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Chapter 1 1
DR. J. S. LEE
SCHOOL OF FOOD SCIENCE & NUTRITION
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Chapter 1 2
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Chapter 1 3
Physical properties of foods ?
Properties that lend themselves to description andquantification by physical rather than chemical
means.
Important in product handling, processing andconsumer acceptance.
Product Handling:
engineering parameter of shape, size, volume,
density & surface area.
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Chapter 1 4
Product Handling:
storage of grains & seeds in silos, mechanical
harvesting, transportation (withstand static &
dynamic loading), etc.
Product Processing:
Thermal, mechnical, rheological, electrical
properties, etc.
Thermal: specific heat, conductivity in food
processing (heat treatment, canning, freezing,
dehydration etc..)
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Chapter 1 5
Product Processing:
Mechanical & rheological: govern thebehaviour of solid materials during reduction
process, flowing of fluid, etc.
Electrical: conductivity while separating similarseed varieties, disperse hydrocolloid in H2O, etc.
Dielectric properties govern the behaviour of food
in dielectric & microwave heating.
others: surface tension, surface rheology, contact
area etc.
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Chapter 1 6
Consumer Acceptance:
related to sensory quality of food products, suchas mechanical properties and rheological properties
affect the sensory property of texture.
Physical Properties of Foods
Geometrical Optical
Mechanical (rheological)
Thermal Electrical
Surface
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Chapter 1 7
Units & Dimensions
3 system of units (std of measures):
1. International System of Units (SI)
2. Centimetre gram second (cgs)
3. Imperical Systems of Units [pounds,ounce,]
The SI metric system has 7 basic/fundamentals
unit (not relate to each other, mutually
independent).
All other SI units are called derived units
(defined in terms of these 7 units).
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Chapter 1 8
There is a set of16 prefixes to form multiples &
submultiples of SI units.
Factor Prefix Symbol
1018 Exa E
1014 Peta P
1012 Tera T
109 Giga G
106 Mega M
103 Kilo k
10-6 Micro
10-12 Pico p
Handout distributed.
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Chapter 1 9
Fundamental Units
1. Mass
Dimension: [M] ; SI unit: kilogram (kg)
Quantity of material making up an object. Differ
from wt.
Wt is a measure of the gravitational force of pull
acting on an object. The corresponding unit is the
Newton (N).
Mass of an object remains constant but its wt
changes according to its distance from earth or
another planet.
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Chapter 1 10
Fundamental Units
1. Mass
Example: The mass of a boy is 40 kg but the wton the earth is 40 kg X 9.80 ms-2 (acceleration due
to gravity), which is 400 N.
2. Length
Dimension: [L] ; SI unit: metre (m)
3. Time
Dimension: [T] ; SI unit: second (s)
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Chapter 1 11
Fundamental Units
4. Temperature
Dimension: [] ; SI unit: Kelvin (K)
Degree of hotness of a body.
Heat transfer until thermal equilibrium isachieved (= temp).
100oC 50oC
Normally reproducible fixed points are used to
set up a scale of temp (often the melting point
or boiling point of pure substances).
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Chapter 1 12
Fundamental Units
4. Temperature
The property chosen must be easily measured
& changes in a uniform manner.
Most commonly used is the melting point of ice
& the boiling point of water under atmospheric
pressure (at sea level).
The 1oC interval is 1/100 times bet the boiling
point & freezing point of water, whereas the 1oF interval is 1/180 times. Therefore, it is >
precise to record temp to 1 oF than 1 oC.
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Chapter 1 13
4 basic temperature scales
Tyep ofscale
Meltingpoint of
water
Boiling
point of
water
Temperatureconversion
Celcius
(oC)
Fahrenheit
(oF)
Kelvin (K)
Rakine (oR)
0 100 TC = 5/9 (TF32)
32 212 TF = 9/5(TC) +32
273.15 373.15T
K= T
C+ 273.15
492 672 TR= TF + 460
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Chapter 1 14
Fundamental Units
4. Temperature
If temp is reduced < 0, a point is finally reached
at which all molecular motion stops & the kinetic
energy of the molecule becomes 0. The temp at
this point is known as absolute zero or zeroKelvin.
The interval 1 K is = 1 oC.
K & R temp are > commonly used for calculation
in equations such as the ideal gas & Arrhenius
equations.
