Effects of freezing on the gelation behaviors of liquid egg yolks affected by saccharides: thermal behaviors and rheological and structural changes.

Monitoring and controlling the freezing process and thermal properties of foods is an important means to understand and maintain product quality. Saccharides were used in this study to regulate the gelation of liquid egg yolks induced by freeze‒thawing; the selected saccharides included sucrose, L-arabinose, xylitol, trehalose, D-cellobiose, and xylooligosaccharides. The regulatory effects of saccharides on frozen egg yolks were investigated by characterizing their thermal and rheological properties and structural changes. The results showed that L-arabinose and xylitol were effective gelation regulators. After freeze‒thawing, the sugared egg yolks exhibited a lower consistency index and fewer rheological units than those without saccharides, indicating controlled gelation. Weaker aggregation of egg yolk proteins was confirmed by smaller aggregates observed by confocal laser scanning microscopy and smaller particle sizes. Saccharides alleviated the freeze-induced conversion of α-helices to ß-sheets in egg yolk proteins, exposing fewer Trp residues. Overall, L-arabinose showed the greatest improvement in regulating the gelation of egg yolks, followed by xylitol, which is correlated with its low molecular weight.

Addition of NaCl or Sucrose on the Protein Content, and Functional and Physicochemical Properties of Egg Whites Liquid under Heat Treatment.

In this study, differences in the protein content and functional and physicochemical properties of four varieties of egg white (EW) were studied by adding 4-10% sucrose or NaCl and then heating them at 70 °C for 3 min. According to a high-performance liquid chromatography (HPLC) analysis, the percentages of ovalbumin, lysozyme and ovotransferrin rose with an increase in the NaCl or sucrose concentration; however, the percentages of ovomucin and ovomucoid decreased. Furthermore, the foaming properties, gel properties, particle size, α-helixes, ß-sheets, sulfhydryl groups and disulfide bond content also increased, whereas the content of ß-turns and random coils decreased. In addition, the total soluble protein content and functional and physicochemical properties of black bone (BB) chicken and Gu-shi (GS) EWs were higher than those of Hy-Line brown (HY-LINE) and Harbin White (HW) Ews (p < 0.05). Subsequently, transmission electron microscopy (TEM) confirmed the changes in the EW protein structure in the four varieties of Ews. As the aggregations increased, the functional and physicochemical properties decreased. The protein content and functional and physicochemical properties of Ews after heating were correlated with the concentration of NaCl and sucrose and the EW varieties.

High-temperature glycosylation modifies the molecular structure of ovalbumin to improve the freeze-thaw stability of its high internal phase emulsion.

In this study, ovalbumins (OVAs) were glycosylated with fructo-oligosaccharide (FO) at different temperatures (80 °C, 100 °C, 120 °C, and 140 °C) and durations (1 h and 2 h) via wet-heating. The glycosylated OVAs (GOVAs) were characterized by the degree of glycosylation (DG), particle size, zeta potentials, and structural changes. GOVAs-stabilized high-internal-phase emulsions (HIPEs) were then prepared to compare their macro- and microstructure and freeze-thaw stability. The results showed that the DG of GOVAs increased with the increase in glycosylation temperature and the protein structure unfolded with it. Glycosylation decreased the particle size, zeta potential, and α-helical structures and increased the ß-sheets and surface hydrophobicity (H0) of GOVAs compared with unmodified OVAs. Moreover, GOVAs-stabilized HIPEs exhibited smaller particle sizes, zeta potentials, agglomeration indexes, oil loss rates, and freezing points and higher viscoelasticity, centrifugal stabilities, flocculation indexes, and freeze-thaw stabilities. Notably, HIPEs prepared by GOVAs (glycosylated higher than 120 °C) showed the least changes in macro- and microscopic appearances after freeze-thawing. These findings will provide a novel method for improving and broadening the functionalities of OVAs and potentially develop HIPEs with enhanced freeze-thaw stabilities.

Effects of CaCl2 on salting kinetics, water migration, aggregation behavior and protein structure in rapidly salted separated egg yolks.

