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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 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 consuming publically
 It is the application of chemistry to the
development, processing, preservation,
packaging, 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
Water content in different foods
Product/ water percentage
Tomato 95% Lettuce 95%
Cabbage 92% Beer 90%
Orange 87% Apple juice 87%
Milk 87% Potato 78%
Banana 75% Chicken 70%
Salmon, canned
67%
Meat 65%
Cheese 37% Bread, white
35%
Jam 28% Honey 20%
Butter and
margarine 16%
Wheat flour
12%
Rice 12% Coffee beans,
roasted 5%
Milk powder 4%

6. 6
Water
 Ever present and one of the most important
constituents
 It is the largest constituent of 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. Existence of water in foods
1. Free water (such as in tomato juice)
2. Droplet of emulsified water (butter)
3. Water in colloidal gels (jellies)
4. A thin layer of adsorbed water (powered
milk)
5. Chemically bound water of hydration (sugar)
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8. 8
Chemical nature of water
 Water's chemical description is H2O
 One atom of oxygen bound to two
atoms of hydrogen

9. 9
 The hydrogen atoms are "attached" to
one side of oxygen atom, resulting in
a water molecule having a positive
charge on the side where hydrogen
atoms are and a negative charge on
other side, where the oxygen atom is
 Since opposite electrical charges
attract, water molecules tend to
attract each other, making water kind
of "sticky"

10. 10
 The side with hydrogen atoms (positive
charge) attracts 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 "universal solvent" because
it dissolves more substances than any other
liquid
 Wherever water goes, either through ground
or through our bodies, it takes along
valuable chemicals, minerals and nutrients

11. 11
 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

12. 12
The addition of an alkali increases
proton acceptors (OH-) and makes
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

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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 32oF and boils at 212oF (at
sea level, but 186.4°F at 14,000 feet)
 In fact, water's freezing and boiling points
are baseline with which temperature is
measured.

14. 14
 0oC on Celsius scale is water's freezing
point and 100oC is water's boiling point.
Water is unusual in that solid form, ice, is
less dense than 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

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 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

16. 16
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%, bones 26% and
striated muscles 75% water
 Regulates the body temperature
 Striated muscles?
A muscle that is connected at either or both
ends to a bone and so move parts of the
skeleton.

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 Serves as medium in which 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
 Acts as transport medium for carrying
nutrients to cells and removing waste
from body

18. Why is water important for our bodies?
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19. 19

20. 20
Nature of water in foods
 Water exists 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 microorganisms
 This water can be frozen or removed from the food
system
 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

21. 21
 Chemically bound water involves 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
 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

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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.

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 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

24. 24
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

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Moulds are capable of growing in very low
available moisture
Yeast and bacteria require more moisture for
their activities
Each organism has a minimum, maximum and
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

26. 26
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
water activity (Aw)

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 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

28. 28
 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

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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

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Aw and growth of microorganisms

32. 32
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
 Humectants is a hydroscopic substance
used to keep thing moist.

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Predicting of Food Spoilage
 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 Aw is lowered to 0.94, 4.3 min are required at
60°C to cause the same tenfold reduction
 The regulations 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

34. SAVE THE WATER PLEASE
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