Samenvatting Food Structuring (FPE30306)

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