food and water, Food Chemistry, Constituent of foods i.e water carbohyfrate lipid protein vitamin inorganic material other substances Physical property of water

1. 1
Food
 Any substance that when ingested, usually will
supply to the body one of the following:
o Materials from which body can produce
movement, heat or other forms of energy
o Materials for the growth, repair or regeneration
and reproduction
o Substances necessary to regulate the
processes of growth and repair

2. 2
Food Chemistry
 It is the study of the chemistry of foods, their
deterioration, and the principles underlying the
improvement of foods for the consuming public
 It is the application of chemistry to the
development, processing, packaging,
preservation, storage, and distribution of foods
and beverages for the purposes of obtaining a
safe, economical, and aesthetically pleasing
supply of food for people worldwide

3. 3
Constituents of foods
 Foods generally are made up of biochemicals,
mainly derived from living sources such as
plants and animals
 The general compositions of a food as well as
the way in which the components are
organized give a food its individual
characteristics
 For example whole milk and fresh apples have
about the same water content, but one is solid
and the other is fluid because of the way the
components are arranged

4. 4
 All foods contain one or more of the
following major constituents:
1. Water
2. Carbohydrates
3. Lipids
4. Proteins
5. Vitamins
6. Inorganic materials
7. Other substances (pigments flavors
organic acids toxicants anti-
nutritional factors etc.)

5. 5
Water, carbohydrates, lipids and
proteins are found in large quantities
and the other three i.e. vitamins
inorganic materials and other
constituents in trace amounts

6. 6
Water
 Ever present and one of the most important
constituents
 It is the largest constituent of the human
body
 More than 60% of an adult man is water,
while woman contain 45-55% water
 Most of the water (55%) is held inside the
cell as intracellular fluid, while the rest
(about 45%) is contained in the extra-cellular
fluid
 About 7.5% water is in blood stream that
forms part of the extra-cellular fluids

7. 7
Chemical nature of water
Water's chemical description is H2O
One atom of oxygen bound to two
atoms of hydrogen

8. 8
The hydrogen atoms are "attached" to
one side of the oxygen atom,
resulting in a water molecule having a
positive charge on the side where the
hydrogen atoms are and a negative
charge on the other side, where the
oxygen atom is
Since opposite electrical charges
attract, water molecules tend to
attract each other, making water kind
of "sticky"

9. 9
 The side with the hydrogen atoms (positive
charge) attracts the oxygen side (negative charge)
of a different water molecule
 All these water molecules attracting each other
mean they tend to clump together
 This is why water drops are, in fact, drops
 Water is called the "universal solvent" because it
dissolves more substances than any other liquid
 Wherever water goes, either through the ground or
through our bodies, it takes along valuable
chemicals, minerals, and nutrients

10. 10
The water molecule dissociates to yield
H+ and OH ions‑
H2O H+
+ OH‑
Hence it is a proton donor as well as
proton acceptor and is neutral
When an acid is added to water, it
increases the proton donors (H+) and
makes the water acidic

11. 11
The addition of an alkali increases the
proton acceptors (OH ) ad makes the‑
water alkaline
Pure water has a neutral pH of 7,
which is neither acidic nor basic
As foods contain numerous
compounds in their water content
therefore have a pH below 7.0

12. 12
Physical properties
 Water is unique in that it is the only natural
substance that is found in all three states --
liquid, solid (ice), and gas (steam) -- at the
temperatures normally found on Earth
 Water freezes at 32o
F (0o
C) and boils at 212o
F
(100o
C) (at sea level, but 186.4°F at 14,000
feet)
 In fact, water's freezing and boiling points
are the baseline with which temperature is
measured

13. 13
 0o
C on the Celsius scale is water's freezing
point, and 100o
C is water's boiling point.
Water is unusual in that the solid form, ice, is
less dense than the liquid form, which is why
ice floats
 Water has a high specific heat index i.e. it
can absorb a lot of heat before it begins to
get hot
 The high specific heat index of water also
helps regulate the rate at which air changes
temperature, which is why the temperature
change between seasons is gradual rather
than sudden, especially near the oceans

14. 14
 Water has a very high surface tension or it is
sticky and elastic, and tends to clump
together in drops rather than spread out in a
thin film. Surface tension is responsible for
capillary action, which allows water (and its
dissolved substances) to move through the
tiny blood vessels in our bodies
 Density: 1 gram per cubic centimeter (cc) at
39.2°F (4o
C), 0.95865 gram per cc at 212°F

15. 15
Functions of water
Water is required in the bodies to
perform the following functions
Used as a building material in every
cell, fatty tissues contain 20%, bone
26% and striated muscles 75% water
Acts as lubricant in the joints and
between the internal organs
Regulates the body temperature

16. 16
Serves as medium in which the
nutrients, enzymes and other chemical
compounds are dispersed and
dissolved
It is a medium in which intracellular
chemical reactions take place
It participates in chemical reactions,
especially in the hydrolytic ones
Acts as transport medium for carrying
nutrients to cells and removing waste
from body

17. 17
Nature of water in foods
Water exists in water in foods as free and
as chemically and physically bound
The free water as found in tomato and
orange juice is available for chemical and
biochemical reactions as well as for use
by the microorganisms
This water can be frozen or removed from
the food system

18. 18
 In physically bound water, the forces involved
are of a physical nature, as is the case when
water is strongly adsorbed to the surfaces of
macromolecules such as proteins, starches and
celluloses
 Chemically bound water involves the chemical
linkages of water molecules to various food
constituents such as carbohydrates and salts as
water of hydration
 Such water is difficult to remove during drying
and may not separate during freezing

19. 19
The bound water provides reduced
chemical and biochemical reactions as
well as microbial activity depending
upon its degree
The stability of foods increases with
lowering of water

20. 20
Nature of food dispersions
 Dispersion is a system of fine particles evenly
distributed in a medium
 Water molecules have a dipole nature
 Non-ionic but polar compounds are dissolved
in water because of hydrogen bonding
between water molecules and groups such as
alcohols, aldehydes and ketones
 Several components are found dispersed in
water phase in the foods
 Important components are carbohydrates,
lipids, proteins, vitamins etc.

