Study On The Depolymerization Of Yolk Granules In Solution

Yolk can be divided into two components by simple centrifuge: yolk plasma and yolk granules.Compared with yolk plasma,yolk granules have a higher protein content and lower cholesterol content,which can be used as a new food raw material to replace yolk,so as to meet people’s pursuit of green and healthy life concept.Yolk granules are not only nutrient-rich,but as a kind of natural nano-assembled granules,the high phosphorus protein of yolk inside has a strong chelating ability to bivalent metal ions,for which related mineral supplements can be developed.Therefore,it is of great significance to analyze the structure of yolk granules and explore the depolymerization rule of yolk granules in solution,and to develop yolk granules themselves and construct new food systems.However,because yolk granules are self-assembled insoluble compounds,their application and development value are greatly limited.Therefore,this topic from the point of view of yolk particle structure,to explore the depolymerization of yolk particles in different solutions.The main research results are as follows:Study on depolymerization of yolk granules in four different solution.Four typical solution systems were selected: ionic strength,acid alkali,hot and cold and ultrasonic treatment.In NaCl solution,with the increase of NaCl concentration,the turbidity and average particle size of the solution decreased significantly,the Zeta potential increased first and then decreased,and the solubility increased significantly(p<0.05).When NaCl concentration was greater than 0.3mol/L,all indexes tended to be stable,which proved that 0.3 mol/L was the critical point of depolymerization of yolk granules in NaCl solution.In different acid-alkali solution systems,the turbidity and average particle size of yolk granules solution decreased first and then increased and then decreased with the increase of pH value.The Zeta potential and solubility in supernatant showed opposite trends(p<0.05),because pH4.50 was the isoelectric point of yolk granules,at which yolk granules aggregated and precipitated.In the extreme acid-alkali solution,the yolk granules were depolymerized on a large scale.After freezing-thawing and heating,the turbidity and solubility of yolk granules solution were significantly decreased,the average particle size was increased,and the Zeta potential was increased(p<0.05).The structure of yolk granules was mechanically damaged by freezing-thawing,and the degeneration of yolk granules was caused by heating.After ultrasonic treatment,the turbidity,average particle size and Zeta potential of the solution of yolk granules decreased significantly,while the solubility increased significantly(p<0.05).Cavitation and micro-turbulence forces in the process of ultrasonic treatment caused reversible changes to yolk granules,but the ultrasonic power had no significant effect on each index.The results of correlation analysis showed that the turbidity,average particle size and zeta potential of the yolk granules solution after ultrasonic were significantly positively correlated with each other,and the solubility was significantly negatively correlated with turbidity,average particle size and Zeta potential(p<0.01).Study on depolymerization of yolk granules in weakly alkaline solution.The absorbance,turbidity and supernatant protein concentration of yolk granules solution under different pH treatments showed that no matter how the concentration of yolk granules solution changed,the absorbance and turbidity decreased significantly with the increase of pH value,while the protein concentration increased significantly with the increase of pH value(p<0.05).After pH 8.00,The change trend of yolk granules solution was no longer obvious,which proved that yolk granules had obvious depolymerization in alkaline solution.20 mg/mL yolk granules solution was selected for the study.With the increase of pH value,the transmittance and Zeta potential of yolk granules solution also increased significantly(p<0.05),and the transmittance and average particle size of yolk granules solution were also increased(P <0.05).It was found that when pH value reached 8.00,the transmittance,turbidity,average particle size and Zeta potential were no longer significantly changed.It is proved that pH8.00 is the critical pH value for the depolymerization of yolk granules.The surface hydrophobicity of yolk granules in weakly alkaline solution increased significantly(p<0.05),and the depolymerization of yolk granules in weakly alkaline solution resulted in the release of a large number of internal hydrophobic lipoproteins and hydrophobic groups,resulting in the increase of surface hydrophobicity of yolk granules.Synchronous fluorescence spectra analysis showed that the protein conformation of yolk granules in the weakly alkaline solution was changed,and tyrosine and tryptophan residues or their local environment were changed,resulting in the chromophore exposure or more polar microenvironment.Fourier transform infrared spectroscopy analysis showed that the hydrogen bonds of the yolk granules in the weakly alkaline solution were strengthened.The possible reason was that the specific surface area of the depolymerized yolk particles increased,exposing more polar groups.The thermal stability analysis of yolk granules showed that the weight loss of yolk granules in the weakly alkaline solution was more than that of the untreated solution during the heating from room temperature to 100 ℃,which might be because the dissolved substances in the depolymerization of yolk granules were lost by evaporation during this period.However,during the heating at 100-800℃,The weight loss of untreated yolk granules at this stage was greater than that of the weakly alkaline solution.Study the rule of the supernatant of yolk granules in the weakly alkaline solution,and explore its solubilization effect.The weakly alkaline yolk granules solution was centrifuged,and the dry matter of the supernatant and precipitate of non-treated and treatment groups was determined.With the increase of pH value,the dry matter content of the supernatant increased significantly,while the precipitate dry matter decreased significantly(p<0.05).The protein content of the supernatant was determined,and it increased significantly with the increase of pH value(p<0.05).SDS-PAGE of proteins in the supernatant showed that the distribution of protein bands in the non-treated yolk granules was basically the same as that in the weakly alkaline solution,but the molecular weight of the protein bands was significantly increased,which confirmed that the yolk high phosphoprotein,yolk high density lipoprotein,yolk low density lipoprotein subunits and γ-vitelloglobulin had been in the supernatant.The results showed that the content of calcium and phosphorus increased significantly with the increase of pH value(p<0.05),which confirmed that the rupture of calcium phosphate bridge led to the separation of yolk high density lipoprotein and yolk high phosphoprotein,thus causing the disintegration of yolk granules.Metabolomics analysis of the supernatant revealed a total of757 metabolites in the supernatant.Principal component analysis showed that the untreated yolk granules solution was completely differentiated from the weakly alkaline yolk granules solution.Organic acids and their derivatives,phospholipids,benzene and their substituted derivatives,and amino acids and their metabolites were the four most abundant metabolites in non-treated.Compared with non-treated,the content of glycerophospholipids in yolk granules in weakly alkaline solution was significantly increased(p<0.01),and amino acids and their metabolites were significantly decreased(p<0.01).The results of metabolomics showed that the yolk granules in the weakly alkaline solution depolymerized,promoting the release of glycerophospholipids,and also inhibiting the dissolution of amino acids and their metabolites.