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Summary Food structuring chapters
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all lectures of the food structuring course (chapters I-VI)
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Chapter I Structures, building blocks and propertiesInduce structuring by 2 means:
Self-assembly: Small structures formed through self assembly structuring by heating and cooling
(Fibril, Micelles, Crystals) <100 nm
Forced assembly: Larger structures through forced assembly deformation by processing (Emulsions,
Product shape, Meso-structure) >1 μm
Building blocks
Water
● Polar component → Due to the shape→ hydrophilic component
● Formation of hydrogen bonds (behave like larger molecule)
▪ High boiling point
▪ Heat of evaporation is large
▪ High heat capacity
▪ High heat conductivity
● Fast exchange of protons between various molecules → fast diffusion of acid and base in
solution
● Density solid is lower than liquid (ice floats on water)
● Present in all living materials: including foods
Oils and fats
● Very hydrophobic
● Characterized by 3-glyceride
● Properties are determined by the length and shape of the tails
o Lang and linear → high melting point
o Short and/or bended → lower melting points (bending sign of unsaturation)
● Room temperature:
o Oil: liquid
o Fat: solid
● = Apolar mix of ingredients:
o Non-miscible with water (emulsions) → will form two fases
● Fats can form crystals
o Formation depends on processing (time-temp profile)
o Melting effect: formation of crystals releases energy, melting requires energy:
cooling effect
Olive oil: Clouding (Sediment heavier than oil). Due to:
● Water forms droplets
● Formation of complexes (polyphenols-proteins)
● Saturated fat crystallisation
● Prevention → Highly purifying the oil
,Biopolymers
● Carbohydrates
o Starch
o Cellulose
o Gums
● Proteins
o Globular
▪ Most of them (+2,3 structure)→ denature by heating and form a kind of gel
at higher concentrations
o Non-globular
▪ Random coil/Colloidal particles → Caseinates form micelles
▪ No clear structure → gluten
● In foods, always in combination with water →Water content determines sensory properties
o Low water content → crispy, rubbery → solid
o Higher water content → viscously → liquid
o Exceptions
▪ Gels
● Low concentration, but solid product
● Network formation
▪ Cellular products (apples, carrots)
● Three main components are not (well) miscible: they will be dispersed into each other
● Phase separation → 1 high in carbohydrates and 1 high in proteins (water-in-water emulsion)
Isotropic = structures have equal properties in all directions (cheese)
Anisotropic = structures have different properties that depend on orientation (meat) fibrous food
Biopolymers are often hydrophilic components in concentrated food systems. They tend to form
amorphous, non crystalline structures at low water content
,Other components
● Salts
o Alters molecular interactions in products
o Changes properties of biopolymers
o Influences water activity (water availability)
o Influences structure formation processes
● Humectants, Plasticizers
o Soften materials
o Interacts and disentangles biopolymers
o Miscible with water
o Glucose, glycerol etc
o Reducing sugar makes product less soft and less sweet
Phase diagram and state diagram
● Water-biopolymer mixtures: sorption isotherm
● Relation water activity and texture
● For almost all food biopolymers the curve looks like this
= Moister content vs water activity
You can sort the sorption isotherm in 3 regions
● Low moisture levels → linear increase in MC and Aw (crispy)
o Low amount of moisture absorbed
o At some point: glassy → rubbery
● Intermediate levels → MC increases a bit but Aw increases a lot (rubbery)
o Aw changes very fast with moisture content
o Unstable behaviour
, ● High levels → MC increases a lot before Aw increases a bit (liquid)
o Aw hardly changes with moisture content
o Product may liquefy at some point
Phase transitions
● Phase transitions are important in food processing
o Solid to liquid
o Liquid to solid
o Solid to gas
o Solid to solid
▪ Crystalline to amorphous
▪ Amorphous to crystalline
Phase diagram of a (biopolymer) product (only thermodynamic transitions)
Increase in temp and/or MC product liquefies (melting of the crystals)
Can also be the other way around:
A system is not always at ThermoDynamic equilibrium
● TD equilibrium might not be reached during processing
● Kinetics influenced by
o Fixing
o Flow conditions
State diagrams: thermodynamic transitions + kinetic effects
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