Rheology of Sodium Caseinate Stabilized Oil-in-Water Emulsions

Area of Science:

• Colloid and Surface Science
• Food Rheology
• Emulsion Science

Background:

• Fine oil-in-water emulsions are common in food and industrial products.
• Sodium caseinate is a widely used food emulsifier.
• Understanding emulsion rheology is crucial for product stability and texture.

Purpose of the Study:

• To investigate the shear rheological properties of oil-in-water emulsions stabilized by sodium caseinate.
• To correlate rheological behavior with protein concentration and oil volume fraction.
• To elucidate the mechanisms of emulsion instability, specifically flocculation.

Main Methods:

• Shear rheological measurements (steady-state viscometry, oscillatory experiments) at 30°C.
• Preparation of emulsions with varying sodium caseinate (1-6 wt%) and n-tetradecane (10-45 vol%) concentrations.
• Analysis of rheological data in relation to protein surface coverage and continuous phase protein concentration.

Main Results:

• Rheological behavior strongly depended on total protein concentration.
• Three distinct regimes were identified: bridging flocculation (insufficient protein), stable Newtonian flow (full coverage, low excess protein), and pseudoplasticity due to depletion flocculation (substantial excess protein).
• Results align with previous findings on creaming stability and microstructure.

Conclusions:

• The protein/oil ratio dictates the rheological properties and stability of sodium caseinate-stabilized emulsions.
• Depletion flocculation by sodium caseinate submicelles explains reversible flocculation in concentrated systems.
• Rheological measurements provide insights into emulsion microstructure and stability mechanisms.