Study On Protein And Flavor In Duck Egg White During Salting And Its Desalting Effect When Forming Gel By Heating Treatment

Salted egg white produced from salted duck egg,which is a high-quality protein resource.However,high salt content and poor flavor led it difficult to directly apply to the food.Therefore,it is necessary to study the protein and flavor of salted egg white during salting to carry out the desalination research of gel produced by salted egg white,which will expand the application in food field of salted egg white.In this study,the egg white was researched to explore the changes of composition,physical characteristics,protein structure and the relationship between the flavor and quality of salted egg whites during salting.At the same time,the effects about desalting efficiency of salting egg white and gel properties were investigated after treatment with shearing assisted heat,so as to provide a theoretical basis for the development of protein ingredients.(1)The changes of egg white components,physical properties and protein structure were systematically compared during salting.With the increase of salting time,the content of salt and fat in egg white increased from 0.55% and0.3% to 4.45% and 0.87% respectively;and the ratio of water content to protein content increased from 6.7 to 10.66,which was caused by the free water permeated from egg yolk;the p H and the viscosity of egg white showed a significant downward trend.There were 8 free amino acids which ratio to total amino acids decreased significantly,and 4 free amino acids which ratio to total amino acids increased significantly.The secondary structure of protein in salted duck egg white changed,which α-helix gradually transformed into β-sheet and β-turn.The relative content of free sulfhydryl group increased first and then decreased,and the surface hydrophobicity decreased first and then increased.The results of UV and fluorescence spectra showed that the microenvironment of aromatic amino acids did not change significantly.SDS-PAGE electrophoresis showed that protein subunits did not change significantly during salting.(2)The sensory characteristics of salted egg white changed greatly after 25 d during salting,with significantly deepened color and stronger fishy smell.A total of 71 volatile organic compounds(VOCs)were identified by GC-MS during salting,which alcohols,aromatics,ketones,heterocycles,esters and aldehydes were the main flavor compounds.The content of alcohol compounds was very high in fresh duck egg white,and decreased significantly after salting,with the same time aldehydes,olefins and amides increased gradually,and the content of esters appeared after 10 days when salting;when salted to 35 days,the content of L-menthol reached to the largest,which is the volatile marker of salted egg white contaminated by bacteria,and there were obvious fishy smell substances such as1-octene-3-alcohol,4-terpenol and acetophenone appeared at the same time.A total of 43 VOCs were identified by Gc-IMS.Ketones and esters were the main flavor compounds in of salted egg white during salting,followed by acids,aldehydes and alcohols.The relative content of ketones in fresh duck eggs was the highest,and then decreased gradually,while the relative content of esters,acids and aldehydes increased steadily during salting;when salted to 25 days,the content of isobutyric acid,propionic acid and other fishy smell substances increased significantly.The OPLS-DA model was established to screen out 33 characteristic flavor compounds in the GC-MS results and 20 characteristic flavor compounds in the GC-IMS results,respectively.Through the analysis of the cluster heat map,the different curing periods of duck eggs can be effectively distinguished.The flavor substances identified by the two methods are complementary,and both start to produce odor substances in 25 ～ 30 days,which effectively verifies the sensory results.(3)Gelatin was prepared by salted egg white to study the effects of protein concentration,shearing rate and heating temperature on desalination rate,gel size,microstructure,rheological properties and texture characteristics.When the protein concentration was 20 mg/m L,the salted egg white gel had the highest desalination rate of 88.83%,and the taste was good and the texture was even.When the shearing rate was 300 rpm,the rate of desalination was the highest,reaching 90.34%.However,the hardness,elasticity,viscosity and chewiness of the gel decreased.The effect of heating temperature on the gel is not as significant as that of the shear rate.With the increase of heating temperature from 80 °C to90 °C,the particle size distribution of the gel was slightly shifted to the left,while the viscosity decreases,the loss factor also increased,and the desalination rate increased from 81.78% to 88,71%.When heated further to 95 C,the gel quality was uneven,and the solid recovery rate was 62.59%.