Characterization of ‘wet’ alginate and composite films containing gelatin, whey or soy protein

Abstract

The following study explored how the addition of various proteins (gelatin, soy protein isolate (SPI) and heated/unheated whey protein isolate (WPI)), at two different concentration levels (1% and 2%), affected the mechanical, microstructural and optical properties of calcium cross-linked ‘wet’ alginate films. Additionally, the water holding capacity and textural profile analysis (TPA) properties were determined for the alginate–protein gels. Adding all types of protein significantly (P<0.05) decreased the force to puncture the ‘wet’ alginate–protein composite films compared to the control alginate film. The tensile test showed significant differences in tensile strength between the various films but interestingly there was no significant difference in the percent elongation at breaks between any of the films. Micrograph images showed that the SPI and heated WPI formed relatively larger protein clumps/regions in the alginate films whereas the gelatin and unheated WPI appeared to be more integrated into the alginate film. The heated WPI films were the least transparent of all the films, followed by the SPI films. Few TPA differences existed between the alginate–protein gels. However, the alginate–gelatin gels did have significantly less water loss than the other alginate–protein gels suggesting that alginate and gelatin may be the most compatible of all the alginate–protein combinations tested.