Microstructural and rheological behaviors of thermo-reversible and thermo-irreversible hemp protein gel

Abstract: Thermo-reversible gels such as gelatin gain extensively utilization for gelling food products. In recent years, there is an urgent demand of gelatin replacement by using plant-based biopolymers such as plant proteins because of consumer’s health conscious, and rapidly growing global markets for Halal and Kosher foods. In this study, thermo-reversible (TR) and thermo-irreversible (TI) hemp protein gels (HPG) could be formed by reverse micelles extracted hemp protein isolate. Based on our findings, protein concentration and gelling setting temperature are the two critical parameters to determine whether is the formation of TR gels or TI gels. To compare the impact of protein concentration and gelling setting temperature on the HPG formation and their properties, HPGs formed by using 4% of protein suspension heated at 85℃ and 90℃, and 12% of protein suspension at 85℃ were investigated. In general, filament structure of TR-HPG could formed with the protein concentration of 4% and gelling setting temperature at 85 ℃. As the protein concentration and gelling setting temperature increased, TI-HPG was formed. According to the gelling mechanism study results, hydrogen bonds and hydrophobic interactions were the major molecular interactions contributed to the gel formation. The microstructure, water holding capacity (WHC), linear and nonlinear rheological behaviors of three abovementioned HPG were further investigated using small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS). In general, the higher protein concentration had higher WHC owing to their denser structures. In terms of rheological behavior, TR-HPG had wider linear viscoelastic region with higher creep compliance, while TI-HPG exhibited greater gel strength and higher modulus during relaxation. The LAOS reflected that HPG could be considered as soft gels with intracycle strain stiffening and shear thinning. These findings could potentially aid in the design of plant protein gels with specific textural and functional properties for gelling food application.