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Samenvatting Food Ingredient Functionality (FQD30306)
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Physical Aspects by ElkeBulk Rheology
1. Viscosity of Biopolymer Solution
Viscosity of biopolymer depends on structure of polymer
Polysaccharides used as thickener -> effective to increase viscosity. Increase of
viscosity depends on concentration, conformation (shape), mW
Viscosity of highly diluted solution-> intrinsic viscosity []= 1+[]C
- C: polymer concentration
- []: intrinsic viscosity -> characteristic property of polymer and represent a measure
of hydrodynamic volume (related to molecule shape and mW of polymer) -> shear
dependent parameter
- Valid when concentration used is low and when polymer are in a dilute regime
In the regime, assumption made that polysaccharide do not interact with othr
molecule
[] relation to conformation and mW via Mark Houwink relation: []=KMa
- K related to conformation and geometry of linkages within polymer chain
- A: exponent depending of polymer stiffness
a. Conformation of Polymers
Conformation influence viscosity. Different conformation:
1. Rigid rod: helical polysaccharide: xanthan and highly charged polysaccharide
2. Semiflexible: anionic polysaccharide -> pectin and alginate
3. Random coil: non-ionic polysaccharide, guar and LBG
4. Highly branched: starch amylopectin
5. Globular: protein
Conformation relation to viscosity : Rh Mb
- M: mW
- Rh: hydrodynamic radius-> related to stiffness of polymer. The more stiff the higher
hydrodynamic radius
- B: exponent related to polymer shape
b. Effect of PH
PH have an effect on viscosity because it changes stiffness parameter
Increase charge density -> increase electrostatic repulsion -> stretched backbone
because charged groups prefer to stay at a certain distance
Increase stiffness and increase viscosity
PH has an effect on anionic poly but not on non-ionic
c. Effect on Ionic Strength
Ionic strength screen charges which effect the stiffness parameter
When charges are screened, less electrostatic repulsion, decrease stiffness
parameter -> decrease viscosity
Polysaccharides do not have just 1 [], it depends on specific structure and
condition
[] protein << [] polysaccharide
- Protein has globular shape resemble hard sphere -> shape does not contribute much
to viscosity
- [] globular WP 0,01 dL/g
, Viscosity can be increased by forming aggregates/ protein network at high
concentration (gel like)
- Aggregate formed by inducing attractive interaction like by heating
- [] depend on geometry of aggregate (depend on concentration, PH, salt content
while heating)
- Both with 20mM NaCl, High concentration heated neutral PH has lower intrinsic
viscosity (act like flexible chain like aggregates) than high concentration heated
acidic ph (3) which act like random aggregates
d. Effect of concentration
When concentration increases, poly come close to each other, interaction effect
start to play role
Concentration of polymer solution in concentrated regime = 1+[]c + k[]c2
- K: huggins constant
- Non-linear increase in viscosity
Overlap concentration (c*): concentration at which concentration starts to
deviate from initial linear relationship
- Polymer start to overlap and don’t act as single molecule
- Define transition between dilute and semi-dilute regimes
2. Viscosity of suspension
Rheological properties of suspension depend on volume occupied by dispersed
particle relative to total accessible volume
Ubbelohde used to measure low concentration suspension : capillary viscometer
in which time is recorded for a certain volume of liquid to flow through vertical
capillary
a. Effect of ph on suspension viscosity
Specific volume of flexible polysaccharide in solution depend on charges present
on groups-> change in ph -> increase viscosity
- Change ph increase internal electrostatic repulsion btween group on poly backbone
- Poly chain take more space and volume fraction -> increased volume fraction
- Increase -> viscosity increasee
Flexibility of chain change because repulsion between polymer resulted in less
mobile particle -> increase viscosity. Higher mobility – lower viscosity
Increased volume of particles -> closer proximity particle-> network forming
Interaction in Food
1. Steric stabilization
Occur when polymers are present in dispersion with colloidal particles
- Particles can be casein micelles, oil, or other large particles
- Polymer can adsorb to particle surface when there is attractive interaction
Some cases chemical bonds can be formed
Most often interaction from electrostatic attraction on opposite charged
molecule or hydrophobic interaction
When adsorption of polymer give thick layer of polymer around particle that
cover the complete surface, layer contributing to dispersion stability
, Polymer layer on different particles can repel each other -> particle can’t
approach in close proximity to make aggregate due to hydrophobic interaction /
vander waals interaction-> this phenomena is steric interaction or steric
repulsion
Only able to stabilize when there is enough polymer present to sufficiently cover
partticles
2. Bridging Interaction
Bridging flocculation happen when polymer adsorb to particle surface through
attractive interaction. But there is not enough polymer to cover the entire
surface particle -> adsorbing polymer does not make dense layer around particle
(not enough polymer)
- Polymer link to 2/more particles to form bridge between particles
- Because of this bridge cluster of particles can be formed
- Cluster size depends on particle polymer ratio and degree of attractive interaction
- Density of cluster cause either sedimentation or creaming
Particle>water (ex. Casein micelles) -> sedimentation
Particle<water (ex. Oil droplets) -> creaming
Macromolecular analogue of salt bridge
3. Depletion interaction
Polymer influence stability even when there is not attraction between polymer
and dispersed phase
When there is no attraction, polymer will stay in continuous phase
Both particle and polymer need space to be distributed evenly throughout the
solution
At higher concentration, there is only limited space for distribution -> particle will
get together and concentrate in one area of solution, whereas polymer will also
get together in other part of system-> phase separation
- One phase enriched in particles, the other with polymers
- Which phase is lower or upper depend on phase density
- In case oof protein aggregates as particle, they form heavy liquid phase at the
bottom and liquid phase with polymer will go up
- In case of oil droplets as particle, they will form lighter upper phase and polymer
liquid will take lower phase
At low concentration: polymer are able to fit between particles-> even
distribution
Increased concentration: 2 colloidal particles approach each other, polymer can’t
fit between colloids -> there is volume between particles that is free of polymers
and outside this region, polymer present in higher concentration
- Theres difference in osmotic pressure between region with no polymer and rich
polymer region
- Result of osmotic pressure difference: water between colloids move to region
outside to decrease polymer concentration –> colloidal particle pushed towards each
other
- Interaction from the 2 particles causing aggregation or flocculation of colloidal
particles
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