Summary
Summary Food ingredient Functionality - Rheology and gels
- Course
- Institution
Summary lectures and reader rheology and gels of course Food Ingredient Functionality (FIF) at wur
[Show more]
Seller
FollowxLianne17
Reviews received
Content preview
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
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller xLianne17. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $3.25. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
75632 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now