PICKLING TIME AND ELECTRODIALYSIS AFFECTS FUNCTIONAL PROPERTIES OF SALTED DUCK EGG WHITE

The Quality Characteristics Formation and Control of Salted Eggs: A Review

Salted egg, a traditional characteristic processed egg product in China, is popular among consumers at home and abroad. Salted egg quality characteristics formation primarily includes the hydration of egg white, the solidification of egg yolk, the unique color and flavor of salted egg yolk, and the formation of white, fine, and tender egg whites and loose, sandy, and oily egg yolks after pickling and heating. The unique quality characteristics of salted eggs are mostly caused by the infiltration dehydration of salt, the intermolecular interaction of proteins, and the oxidation of lipids. In recent years, to solve the problems of salted eggs having high salinity, long production cycle, and short storage period, the pickling technology for salted egg has been improved and researched, which has played a significant role in promoting the scientific production of salted eggs. This paper summarizes the mechanisms of salted egg quality characteristics formation and factors influencing quality, with a perspective of providing a theoretical basis for the production of high-quality salted eggs.

Fabrication and characterization of Pickering emulsions stabilized by desalted duck egg white nanogels and sodium alginate

BACKGROUND

The waste of salted egg white resources has always been a serious problem in the food industry. In this current study, we report on a kind of Pickering emulsion system, which was stabilized by duck egg white nanogels (DEWNs) and sodium alginate (SA), followed by which this system was crosslinked by calcium carbonate (CaCO₃ ) via controlling the gluconolactone (GDL) concentrations, aiming to open up a promising route for making full use of these protein resources.

RESULTS

The droplet size of the emulsion exhibited a reduction with an increase in SA concentrations, indicating that higher negative charges and steric hindrance was useful for a stable emulsion system. Meanwhile, the result of rheology measurement showed that storage modulus (G') values were higher than loss modulus (G″) values of the samples at higher GDL concentration, revealing the formation of elastic gel-like networks in the system, which was fabricated by SA and Ca²⁺ released by the CaCO₃ particles. The gel-like network structure in the continuous phase improved both the freeze-thaw and thermal stability of the obtained Pickering emulsion system. Encouragingly, the Pickering high internal phase emulsions (HIPEs, φ = 0.75) stabilized by DEWN/SA₃ -GDL₃ were prepared, which could be stored at 4 °C for at least 30 days without oiling-off and creaming.

CONCLUSION

These findings not only develop a green ultra-stable Pickering emulsion system but also extend the potential commercial applications of duck egg white proteins in the food, cosmetics, and pharmaceutical industries. © 2021 Society of Chemical Industry.

Effects of partial replacement of NaCl by KCl and CaCl2 on physicochemical properties, microstructure, and textural properties of salted eggs

KCl and CaCl₂ were used as partial substitutes for NaCl during pickling salted eggs process in this study. The effects on the physicochemical properties, microstructure, textural properties and sensory quality of the salted eggs were evaluated, while comparing with the 18% NaCl group (Na group). The 3% replacement of NaCl by KCl reduced the Na content (p < 0.05), accelerated the water migration (p < 0.05) in salted eggs and increased the apparent oil yield and oil exudation of salted egg yolk (p < 0.05); but the rheological properties and microstructure of salted egg yolk were minimally affected. The 3% replacement of NaCl by CaCl₂ reduced the Na content (p < 0.05), delayed the water migration rate (p < 0.05) in salted eggs and decreased the apparent oil yield and oil exudation of salted egg yolk (p < 0.05). Additionally, the process of egg white thinning and egg yolk hardening were delayed. The results indicate that the partial substitution of NaCl by KCl or CaCl₂ during the pickling process of salted eggs could effectively inhibit the infiltration of Na⁺ , and the presence of KCl could improve the quality of salted eggs. Still, the presence of CaCl₂ delay the ripening of salted eggs. PRACTICAL APPLICATION: KCl and CaCl₂ as substitutes of sodium salt could play the role of reducing Na content but not affecting saline taste of salted eggs, which is conducive to the development of low-sodium salted eggs.

