Samenvatting
Summary Food ingredient Functionality - Rheology and gels
Summary lectures and reader rheology and gels of course Food Ingredient Functionality (FIF) at wur
[Meer zien]Voorbeeld 3 van de 24 pagina's
Voorbeeld 3 van de 24 pagina's
In winkelwagengesponsord bericht van onze partner
Voorbeeld van de inhoud
Rheology• Interactions between ingredients in
different foods determine final structure of
food and the structure determines the final
properties of the food
• Subjects rheology
1. Types of material behaviour:
- Purely elastic solid
- Purely viscous fluid
- Viscoelastic materials
2. Rheology of dispersed systems:
- Hard spheres in Newtonian fluid
- Spheres with steric stabilization
- Emulsions
• Rheology is the science that studies the relation between amount of applied force and
deformation of a system:
- Applied force is referred to as the stress
- Deformation can be seen as flow of the product
- Amount of deformation depends on whether the food is more liquid or more solid like
o Gels: elastic properties + elasticity of solids
▪ Do not really deform and have more elastic behaviour
▪ Example: gelatin gel or gels prepared from polysaccharide
▪ Relevant property: elasticity of the solids
o Solutions: viscous properties + viscosity of liquids
▪ More liquid foods deform very easily more flow properties
▪ Viscous properties relevant for solutions
▪ Example: Sugar solution/sugar syrup
▪ Relevant property: viscosity of liquids
• Elastic solids
- 2 different types of deformation upon application of a force
o Simple shear: solid is moved in horizontal direction
▪ Relative deformation that can be described by a certain angle alfa
▪ Relative deformation determined by the force applied/stress force divided
by area
▪ Applied stress and deformation are related through a parameter that is called
the shear modulus (Pa)
o Elongation/compression: solid is moved in vertical direction
▪ Due to a compression in the z-direction, the length of the solid will increase
▪ Relative change in length is relevant deformation
▪ Stress related to the change in length via the elongational modulus
- Apply force in both directions 2 ways of changing solid
32
,• Viscous liquids
- The force applied will deform the liquid different than in solids
- Deformation often applied with rotation stirring motion
- Using cylinders: Liquid placed in cup and a cylinder cup does not move + cylinder will
rotate difference in movement of the liquid
o Exert stress δ (force per unit area)Measure shear rate with viscometer Viscosity η
o Close to the cup (outer cylinder) no movement
o On inside (close to inner cylinder) movement of liquid will be high
o Deformation measured as shear rate
o Applied stress related to shear rate, via a viscosity denoted as eta
o 2 methods to measure: Applying shear rate of applying force
- Newtonian liquid
o Stress linearly related to shear rate viscosity is constant Newtonian liquid
▪ Viscosity independent on shear rate
o Viscosity determined as slope between stress and the shear rate
o Low viscous liquid
o In food: often not newtonian
- Non-Newtonian behaviour Shear rate thinning and Shear rate thickening stress and
shear rate effect not proportional viscosity does depend on shear rate
o Shear thinning:
▪ Start shearing become more liquid lower force required
▪ Faster change in shear rate than the applied shear stress
o Shear thickening:
▪ Start shearing becomes more solid higher force required
▪ Faster increase in shear stress than shear rate
▪ Starch solutions and peanut butter
- Viscous liquids with yield stress
o Yield stress: minimum amount of force/stress needs to be applied before the product
starts to flow
o Stress versus shear rate does not start in origin
o Applied stress lower than yield stress material behaves as elastic solid
33
, o Applied stress higher than yield stress material behaves as a viscous liquid and
materials starts to flow
o After the material starts to flow 2 different options
▪ Viscosity constant and independent of shear rate Bingham fluid
(Newtonian) does not exist in food materials
▪ Material behaves as non-Newtonian fluid when starts to flow most often
shear thinning referred to as general plastic flow shear rate and stress not
proportional (shear thickening/thinning)
➢ Behaviour can be modelled power law model extended by yield
stress
➢ A lot of products have a yield stress: in rest they behave as a solid and
there is no movement a lot of force applied material starts to flow
- Dense emulsion
o Network of oil droplets Force needed to break up network/clusters
o Droplets line out
o Non-Newtonian:
▪ Yield stress
▪ Shear thinning
- Examples of materials with a yield stress
o Plastic flow products have a
structure that allows a certain stress
required for moving
o Products often contain a network and
form a gel formation of oil droplet
network, casein network, polysaccharide network, combined network of particles and
polysaccharides
▪ Tomato ketchup
▪ Margarine
▪ Soft (cream) cheese
▪ Marmalade
▪ Mayonnaise
▪ Salad dressings with suspended particles needs a yield stress prevents
suspended particles from sinking to the bottom
- Thixotropic behaviour
o Time dependent viscosity viscosity profile changes
o Breakdown and restoring of a
structure takes time
o At constant shear rate
viscosity lower
o Structure broken viscosity not
the same as before time
required to repair the structure
o Hysteresis: amount of
thixotropic behaviour
34
Voordelen van het kopen van samenvattingen bij Stuvia op een rij:
Verzekerd van kwaliteit door reviews
Stuvia-klanten hebben meer dan 700.000 samenvattingen beoordeeld. Zo weet je zeker dat je de beste documenten koopt!
Snel en makkelijk kopen
Je betaalt supersnel en eenmalig met iDeal, creditcard of Stuvia-tegoed voor de samenvatting. Zonder lidmaatschap.
Focus op de essentie
Samenvattingen worden geschreven voor en door anderen. Daarom zijn de samenvattingen altijd betrouwbaar en actueel. Zo kom je snel tot de kern!
Veelgestelde vragen
Wat krijg ik als ik dit document koop?
Je krijgt een PDF, die direct beschikbaar is na je aankoop. Het gekochte document is altijd, overal en oneindig toegankelijk via je profiel.
Tevredenheidsgarantie: hoe werkt dat?
Onze tevredenheidsgarantie zorgt ervoor dat je altijd een studiedocument vindt dat goed bij je past. Je vult een formulier in en onze klantenservice regelt de rest.
Van wie koop ik deze samenvatting?
Stuvia is een marktplaats, je koop dit document dus niet van ons, maar van verkoper xLianne17. Stuvia faciliteert de betaling aan de verkoper.
Zit ik meteen vast aan een abonnement?
Nee, je koopt alleen deze samenvatting voor €2,99. Je zit daarna nergens aan vast.
Is Stuvia te vertrouwen?
4,6 sterren op Google & Trustpilot (+1000 reviews)
Afgelopen 30 dagen zijn er 53068 samenvattingen verkocht
Opgericht in 2010, al 14 jaar dé plek om samenvattingen te kopen