Viscosity is a measure of a liquid's resistance to flow. The viscosity of a solution relates to how strongly the solute molecules interact with each other and resist an applied shear stress. Viscosity depends on factors like the size, shape, flexibility, and hydration of solute molecules. High molecular weight polymers and proteins can greatly increase viscosity even at low concentrations. Most protein solutions do not behave according to Newtonian fluid dynamics and instead display shear thinning or pseudoplastic behavior where viscosity decreases with increasing shear rate. The viscosity of protein solutions is influenced by molecular interactions between proteins as well as protein-solvent interactions and hydrodynamic volume.

1. VISCOSITY

2. Viscosity
• Consumer acceptability
depends on the viscosity or
consistency of the product
• Liquid and Semisolid-type food

4. • Viscosity of a solution relates to its resistance to flow under an
applied force or shear stress
• Ideal solution
• The shear stress is directly proportional to the shear rate
𝑭
𝑨
= 𝜼
𝒅𝒗
𝒅𝒓
• Proportional constant (Viscosity Coefficient)
• Fluid that obey this expression are called Newtonian fluids

5. • Flow behavior of solutions is
greatly influenced by solute type
• High-molecular-weight soluble
polymers greatly increase viscosity
even at very low temperature

6. Molecular Properties
1. Size
2. Shape
3. Flexibility
4. Hydration

7. • Solutions of randomly coiled macromolecules have greater viscosity
compare to solutions of compact folded macromolecules
• Most macromolecular solutions do not display Newtonian behavior
• Especially at high protein concentrations
• Viscosity coefficient (η) decreases as the Shear Rate (
𝑑𝑣
𝑑𝑟
) increases
• This behavior is known as Pseudoplastic or Shear thinning

8. Pseudoplastic
• This behavior arises in protein solutions because of the tendency of
protein molecules to orient their major axis in the direction of the
flow.
• When shearing or flow is stopped, the viscosity may or may not
return to the original value
• Solutions of
• Fibrous proteins remains oriented and do not regain their original
viscosity
• Globular proteins rapidly regains their viscosity (Thixotropic)

9. • At high protein concentrations or in protein gels, where
protein-protein unteractions are numerous and strong,
proteins display plastic viscoelastic behavior
• specific amount of force, known as “yield stress,” is required to
initiate flow

10. • Viscosity behavior of proteins is a manifestation of complex
interactions among several variables
• Size
• Shape
• Protein-solvent Interactions
• Hydrodynamic volume
• Molecular flexibility

11. • When dissolved in water proteins absorbs water and swell
• Volume of the hydrated molecule (size and volume) is larger
compare to their unhydrated size or volume
• Protein–associated water induces long-range effects of the
flow behavior
• The greater the specific volume of the protein = greater
flexibility

12. •The viscosity of dilute protein solutions is expressed in
several ways
• Relative viscosity
• Ostwald-Fenske type capillary viscometer
• Specific viscosity
• Reduced viscosity
• Intrinsic viscosity