Material For food technology students

1. Water soluble interaction
G BHARATHI
Assistant Professor
Department of Food and Dairy Technology

2. Macroscopic Level (Water Binding,
Hydration, and Water Holding Capacity)
 Water binding and hydration - tendency for water to
associate with hydrophilic substances, including cellular
materials.
 Water holding potential or capacity - The degree and tenacity
of water binding or hydration depends on a number of factors
including the nature of the non-aqueous constituent, salt
composition, pH, and temperature.
 The ability of a matrix of molecules, usually macromolecules
present at low concentrations, to physically entrap large
amounts of water in a manner that inhibits exudation.
 Familiar food matrices that entrap water in this way include
gels of pectin and starch, and cells of tissues, both plant and
animal.

3. Water holding potential or
capacity
 Physically entrapped water does not flow from
tissue foods even when they are cut or minced.
 Acts as pure water during food processing
 Examples: water in tissues and gels can be
categorized as physically entrapped.
 impairment of the entrapment capability of foods
has a profound effect on food quality.
 Examples of quality defects arising from
impairment of water holding capacity are syneresis
of gels, thaw exudate from previously frozen foods,
and inferior performance of animal tissue in
sausage resulting from a decline in muscle pH
during normal physiological events postmortem.

4. Molecular Level
Mixing of solutes and water - altered
properties of both constituents.
Hydrophilic solutes cause changes in the
structure and mobility of adjacent water,
and water causes changes in the
reactivity, and sometimes structure, of
hydrophilic solutes
 Hydrophobic groups of added solutes
interact only weakly with adjacent water,
preferring a non-aqueous environment.

5. Molecular Level: Bound Water – hindered mobility

6. Interaction of Water with Ions and Ionic Groups

7. What effect does the intervening solvent have?
in solution
+ -
charge e1
charge e2
r
F 
e1e2
r2
Solvent Dielectric constant (D)
water 78.5
methanol 32.6
acetone 20.7
benzene 2.3
As D increases, ions in solution
interact more weakly with each
other & more strongly with the
solvent
F =
e1e2
Dr2
D: the dielectric constant of the solvent
Ionic interactions

8. Interaction of water with ions:no naked ions
Cl-
Na+
Chloride anion
Sodium cation
+ +
-
water
Dipoles of water screen the charges of the ions so they
don’t sense one another- water has a high dielectric
constant
Ions and ionic groups of
organic molecules hinder
mobility of water molecules to
a greater degree than do any
other types of solutes.
The strength of water-ion bonds
is greater than that of water-
water hydrogen bonds, but is
much less than that of covalent
bonds.

9. Interaction of Water with Neutral Groups Possessing Hydrogen-Bonding
Capabilities (Hydrophilic Solutes)
 Interactions between water and non-ionic, hydrophilic
solutes are weaker than water-ion interactions.
 Solutes capable of hydrogen bonding does not disrupt the
normal structure of pure water.
 However, in some instances it is found that the
distribution and orientation of the solute's hydrogen-
bonding sites are geometrically incompatible with those
existing in normal water.
 Thus, these kinds of solutes frequently have a disruptive
influence on the normal structure of water.

10. Continued….
Glucose molecules have polar hydroxyl(OH) groups in them and
these attract the water to them. When sugar is in a crystal the
molecules are attracted to the water and go into solution.
Once in solution the molecules stay in solution at least in part
because they become surrounded by water molecules. This layer of
water molecules surrounding another molecule is called a hydration
shell.

11. What does the strength of Hydrophilic Interactions depend on?
 Inhibitory effect mainly depended on their concentration and to a
lesser extent on the ion charge and hydrated ion radii.
 The strength of interaction depends on the polarity parameters of
solute and is independent of their chemical structure.

12. Water & polar neutral molecules: hydrogen bonding
O
H
OH
H
H
H
H
OH
O
H
O
H
OH
Water forms extensive H-bonds with molecules such as glucose,
rendering it highly soluble

13. • Some of the common natural
Hydrophobic materials are
waxes, oil and fats.
Hydrophobicity comes also from the greek word Hydro(water)
and Phobicity (fear) it refers to the physical property of a
material that repels a mass of water.
Interaction of Water with Nonpolar Substances
The evaluation of hydrophobicity
is made through water contact
angle measurements.
A water droplet would be
spherical so the water contact
angle will be significantly high.

14. Causes of Hydrophobic Interactions
• American chemist Walter Kauzmann discovered that nonpolar
substances like fat molecules tend to clump up together rather
that distributing itself in a water medium, because this allow the
fat molecules to have minimal contact with water.
Hydrophobic interactions -
ChemWiki

15. • At the molecular level, the hydrophobic effect is important in
driving protein folding formation of lipid bilayers and micelles,
insertion of membrane proteins into the nonpolar lipid
environment and protein-small molecule interactions. Substances
for which this effect is observed are known as hydrophobes.
HYDROPHOBIC EFFECT
The hydrophobic effect represents the
tendency of water to exclude non-polar
molecules. The effect originates from
the disruption of highly dynamic
hydrogen bonds between molecules of
liquid water.
Continued….

16. Water & nonpolar molecules: Hydrophobic Interactions
• H-bond network of
water reorganizes to
accommodate the
nonpolar solute
• This is an increase in
"order" of water (a
decrease in entropy)
• number of ordered water
molecules is minimized
by herding nonpolar
solutes together
Yellow blob: nonpolar solute (eg oil)

17. SUMMARY
Water forms H-bonds with polar solutes
Ions in water are always surrounded by a
hydration shell (no naked ions)
 Hydrophilic (polar): water-soluble molecules
Hydrophobic (nonpolar): water insoluble (greasy)
Hydrophobic interaction: fewer water molecules
are needed to corral one large aggregate than
many small aggregates of a hydrophobic molecule

18. Water activity and relative vapor pressure

19. Water Activity
• Water activity (aw) is a measure of how easy the water content
may be utilized.
• In 1952, Scott came to the conclusion that the storage quality
of food does not depend on the water content but on water
activity (Aw)
Aw = P/ P0 = ERH/100
Where,
ERH= Equilibrium relative humidity - RH of air and
sample at equilibrium.
P = Partial vapor pressure
P0 = Saturation vapor pressure
.

21.  In figure the desorption isotherm, indicating the course of a
drying process lies slightly above the adsorption isotherm
pertaining to the storage of moisture sensitive food.
 Decreased water activity retards the growth of micro
organisms, slow enzyme catalyzed reactions and lastly
retards non enzymatic browning.
 Foods with aw values between 0.6 and 0.9 are known as
“Intermediate Moisture Foods” Those foods are largely
protected against microbial spoilage.

22. Sorption Isotherm
 The relationship between water activity and water content is
indicated by sorption isotherm of food.
 At low water content (<50%) even minor changes in this
parameter lead to major changes in water activity.
 Resorption means addition of water to the previously dried
samples.

23. RELATIVE VAPOR PRESSURE AND FOOD STABILITY
(a) Microbial growth vs. (p/po)T, (b) Enzymic hydrolysis vs. (p/po)T,
(p/po)T
FIGURE

24. (c) oxidation (nonenzymic) vs. (p/po)T (d) Maillard browning vs.(p/po)T,
(p/po)T

25. (e) miscellaneous reaction rates vs.(p/po)T, (f) water content vs.(p/po)T.
(p/po)T

27. THANK YOU