Reversible and irreversible changes in protein secondary structure in the heat- and shear-induced texturization of native pea protein isolate

The molecular mechanism of plant protein texturization under extrusion conditions was unraveled at the secondary structure level by decoupling the effects of heating, cooling and shearing on protein secondary structure. Native pea protein isolate hydrated at 50 % w/w in H₂O and in D₂O, to allow detailed resolution of protein secondary structure, was subjected to temperature cycling in a temperature-controlled ATR-FTIR and was texturized at the gram scale by microcompounding. Upon heating without shearing, native α-helices and intramolecular-β-sheets unfold to random domains, followed by the formation of intermolecular β-sheets, inducing aggregation. During cooling, the intermolecular β-sheets become increasingly ordered, and random domains partially fold into non-native β-structures. Combined heating and shearing results in more extensive β-sheets than heating alone. The resulting β-rich structures provide for an entangled network of protein chains and a cohesive protein matrix. The effect of shear on protein association/dissociation is controlled by the specific mechanical energy (SME), with the degree of intermolecular β-sheet formation increasing with increasing SME values up to ∼1000 kJ/kg, followed by a gradual decrease with further increases of the SME. The detailed molecular insights in the mechanism of plant protein texturization allows for a more controlled design of novel food products, including matrices for use in meat analogues.