecule due to the high-activity of water molecules at the surface of the solute. • 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. • Hydration of the solute by a chemical complex such as the "hydrogen bond“

5. EFFECTS OF DIELECTRIC CONSTANTS ON SOLUBILITY Dissolving of ions by high di-electric constants of water   F = Q1 x Q2 / DR2

6. 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

7. 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.

8. REACTION RATES IN FOOD AS A FUNCTION OF WATER ACTIVITY

9. 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)

10. WATER DETERMINATION METHODS • 1. Drying methods • 2. Distillation method • 3. Chemical methods • 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.

11. CONSIDERATIONS IN SELECTING THE METHODS OF WATER ANALYSIS 1. Form of water present (free vs. bound water) Example: % water in milk vs. non-fat dried milk. 2. Nature of product: Volatile compounds Heat stable - loss of some food compounds Unsaturated fat - oxidation - weight. 3. How fast you can analyze sample. 4. Accuracy and reproducibility. 5. Availability and cost of equipment.

12. DRYING METHODS – DRY THE FOODS UNDER THE SPECIFIC CONDITIONS Types of Oven, Temperature, Time. Advantages: Simple, Relatively rapid, Analysis of large number of samples at a time. Disadvantages:Loss of other organic compounds or gases formed by thermal decomposition of organic compounds. Oxidation of oil. Error Source: Crust formation from sugar.

13. DRYING METHODS 1. Air-oven Method --- put the sample (10g) in flat, tarred dish - specified time and temperature (150C for 1 hr) - measure the loss of water. 2. Vacuum oven Method --- use it if you do not want to expose to high temperature. Use 50 mm Hg and around 100C. Food rich in fructose must be dried at 70C or below. 3. Hot plate Method ---rapid, quality control, use some time, put in vacuum at 100C, cool in desiccators, "Mojonnier". 4. Moisture-balance --- balance in oven with IR light and heat. Measure the moisture loss.

14. DISTILLATION METHOD Cold Solvent Toluene Condenser Cold water Refluxing & Water Separation Method Graduated Trap Samples & Solvent Heating Mantle

15. CHEMICAL METHODS Karl Fisher Method---Standard technique for low moisture foods. Especially good for reducing sugars and protein-rich foods and good for foods with high volatile oils.

16. KARL FISHER METHOD Karl Fisher Reagent: Dissolve 132 g of Iodine + 425 ml of Pyridine + 425 ml of MeOH + 105 g of SO2. Titrate 120 mg of H2O with Carl Fisher Reagent. Calculated Concentration = mg H2O/ml of Reagent = 5 mg/ml of Reagent % H2O = Conc. x ml Reagent / mg of Sample x 100

17. KARL FISHER METHOD

18. PHYSICAL METHODS m. 1. Infrared Method: Absorption Method --- measuring the absorption of OH group at wavelength of 2.8 m. Common Method - 1 ppm (sensitivity) 75 60 45 % IR Transmission at 2.8 30 15 0 20 40 80 60 100 % Moisture by Oven Method

19. NUCLEAR MAGNETIC RESONANCE SPECTROMETER 2. NMR: Measure the hydrogen nuclei   H2 nuclei of water will vibrate (spin-oriental) in a fixed magnetic field and proper radio frequency. Absorption of radio frequency by the hydrogen nucleus. Rapid/Non-destructive/Accurate

20. Nuclear Magnetic Resonance Spectrometer Relative Detector Response Sample Detector R-F Transmitter 0 20 40 60 100 80 % Moisture by Oven Method Receiver Coil Transmitter Coil