physical prop of foods

7/29/2019 physical prop of foods

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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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physical prop of foods