Protein adsorption onto alginate-pectin microparticles and films produced by ionic gelation

• Microparticles and films produced by ionic gelation were coated with whey and egg white proteins.
• The amount of calcium was significantly higher in the films compared with the microparticles.
• Protein adsorption onto the microparticles was significantly higher than onto the films.
• Although it was simple and easy to produce the films, homogeneous drying of the films was difficult.

Microparticles and films containing sunflower oil were produced by ionic gelation using a 1:1 alginate:pectin mixture and were electrostatically coated with whey and egg white proteins. Emulsions of the polysaccharide mixture and the protein solutions were evaluated in terms of their zeta potentials. The microparticles were characterized based on their mean size, size distribution, moisture content, calcium content, adsorbed protein content, encapsulation efficiency and morphology. The films were characterized with respect to their thickness, moisture content, calcium content, adsorbed protein content, mechanical properties, water vapor permeability and morphology. High encapsulation efficiency (87.6% at pH 3.5 and 90.8% at pH 3.75) was obtained for the microparticles produced by ionic gelation. The calcium content after ionic gelation was significantly higher in the films (on average, 3.0 μmol/mg db) than in the microparticles (on average, 1.62 μmol/mg db). For the microparticles, an increase in the protein content in solution yielded an increase in the protein content adsorbed, independent of the type of protein used. When 4% protein in solution was used, protein adsorption onto the microparticles (59.2% for whey protein and 45.5% for egg white protein) was significantly higher than that onto the films (25.3% for whey protein and 24.1% for egg white protein) likely due to the smaller amount of calcium present on the microparticles and the larger surface area of the particles relative to that of the films. Although the process of producing films by ionic gelation and later coating them with proteins was straightforward, homogeneous drying of the films was difficult.