4. Size
Size is very important feature since it can determine
the loss of products during processing and the final
product yields.
Size can be measured in three dimensions such as
volume in the real world. However, it is usually
reduced to one or two dimensional measurements.
Size features include weight, volume, diameter,
area, surface area, perimeter, length, skeleton
length and width.
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5. What is a particle?
A discrete sub-portion of a substance.
Definition includes solid particles, liquid droplets or
gas bubbles with physical dimensions ranging
from sub-nanometer to several millimeters in
The most common types of materials consisting of
particles are:
1. powders and granules e.g. pigments, cement,
pharmaceutical ingredients
2. suspensions, emulsions and slurries e.g.
milk
3. aerosols and sprays e.g. asthma inhalers, crop
protection sprays.
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6. Importance of Particle size-Why to measure?
Many food ingredients exist in some particulate form
whether it be powders, emulsions, suspensions, and/or
pellets.
The stability, chemical reactivity, opacity, flowability and
material strength of many materials are affected by the size
and characteristics of the particles within them.
Moreover, the shape and size of these particles as well as
their distribution affect flavour, texture, and appearance of
foods that we eat.
Particle science and technology is a rapidly developing
interdisciplinary research area with its core being the
understanding of the relationships between micro and
macroscopic properties of particulate/granular matter - a
state of matter that is widely encountered but poorly
understood (Zhu et al., 2007).
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7. Particle size is an important physical property of powder and
can relate to various powder characteristics.
Advancements in research in terms of general food
technologies, biotechnologies, and nanotechnologies are
bringing about an awareness of the importance of food
particle size/shape and its significance on palatibility,
digestion, bioavailability, and metabolism along with
handling, packaging, storage and transport of food stocks.
Understanding and controlling particle size distribution in the
raw material can be critical to the success of today's food
manufacturing process.
Particle size can affect
Final formulation: performance, appearance,
stability
“Processability” of powder
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8. Effect of Particle size on Various properties
Rate of Reaction
Chemical reactions are dependent on the surface area
of a particle.
Biological systems have developed enzymes to
increase the rate at which chemical reactions take
place.
Non-biologically, particle size is another way to
increase reaction rates.
Dissolution Rate
Particle size affects how well it will go into solution.
Related to bioavailability.
The smaller the particle whether drug or food, the
greater the chance of it being absorbed by the gut.
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9. Packing Density
Packing density refers to how well particles fit
together.
Usually, larger particles don't pack as well in that
they have more space between them because they
have a larger surface area.
Smaller particles tend to pack more densely
because they have a smaller surface area.
Sedimentation
Sedimentation has to do with a particle's ability
precipitate out of solution or soft solid.
Many products require that they remain evenly
distributed in solution (suspended).
It could be salad dressings (oil and vinegar
suspension) which has more to do with product
perception.
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10. Product Appearance
Particle size affects the overall bulk properties of the
food item such as visual texture and density as well as
color.
Food products such as chewy health bars require larger
particles to maintain their integrity.
Smaller food particles tend to be to hard to chew and
crumble.
Product Texture & Flavour
Large particle size and hence a more coarse texture
alters flavor.
Large particle size tends to have less distinct flavour,
whereas fine particles have more flavour.
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11. Flow properties of powders
The flow properties of powders are strongly
dependent on particle size and, in particular, particle
shape.
Since most powders are moved from one place to
another by flowing, control of flow behavior is highly
important.
Generally, coarse, roughly spherical particles flow
much more easily than small or elongated particles.
Stability of dispersions
The stability of dispersions, such as suspensions and
emulsions, depends on the size of the dispersed
material.
The forces between colloidal particles depend on
their dimensions, and the settling.
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12. Particle Size Distribution
The particle size distribution (PSD) may be defined as “Particle
size distribution (PSD) of a powder, or granular material, or
particles dispersed in fluid, is a list of values or a mathematical
function that defines the relative amounts of particles present,
sorted according to size.”
Particle size distribution is also known as grain size distribution.
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14. Sieve analysis is one of the oldest methods of size analysis.
Sieve analysis is accomplished by passing a known weight of
sample material successively through finer sieves and weighing
the amount collected on each sieve to determine the percentage
weight in each size fraction.
Sieving is carried out with wet or dry materials and the sieves
are usually agitated to expose all the particles to the openings.
Sieves can be referred to either by their aperture size or by their
mesh size (or sieve number).
The mesh size is the number of wires per linear inch.
Approx. size range : 5µm - ~3mm
Sieve Analysis
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15. United States Pharmacopeia
General Chapters: <811> POWDER FINENESS
Classification of Powders by Fineness
Classification of Powder d50 Sieve Opening (µm)
Very Coarse > 1000
Coarse 355–1000
Moderately Fine 180–355
Fine 125–180
Very Fine 90–125
d50= smallest sieve opening through which 50% or more of the material passes
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16. Sedimentation Methods
Methods depend on the fact that the terminal velocity of a
particle in a fluid increases with size.