Evaluation of nutrient content, physicochemical and functional properties of desalted duck egg white by ultrafiltration as desalination

In this study, the effects of ultrafiltration technique on the desalination efficiency, nutrient content, physicochemical properties, functional properties, texture profile, and microstructure of salted duck egg white were evaluated. The results showed that ultrafiltration can remove 92.93% salt from salted duck egg white (SDEW) and final salt% of desalted duck egg white (DDEW) was 0.65%. The analysis of nutrient content and amino acid of SDEW and desalted duck egg white powder (DDEWP) sample was significantly lower than those of fresh duck egg white (FDEW). Although emulsifying capacity of SDEW, DDEW, and DDEWP exhibited significantly lower than that of FDEW, an excellent foaming ability was found in those samples. Moreover, the texture profiles (gel strength, hardness and elasticity) of SDEW, DDEW, and DDEWP samples presented lower value than FDEW. The observation of microstructure, DDEWP possessed smooth surface of protein globules with deep hole liked donuts and distribution of a few of salt crystals. While salted duck egg white powder (SDEWP) had a raisin-like surface formation with salt formed cubic crystals. Overall, both liquid and dried material of desalted duck egg could be used as a good ingredient in baking food due to their excellent foaming capacity.

Antioxidant and antimicrobial activities of different enzymatic hydrolysates from desalted duck egg white

Objective

The objective of this study was to look for optimal preparation of hydrolysates of desalted duck egg white powder (DDEWP) by the three different proteases and to investigate their antioxidant and antimicrobial properties.

Methods

DDEWP was hydrolyzed by three proteases, including pepsin (PEP), Bacillus spp. (BA) and natokinase (NAT) with three different enzyme concentrations (0.1%, 0.3%, and 0.5%), individually. The important key hydrolysis parameters such as hydrolysis degree, yield, antioxidant and antimicrobial activity were evaluated in this experiment.

Results

The results showed that the degree of hydrolysis (DH) of all treatments increased with increasing hydrolysis time and protease concentrations. The antioxidant and antimicrobial activities of the hydrolysates were affected by type and concentration of protease as well as hydrolysis time. Hydrolysis of PEP significantly (p<0.05) obtained the highest yield of hydrolysates, however, both of BA and NAT showed substantially lower DH values and still did not exceed 5% by the end of hydrolysis. Among the different hydrolysates, PEP exhibited significantly higher 2, 2–diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity than BA and NAT. All DDEWP hydrolysates from PEP had low ferrous ion chelating activity (<37%) that was significantly lower than that of NAT (>37% to 92%) and BA (30% to 79%). Besides, DDEWP hydrolysates of PEP presented significantly higher reducing power than BA and NAT. In antimicrobial activities, Escherichia coli, Salmonella typhimurium, and Pseudomonas aeruginosa were not effectively inhibited by any DDEWP hydrolysates of PEP except for Staphylococcus aureus. Especially, the excellent antibacterial activity against S. aureus only was displayed in DDEWP hydrolysates of PEP 0.1%.

Conclusion

DDEWP hydrolysates from PEP demonstrated significantly better DH, yield, DPPH radical scavenging activity and reducing power, furthermore, had excellent inhibitory on S. aureus due to large clear zone and moderated inhibitory in bactericidal inhibition.

Salt-tolerant Staphylococcus bacteria induce structural and nutritional alterations of salted duck egg white

Salted duck egg white, a major by-product of salted egg yolk production, is rich in nutrients. However, its high salinity limits its application in the food industry. In the present study, three haloduric bacterium strains (C1, C2, and C3) were isolated from Jinhua ham, and strain C1 exhibited higher ratio of the transparent circle diameter to the colony diameter (HC) and gelatin liquefaction. Strain C1 was further identified as a member of the genus Staphylococcus through gene sequencing and EzTaxon-e analyses. Salted duck egg white was fermented by strain C1, and the thermal stability, microstructure, amino acid composition, and γ-aminobutyric acid of the egg white were compared with egg white without fermentation. The fermented salted duck egg white had a significantly low salinity. Meanwhile, it increased its thermal stability compared with the control through losing an endotherm at around 85°C and forming a new endotherm peak starting at 91.8°C. Additionally, free amino acids and γ-aminobutyric acid were found only in the fermented salted duck egg white. These indicated that fermentation with salt-resistant strains could alter the structure of salted duck egg white and improve its nutritional quality.

