Mechanical Failure Characteristics of Native and Modified Egg White Gels

Abstract

Mechanical failure characteristics of cooked egg white were evaluated using a torsion test and a uniaxial compression test. Native egg white and egg white modified with acetic anhydride, succinic anhydride, and oleic acid were evaluated. Gels were formed by cooking egg white to 80 C in stainless steel cylinders submerged in a 90 C waterbath. All gels had a Poisson's ratio of .49, indicating that the gels were incompressible materials. Gels made from succinylated or oleic acid-treated albumen were highly deformable and did not fail in compression. When comparing torsion and compression results, shear stresses, true shear strains, and shear moduli for native and acetylated egg white gels were in good agreement. Shear stresses at failure by torsion testing ranged from 13.0 to 19.8 KPa. True shear strain at failure for oleic acid-treated and succinylated egg white gels were approximately three times as great as for native egg white gels. Shear modulus values were about half as large. The results confirm that changes in physicochemical properties of proteins prior to heat gelling significantly affect the failure properties. The sensitivity of the torsion test suggests that earlier examination of egg white gel texture properties by texturometer testing may have underestimated the differences in gels due to the modification procedures applied.