Samenvatting
Samenvatting Food Structuring (FPE30306)
- Instelling
- Wageningen University (WUR)
important summary of Food structuring hundred pages reader
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Voorbeeld van de inhoud
FS Chapter 2 (State diagram and Glass Transition)Food States
3 important steps in structured food creation: hydration and mixing, heating, cooling
Rubber: material with consistency but deformable; liquid with entanglements
preventing high flow
Glass: resulted by heating or drying of fluid to remove water and cooling of of
concentrated system
Slow cooling leads to crystalline material which usually only happen with component
that have relatively low mW like sugar and fat
Gasses, Vapours and liquid
1. Gasses and vapours
Gases: co2 from drinks or co2 that emerges from bread dough when fermenting
which is responsible for cellular structure formation in bread
- Same effect using baking soda which react with proton to give co2 -> create gas
cells in cake and cookies
Air: is not vapour because it cannot condense close to RT
Vapour: gas that can be. Condensed into liquid under conditions that are close to
ambient
a. Liquid, rubbers, gels
Liquid get mobility from thermal motion -> withstand attractive forces between
molecule
- If forces are large/ Brownian thermal motion become smaller-> liquid will solidify
partially or completely
- Viscous flow dominate in liquid
Elasticity: material flow and deform but when stress is released, it will partially move
back towards its original shape (liquid with rubber like behaviour)
- Viscoelstic behaviour -> gelation
- Rubber-> elasticity deformation; may or may not return to original shape, flow to
some extent
b. The glassy state
Kinetic state -> not fully stavle
Viscosity increases to really nigh and it resembles solid
- Even if it is normally still liquid, it feels like a brittle hard solid
- This is called glass
Glasses are brittle.
- Crispiness: If glass are porous (with many air bubbles), breaking will involve
complex series of small breakages
- Molecules in glass are still liquid, more or less randomly oriented but can hardly
move
Immobility means that they can’t flow and molecule not able to adjust a
stress exerted to the material
Protein and carbohydrates can easily form glass
- Slow mass diffusion
Glass is not in TD equilibrium -> it is liquid in vitrified state -> can’t respond to any
more changes in its. Condition but would have driving force to do so
, Very high viscosity, viscosity increases near glass temperature
c. Crystalline state
Highly ordered structure with low diffusion and molecular mobility
Cooling down a liquid and allow molecules time to settle they can order in very
regular arrangements -> crystal
Density crystal is generally higher than that of corresponding liquid because of
regular packing
- Molecules in crystal can only vibrate slightly
- Order is extremely high, minimal freedom to move
Larger molecules take more time to become crystal because of movement velocity
Biopolymer that behave like random chain often crystallise partly -> semi-crystalline
- Ex: gelatinized starch -> retrograde into a partly crystalline state where only small
crystals are present and incorporate only small part of starch chain, rest of chain
remain liquid (with liquid or rubber like behaviour)
- Cooling down leads to non-crystallised part to glassy state
Diagrams
1. Diagrams
a. Phase Diagram
To see water related phase behaviour of food as a function of temperature
Contain lines as curves which partition areas in which a particular equilibrium state
will be stable
Liquidus: line that indicates the point at which ice crystals will start to form
- Hardly any surcrose: happen near 0 degrees
- At higher concentration this will happen at slightly lower temperature -> freezing
point depression
b. Ternary phase diagram
Form: isosceles triangle and Orthogonal axes
Form 2 phases at higher concentration: one phase will be rich in one polymer and
poor in other and vice versa
c. State diagram
Used because not all state is at equilibrium
Shows both equilibrium states and states that might be encounter in practice
Same as phase diagram but differ at higher concentration of dissolved component
Crystallization takes time and shows when two crystallization lines cross
Glass transition in state diagram shows temperature and moisture level it gives what
states to expect at which level of moisture and temperature
Usage
- Visualization of structuring process
- Understanding structural changes
- Give behaviors as function of rough composition and temperature
Glass transition
1. Viscosity and temperature dependence of glass transition
, Liquid: molecule moving constantly in random fasioon due to their thrmal energy
and constant collision with neeighbouring molecules
- Not completely dense but also have free volume/ holes (spaces in between
