Interfacial protein engineering for spray-dried emulsions – Part II: Oxidative stability

• Increased humidity increased stability of spray-dried sunflower oil emulsions.
• Powder caking of Na-caseinate–maltodextrin matrix retarded oxidation.
• Oxidation of surface lipids was only up to twofold compared to total lipids.
• Cross-linking of protein slightly improved oxidative stability.

The aim of this work was to investigate how the oxidative stability of encapsulated oil is affected by the humidity response of a Na-caseinate–maltodextrin matrix. Furthermore, the effect of modification of the interfacial Na-caseinate layer through cross-linking was studied. For this purpose, two model spray-dried emulsions containing sunflower oil, maltodextrin, and either non-cross-linked or cross-linked Na-caseinate were stored at different relative humidities (RHs; ∼0%, 11%, 33%, 54%, and 75%). Increasing RH improved the oxidative stability of the spray-dried emulsions. This behaviour was mainly linked to the loss of individual powder particles upon caking and collapsing of the matrix at RH 75%. Oxidation of non-encapsulated surface lipids with a proportion of ca. 5% of total lipids was only twofold compared to total lipids. Excess protein on particle surfaces may have delayed oxidation, e.g., by its radical scavenging activity. Under several storage conditions, cross-linking of the protein slightly improved the oxidative stability.