Salted egg yolks are valued by consumers for their delicious taste good processing characteristics. To improve the quality of rapidly salted separated egg yolks, we compared changes in the salting kinetics, textural properties, water migration, protein aggregation and structure of salted egg yolks in the presence or absence of CaCl2 for 24 h. CaCl2 increased the mass transfer driving force and diffusion coefficient during the salting process; as a result, the salted egg yolks exhibited increased hardness and decreased springiness and cohesiveness. Through low field nuclear magnetic resonance (LF NMR), it was confirmed that CaCl2 promoted the precipitation of lipids and the dehydration of egg yolk. Furthermore, CaCl2 promoted the bulk aggregation of proteins. The analyses of protein structures showed that the contents of ß-sheets and irregular curls in CaCl2-salted egg yolk protein increased, while the contents of α-helices and ß-turns decreased. CaCl2 affected the microenvironment of tryptophan residues and embedded these residues, enhancing protein aggregation. Based on the comprehensive information obtained in this study, adding CaCl2 to the salting solution improved the degree of protein polymerization in egg yolk; thus, this method might be used to improve the quality of egg yolks separated by salt.

Effects of rice vinegar treatment on the antioxidant activities and protein structures of whole egg liquid before and after gastrointestinal digestion.

In this study, the effects of vinegar treatment on the antioxidant and structural properties of whole egg proteins were investigated. The results showed that the degrees of hydrolysis (DH) of vinegar-treated egg liquid (VE) and digested VE (DVE) increased after vinegar addition. A similar trend was also found for the antioxidant activity of DVE but not for that of VE. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results showed that vinegar treatment increased the gastrointestinal hydrolysis of whole egg protein compared with that of digested egg liquid (DEL) protein, which was in agreement with the free amino acid content results. The Fourier transform infrared (FTIR) analysis results indicated that proteins from VE1:3 tended to form ß-sheet structures, whereas proteins from DVE1:3 accumulated α-helices and turns. Vinegar treatment has great potential as a nonthermal processing method for promoting gastrointestinal digestion and producing superior antioxidant peptides.

Glycosylation of egg white protein with maltodextrin in the dry state: Changes in structural and gel properties.

The glycosylation of egg white proteins (EWP) with maltodextrin (MD) was investigated by monitoring their gel properties and protein structure. The improved gel properties of glycosylated EWP (GEWP) were confirmed by the increase in gel hardness, gel water holding capacity (WHC), rheological parameters, and finer gel microstructures. The protein structures were characterized by monitoring changes in the content of sulfhydryl (SH) group, circular dichroism (CD) and X-ray diffraction (XRD) spectra, and differential scanning calorimetry (DSC). The GEWP structures were unfolded due to extended glycosylation, as observed by increased content of exposed SH group and ß-sheet and decreased crystallinity, thermal denaturation temperature (Td), and enthalpy (ΔH). A correlation was also found between the gel properties and the protein structural changes. Overall, this study is beneficial for determining the mechanism of glycosylation and provides a convenient approach to improving the gel properties of EWP, which can further broaden the application of EWP in the food industry.

Molecular interactions in the dry heat-facilitated hydrothermal gel formation of egg white protein.

A comprehensive investigation was conducted regarding the molecular forces involved in the formation of dry heated egg white protein (DEWP) gels. From the preparation of DEWP powders to the formation of DEWP gels, multiple interactions are involved: the aggregation of DEWP powders in the dry state, the aggregation of DEWP solutions in the water state, and the subsequent gelling process of DEWP gels. The methods included analyses of zeta-potentials, surface hydrophobicity, reducing and nonreducing SDS-PAGE, sulfhydryl (SH) group content, molecular forces, particle size, and critical gel concentration. The results indicated that dry heat promoted the electrostatic and hydrophobic interactions in DEWP and DEWP aggregates. Disulfide (SS) bonds dominated the aggregation process of DEWP solutions in the water state, while hydrophobic and electrostatic interactions dominated the gel forming process. This phenomenon became even more obvious with a longer dry heat time. Furthermore, the intensified molecular interactions induced by dry heat resulted in the formation of smaller gel particles, and a relatively lower protein concentration was required for gel formation. All these factors contributed to the ultimate linear and fine-stranded DEWP gel network, which is more favorable in food processing and application.

Mechanistic insights into the improved properties of mayonnaise from the changes in protein structures of enzymatic modification-treated egg yolk.

Heat treatment is an important step in mayonnaise production but can affect the quality of mayonnaise because thermal treatment can accelerate oil droplet coalescence. To resolve this issue, in this study, enzymatically modified egg yolks were applied to produce mayonnaise. Egg yolk hydrolyzed with 0.2% neutral protease could effectively produce mayonnaise with superior heat stability, and this effect was attributed to enzymatic modifications that increased the degree of amino acid ionization, the overall hydrophilicity and the ability to adsorb proteins. Moreover, electrophoresis and FT-IR results showed that the enzymatically modified egg yolk proteins had a smaller molecular weight and more flexible structure, which could also favor the improved properties. The study elucidated why mayonnaise prepared by enzymatic modification-treated egg yolk has better thermal stability.