molecules which are larger than average)
- Holes occur randomly because of random motion and usually short lived
- Molecule that is in proximity to an available hole can jump with sufficient
thermal energy -> creating net movement of liquid
If happen often resulted in macroscopic fluid motion
If shear/ deformation is applied -> jumps happen in one direction-> net
transport and deformation of liquid
- Rate of jumping depends on:
Amount of molecule motion
Number of holes available
- Solution with many strong bonded molecule will not easily mak e jumps -> higher
viscosity
- Larger molecule have hard in finding hole that fits. So eventhough there is
movement, it is hard to jump
Reduction of temperature effects on viscosity:
- Molecules have less thermal (Brownian) motion-> jumps will be less frequent
- Lower amount of thermal motion mean that molecule come closer together ->
less space needed to accommodate all motion -> increase in density and
decrease in molar volume-> reduced free volume
- Summary: number of energetic jump is reduced but amount of space to
accommodate molecules that have jumped also become less
Arrhenius equation: when there is sufficient free volume
- Way to describe dilute solutions
- Viscosity vs temperature for liquids and gasses
- Free volume decreasing with temperature
- Super high viscosity that molecule can’t jump in any reasonable time frame
Further reduce in T: molecule unable to reconfigure and fill the gaps that are
present as free volume
From certain T (glass T): fractional free volume is effectively frozen
Fractional free volume with freezing effect -> Doolittle equation
Williams Landell Ferry (WLF) equation: knowing change in viscosity compared with
the viscosity at glass transition temperature
- Way to describe viscosity system in the area above glass transition ( less than 70-
100 C) called leathery/rubbery
- Equation only valid for temperatures that are not too far away from glass
transition
- For thin viscous liquid (ex. Ethanol water), distance from glass temperature is so
large that Arrhenius equation applies better
- Sugar solution from 30% weight WLF kinetic applys
- WIF kinetics imply universal behavior, applicable for any system that is relatively
close to its glass transition (within 50 – 100 C of Tg)-> high viscosity slow diffusion
- Viscosity depend strongly on distance from glass transition
- Also valid for diffusion
, When viscosity rises very quickly to high values, the diffusion coefficient is
reduced to low
2. Dependence on mW
Longer molecule will have less mobility and will become glassy at higher
temperature than lower mW molecule’
For homologous components (ex.maltodextrin), glass transition depends on mW and
is linearly dependent on the inverse of mW
Longer chains have even higher glass transition but less strong increase
a. WLF Kinetics: not only viscosity
When viscosity rises very quickly to high values in WLF area, diffusion coefficient
reduced to exteremly low value, so low that the rate of diffusion in glass is virtually 0
Application in packaging but also in instant cappuccino foam
b. Concentration dependence
Couchmann karasz equation: At their glass transitions: entroopies of individual
component have to be equal
Gordon Taylor equation: when there is no difference of heat capacities between
liquid and glass of each component
Plasticization: addition of small amount of second component to strongly reduce the
glass transition of first component
- Relatively large reduction of glass transition with addition of small amount of
plasticizer (usuallt LMW component with low T glass transition) that have good
interaction with material
- Plasticizer needs to have low Tg and has good interaction with glass former
Semi Crystallinity, chemical, and physical crosslinking
1. Melting temperature of food biopolymers
Small components can cystallise completely but biopolymers show semi-crystallinity
- Not the whole molecule but small parts of it crystallizes out
- Ex: starch
Native starch is crystalline but not completely (15-39%), only specific
domains.
Gelatinization of starch -> heat above crystallization temperature-> lose
crystallinity and mix (swell) in water
Lowering T < Tm (around 60 C), starch will slowly re-crystallise, crystallise in
small domains and act as crosslink (network formation of starch -> starch
retrogradation)
- Ex: Gelatin
Dry sheets or granules= glassy, brittle but transparent
Dissolve in warm water and cooled < Tm (35 C), small part of gelatine
crystallise partly (20%) -> stiffening/ setting
Semicrystalline biopolymer act as purely glass material -> show WLF kinetics near
glass transition -> fast reduction of viscosity starting from glass transition but their
modulus strength is remarkably constant
Area of gelatine/ starch gel
More less same properties even in high or low range of gelling area
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