| Hen egg, in addition to its high nutritional quality, contributes functional properties to food such as emulsifying, foaming and gelling, however, fresh egg can not store for a long lime, and it is more convenient and safer when they were processed into liquid egg products, which make it widely used in food products. During the production and application of liquid whole egg (LWE), the proteins are subjected to several processing steps with thermal, physical and mechanical treatments that may damage egg protein functional properties, however, due to the material's complicated composition and structure, its functional properties have not received the attention they deserved. The aim of this study was to investigate the influence of pH adjustment, homogenizing treatment, heat treatment and addition of sugar/salt on the functional and physicochemical properties of LWE, to understand the mechanism responsible for the functional property change in order to limit their harmful effects and promote the development of LWE production.First, the effects of pH adjustment (6.5-9.0) on functional property of LWE were investigated. Results showed that the solubility, emulsion stability and gel hardness significantly increased as pH increased, while the emulsifying activity of LWE decreased. It was also foud that the foaming ability and foaming stability was under the best when pH was 7.0 and 7.5 respectively.Secondly, we studied the influence of homogenizing treatment (5-40Mpa) on the properties of LWE. Results showed that homogenizing treatment significantly affected the functional properties of LWE, homogenizing at high pressure led to a decrease in foaming ability and emulsifying ability, but a increase in emulsion stability, foaming stability and gel hardness, however, it led to a slight change in solubility. Homogenizing treatments could distrubte the structure of egg proteins and polymer. Resultes suggested that the factory should use appropriate homogenizing treatment when producing liquid whole egg.Then,the paper dealed with the effect of heat treatment (58℃,61℃,64℃and 67℃,2.5-10min) on the physicochemical properties such as emulifying property, foaming property, rheology property and extent of protein denaturation of LWE. Results showed that heat treatments induced different proteins denature and influenced functional properties; it was found that the emulsifying activity of LWE changed slightly when the temperature was between 58-64℃and significantly decreased when the temperature was at 67℃,while heat treatments above 64℃significantly improved the emulsion stability. Foaming property changed more complex after heat treatment, moderate heat treatment (58-61℃) improved the foaming ability, which would decrease when the temperature increased. These changes induced the decrease of sponke cake volume; the changes in functional properties were related with the protein structure, heat treatment induced proteins unfold and aggregate, which resulted in the surface hydrophobicity and free sulfydryl content significantly changed after heat treatment. We also found that heat treatment increased the viscosity and changed the rheology property of LWE. Finally, Native-page electrophoresis proved that different heat treatments induce different proteins denaturation. Finally, we studied the effect of addition of sugar/salt (4%-8%) on the properties of LWE. Addition of sugar or salt resulted in the increase of heat resistance of LWE and the gelation temperature increased 3-7℃. LWE with salt had better emulifying activity and foaming ability after heat treatment, and LWE with sugar had better emulsion stability and foaming stability than others, meanwhile, LWE with sugar and salt(4%) had good emulifying property, foaming property, which indicates that there is a synergistic reaction between sugar and salt. It was also found that addition sugar or salt decreased the hardness of LWE gel . |
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