WATER

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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

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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
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THE EFFECTS OF HYDROGEN BONDS OF WATER
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• 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

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EFFECTS OF DIELECTRIC CONSTANTS ON SOLUBILITY
Dissolving of ions by high di-electric constants
of water   F Q1 x Q2 / DR2
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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
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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. Multila
yer Water - additional layer of water around food
particle. Not as hard to remove as the
monolayer. Mobile or Free Water - consisted
with ideal solution.
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REACTION RATES IN FOOD AS A FUNCTION OF WATER
ACTIVITY
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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)
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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.

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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. Availa
bility and cost of equipment.
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DRYING METHODS DRY THE FOODS UNDER THE SPECIFIC
CONDITIONS
Types of Oven, Temperature, Time. Advantages Si
mple, Relatively rapid, Analysis of large
number of samples at a time. DisadvantagesLo
ss of other organic compounds or gases formed
by thermal decomposition of organic compounds.
Oxidation of oil. Error Source Crust
formation from sugar.
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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.
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DISTILLATION METHOD
Cold
Solvent Toluene
Condenser
Cold water
Refluxing Water
Separation Method
Graduated Trap
Samples Solvent
Heating Mantle
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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.
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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
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KARL FISHER METHOD
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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
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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
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Nuclear Magnetic Resonance Spectrometer
Sample
Relative Detector Response
Detector
R-F
Transmitter
20
40
0
60
100
80
Moisture by Oven Method
Receiver Coil
Transmitter Coil