Hydrocolloids

Question 1

Behaviour of colloids in bulk solution is important to create what kind of food structures

Answer 1

Thickening/ gelling / water binding

Question 2

Define hydrocolloids

Answer 2

a colloid system wherein the colloid particles are dispersed in water
e.g. poly-saccharides and proteins

Question 3

Define gum

Answer 3

Polysaccharide food hydrocolloids

Question 4

ex of Hydrophilic polymers origin (4)

Answer 4

Hydrophilic polymers of vegetable, animal, microbial or synthetic origin
mainly polysaccharides

Question 5

ex of Polysaccharide Hydrophilic polymers

Answer 5

e.g. agar, alginates, carrageenan, cellulose derivatives, gellan, guar gum, gum arabic, locust bean gum, pectin, starch, xanthan gum

Question 6

Plant-derived hydrocolloids (3 & e.g.)

Answer 6

Exudates (protective colloids being deposited on wounds)
E.g. acacia gum/gum Arabic

Seed flours (reserve polysaccharides)
e.g. guar gum, locust bean gum

Extracts from land plants and marine algae (scaffolding substances)
e.g. pectins, agar, alginate, carrageenan, starches, cellulose

Question 7

Other hydrocolloids from other origins (3 & e.g.)

Answer 7

Microbial or bacterial polysaccharides
e.g. xanthan, gellan

Modified polysaccharides
e.g. propylene glycol alginate, amidated pectin, modified starches, cellulose derivatives

Proteins of animal origin
e.g. gelatin, caseinates

Question 8

hydrocolloid polymers classed as ____(4) based on their funcions

What faactors can influence their funcions?

Answer 8

thickeners / gelling agents
water binding / emulsion stabilisation

Naturally present or added to control functional properties by modifying liquid behaviour

The solution behaviour of hydrocolloid polymers is important to their function

Question 9

when Polysaccharides in solution, their Behaviour depends on?

Answer 9

• Size (molecular mass)
• Molecular shape [Time-averaged (ordered vs. disordered in equilibrium) ]
• -> depends on rotational freedom
• -> extended, random coil, etc.
• Polysaccharide/polysaccharide interactions
• -> non-covalent H-bonds
• Solvent/solvent interactions
• Solvent/polysaccharide interactions

Question 10

Rotational degrees of freedom

Answer 10

Saccharide linkage at
1,4 ordered
1,6 disordered – difficult to stabilise

Question 11

Overall conformational state of polysaccharide may be assessed by ?

Answer 11

measuring solution viscosity

Question 12

Solution viscosity equation?

graph of 3 different types of solution viscosity ?

Answer 12

viscosity = stress/rate
–> viscosity will change with rate

Sheer thinning / Sheer thickening/ Newtonian fluids
slide 9

Question 13

The behaviour of the polysaccharide is related to ?

Answer 13

The behaviour of the polysaccharide is related to the shear stress against shear rate profile
–> viscosity will change with rate

Question 14

what is Zero shear viscosity ?

Answer 14

when viscosity remain consistent as sheer rate increases

it gives us a consistent measure to characterise polysaccharide system conformation, which is random coils

Question 15

Describe graph on slide 11

Answer 15

Plot shows

Extended polymer (molecules align at high strain rates)

Monomer with same molecular volume but more compact shape

Question 16

η∞ =

Answer 16

= infinite shear strain rate (respectively )

Question 17

τ =

Answer 17

= shear-dependent time constant

which represents the reciprocal of the shear strain rate required to halve the viscosity

Question 18

At moderate concentrations above a critical value (C*) , what will happen?

Answer 18

hydrocolloid solutions exhibit non-Newtonian behavior where their viscosity depends on the shear strain rate

Question 19

γ (with a dot on top) =
Unit?
Equation

Answer 19

Shear rate
= the difference in velocity between the different layers

s^−1

γ = v/ h

v is the velocity of the moving plate, measured in meters per second;
h is the distance between the two parallel plates, measured in meters.

Question 20

γ =

Answer 20

shear strain rate
= the change in strain (deformation) of a material with respect to time

[the longer time you mix it won’t change its viscosity ]

Question 21

How to measure viscosity ?