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Chapter 1 15
Fundamental Units
5. Electric Current
Dimension: [I] ; SI unit: Ampere (A)
A measure of the flow of electrons.
Dimension: [?] ; SI unit: mole (mol)
7. Amount of Substance
6. Luminous Intensity
Dimension: [?] ; SI unit: candela (cd)
A measure of brightness of a light source.
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Chapter 1 16
Fundamental Units
7. Amount of Substance
When the mole is used, the elementary entity in
the system must be specified & may be atoms,
molecules, ions, electrons, other particles or
specified groups of such particles.
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Chapter 1 17
Derived Units
Units derived from the 7 fundamental units.
Examples:
Area: [L2] (m2) Density: [ML-3] (kgm-3)
Velocity: [LT-1] (ms-1)
Acceleration: [LT-2] (ms-2)
Force: [MLT-2] (kgms-2 or N)
Pressure: [ML-1T-2] (kgm-1s-2 or Nm-2)
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Chapter 1 18
Units & Dimensions
The unit of a physical quantity and its dimension
are related, but not precisely identical concepts.
The units of a physical quantity are defined by
convention and related to some standard; e.g.length may have units of meters, feet, inches,
miles or micrometres;
any length always has a dimension of L,
independent of what units are arbitrarily chosen to
measure it.
BUT
http://en.wikipedia.org/wiki/Units_of_measurementhttp://en.wikipedia.org/wiki/Units_of_measurement -
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Chapter 1 19
Two different units of the same physical quantityhave conversion factors between them. For
example: 1 in = 2.54 cm; then (2.54 cm/in) is
called a conversion factor (between two
representations expressed in different units of acommon length quantity) and is itself
dimensionless and equal to one.
Units & Dimensions
There are no conversion factors between
dimensional symbols.
http://en.wikipedia.org/wiki/Conversion_of_unitshttp://en.wikipedia.org/wiki/Conversion_of_unitshttp://en.wikipedia.org/wiki/Conversion_of_unitshttp://en.wikipedia.org/wiki/Conversion_of_units -
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Chapter 1 20
In the physical sciences and in engineering, the
dimension of a physical quantity is theexpression of the class ofphysical unit that such
a quantity is measured against.
The dimensions of a physical quantity areassociated with symbols, such as M, L, and T
which represent mass, length, and time.
Units & Dimensions
Depending on the field of physics, it may be
advantageous to choose one or another extended
set of dimensional symbols.
http://en.wikipedia.org/wiki/Units_of_measurementhttp://en.wikipedia.org/wiki/Physical_quantityhttp://en.wikipedia.org/wiki/Physical_quantityhttp://en.wikipedia.org/wiki/Physical_quantityhttp://en.wikipedia.org/wiki/Physical_quantityhttp://en.wikipedia.org/wiki/Units_of_measurementhttp://en.wikipedia.org/wiki/Units_of_measurementhttp://en.wikipedia.org/wiki/Units_of_measurement -
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Chapter 1 21
Units & Dimensions
Most common: M, L & T
In electromagnetism: Q (electric charge)
In thermodynamic: T (temperature)
In chemistry: no of molecules
The choice of the base set of dimensions is thus
partly a convention, resulting in increased utility
and familiarity.
It is important for ease of communications to
have the entire community of scientists making
the same choices.
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Chapter 1 22
Units & Dimensions
The SI system of units, with the associatedchoices of their corresponding dimensions is most
widely used and has essentially replaced several
confusing and overlapping choices.
The choice of the dimensions or even the number
of dimensions to be used in different fields of
physics is to a certain extent arbitrary, but
consistency in use and ease of communications
are paramount.
http://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/SI -
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Chapter 1 23
Dimensional analysis may be used to check theplausibility of physical equations: the two sides of
any equation must be commensurable or have the
same dimensions, i.e., the equation must be
dimensionally homogeneous.
Units & Dimensions
Physical quantities having different dimensions
cannot be compared to one another either.
Only like dimensioned quantities may be added,
subtracted, compared, or equated.
http://en.wikipedia.org/wiki/Commensurability_%28philosophy_of_science%29http://en.wikipedia.org/wiki/Commensurability_%28philosophy_of_science%29 -
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Chapter 1 24
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