particle size analysis

Question 1

What effect does the size of a particle have on properties?

Answer 1

It can effect the flow, hydration and molecule release of a food.

Question 2

What measurements are considered in particle size analysis?

Answer 2

Particle, diameter, volume, surface area and number are the most common.

Question 3

Why do we do food particle size analysis?

Answer 3

Particle size and distribution affect things such as texture, taste, appearance and stability.
it influences the hydration and dissolving capabilites
paste and suspension flow is affected by particle size
in functional foods, particle size can affect bioavailability. Particle size can also relate to droplets, bubbles and pores.

Question 4

what are some examples of particle size effecting food properties.

Answer 4

Coffee beans need to be ground into a fine particulate after roasting to match desired flavour.

Question 5

What is the simplest shape of food particles to determine parameters?

Answer 5

Sphere, we can determine size and diameter easily, allowing us to calculate surface area and volume.

Question 6

What is a PSD?

Answer 6

A particle size distribution.

Question 7

How are PSD’s data represented and why?

Answer 7

By using a histogram, this allows for statistical analysis of distribution. this gives you a range of particle sizes and their distribution

Question 8

How do you calculate the volume of a sphere?

Answer 8

(pi * diameter cubed) / 6

Question 9

How do you calculate the surface area of a sphere?

why would you do this?

Answer 9

pi * diameter squared

This is useful to calculate dissolving properties

Question 10

as non-spherical particles are significantly harder to deal with, what do we do?

Answer 10

We reference either the volume or surface area to that of a spherical particle

Question 11

What is the difference between a unimodal and a bimodal particle size distrubtion? why is this improtant?

Answer 11

a unimodal will have one peak, and a bimodal would have two.
This shows you might have two separate materials appearing, such as milk showing fat droplets and milk solids.

Question 12

How do we measure non-spherical particles?

Answer 12

By comparing them to a suitable spherical measure (changes with circumstance). We try to treat them as spheres with equivlaance in certain parameters.

Question 13

What spherical measures are available for non-spherical particles?

Answer 13

Sphere of same maximum length
Sphere of same weight
sphere of same volume
sphere of same surface area
sphere of same minimum length
sphere passing same sieving aperture
sphere with the same sedimentation rate

Question 14

what is the formular for the volume of a cylinder?

Answer 14

((pi * Diameter squared)*height) / 4

Question 15

How to we equate a cylinder to a sphere?

Answer 15

by relating the volumes.

Question 16

What is ‘Characteristic diameter’ and number means?

Answer 16

characteristic diameter is the type of diameter used for equating
D[1,0] is the number length mean
D[2,0] is the number surface area mean
D[3,0] is the number volume mean
number mean is just the total mean from all particles
eg particle sizes of 1,2,3,4
for characteristic diameter of [1,0] (1 + 2 + 3 + 4) / 4 = 2.50dp

Question 17

what is moment means?

Answer 17

it is more useful for larger scale.
d[4,3] is the most common in food science which is ((sum of all diameters) to the power of 4) / ((sum of all diameter) cubed)

Question 18

Is it better to go by volume or number?

Answer 18

Volume is more representative of all samples which is more effective when considering parameters.

Question 19

What is important to remember about each characterisation technique?

Answer 19

None are incorrect, they only give a different perspective on the particle

Question 20

What is sieve analysis?

Answer 20

It is the oldest technique, it uses a stack of different aperture sizes which shake the material, this separates particles by size and you can count the number or measure the weight of particles on each aperture

Question 21

What is the disadvantage to sieve analysis?

Answer 21

It is dificult to analyse particle sizes less then 40 micrometers. you are limited by the amount of apertures you can use at once. it is hard to measure products that agglomerate.
it is also dependent on how much it is shook.

Question 22

What data can you take from a sieve analysis? what are is disadvantages?

Answer 22

You can take the weight of each particle size, this allows you to make a PSD histogram and culmutive distribution. the amount of data points is limited and therefor the PSD can be quite jagged

Question 23

what is a sedimentation method?

Answer 23

It is where you put your material of choice into a liquid that will not dissolve your material, the settling rate is then measured for it.

Question 24

What is the settling rate indicative of?

Answer 24

It is indicative of terminal velocity and relates to particle diameter using stokes law.

Question 25

what are the limitations of the sedimentation method?

Answer 25

You need to know the density
Must be spherical to be accurate
temperature has to be controlled
very limited range of 2 to 10 micrometers
gravity based takes a long time.

Question 26

what is x-ray sedimentation?

Answer 26

it measure a range of 0.1 to 300 micrometers by using an xray focused onto a known height of a sample cell. Particle volume is taken from the amount of x-ray absorbed by the particles.

Question 27

What is stokes law?

Answer 27

It is the equation we use to determine particle size from sedimentation analysis. The PSD is determined by measuring the different settling rates( which means different diameter)

Question 28

What is microscopy?

Answer 28

It is a method of measuring particle size through microscopy, a graticule bar is used for reference for length.
It can only measure small samples sizes easily, however you can use software to speed it up. It is also a 2d representation of a 3d object. As it is a counting method we would use a number mean such as d[1,0] for size or [2,0] for area

Question 29

What is electrozone sensing?

Answer 29

It is a orifice with a voltage potential, a dilute suspension flows through the orifice which provides resistance proportional to the particles volume.

Question 30

What are the limitations of a electrozone sensor?

Answer 30

large particles get stuck and small particles may go through together giving an incorrect reading.

Question 31

What characteristic diameter does electrozone sensing use?

Answer 31

Electrozone sensing is a counting method based on volume, therefor we use a characteristic of D[3,0]

Question 32

What is laser diffraction method? (LALLS)

Answer 32

This shines an incident light into a solution containing the particle in question. the angle of scattered light gives you your volume of particle. the smaller the particle the larger the angle scattering.

Question 33

What are the limitations to laser diffraction?

Answer 33

Particle and liquid must not have same refractive index
particles must not be too big
solution must be dilute (so it doesnt obscure too much).

Question 34

What are the three main components of a laser diffraction equipment?

Answer 34

Optical bench
Sample dispersion unit
Software

Question 35

What type of information do you get from a laser diffraction instrument?

Answer 35

You get an intensity distribution which can be related to a particle size distribution.

Question 36

What type of particle densities can you have?

Answer 36

Bulk density which is aprticles with air spaces in between.
Tapped density is where the bulk density is tapped down to remove some space.
True density is the accurate density of the material itself with no space.

Question 37

What can we derive from bulk and tapped density for particles?

Answer 37

A powders flowability, this can be calculated using the compressibility index and the hausner ratio

Question 38

if you have a low compressibility or hausner ratio for a powder what type of flow do you have?

Answer 38

a excellent flow character.

Question 39

What is a tapped density instrument?

Answer 39

It is used to determine tapped powder volume.

Question 40

How do you measure a true density?

Answer 40

by using a gas pycnometer

Question 41

What is particle porosity?

Answer 41

It affects things like rehydration and dissolution, it is the relationship between bulk density and true density.

Question 42

What is shape aspect ratio?

Answer 42

it is the ratio of the maximum dimention length to the minimum dimension length, it tells you how isotropic your shape is.