The behaviour of protein preparations from blue-green algae (Spirulina platensis strain Pacifica) at the air/water interface

The surface tension of a protein sample isolated from the blue-green algae (cyanobacteria) Spirulina platensis strain Pacifica was studied using the Wilhelmy plate method. The isolated material was characterised by determining the protein and lipid content, SDS-PAGE electrophoresis, isoelectric focusing, and visible spectroscopy. The protein is capable of reducing the interfacial tension at the aqueous/air interface already at relatively lower bulk concentrations compared to common food proteins. The surface tension of the protein preparation seems to be quite independent of pH, which indicates that electrostatic interactions are of minor importance for the interfacial behaviour. We have also separated out fractions with different interfacial properties by centrifugation. When the protein was spread at the air/aqueous interface, the pressure area isotherm somewhat resembles those recorded for lipids, with a higher collapse pressure than usually observed for proteins. The interfacial behaviour of extracted lipids confirms that remaining traces of lipids in protein powder have only a minor influence on the surface activity of Spirulina protein. The surface-active components are likely to be protein and/or protein-pigment complexes rather than individual protein molecules.