Insight Into The Mechanism Of Egg White Protein Gelling Properties Influence By Sulfated Polysaccharides

Food gels play a key role in the modern food industry due to their wide range of functional properties,high water content and low calories.Composite systems of different types of biopolymers,such as polysaccharide-polysaccharide mixtures and protein-protein mixtures are often offer more advantages in the production of binary food gels than single systems.Egg white is a high quality natural food gel.It consists mainly of 87% water and 13% solids,with 90% of the solids being protein.Egg white proteins(EWP)are widely used in food production due to their excellent processing properties.Gelation is one of the most important properties of EWP.Thus EWP often used as gelling agent,edible film and fat substitute in food products.However,heat treatment techniques often result in a greater rate of protein aggregation than unfolding,which promotes the formation of insoluble aggregates and cloudy gels that don’t meet the demands of consumers.Polysaccharides are common biomolecules that play an important role in the modification of food structure.Polysaccharides and proteins can comform complex cohesive systems byelectrostatical interaction.The charge density of the polysaccharide is an important factor affecting the cohesion and gelling properties of the complex.Previous study have found that any polysaccharide with a sulphate group can induce egg white proteins to form excellent gels.Therefore,in this study,the mechanism of the formation of transparent hydrogel by dextran sulfate(DS)was comprehensively investigated from the viewpoint of protein molecular conformation,aggregate morphology and gel formation kinetics;based on this,polysaccharides with different degrees of sulphate esterification(Microcrystalline Sodium Sulphate(MCS))were further investigated.Finally,a representative sulphated polysaccharide(kappa carrageenan(KC))was used to regulate the gelation properties of meat sausages in a complex system with egg white proteins,which laid a theoretical foundation for the preparation of special high gelation egg powders and their application in food processing.This study provides a theoretical basis for the preparation of specialised high gelatin egg powders and their application in food processing.The main findings and conclusions of this paper are as follows:This paper investigates the mechanism of DS-induced EWP transparent hydrogel formation by monitoring the changes in EWP/DS gel properties and intermolecular forces during gel formation using rheological properties,microstructure,water distribution,intermolecular forces and molecular conformation.The results showed that the addition of DS inhibited the formation of insoluble aggregates during the heating process,and the EWP/DS gels had a highly ordered fibrous network structure after heat treatment,resulting in better textural properties and water-holding capacity.In addition,the addition of DS promotes the denaturation of EWP and hydrophobic interactions become the main intermolecular force in EWP/DS.Overall,the electrostatic repulsion in the formation of the EWP/DS complex effectively inhibits further disordered aggregation of the denatured protein,while allowing the hydrophobic groups within the protein molecules to be fully exposed and to aggregate in an orderly manner through hydrophobic interactions during heating,resulting in a transparent gel with a refined structure.The effect of MCS with different degrees of substitution on the gel properties of EWP was investigated to determine the dependence of the improved gel properties of EWP on the charge density of the sulphate group of the polysaccharide.MCS with different degrees of substitution were prepared by the chlorosulfate-pyridine method(CSA-Pyr)and the degrees of substitution of the corresponding MCS were calculated by barium sulfate turbidimetry and infrared spectroscopy.The results showed that the rheological characteristics,hardness and water holding capacity of EWP gels were significantly improved after the addition of MCS,with a positive correlation with the DSs of MCS.The gel porosity in the microstructure decreased continuously with increasing MCS substitution.In contrast,the hydrophobic interaction content increased with increasing degree of substitution of MCS.In addition,the addition of MCS inhibited the formation of insoluble aggregates during the heat treatment process and promoted the unfolding of the tertiary structure of EWP molecules and the exposure of hydrophobic groups.Principal component analysis(PCA)revealed a significant correlation between the colloidal properties and the thermal aggregation behaviour of the proteins.The effect of the addition of different binders(soya protein isolate(SPI),egg white protein(EWP),whey protein isolate(WPI),κ-carrageenan(KC)and different ratios of EWP/KC complexes R20/R50/R5)on sausage characteristics was studied.The results of the study showed that sausages from the EWP/KC-R20 group had lower cooking losses(1.49%)and higher firmness(3024.25 g)(P < 0.05).This could be attributed to the interaction between EWP and KC.In addition,the addition of KC resulted in increased hardness and decreased emulsion stability and water holding capacity(P <0.05).The colloidal properties of the sausage samples were not affected by WPI and SPI.The results of the intermolecular interactions indicated that the qualitative properties of the sausages were related to the ratio between the disulphide and hydrophobic bonds.This work provides a theoretical basis for the use of sulphated polysaccharides in colloidal foods by systematically investigating the mechanism of interaction between and sulphated polysaccharides and egg white proteins to form complex gels and the effect of sulphate substitution of the polysaccharides on this interaction.Theory of the development of the gelling properties of EWP in the food industry.