Tailor made protein based aerogel particles from egg white protein, whey protein isolate and sodium caseinate: Influence of the preceding hydrogel characteristics

Abstract

Protein based aerogel particles derived from heat set whey and egg white protein hydrogels were prepared. The influence of the hydrogel preparation on aerogel properties was studied. Variations in pH, ionic strength and protein type and concentration were assessed as a means to vary hydrogel and corresponding aerogel structures in a targeted manner. An adjustment of pH of the precursor protein solution led to fragile hydrogels with obvious syneresis in the pH region around the isoelectric point. Corresponding aerogels were brittle and lacked the typically large specific inner surface area of aerogels. In an acidic environment, hydrogels were firm but also fragile. Aerogels were brittle but had a large specific inner BET-surface area. In an alkaline environment, the hydrogels were soft and elastic. Thus, resulting aerogels were mechanically stable and possessed a large BET-surface area. The addition of sodium chloride or calcium chloride to the protein solution had the same effect as lowering the pH towards the isoelectric point. The process of supercritical drying was also applied to enzymatically cross-linked sodium caseinate hydrogels with varying protein concentration. Corresponding aerogels had a smaller BET-surface area compared to heat set gels. The protein concentration did not affect the BET-surface area of the aerogel. Finally, an emulsion method was used to produce protein aerogel particles, suitable for microencapsulation purposes. All three types of protein formed single spherical aerogel particles with comparable aerogel properties to the related aerogel monolith. The properties of the protein aerogel particles may be tailored towards special needs for microencapsulation purposes in food, cosmetic or pharmaceutical applications.