MECHANICAL AND SENSORY ASSESSMENT OF THE TEXTURE OF REFRIGERATOR-STORED SPRING ROLL PASTRY

Spring roll (or popiah) consists of a filling surrounded by a remarkably thin pastry that is subjected to tension as it is wound around the filling. It cracks easily if stored before use. Textural perception of the pastry in the mouth is also affected. Within 1 day of manufacture, the Young's modulus of the pastry increases ten-fold, the tensile strength and critical stress intensity factor (K(IC)) increase to a lesser extent, but the strain to failure decreases. In the single-edge-notched test (mode I fracture) and trousers tear test (mode III fracture), which gave free-running cracks, fresh pastries were tougher than stored pastries because of blunting of the crack tip by large elastic strains. When the radii of curvature of crack tips in both fresh and stored pastries were constrained to be more equal in a cutting test, which induced out-of-plane shear in mode III fracture, fresh pastries were less tough than stored pastries. This paradox could be important in understanding otherwise contradictory textural assessments made by human subjects at the front versus the back of their mouth.