Xylitol-NaCl complexes mitigate the thermal instability behaviour of liquid egg yolks: Effect on rheological...

Liquid egg yolk (LEY) is a type of heat-sensitive food ingredient, and its wider applications are limited by the denaturation, increased viscosity and decreased emulsifying property caused by the thermal treatment such as pasteurization and processing. Traditionally, NaCl was used to address this issue, however, with the diversified development of food, this method can no longer meet people's demand for healthier food, hence, new method was needed. The influences of xylitol, NaCl and xylitol-NaCl complexes on thermal tolerance, thermal aggregation behaviour and structure were investigated. The thermodynamic results show that xylitol, NaCl and xylitol-NaCl complexes could enhance thermal denaturation temperature, slow down the increase in consistence, particle size and turbidity caused by heat treatment, as well as the decrease in the absolute value of potential and protein solubility. Differential scanning calorimetry (DSC) analysis showed that Td increased from 82.10 °C (control group) to 83.30 °C, 84.00 °C, 87.80 °C, 90.10 °C, and 91.20 °C (experimental groups) respectively. Compared with that in the control group, K changed by -37.39%, 55.72%, 48.97%, 105.28%, and 217.30% in the experimental groups. Compared with those in the control group, emulsification index (EI) increased by 4.23%, 6.21%, 10.83%, 8.72%, and 6.08% in the experimental groups, respectively. Similar trends were observed at 65, 70, and 75 °C. The crystallinity shows different variations and ultraviolet spectroscopy revealed the change of tertiary structural influenced by xylitol-NaCl. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed that the deterioration of functionality may be related to α-livetin + apo-LDL III and α-livetin through tracking protein changes induced by thermal treatment. The microenvironment of tryptophan residues was influenced by thermal treatment, according to Raman spectroscopy studies, and xylitol, NaCl and xylitol-NaCl complexes could improve protein stability. Microstructure analysis confirmed the phenomenon from aspects of microscopic morphology and distribution of lipids and proteins. Overall, this study proposes different formulation strategies that can both enhance thermal stability and adjust fluidity and emulsifying property.