Study On The Poultry Egg Lipids Analysis And The Lipid Changes Of Hen Egg During Storage

As an important nutrient component of poultry eggs, lipids are not only good for human health, but also are the essential nutrient materials for the chicken embryos. Thus, the analysis and identification of egg lipids may be important aspects of egg scientific research, and at the same time are the research premise and foundation of lipid metabolism and lipidomics research. This study focused on the lipid analysis and identification. On the basis of constructing fingerprint of egg fatty acids, the flavor of different poultry eggs has been detected by gas chromatography-mass spectroscopy(GC-MS) and electronic nose(E-nose). A comparative lipidomics analysis about three poultry egg lipids was conducted by HPLC-MS/MS, and a series of experiments related to hen egg lipids during storage were performed. The main research results are as follows:(1) Fatty acid profiles of conventional egg yolks from seven different species(chicken, duck, quail, goose, free-range chicken, silky chicken and pigeon) were compared with GC-MS, then the fingerprint of fatty acid profiles were constructed. A total of 22 fatty acids were identified in all of the 7 egg samples. The content of monounsaturated fatty acids(MUFA) in yolks was significantly higher than the contents of the saturated fatty acids(SFA) and PUFA(p<0.05), and the content of ω-6 PUFA was higher than that of ω-3 PUFA. The predominant fatty acids in the yolks were oleic(C18:1 ω-9) and palmitic(C16:0) acids, but no remarkable difference was found among the fatty acid composition. A significant difference was measured among the fatty acid contents of seven egg samples. Free-range chicken and goose eggs had the significantly highest SFA content(p<0.05), 37.62% and 38.15%, respectively, while pigeon egg had the lowest content(31.33%). The MUFA content in pigeon(49.56%) and goose(49.53%) egg yolks was significantly higher than that in other species. The results of our research indicate that the PUFA content was the significantly lowest(p<0.05) in goose eggs(16.21%) and the highest in free-range chicken eggs(31.30%). The significant highest docosahexaenoic acid(DHA, C22:6 ω-3) level was reached to 1.97% in silky chicken egg. No eicosapentaenoic acid(EPA, C20:5ω-3) was detected in the seven egg yolk samples, C22:5ω-3 was detected only in duck egg yolk and C22:5ω-6 was detected in most of the samples. The fingerprint profile of common model fatty acids was constructed based on the GC-MS results and the similarity value and correlation coefficient were both above 0.98, which indicating a good fingerprint profile.(2) Researches on qualitation, quantification and discrimination of volatile compounds of different poultry eggs by HS-SPME/GC-MS were performed. A total of 41 volatiles were tentatively identified by GC-MS, and were grouped into 10 classes, including esters, alkenes, nitrogenous compounds, alcohols, and so on. For different egg species, the number of volatile compound was 26 for hen egg, 24 for goose egg, 23 for free-range chick egg, 20 for silky chicken egg and pigeon egg, 19 for quail egg, and 18 for duck egg. In terms of quantity, esters ranked the first in volatile components, followed by alkenes. The volatile compounds of the examined egg yolks exhibited noticeable differences, for example, the ethyl acetate contributed over 42% to the aroma volatiles of the free-rang and silky chicken eggs, volatile compounds contributed more than 40% of volatile compounds in hen egg and quail egg, phthalic acid butyl isohexyl ester was abundant in duck and goose egg, and sulfocompound accounted for 40% of the pigeon egg. A discrimination of flavor profiles by E-nose analysis indicated that sensor T30/1, LY2/AA, P10/1, LY2/g, P10/2 and P40/1 play a key role in distinguishing the egg samples.(3) Lipidomic research about egg lipids was conducted based on HPLC-MS/MS. A liquid chromatography coupled with APCI tandem mass spectrometry was employed to analysis TAGs of three poultry eggs, with a single phenyl-hexyl column. A total of 35 TAG molecular species were identified and quantified in hen eggs, duck eggs and quail eggs, and the relative content of PPOO, PLO, OLO, POP, OPO and OOO were more than 5% in all the samples. The composition of TAGs molecular species of different eggs has no significant difference but the content different significantly(p<0.05). Phospholipid profile of different poultry eggs has been identified of direct-infusion electrospray ionization tandem mass spectrometry(ESI-MS/MS) in negative ion mode, and the lipids species for different samples were 255 for egg yolk, 216 for duck egg tolk and 223 for quail egg, including 2 classes of sphingolipids(ceramide and sphingomyelin) and 8 classes of glycerophospholipids(d Me PE, LPC, LPE, PA, PC, PE, PG and PI). Cholersteryl esters(CE) were analyzed by TSQ Quantum in positive ion mode, ten species of CE were identified. Most of the CE in duck egg was significant different with hen egg while quail egg with insignificant difference.(4) The changes of physicochemical index and lipid fractions of stored eggs at 4°C, 22°C and 37°C was investigated, the results indicated that egg freshness decreased gradually during storage at both temperatures, the content of total lipid(TL) relative stable during storage, whereas the TL content decreased significantly(p<0.05) from 28.93 g/100 g to 24.20 g/100 g when stored at 37°C for 15 d. There is a ramsay rule between PL content and FFA content. The PL content significantly decreased during correlation analysis. The results were as follows:In fresh eggs, neutral lipase showed a highest enzyme activity(6.17×106 U/g protein), phospholipase(6.02×105 U/g protein) came second, and acid lipase showed a lowest enzyme activity(3.16×105 U/g protein). The activity of endogenous lipases decreased gradually throughout the storage period, and showed a significant negative correlation with storage temperature. The increase of POV and TBARS indicated that egg storage was the cumulative process of primary oxidation product and secondary oxidation product. The LOX activity was 55.49 U/g in fresh egg yolk, and decreased to 35.46 U, 34.90 U and 35.01 U at 4°C, 22°C and 37°C storage, respectively. In the later period, a raising inflection point appeared. Correlation analysis proved a significant negative correlation between lipase activity and lipid oxidation, phospholipase and free fatty acid content, while a significant positive correlation between phospholipase and PL content, indicating that the decrease of PL content and increase of FFA are caused by the hydrolysis of phospholipase.