Summary of the course Food Structuring (FPE-30306) at Wageningen University (Master Food Technology)
Content of summary:
- Food structures, building blocks and food properties
- State diagram and the glass transition
- Crystallization and matrix formation
- Barrier technology
- Emulsions: Principl...
Summary Food Structuring – FPE 30306
Chapter 1 – Food structures, building blocks and food properties
• Food Structuring for making more sustainable, healthy products
• Structure can have influence on bio availability, taste, growth of micro-organisms, make use of
plant materials possible
• We want a controlled in-homogeneity in the product → so not the same properties everywhere!
• Different types of structures:
→ Properties are depended on the
direction (meat, broccoli)
→ Properties are the same in all
directions of the product (milk,
yoghurt, cheese)
• Structures <1 micron are depended on self-assembly processes. But you do have to create the
right circumstances. For instance cooling, heating so crystals can be formed.
• Forced assembly can be used for larger structures (droplets, >1 micron). To make structures
you can use temperature (heating, cooling) AND deformation
• To keep the structure in your product → solidification is needed (e.g. remove water by heating
or solidification by cooling)
Building blocks of food
• Water
o Formation of hydrogen bonds and because of that it has:
▪ High boiling point (compared to other molecules of same size)
▪ Heat of evaporation is high
▪ High heat capacity
▪ High heat conductivity
▪ Fast diffusion of acids
o Polar component
o Density of its solid (ice) is lower than liquid (normally other way around
• Oils and fats
o Consist of glycerol backbone with three fatty acids
o Apolar, so will not dissolve in water
o Can form crystals!
• Biopolymers (polysaccharides and proteins)
o In food, biopolymers are always present in combination with water
o Low concentration biopolymer: liquid product
o High concentration biopolymer: solid product
• Other components
o Salt: changes molecular interactions and water activity
o Plasticizer/humectant: water, glycerol, soften a product that normally would be harder.
Most components are not miscible! They can only be dispersed into each other.
Carbohydrates can dissolve in water. Proteins can dissolve in water. But not with each other.
,Sorption isotherms
• Most food products will have a
sorption isotherm similar to this one
→ GAB relation
o Region where water activity
changes but moisture content
stays the same → so for dry
products, a little amount of
moisture already changes the
water activity a lot.
o Region where moisture
content changes but the
water activity stays the same
→ so for wet products you
need to change the moisture content a lot to get a different water activity
But there are different models that describe the sorption isotherm of systems:
Model Valid for Graph
Henry • Simple liquids (water) Linear, the amount of water
• Dilute systems absorbed is linear with the water
activity of the product
Langmuir • Monolayer adsorption Amount of water absorbed levels
• Surfaces and porous systems off for higher water activity
• Some glassy polymers because at a certain moment the
surface is full with water and no
more water can be absorbed.
Multilayer • Polymeric materials and solutions Combination of Henry and
adsorption • For instance sythetic food Langmuir equitation
packaging materials
BET • Multilayer adsorption At higher water activity, more
• Many food matrices water is absorbed because water
GAB • Multilayer sorption is not only at the surface but also
• Food matrices absorbed by the matrix inside
Equitons are on the formula sheet. With the formulas you can calculate the weight fraction of
ingredient i.
Langmuir
GAB
There is a difference when you measure the adsorption or desorption (removing water) of a
material. This is because sometimes water is kept in the matrix when water is removed.
, Crystallization
• Water, sugars and fat can crystallize
• Some biopolymers as starch can crystallize under specific
conditions
• Melting temperature
o Below: the material will crystallize
o Above: the material is liquid
o For instance, melting temperature of water is 0
degrees Celsius. Below it forms ice, above it is
liquid.
The figure below shows a phase diagram. Above the line, we
have a liquid. Under the line, crystals of A or B are formed. At
the eutectic point, we have crystals of both components. This
point does not exist for food!
Chapter 2 – The state diagram and the glass transition
States of food
Low moisture content → crispy
Increase moisture content → rubbery
Even more water → liquid
Transport phenomena can deviate due to
structural effects
• Diffusion → transport of mass
• Heat conductivity → transport of thermal
energy
• Viscosity → transport of impulse
Effect of a filler
• Adding glass beads to a protein gel
• Properties depend on properties continuous phase and dispersed phase
• Only little amount of filler → linear relation (Einstein)
• If there is interaction between the glass beads (higher concentration) → curve changes, not
linear. You will get a maximum packaging density.
Phase diagram
• You can read when a certain transition happens
• For instance when solid, when liquid?
• Y-axis temperature, x-axis moisture content or solid content
• You can also make a phase diagram with component A (water) and component B (sugar).
When are there ice crystals? When sugar crystals?
o Above the line everything is liquid
o On the left side, you will get ice crystals. What is left, is an enriched solution of sugar in
the little amount of water that is not crystallized.
o On the right side, you will get sugar crystals in a solution enriched in water
o Below the line, no liquid anymore, only crystals A and B (=eutectic point, not in food)
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