Comparison Of Physicochemical Properties Of Three Pickled Salted Eggs And Preliminary Exploration On The Cause Of "Black Circle" Formation

Salted duck egg is a kind of traditional remanufacturing eggs,which enjoys a good overseas reputation.However,the traditional processing method of salted duck egg has some disadvantages,such as long cycle,uneven quality and the phenomenon of "black circle" in egg yolk,which restrict the development of salted egg industry.In this study,three methods of pickling salted duck eggs were compared:vacuum waterflooding,atmospheric waterflooding and mud wrapping.The effect of processing method of salted duck egg was investigated by measuring the physical and chemical indexes of egg weight,yolk index,yolk hardening rate,yolk and egg white salt content,yolk oil yield,yolk white texture and yolk flavor.It was found that the salted duck eggs can be prepared after 12 days by vacuum decompression method,while the mud wrapping method needed 22 days and the normal pressure flooding method needed 32 days.Compared with the traditional method of mud-packing and atmospheric water flooding,the vacuum water flooding method was able to reduce pickled time,and promote similar quality.The egg white was getting thinner during the pickling process of salted duck eggs.A comparative study on the physicochemical properties of thick proteins and thin proteins.The result showed that the egg white index of fresh duck eggs was 0.91,which decreased by 52.7%at the end of pickling,and the thick protein had less free water content and more water content than the thin protein.The surface hydrophobicity of the thick protein increased by 27.40%,while the thin protein increased by 3.94%.About the thick protein,the total sulfhydryl group decreased by 22.14%,and the free sulfhydryl group decreased by 28.83%.About the thin protein,the total sulfhydryl group decreased by 22.14%and the free sulfhydryl group decreased by 54.93%.Protein structure:both α-helix and β-sheet of thick protein and thin protein were reduced,β-turn and random curl were increased.SDS-PAGE gel electrophoresis showed that there was no protein type change in egg white during pickling.And scanning electron microscopy showed that the thick protein was dense and orderly,while the thin protein structure was unordered.A preliminary study on the formation of the "black circle" of salted eggs,analysis of egg yolk and egg yolk "black circle" by thermogravimetric analysis,and the results showed that there were differences in chemical composition,the content of iron was higher in the"black circle".During the pickling process,the content of ferrous ions increased slowly,but increased rapidly after autoclaving;the pH of the egg white was gradually reduced from 9.08 to 6.45,and the pH of the egg yolk was decreasing gradually,from 6.91 to 5.81.In the egg whites,the methionine decreased by 7.42%,and the cystine decreased by 22.72%.And in egg yolk,the methionine decreased by 6.90%,and the cystine decreased by 7.29%during the pickling process.After aging,the methionine decreased by 76.37%,and the cystine decreased by 66.83%in the egg white,but in the egg yolk,the methionine decreased by 36.66%,and the cystine decreased by 34.42%.In addition,EDTA and citric acid could inhibit the phenomenon of "black circle" of salted egg yolk.