Interfacial rheology of soy proteins – High methoxyl pectin films

Surface aggregating soy protein-pectin solutions are used in the production of biodegradable films intended for food packaging applications. Structural properties of the surface biopolymer network influence the engineering properties of the films, such as permeability and mechanical strength. Soy protein isolates (SPI) – high methoxyl pectin (HMP) films that develop at the air–water interface were therefore investigated by a combined interface rheological and ellipsometric approach. The behavior of pure SPI interfacial layer is that of a light cross-linked polymer network with a small regime of linear viscoelasticity response. Since SPI progressively accumulate at the air–water interface, higher protein concentration in the solution does not lead automatically to higher surface coverage but due to restricted unfolding of the proteins to weaker and fluid-like films. The rheological behavior of composite SPI–HMP solutions at the air–water interface shows that the HMP addition increases the elastic interfacial modulus. The stabilizing effect in presence of the polysaccharide is attributed to a protein–polysaccharide complex formation at the interface.