Thermally reversible emulsion gels and high internal phase emulsions based solely on pea protein for 3D printing

Abstract

This work compared thermally reversible emulsion gels and high internal phase emulsions (HIPEs) based on pea protein for 3D printing at different oil volume fraction (ϕ) ranging from 0.2 to 0.8. Thermally reversible emulsion gels were obtained with ϕ from 0.2 to 0.65, which melt into liquid emulsion as temperature increased, and recovered into emulsion gels upon cooling as reflected by consistent rheological measurements. The Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed the transition between intermolecular β-sheet at 1630 cm−1 and intramolecular β-sheet at 1618 cm−1 through reversible H-bonds upon changes in temperature, which was responsible for the repeated thermo-reversibility. With ϕ increased to 0.74–0.8, HIPEs were confirmed by Scanning Electron Microscope (SEM) and Confocal Laser Scanning Microscope (CLSM), yet the thermo-reversibility was not maintained. In addition, the thermally reversible emulsion gels exhibited strong shear-thinning and thixotropic recovery through the untangling and reformation of the H-bonded gel network. Whereas deformation and restructuring of the close packed droplets were responsible for such behaviors in HIPEs. 3D printing test has further demonstrated excellent performance of thermally reversible emulsion-filled gel with ϕ 0.4, comparable to HIPE with ϕ 0.74 b y enabling printed objects with high shape fidelity (printability index (Pr) of 0.95–1.08) and shape stability (prints height maintenance (Hm) of 82.2%–87.8%). This research opens up thermally reversible emulsion gels solely from sustainable protein source for 3D printing, with low oil content and no synthetic ingredients needed.