Effect of lipid-protein interactions on extrusion of offal protein isolates

Lung protein isolates after defatting with carbon tetrachloride, chloroform, dichloromethane, iso-propanol, ethanol and methanol, were extruded with and without admixed soya grits. Extrusion of these isolates showed a clear dependence of the process on the lipid content. Extruded products with better characteristics were obtained by defatting the samples. Progressive removal of lipid, as the polarity of the solvent used increased, however, did not promote a corresponding progressive improvement in the textural quality of the extrudates. Protein-protein interaction was assessed by the primary mechanical parameters, hardness, springiness and cohesiveness. It was maximal at intermediate lipid contents. These broadly corresponded to the range of lipid contents where maximum hydration and affinity towards water occurred. It was concluded that residual lipid is necessary in order to maximize protein-protein interactions during extrusion. The effects of lipid-protein interactions on the texturization of offal protein caused a wide variation in the degree of cross-linking between protein molecules during extrusion. The results showed that hydrophobic and electrostatic interactions can play an important rôle in texture formation during thermoplastic extrusion.