Study On The Egg Yolk Comparative Proteomics During Egg Storage

In order to study on egg yolk protein changes during egg storage systematically, we choosed different temperatures (4℃,22℃,37℃) for storage experiments. We measured freshness indicators and egg yolk protein content.etc firstly. Then studied egg yolk proteins’changes during storage by SDS-PAGE. Finally, selected temperature and time in which protein have significant changes for two-dimensional electrophoresis and mass spectrometry. The aim of this study was to detect egg yolk proteins’changes in content and species during storage and their change mechanism.We choosed Hy-line brown eggs laid within24hours for22℃storage test and storaged eggs for40d and test10d once. The result showed that YI decreased significantly(p<0.01)during storage. Egg yolk pH and the percentage of egg yolk protein increased significantly(p<0.01), while WI and HU decreased significantly (p<O.Ol) during storage. Egg yolk TVB-N increased significantly(p<0.01), from4.89±0.36mg/100g to12.37±0.46mg/100g. We measured the total protein content in egg yolk by coomassie blue colorimetric, and it showed significantly decreased(p<0.01)during storage. Further changes of the egg yolk protein and egg yolk plasma were analyzed by SDS-PAGE and we found that proteins which had significantly changes were most in egg yolk plasma. For example,95KDa protein in plasma was slightly less at20d.76KDa protein(ovotransferrin)in plasma were reduced during storage.65KDa protein(y-livetins heavy chain)in plasma was slightly less at20d.Fresh Hy-line brown eggs were stored at37℃for15d, and we tested once5d.. Compared with22℃, YI decreased more rapidly during37℃storage, from0.43℃0.01to0.15℃0.02. At the same time, the percentage of egg yolk protein, egg yolk pH and egg yolk TVB-N increased significantly (p<0.01). WI and HU significantly decreased (p<0.01). Egg yolk protein content remained stable from0d to10d and sharply decreased from10d to15d. We studied egg yolk protein and egg yolk plasma by SDS-PAGE and found72KDa protein(ovotransferrin BB/BC type) and68KDa protein (PIT54protein precursor) in egg yolk were less at0d. Proteins in egg yolk plasma also changed significantly, for example,66KDa (y-livetins heavy chain) and55KDa protein (LDL fragments) were increased and49KDa protein (LDL fragments) were decreased during storage. Fresh Hy-line brown eggs were stored at4℃for120d, and we tested once20d. The result showed that YI decreased significantly (p<0.01)during4℃storage, but it decreased slower than22℃and37℃storage. Egg yolk percentage increased significantly (p<0.01), from23.12±0.56to28.31±0.54. WI and HU significantly decreased (p<0.01). Egg yolk pH and egg yolk TVB-N significantly increased(p<0.01). We measured the total protein content in egg yolk by coomassie blue colorimetric, and it showed significantly decreased(p<0.01) during storage.We analysised egg yolk proteins and egg yolk plasma by SDS-PAGE. Huge changes were found such as120KDa proteins (HDL fragments) and31KDa protein (PREDICTED:beta-2-glycoprotein1) in egg yolk were less at80d and100d,48KDa protein (β-livetin) in plasma was less at60d,38KDa protein (TPRXL211KDa protein) in plasma was more at120d.We identified egg yolk plasma by2-DE and MS and ultimately identified23proteins in egg yolk plasma. There were egg yolk proteins in literature like TPRXL211KDa protein, PIT54, VTG, and so on. Some were previously identified in egg white, such as ovotransferrin BB/CC type, inhibitor precursors. We identified some proteins in egg plasma, including unnamed protein(IPI63524, IPI1334751), VYGIII180KDa protein, PREDICTED:beta-2-glycoprotein1. This experiments had further expanded the egg yolk plasma protein databases.According to above experiment, we selected22℃(0d,20d and40d)to do comparative proteomics analysis.21proteins in egg yolk plasma had significantly change(p<0.05)during22℃storage.7proteins increased and7proteins decreased in abundance after20days storage.10proteins increased and11proteins decreased in abundance after40days storage.7proteins increased and12proteins decreased in abundance from20days to40days.10protein changed continuously during the storage, including Ig light chain [Gallus gallus], ig lambda light chain, partial [Gallus gallus], immunoglobulin lambda light chain precursor [Gallus gallus], vitellogenin [Gallus gallus], vitellogenin-2precursor [Gallus gallus], vitellogenin-1precursor [Gallus gallus], vitellogenin I [Gallus gallus], transthyretin precursor [Gallus gallus], transthyretin[Gallus gallus]. The reasons for the changes of these proteins may be degradation, aggregation, combination with other substances involved in the metabolism.