For the frictional force – also called drag force – exerted
on spherical objects with very small Reynolds numbers (e.g.,
very small particles) in a continuous viscous fluid.
Fd is the frictional force – known as Stokes' drag – acting on
the interface between the fluid and the particle (in N),
μ is the dynamic viscosity (kg /m*s),
R is the radius of the spherical object (in m), and
v is the particle's velocity (in m/s).
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17. A much quicker and less-tedious method of
sedimentation analysis is the Andreasen Pipette
Technique.
The method is much quicker than beaker
decantation, as samples are taken off
successively throughout the test for increasingly
finer particle sizes.
Andreasen Pipette Technique
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18. Microscopic Sizing and Image Analysis
An absolute method of particle size analysis
Two dimensional image.
Microscopic sizing involves comparing the
projected area of a particle with the areas of reference
circles of known sizes.
Optical microscopy (1-150µm)
Electron microscopy (0.001µ-)
Being able to examine each particle individually
Coupled with image analysis, a particle size
distribution can be obtained
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19. SCANNING ELECTRON MICROSCOPE (SEM)
It is a microscope that produces an image by using an electron
beam that scans the surface of a specimen inside a vacuum
chamber.
1965 first commercial SEM by Cambridge Scientific Instruments
Resolution at that time ~ 50 nm : Today < 1 nm
Specimen is coated to emit electrons, the emitted energies are
picked up by a collector and a true three-dimension image is
presented.
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20. It uses electrons instead of light to form an
image.
Beam of electrons is produced
Electron beam follows a vertical path
through the column of the microscope through
electromagnetic lenses, which focus and direct
the beam down towards the sample.
Upon hitting the sample, electrons
(backscattered or secondary ) are ejected from
the sample.
Detectors collect these electrons, convert
them to a signal and send to the viewing
screen, thereby resulting into an image.
HOW THE SEM WORKS?
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22. Laser Diffraction Technique
Particles pass through a laser beam
and scatter the light, which is
collected at various angles.
Angles of diffraction are inversely
related to the particle size.
Particles pass through an expanded
and collimated laser beam in front of
a lens in whose focal plane is
positioned a photosensitive detector
consisting of a series of concentric
rings.
Distribution of scattered intensity
yields the particle size distribution.
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24. Observations at Nanoscale
Scanning Tunneling Microscope(STM)
Magnetic-resonance force microscope (MRFM)
Atomic Force Microscope(AFM)
Assemblers
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25. Scanning Tunneling Microscope
Measures a weak electrical current
flowing between tip and sample
Provides a three-dimensional profile of
the surface to obtain atomic-scale
images of metal surfaces, uses the
quantum tunneling effect to view and
manipulate nanoscale particles, and to
map surfaces.
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26. Atomic Force Microscope
Developed to overcome a basic
drawback with STM - that it can only
image conducting or semiconducting
surfaces.
An atomically sharp tip is scanned
over a surface and measures the
interaction force between the tip and
surface and map the surface.
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27. Magnetic-resonance force microscope
Acquires magnetic resonance images
(MRI) at nanometer scales.
Combines the ideas of magnetic
resonance imaging (MRI) and atomic
force microscopy (AFM).
Conventional MRI employs an inductive coil as an antenna to sense
resonant nuclear or electronic spins in a magnetic field gradient. MRFM
uses a cantilever tipped with a ferromagnetic (iron cobalt) particle to
directly detect a modulated spin gradient force between sample spins
and the tip.
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28. Assemblers
Assemblers will position molecules,
bringing them together to the specific
location at the desired time, by holding
and positioning molecules.
Assemblers will control how the
molecules react, building up complex
structures with atomically precise
control.
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36. Nanosized Nutraceuticals
Nutraceuticals like lycopene, beta-carotene, lutein, phytosterols, CoQ10
and DHA/EPA have been incorporated into nanosized self assembled
liquid structures to deliver nutrients to cells (Dietary Supplements
bioavailability, 2010).
Royal Body Care Company has marketed a new product called
Nanoceuticals, which is a colloid of particles of less than 5 nm in diameter.
The company has also developed NanoclustersTM that enhances the
absorption of nutrients.
Unilever has developed low fat ice creams to use upto 90% less of
emulsion and decreased fat content from 16% to about 1% (The
Telegraph, 2005).
Vitamin D2 loaded casein micelles have been developed utilizing the
natural self-assembly tendency of bovine caseins (Semo et al., 2007).
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37. Different Types of Nanosensors
Nanosensors
Detection of food borne
contamination
Level of Capsaicinoids
in Chilli pepper
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38. Conclusion
Research is paving the way to finding
approaches that create a balance between
particle size reduction and improving the
functional aspects of foods.
Particle size influences sensory perception
such as taste and texture, bioavailability of
bioactive molecules, nutritional properties,
texture, thermal and many more.
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