New insights into the microencapsulation properties of sodium caseinate and hydrolyzed casein

The aim of the present study was to describe the fundamental physical characteristics of spray-dried carrier matrices based on sodium caseinate and casein hydrolyzate and microcapsules as well as their impact on the stability of a microencapsulated functional ingredient. Spray-dried carrier matrix was characterized by different physical methods (helium pycnometry, nitrogen displacement for surface area analysis, X-ray photoelectron spectroscopy, positron annihilation lifetime spectroscopy). Surface viscoelasticity of protein-stabilized oil–water interfaces was analyzed using dynamic pendant drop tensiometry. Fish oil was microencapsulated and microencapsulation efficiency as well as oxidative stability over time was monitored. Surface accumulation of proteins at the air–water interface led to a modified surface composition of spray-dried carrier matrix particles for microencapsulation. However, interfacial elasticity was markedly altered when using hydrolyzed casein as emulsifier, which is related to a decrease in microencapsulation efficiency. Lipid oxidation during storage of the microencapsulated oil increased with the protein content in the formulation. Excess protein led to an increase in free volume elements and is suspected to negatively affect oxygen diffusion.