Water

1
Water
2
Water Function

• 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

3
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
4
Effects of Hydrogen Bonds of Water
H2S
34
-86
-16
H2O
18
0
100
5

• Water is a good dissolving solvent - Why?
• 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

6
Hydration of Protein


d
H
-

d

d
O
H
-
d

O
d
H

d

H
d
H
-
d
-
O
d
O

d

d

H
d
H
H
7
Effects of Dielectric Constants on Solubility
8
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
9
Kinds of Water-Degree of Water Bond
Monolayer Water -Bound water 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.
10
Reaction Rates in Food As a Function of Water
Activity
11
MOISTURE ANALYSIS
12
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. Economic importance (H2O is cheap)
13
Water Determination Methods

• 1. Drying methods
• 2. Distillation method
• 3. Chemical methods
• Spectrometry methods

14
Considerations in Selecting Water Analysis Methods
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.
15
Drying Method
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.
16
Drying Methods

• Air-oven Method --- put the sample (10g) in flat,
  tarred dish - specified time and temperature
  (150C for 1 hr) - measure the loss of water.
• 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.
• Hot plate Method ---rapid, quality control, use
  some time, put in vacuum at 100C, cool in
  desiccators.
• 4. Moisture-balance --- balance in oven with
  Infra Red light and heat. Measure the moisture
  loss.

17
Distillation Method
Cold
Solvent Toluene
Condenser
Cold water
xx
x
Refluxing Water
x
x
x
xx
xx
x
Separation Method
x
xx
Graduated Trap
x
x
X x X x
xx
xx
x
x
x
Samples Solvent
x
x
x
Heating Mantle
18
Chemical Method
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.
19
Karl Fisher Method
20
Karl Fisher Method
Karl Fisher Reagent Dissolve the Iodine in the
mixture of Pyridine, MeOH and SO2. Titrate 100
mg of H2O with Carl Fisher Reagent. If the 100mg
required of 20ml KF Reagent, what is the
concentration of KF Reagent to titrate the
H2O? Calculated Concentration of K F Reagent
mg H2O / ml of Reagent H2O
Concentration x ml Reagent / mg of Sample x 100
21
Extra Water Formation
H

C
H
O
H


from KARL FISHER reagent

R
C
O
3
Hemiacetal
H
R
C
O
H
O
C
H
O
H


from KARL FISHER reagent


C
H
3
3
H
R
C
O
C
H
Acetal
H
O
3

2
O
C
H
3
22
Karl Fisher Method Exercise

• The water content of one gram dry milk from Kraft
  Co was determined by Karl Fisher method. The
  sample required 10 mL Karl Fisher reagent.
• Can you determine the water content with the
  information provided? If not, what information
  do you need to determine the water content?
• What is the moisture content in of the dry milk
  if 20 mg pure water required 10 mL K. F. reagent
  at the end point?

23
SPECTROSCOPIC METHODS
24
Compounds
H
O
H
O
H
C
H
3
C
H
O
H
C
H
2
3
25
Infrared Spectrum OH group
OH group
26
Infrared Method
Absorption Method --- Measuring the absorption
of OH group at wavelength of 2.8 m. 1 ppm
(sensitivity)
A a 2.8
2.0
m.
1.5
X
1.0
X
X
0.5
0
20
40
80
60
100
Moisture by Oven Method
27
Nuclear Magnetic Resonance Spectrometer
Measure the hydrogen nuclei Hydrogen nuclei of
water will vibrate (spin-orientation) in a fixed
magnetic field and proper radio frequency.
Absorption of radio frequency by the hydrogen
nucleus. Rapid, Non-destructive, Sensitive and
Accurate
28
Nuclear Magnetic Resonance Spectrometer
Sample
Relative Detector Response
R-F
Detector
Transmitter
20
40
0
60
100
80
Receiver Coil
Transmitter Coil
Moisture by Oven Method
29
Compounds
H
O
H
O
H
C
H
3
C
H
O
H
C
H
2
3
30
NMR of CH3OH