Effect of water content and aging on the elastic properties of extruded pea protein isolate

Abstract

The effects of water on the elastic properties of extruded pea protein isolate (PPI) are investigated transversally to the fiber direction in the water content range between 40% w/w to 60% w/w. Young's modulus of elasticity in the transversal direction was found to decrease linearly with the water content from 2.6 MPa at a water content of 40% w/w to 0.6 MPa at the water content of 60% w/w at T = 21 ± 1 °C. Matrices extruded at different water contents of which the water content was adjusted to 60 ± 1% w/w showed decreasing values of Young's modulus. This variation in the transversal Young's modulus correlates linearly with the specific mechanical energy, confirming the impact of processing on the development of the protein network. The kinetics of aging of the extruded PPI matrices at T = 4 °C were fitted using an exponential equation and were observed to be dependent on the water content. Characteristic aging rates varied from an aging rate of ∼0.1 h−1 for the matrices extruded at a water content of 40% w/w to ∼0.015 h−1 for the matrices extruded at a water content of 60% w/w. The degree of aging was found to be 43.2 ± 7.5%, independent of the protein content of the matrices. The current study is the first systematic investigation of the elastic properties of extruded plant protein matrices in the concentration range that is relevant for meat analogs and may serve in process optimization and product development as well as for fundamental studies into the properties of concentrated protein networks.