Changes in aggregation behavior of raw and cooked salted egg yolks during pickling

Abstract

In this study, we aimed to investigate the changes in gelation behavior of raw (without heating) and cooked (with heating) salted egg yolks during pickling. Results indicated that the decreasing trend in the main peak T22 of raw and cooked salted egg yolks. Cooked salted egg yolks after 28 days of pickling had a higher release of free lipids as visualized using a confocal laser scanning microscope (CLSM). Transmission electron microscope (TEM) micrographs showed that protein granules were distributed together with lipid spheres in raw and cooked salted egg yolks, and the liberated constituents (lipids and proteins) reorganize and aggregate in cooked salted egg yolks after 28 days of pickling. As the pickling proceeded, the soluble protein content and free sulfhydryl content of raw salted egg yolks, the free sulfhydryl content and surface hydrophobicity of cooked salted egg yolks showed an overall increasing trend, followed by significant decrease. The surface hydrophobicity of raw salted egg yolks exhibited an increasing trend. Differential scanning calorimetry (DSC) results demonstrated that salting can stabilize the protein molecules by an increase in denaturation temperatures. Fourier transform infrared spectroscopy (FTIR) revealed that the secondary structures of egg yolk proteins underwent changes, but no difference in protein patterns of either raw or cooked salted egg yolks was observed by SDS–PAGE during pickling. These results suggested that the characteristic gel of salted egg yolks is formed, as the result of multiple interactions between protein molecules and between protein and lipid molecules.