Study On The "Alkali-induced Liquefaction" Behavior Of Egg White Protein Gel Induced By Strong Alkali

Preserved eggs are traditional Chinese egg products,and the formation of the gel texture is usually attributed to the denaturation and aggregation of proteins under strong alkaline conditions.In this process,the alkalinity of the pickling liquid is an important factor in determining the quality of preserved egg white gel.If the concentration is too low,it will be difficult for some denatured proteins to condense into a stable gel.If the concentration is too high,it will cause the formed preserved egg gel to appear sticky shell and liquefaction.However,at present,the exploration of the law and mechanism of alkali-induced liquefaction of preserved egg protein gel under heavy metal-free conditions is relatively weak.Based on this,this paper used modern instruments such as texture analyzer,rheometer,Fourier infrared spectroscopy(FTIR),fluorescence spectroscopy,and liquid-phase mass spectrometry(LC-MS/MS)to study the alkali-induced preserved egg model and egg white protein model.Compared with the ovalbumin model,the state transition,structure transition,and the number and nature of the peptides of the protein sol-gel-sol at three different levels have been investigated.The influence of the induction of different alkalinity on the properties of protein gels and sols has been investigated.The solution of this problem will help to break through the heavy metal compounds that must be added during the processing of preserved eggs,and provide a further theoretical basis for the in-depth understanding of the behavior of "alkali-induced liquefaction".The main results are as follows:1.The preserved egg pickling model without heavy metal addition showed that during the alkali treatment,the total alkalinity of the pickling liquid continued to decrease,and the p H of preserved egg protein increased rapidly in the first 14 days,and then slowly increased.The hardness,elasticity and water holding capacity all showed significant changes that increased first and then decreased,and the hardness and water holding capacity reached their maximum at 28 days.After 42 days of liquefaction,the rheology and particle size distribution of preserved egg protein were tested.The results show that high concentration of lye helps to obtain a sol with lower shear viscosity and smaller particle size.Quantitative analysis of peptides showed that the number of peptides released during curing continued to increase,and the number of common peptides identified between groups was much smaller than the number of specific peptides.In general,there was a positive correlation between the concentration of alkali and the transformation of liquefaction.2.The alkali-induced egg white protein model showed that the hardness,brightness,surface hydrophobicity and total amount of released peptides increased in the initial stage of gel formation,but decreased significantly when the gel was liquefied.The rheological behavior showed that the egg white protein induced by the high concentration of alkali first reached the flowing state,which appeared as a shear-thinning fluid.The infrared spectrum showed that during the gel-sol transition process,the ?-sheet gradually decreased with the increased of the ?-helix.The gel structure of egg white protein was mainly supported by ionic bonds and disulfide bonds.The non-covalent cross-linking in the sol phase gradually weakened,and the content of ionic bonds increased rapidly,indicating that fully denatured protein molecules might expose more free groups.Quantitative analysis of peptides showed that the types and quantities of peptides obtained by alkaline hydrolysis at different concentrations did not show a high degree of similarity.The response of egg white protein under high alkalinity system was fast and violent,and the induction of low alkali concentration was more conducive to maintaining the stability of the gel state.3.The alkali-induced ovalbumin model showed that: regardless of the alkalinity,with time,the hardness,water holding capacity,particle size,surfa ce hydrophobicity and total number of released peptides of ovalbumin gel increased sharply,and then gradually decreased.Furthermore,the p H and elasticity of the ovalbumin gel showed a steady downward trend.The rheological behavior showed that the liquefaction process of the ovalbumin gel network was gradually degraded from a high-viscosity semi-fluid to a water-like sol.The ordered gel structure was mainly contributed by ?-sheets,which was accompanied by the continuous transformation of ?-helices,and the liquefaction was caused by the destruction of stable ?-structures.LC-MS/MS showed that under different induction times,the degradation of each group of proteins released a large number of specific peptides and a small amount of common peptides.At all the time of monitoring,only two groups were obtained between the high concentration group and the low concentration group.The peptides of the same sequence fully reflected the disorder and product randomness of alkaline hydrolyzed proteins,which ma de it difficult to quantitatively express the properties of small peptides in the sol-gel-sol transformation process.