Impact of thermal treatment on the rheological, microstructural, protein structures and extrusion 3D printing characteristics of egg yolk

Abstract

This study investigated the effects of heat treatment (at 72, 76, 80, 84 °C for 2, 4, 6, 8, 10, 12 min) on the rheological, microstructural, protein structures and 3D printing characteristics of egg yolk. The results showed that the storage modulus (G′), loss modulus (G″) and viscosity exhibited an increasing trend with increasing heating time. Confocal laser scanning microscope (CLSM) showed that after heating for 8 min at 76 °C, 80 °C and 84 °C, lipids were released from viscous yolk paste, followed by second recombination and aggregation among yolk components. At these points above, the solid behaviors (G' ≥ G″) of egg yolks were observed, which caused a restraint of proton migration of water and lipid. Fourier transform infrared spectroscopy (FTIR) demonstrated that after heating at 72 °C for 8 min, 76 and 80 °C for 6 min and 84 °C for 4 min, a left shift began to appear in the heat-induced egg yolk paste at wavenumber 1631 cm−1, which were in accordance with a decrease in the shorter relaxation time (T21) and fluorescence intensity and an increase in apparent viscosity of egg yolks. The results of printing performance showed that the viscous yolk pastes induced by heat treatment (at 76 °C for 8 and 10 min or 80 °C for 6 min) can be used for 3D printing.