Magnitude Flashcards
What is a Newtonian Fluid
A fluid whos viscosity is independent from shear.
What is shear rate?
Shear rate is the rate of change of velocity at which one layer of fluid passes over an adjacent layer.
Provide some examples of shear thinning and shear thickening and explain what these terms mean.
Shear thinning is the decrease in viscoity with increase in shear rate. Examples include most sauce and dressing.
Shear thickening is the increase in viscosity with increasing shear rate. Example include starch in water.
How does viscosity of random coil polymers behave with increasing shear rate?
At start, shear rate increase has no effect on viscosity. This is because random coil polymers are physically entangled and the shear rate promotes disentanglement. However at low shear rate the polymers can form entanglements quickly so that viscosity does not appear to change. When shear rate increases entanglements are broken and polymers tend to align so that entanglements cannot reform and thus viscosity decrease.
What is an example of polysaccharide that decreases viscosity immediately as shear rate is applied?
Xanthan Gum.
Describe xanthan gum
Xanthan gum is a polysaccharide which is used because of its properties. Low quantities are required and is useful in salad dressing, emulsions and to suspend solid particles. This is because at rest viscosity is high but when shear rate is applied from applied shaking etc, viscosity decreases.
Does higher thickness lead to higher retention of flavors?
Yes. Meaning that higher amount of flavors must be used to reach those recpetors.
Is CMC or xanthan gum better for flavors?
Xanthan gum as flavors are suppressed less than in CMC
Why does rotational viscometer underestimate xanthan thickness comparing acutal viscosity to perceived thickness?
The mouth can perceive the weak gel like structure as thickness and hence it contributes to the thickness values before it is broken down in mouth.
