Interfacial protein engineering for spray–dried emulsions – Part I: Effects on protein distribution and physical properties

• Excess amount of protein was needed for optimum emulsion and powder performance.
• Maltodextrin induced depletion flocculation of oil-in-water emulsions.
• Cross-linking concentrated protein on droplet interface and particle surface.
• Glass transition of powder matrix occurred between RH 54% and 75% at 20 °C.

Distribution of protein and oil in aqueous and spray–dried emulsions and the effect of protein cross-linking on emulsion properties and matrix–water interactions were investigated. Sodium caseinate and sunflower oil were used to make emulsions which were spray dried using maltodextrin as a wall material. 3% Na–caseinate concentration showed optimum emulsion and process stability as observed in CLSM images, droplet size data and in the amount of heptane-extractable oil from spray–dried emulsions. Transglutaminase cross-linking prior to emulsification slightly increased the amount of protein both on the oil droplet interface and on the particle surface as confirmed by analysis of continuous phase protein in the feed emulsion and by XPS measurements from the powder surface. DSC and water sorption measurements were used to study the physical state of the matrix. Glass transition occurred between RH 54% and 75% at room temperature and it was not affected by cross-linking.