Spray Drying of Casein Aggregates Loaded with β-Carotene: Influences of Acidic Conditions and Storage Time on Surface Structure and Encapsulation Efficiencies

Abstract

Spray-dried casein-encapsulated β-carotene powders were prepared for encapsulation efficiency studies with respect to structural changes in casein aggregates prior to drying. The use of casein aggregates as shell matrix materials for encapsulation is of interest in encapsulation research; however, the relationship between process conditions and casein aggregation is not completely understood. Here, we report the investigation of the influence of solution pH and storage time on casein aggregate structural changes, in addition to encapsulation efficiency after spray drying. Total β-carotene loading quantities observed were higher when a solution with lower pH was employed in the dried powder preparation. Specimens obtained from a solution with pH 5.5 gave the highest total loading efficiency. Loading efficiencies were largely improved when the solutions were stored for 5 days prior to spray drying. Small-angle X-ray scattering analysis confirmed that surface structures and particle sizes were correlated to the solution pH used, as well as to storage time. At lower pH conditions (pH 5.5), particle sizes greatly increased over the entire storage duration, with a rough surface formed in the first 6 h, followed by a gradual surface smoothing. At higher pH conditions (pH 6.0–7.0), a rough surface formed accompanied by an increase in the particle size in the first 24 h, after which the size gradually decreased with the smoothed surface formation. The encapsulation efficiencies could be correlated with these structural changes during storage. The results obtained provide important insights into the encapsulation process and are expected to improve applications involving casein aggregation.