Mechanism Research Of Quality Formation Of Salted Duck Egg And Quality Changes In Storage Process By LF-NMR

As one kind of traditional egg products,salted duck egg is popular in China and Southeast Asia.The methods of quality valuation in the slating and storage process for salted duck eggs mainly including physicochemical properties detection,microorganism and conventional spectrum testing,such as acoustics,optics,electricity etc.These methods can not directly and quickly valuate the quality of salted duck eggs.As a non-destructive and quickly technique,low-field nuclear magnetic resonance（LF-NMR）and magnetic resonance imaging（MRI）can reflect the distribution and dynamic migration of water or oil.Changes of quality of salted duck egg during salting and storage were investigated by LF-NMR,MRI,confocal laser scanning microscope（CLSM）,as well as physicochemical analysis（includ moisture,salt,oil,hardening rate,egg yolk index,pH and TBARS）.This study include four parts,they are the research of proton component identification for duck egg,quality formation of salted duck egg in the salting process,quality changes of salted duck egg in the storage process and the research about bad quality of salted duck egg.The mechanisms of quality formation and deterioration of salted duck eggs were explained.It provides a theoretical guidance for quality controling in the salting and storage process of salted duck eggs.The summarizations of this paper are listed as follows:（1）In the first study,the proton components of raw and cooked duck eggs were identified by means of dehydration and comparative analysis.It was found that there are four kinds protons in raw duck eggs,including protein or the protons tightly bound with protein(T₂₁),protons of multi-layer bound water(T₂₂),protons of oil and the protons intergrate with oil(T₂₃)and protons of free water(T₂₄)in raw duck eggs.Three or four kinds protons are shown in boiled duck eggs,they are protons of the interaction of protein and water(T₂₁),protons of multi-layer bound water(T₂₂)and protons of free water(T₂₃).（2）In the second study,salted duck eggs,egg white and egg yolk are the research object with salting for 0 to 6 weeks.Distributions and migrations of water and oil in salted duck egg were tested by LF-NMR and MRI in the salting process,combining with physicochemical analysis and microstructure characteristic,to explore the mature quality formation mechanism of salted duck eggs.Through relaxation characteristics,it is found that the degree of freedom for multi-layer bound water is reduced,free water and oil content increased in the egg white and yolk,respectively.The multi-layers bound water and free water content decreased obviously.In the MR images,the density of the low-flow protons of the yolk reduced.It is found that moisture content of salted egg white and yolk decreased with the increase of salt content.The hardening rate,egg yolk index,the free lipids and oil exudation ratio are increased.It was found that the lipoprotein diameter of salted egg yolk decreased and free oil was released from lipoprotein by CLSM.LF-NMR can evaluate quality of duck eggs and explain quality formation mechanisms such as phase transform of egg yolk and oil exudation.（3）In the third study,using LF-NMR and MRI to monitor water distribution and migration of raw salting,no packed and vacuum packed storage process of salted duck eggs.The quality degradation mechanism of salted duck eggs was studied by combining with physicochemical tesing and inner quality analysis.The multi-layer bound water and oil were integrated in the raw salting storage process.The content of multi-layer bound water decreased,while,the free water increased in no packed storage process.It is not obvious for water migration in the vacuum packed storage.MR imagies show that the yolk dissolved into the egg white liquid,while,the salted duck egg appeared shrinkage phenomenon in the no packed storage style.The pH value has a decrease trend of in egg white.The TBARS increased in vacuum and no packed storage process,while,the TBARS is lowest in the raw salted storage style.The principal component analysis can distinguish salted duck eggs with different storage time.（4）In the fourth study,salted duck eggs with different desolvation degree,black yolk eggs and decayed eggs were act as the research object,using LF-NMR and MRI to detect the distribution of water and to explain the formation mechanisms of bad quality.The higher the degree of desolvation,the lower the free water fluxion,the lower of the multi-layer bound water in the cooked desolvation salted duck eggs,.Black yolk eggs and decayed egg II is more liquid,and the T₂ of multi-layer water,bound water and free water is higher in the decayed egg I.The egg white and yolk were dissolved together in MRI for raw salting process.Low liquid protons are shown in egg yolk with high density in black yolk eggs and decayed egg,and the low liquid protons with high density in decayed egg II in both egg yolk and white.The PCA analysis based on LF-NMR decay data can distinguish the good quality eggs,desolvation eggs,black yolk eggs and decayed eggs.