21. 21
 Food solutions are dispersions in which solid
or semi-solid particles are evenly distributed in
water
 Colloidal solutions are made up of long chain
macromolecules consisting of aggregated
molecules of proteins, lipids etc.
 Important example is ketchup
 Food gel is a type of dispersion that consists
of a continuous phase of interconnected
particles intermingled with a continuous water
phase

22. 22
Emulsion is another type of dispersion
in which two immiscible liquids are
dispersed
In emulsion there are two phases;
dispersed phase (droplets of one liquid)
and continuous phase (the the other
liquid)
Important examples are butter, milk,
margarine etc.

23. 23
Role of water in foods
 Water contributes greatly to the desirable
native qualities of foods
 Presence of water in the required amount and
form is necessary for acceptable quality of
food
 The amount and state in which it appears are
important in determining the storage life of a
food
 Fresh fruits and vegetables are high in
moisture with sufficient available moisture

24. 24
Such foods have shorter shelf life than
grains and dry seeds that contain much
less water, mostly bound in the cells
Recognition of water amount and its
availability for physical, chemical and
biological changes in food systems helps
to understand about the spoilage of foods
and their prevention

25. 25
Water activity
Water is an essential elements for all
forms of life
Serves as a medium for most
metabolic activities
Act as a carrier of nutrients and
waste products to and from the body
of an organism
Like higher plants and animals
microorganisms require moisture for
their activities

26. 26
Moulds are capable of growing in very low
available moisture
Yeast and bacteria require more moisture
for their activities
Each organism has a minimal, maximal
and an optimal water activity (Aw) for
growth
Amount of moisture available for
microbial and other activities, as it affects
the foods, can be considered in terms of
equilibrium relative humidity and water
activity

27. 27
 Relative humidity (RH) refers to the macro-
environment (air) surrounding the material
It is the percentage of water vapors in
the air compared to maximum quantity
of water vapors which the same
volume of air can hold at the same
temperature and pressure
Most commonly free moisture
available in foods for microbial and
other activities is described in term of
another term water activity (Aw)

28. 28
This can be defined as equal to one
hundredth part of the corresponding
relative humidity in moisture
equilibrium with the food i.e.
Pure water has Aw=1 whereas most of
the fresh foods have Aw=0.99
Available water and water activity
decreases exponentially with the
addition of sugars and salts in a
particular food
=Aw
100
ERH

29. 29
 Dry foods like wheat and rice are regarded as
safe because of their low moisture contents
available for microbial growth
 During humid conditions, some mould
growth may be evident due to condensation
of moisture, as it provides free moisture
necessary for proliferation of these
organisms
 The foods with higher moisture contents than
in the stable foods support the growth and
activities of most microorganisms leading to
spoilage

30. 30
Role of Aw in food processing
 Most of the microorganism require an
optimum amount of water for their growth
 Lesser is the moisture, lesser is the microbial
growth and greater is the shelf life
 Manipulation of water contents is the
principle rule in food processing to control
microbial activities
 This basic principle is kept in mind during
the processes of dehydration, evaporation
and concentration when sugars salts and
other water binding substances are used in
foods

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1.0
Aw
0.9
0.8
0.6
0.5
0.7
Foods Microorganism
Distilled water, fresh meat,
fish, milk, fruits, vegetables
Sauces
Flours, cakes, cereals
Salt preserved foods, jams
Dried fruits
Dehydrated foods
Cl. Botulinum
Most bacteria
S. aureus (anaerobic)
Most yeast
S. aureus (aerobic)
Xerophilic fungi
Extremely osmophilic
microorganism

32. 32
aw and growth of microorganisms

33. 33
Controlling aw in foods
 Equilibration with atmosphere of known
relative humidity
 Water removal (e.g., dehydration)
1. Addition of solutes (humectants)
2. Sugars
3. NaCl
4. polyhydric alcohols (glycerol, sorbitol),
propylene glycol
 Control loss or gain of moisture in
packaged foods

34. 34
Predicting Food Spoilage
 The aw of a solution may dramatically affect the
ability of heat to kill a bacterium at a given
temperature
 A population of Salmonella typhimurium is
reduced tenfold in 0.18 minutes at 60°C if the aw
of the suspending medium is 0.995
 If the aw is lowered to 0.94, 4.3 min are required
at 60°C to cause the same tenfold reduction

35. 35
The regulations (21 CFR 113.3(e) (1) (ii))
state that commercial sterility can be
achieved by the control of water activity
and the application of heat
The risk of food poisoning must be
considered in low acid foods (pH > 4.5)
with a water activity greater than 0.85