Answer 21

it is impossible to measure!! –> calculate by extrapolation

η = η∞ + (η[0] - η∞) / (τ . γ)^m

The exponent (m) gives the degree of thinning (0 = no thinning, that is, Newtonian behavior; 1 = maximal thinning; < 0 = shear thickening) and determines the slope of the graph (that is, the slope is greater when m is greater).

slide 11

Question 22

Describe critical conc.

Answer 22

Thickening occurs above the critical concentration (C*)
= the non-specific entanglement of conformationally disordered polymer chains

below C* , mainly polysaccharide/solvent ; the polymer dispersions exhibit Newtonian behaviour

above C* polysaccharide/polysaccharide interactions dominate ; show a non-Newtonian behaviour

Question 23

what is Non-Newtonian Fluids?

draws graph to describe relationship between shear stress and shear rate

Answer 23

fluids which their viscosity is dependent on shear rate (Shear Thinning or Thickening) or the deformation history (Thixotropic fluids).

–> non-Newtonian fluids display either a non-linear relation between shear stress and shear rate, have a yield stress
or
viscosity that is dependent on time or deformation history (or a combination of all the above)

Question 24

Shear stress symbol ?
Unit?
Equation

Answer 24

Greek letter (r)

SI unit = pascal (Pa)

r = F/ A

[letters in italic]
F = the force applied;
A = the cross-sectional area of material with area parallel to the applied force vector.

Question 25

Shear thinning fluids is also known as ?

ex ?

Answer 25

pseudo-plastics

e.g. ketchup, paints

Question 26

shear thickening fluids is also known as ?

ex ?

Answer 26

dilatant

e.g. a mixture of cornstarch and water

Question 27

Shear strain

Answer 27

Shear strain is the ratio of deformation to original dimensions

change in length / original length

Question 28

describe Newtonian fluids
ex?
graph?

Answer 28

Newtonian fluids viscosity is independent of shear strain rate
[the longer time you mix it won’t change its viscosity ]

(e.g. water and solutions containing only low molecular mass material)

a plot of shear strain rate (for example, the rate of stirring) against shear stress (for example, force, per unit area stirred, required for stirring) is linear and passes through the origin.

Question 29

The process of thickening involves

Answer 29

the non-specific entanglement of conformationally disordered polymer chains; it is essentially a polymer-solvent interaction

Question 30

Absolute value of C* depends on: ? (4)

Answer 30

Nature of polysaccharide (molecular mass, etc.)

Type of solvation interaction (hydration)

Polysaccharide chain length/conformation

Degree of polysaccharide/polysaccharide interaction
-regions of dilute and concentrated behaviour

Question 31

how polysaccharide can influence C*

Answer 31

Polysaccharide “fills” the solution and gels
= total hydrodynamic volume > solution volume

“Families” of polysaccharides may be made to fit this type of plot
–> e.g. different polysaccharides each with 1,4 linkage will show similar behaviour

Question 32

Explain Hydrodynamic volume

Answer 32

Polysaccharide effects mainly due to the volume they occupy in solution (water)
–> enhancement of viscosity proportional to hydrodynamic volume

The volume occupied in solution is not just that of the molecule itself
–> monomers vs. polymers

It is volume swept out as it tumbles in the solvent

Question 33

Comparing Hydrodynamic volume between polymer A [single liner chain] vs polymer B [ chain with lots of braches]

Answer 33

hydrodynamic size A = B
intrinsic viscosity A > B
molecular mass A < B

Question 34

Hydrodynamic volume Differences may due to

Answer 34

polymer molecular mass and concentration

Question 35

factors of lower hydrodynamic volume

Answer 35

Greater degree of free rotation leads to more compact structure –> more compact structure

Question 36

Rotation between monomer units can produce

Answer 36

random coils of polysaccharide

• in practice free rotation may be reduced by steric or electrostatic considerations
• -> leads to ordered structure (e.g. ribbon or helix)

Question 37

Hydrodynamic volume may also indicate

Answer 37

how “full” the solution is

Question 38

coil overlap parameter indicates ?

coil overlap parameter can be calculated by using ____

Answer 38

if the hydrocolloid has Individual domains or Domain overlap

Intrinsic viscosity

Question 39

Explain coil overlap

Answer 39

Once overlap occurs an entangled system results
Measurement of the viscosity of such systems is difficult

Such solutions adopt gel-like states
These systems, while retaining some flow characteristics, often show marked elastic behaviour