Water in Foods

1. WATER
 Water is the predominant constituent in many foods
 Supports chemicals reactions and direct reactant in hydrolytic
processes
 Inhibits the growth of microorganisms
 Improves the shelf-lives of a number of foods
 Physical interaction with proteins, polysaccharides, lipids
and salts
 Contributes significantly to the texture of the food

2. Two main sources of water available in the Planet:
 Surface water - Lakes, streams, reservoirs, Bay, Sea,
Ocean and rainfall
 Ground water – Wells and springs
Out of the total water sources:
- Saline water: 97.20%
- Ice ( deposited in hills and mountains) : 2.15%
- Sweet water: 0.65% ( Fresh water- 0.20% and GW – 0.45%)

3. Table 1. Moisture content of some foods
Foods Moisture
(% W.B)
Foods Moisture
(% W.B)
Meat 65-75 Butter,
margarine
16-18
Milk 87 Cereal flour 12-14
Fruits &
vegetables
70-90 Milk Powder 4
Bread 35 Edible oil 0
Honey 20 Refined sugar 0

4. Free liquid- in which substances are dissolved or dispersed i.e.
cytoplasm, intercellular fluid, and many of circulating fluids
of tissues
Hydrates-hydrogen bonds are established between water
molecules and ions or molecules which contain oxygen or
nitrogen i.e. Starch, proteins and many other organic
compounds as well as salts from hydrates.
Imbibed water in gel-some substances picked up water and
swell when they come in contact with water
Adsorption on the surfaces of solids-held on all surfaces
exposed to air in which water vapour is present.
Forms of water:

5. Water molecules:
 Water molecules are able to attach themselves to other
molecules by means of hydrogen bond
 Dipoles in which the hydrogen atoms are slightly positive and
oxygen atoms slightly negative
 Hydrogen atoms are bonded to oxygen by a covalent pair of
electrons
 Angel between these atom is 105°
 Each water molecules is tetra-hydrally coordinated with four
other molecules through hydrogen bonds

6.  Two unshared electron pairs of oxygen act as H-bond acceptor
sites
 H-O orbital act as hydrogen bond donor sites
 Dissociation energy of this hydrogen bond is about 25 kj mole-1
 Simultaneous presence of two acceptors and two donor sites in
water permits association in a three-dimensional net work
 Water is unusual for other small molecules-alcohol, ammonia
that form only linear or two dimensional associations.
H+
H+
O-
105° H+
O-
H+
105°

7. o Here are three-dimensional views of a typical local structure of water
(left) and ice (right.)
o Notice the greater openness of the ice structure which is necessary to
ensure the strongest degree of hydrogen bonding in a uniform,
extended crystal lattice.
o The more crowded and jumbled arrangement in liquid water can be
sustained only by the greater amount thermal energy available above
the freezing point.

8.  The stable arrangement of hydrogen-bonded
water molecules in ice gives rise to the beautiful
hexagonal symmetry that reveals itself in every
snowflake.
Ice structure

9. What holds the molecules together in
Ice?
In ice the Oxygens are "linked" to each
other by the combination of a covalent
bond + a hydrogen bond

10. How are the molecules arranged in Ice ?
Each Oxygen is "linked" in by a
combination of a covalent bond and a
hydrogen bond to 4 other Oxygens

11. Liquid water and Ice:
 Due to pronounced tendency of water to associate through
H-bridges, liquid water and ice highly structured
 They differ in the distance between the molecules,
coordination number and time-range order
 Stable ice formed at a 0°C and 1 atm pressure
 When ice melts and the resultant water is heated, both the
coordination number and the distance between the nearest.
This changes has opposite influence on density
 An increase in coordination number increases the density
 Whereas the increase in distance between nearest
neighbour, decrease the density.

12.  The effect of increase in coordination number is predominant
during the temperature increase from 0 to 4°C.
 As a consequences, water has an unusual property: density in
liquid state at 0°C (0.9998 g cm-3) and solid state (Ice-I,
0.9168 g cm3)
Table 2. Coordination number and distance between two
water molecules
Coordination
number
O-H...O distance
Ice (0°C) 4 0.276nm
Water (1.5°C) 4.4 0.290nm
Water (83°C) 4.9 0.305nm

13. Water and Nutrition:
 Water is the largest constituent of the body, about 60-70 per cent
of the total body weight consisting of water.
 The water content of soft tissues ranges from 70-80 per cent
while that of bone about 20 per cent.
Table 3. Distribution of water in the body
% of body weight
Total body weight 70 kg 100
Total water 50 kg 70
(i) Intracellular 35 kg 50
(ii) Extra cellular 12 kg 17
(a) Plasma 3 kg 4
(b) Lymph 5 kg 7
(c) Tissue fluid 4 kg 6
(iii) Miscellaneous 3 kg 4
In additional water is present in cerebrospinal fluid and aqueous humour

14. Water intake and loss:
Water is lost continuously from the body in the following ways:
 Via kidney as urine
 Via skin in the form of insensible perspiration and as sweat
 Via the lung in the expired air
 To a small extent via the large intestines in the faeces
 In lactating women in the milk
 In addition, water is formed in the tissue by the oxidation of H2
present in fats, carbohydrates and proteins

15. Table 4. Water intake and loss from the body of an adult
weighing 70 kg
Temperature
climate (ml)
Tropical
climate (ml)
Water intake
Drinking water 1500 2000-5000
In food 1000 1000-2000
By oxidation of CHO, protein and
fat in the tissues
300 300
Total 2800 3300-7300
Water loss
In urine 1500 1000-1500
Via skin 800 1800-5200
Via lungs 400 400-400
In faeces 100 100-200
Total 2800 3300-7300

16. Exchange of water in the body:
 Water is absorbed rapidly from the small intestines through
the portal vein to the general circulation
 It rapidly passes to the tissue space as tissue fluid
 A greater part of the ingested water is excreted by the kidneys
within an hour

17.  Excess intake water is distributed rapidly throughout the body
 The kidney responds to the increased water intake after about
15-30 minutes
 The flow of urine rises from normal value of 50 ml per hr to its
peak of 1500 ml per hr
 The extra water is excreted by the kidney within 3 hrs
 The excess urine output may (in temperate climate) be almost
equal to the water ingested
 In tropical climate, a part of ingested water is lost in the sweat
Effect of excess water intake on water balance
in the body:

18. Effect of water deprivation on water balance
 Water is being constantly lost from body in urine, sweat,
expired air and faces
 If corresponding quantity of water is not ingested, water
depletion occurs
 The body leading to the changes in body fluids
 A reduction in the volume of the extra cellular fluid and
intracellular fluid takes place
 The urine output is reduced
 Rapid decrease in body weight and a stage of dehydration of
cells occurs
 A decrease in plasma volume (and in blood volume) occurs
which will lead to circulatory failure
 A adult who has lost 5-10 litres of water from the body will be
seriously ill
 Death may occurs when the water loss from the body is about
15 litres