Hydrocolloids Flashcards
Behaviour of colloids in bulk solution is important to create what kind of food structures
Thickening/ gelling / water binding
Define hydrocolloids
a colloid system wherein the colloid particles are dispersed in water
e.g. poly-saccharides and proteins
Define gum
Polysaccharide food hydrocolloids
ex of Hydrophilic polymers origin (4)
Hydrophilic polymers of vegetable, animal, microbial or synthetic origin
mainly polysaccharides
ex of Polysaccharide Hydrophilic polymers
e.g. agar, alginates, carrageenan, cellulose derivatives, gellan, guar gum, gum arabic, locust bean gum, pectin, starch, xanthan gum
Plant-derived hydrocolloids (3 & e.g.)
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
Other hydrocolloids from other origins (3 & e.g.)
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
hydrocolloid polymers classed as ____(4) based on their funcions
What faactors can influence their funcions?
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
when Polysaccharides in solution, their Behaviour depends on?
- 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
Rotational degrees of freedom
Saccharide linkage at
1,4 ordered
1,6 disordered – difficult to stabilise
Overall conformational state of polysaccharide may be assessed by ?
measuring solution viscosity
Solution viscosity equation?
graph of 3 different types of solution viscosity ?
viscosity = stress/rate
–> viscosity will change with rate
Sheer thinning / Sheer thickening/ Newtonian fluids
slide 9
The behaviour of the polysaccharide is related to ?
The behaviour of the polysaccharide is related to the shear stress against shear rate profile
–> viscosity will change with rate
what is Zero shear viscosity ?
when viscosity remain consistent as sheer rate increases
it gives us a consistent measure to characterise polysaccharide system conformation, which is random coils
Describe graph on slide 11
Plot shows
Extended polymer (molecules align at high strain rates)
Monomer with same molecular volume but more compact shape
η∞ =
= infinite shear strain rate (respectively )
τ =
= shear-dependent time constant
which represents the reciprocal of the shear strain rate required to halve the viscosity
At moderate concentrations above a critical value (C*) , what will happen?
hydrocolloid solutions exhibit non-Newtonian behavior where their viscosity depends on the shear strain rate
γ (with a dot on top) =
Unit?
Equation
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.
γ =
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 ]
How to measure viscosity ?
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
Describe critical conc.
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
what is Non-Newtonian Fluids?
draws graph to describe relationship between shear stress and shear rate
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)
Shear stress symbol ?
Unit?
Equation
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.
Shear thinning fluids is also known as ?
ex ?
pseudo-plastics
e.g. ketchup, paints
shear thickening fluids is also known as ?
ex ?
dilatant
e.g. a mixture of cornstarch and water
Shear strain
Shear strain is the ratio of deformation to original dimensions
change in length / original length
describe Newtonian fluids
ex?
graph?
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.
The process of thickening involves
the non-specific entanglement of conformationally disordered polymer chains; it is essentially a polymer-solvent interaction
Absolute value of C* depends on: ? (4)
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
how polysaccharide can influence C*
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
Explain Hydrodynamic volume
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
Comparing Hydrodynamic volume between polymer A [single liner chain] vs polymer B [ chain with lots of braches]
hydrodynamic size A = B
intrinsic viscosity A > B
molecular mass A < B
Hydrodynamic volume Differences may due to
polymer molecular mass and concentration
factors of lower hydrodynamic volume
Greater degree of free rotation leads to more compact structure –> more compact structure
Rotation between monomer units can produce
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)
Hydrodynamic volume may also indicate
how “full” the solution is
coil overlap parameter indicates ?
coil overlap parameter can be calculated by using ____
if the hydrocolloid has Individual domains or Domain overlap
Intrinsic viscosity
Explain coil overlap
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