Trypsin inhibitor from duck albumen: Purification and characterization

Egg albumen is a potential source of trypsin inhibitor (TI), which has been widely used to improve textural property of surimi or surimi-based food products. TI from duck albumen was isolated and purified using ammonium sulfate precipitation at 20%-40% saturation and affinity chromatography using trypsin-CNBr-activated Sepharose 4B column. TI was purified with purity and yield of 111.8-fold and 0.6%, respectively. The purity of inhibitor was confirmed using Native-PAGE as indicated by the presence of single band. Molecular weight of purified TI was 43 kDa based on SDS-GAGE and gel filtration. The purified TI remained unchanged at temperatures below 60°C and the pH in the range of 7-9. The inhibitory activity of TI was decreased with the addition of salt higher than 5%. Inhibition kinetic study revealed that purified TI from duck albumen was uncompetitive inhibitor and the inhibition constant (Ki) was 508 nM. TI from duck egg albumen could serve as a food grade inhibitor for controlling undesirable proteolysis. PRACTICAL APPLICATIONS: Duck egg albumen has been known to be rich in protease inhibitors, which can be used as a protein additive to enhance gelling properties of surimi or surimi-based products. Therefore, it is of interest to isolate and purify TI from duck egg albumen. Information regarding characteristics of TI from duck albumen could be beneficial for further applications, in which duck albumen is better exploited.

Duck egg albumen: physicochemical and functional properties as affected by storage and processing

The demand for duck meat and eggs in Asian countries increases every year. Duck egg albumen has become an important ingredient in the food industry alongside its hen counterpart, because of its excellent nutritive and functional properties. The major proteins in duck albumen are ovalbumin, ovomucoid, ovomucin, conalbumin, and lysozyme. Comparing with hen albumen, lower contents of ovalbumin, conalbumin, lysozyme and ovoflavoprotein are found in duck albumen. Nevertheless, duck albumen shows better gelling and foaming properties than hen albumen. During storage, duck albumen gel properties are enhanced, while foam volume and foam stability are decreased. Moreover, the changes in quality indices of duck egg including the thinning of the albumen, an increase in albumen pH, loss of water and carbon dioxide occur as storage time is increased. Some processes such as alkaline treatment also cause the loss in nutritive value of egg albumen. In this review, the composition and functional properties of duck albumen and how they are affected by processing conditions are also addressed, in comparison with hen albumen. A better understanding of duck egg albumen would be beneficial so that the food processing industry can exploit the potential of this avian protein.

Effects of salting treatment on the physicochemical properties, textural properties, and microstructures of duck eggs

In order to illuminate the forming process of salted egg, the effects of the brine solution with different salt concentrations on the physicochemical properties, textural properties, and microstructures of duck eggs were evaluated using conventional physicochemical property determination methods. The results showed that the moisture contents of both the raw and cooked egg whites and egg yolks, the springiness of the raw egg yolks and cooked egg whites exhibited a decreasing trend with the increase in the salting time and salt concentration. The salt content, oil exudation and the hardness of the raw egg yolks showed a constantly increasing trend. Viscosity of the raw egg whites showed an overall trend in which it first deceased and then increased and decreased again, which was similar to the trend of the hardness of the cooked egg whites and egg yolks. As the salting proceeded, the pH value of the raw and cooked egg whites declined remarkably and then declined slowly, whereas the pH of the raw and cooked egg yolks did not show any noticeable changes. The effect of salting on the pH value varied significantly with the salt concentration in the brine solution. Scanning electron microscopy (SEM) revealed that salted yolks consist of spherical granules and embedded flattened porosities. It was concluded that the treatment of salt induces solidification of yolk, accompanied with higher oil exudation and the development of a gritty texture. Different salt concentrations show certain differences.

Electrodialysis desalination of fish sauce: electrodialysis performance and product quality

Fish sauce has a unique, pleasant flavor, but contains high levels of sodium chloride, which is nowadays not desirable for health-conscious consumers. Although many researchers have attempted to solve this problem by substituting sodium with potassium in fish sauce, potassium-based products are still unsuitable for patients with kidney disease. Thus, electrodialysis (ED) desalination of fish sauce was carried out. The rate of salt removal, evolution of total soluble solids, and electrical conductivity of the electrodialysis-treated fish sauce were investigated. Moreover, the system performance in terms of yield, energy consumption, and current efficiency were examined. Density, viscosity, ion concentrations (that is, Na(+), K(+)), total nitrogen, amino nitrogen, and color were investigated at various values of input voltage (6, 7, and 8 V) and remaining salt concentration (22%, 18%, 14%, 10%, 6%, and 2%[w/w]). The results indicated that an increase in the input voltage led to an increase in the rates of salt removal, electrical conductivity, and total soluble solids. The energy consumption increased whereas current efficiency and yield decreased significantly with an increase in input voltage and the salt removal level. Physicochemical properties of the treated fish sauce, in terms of the total soluble solids, density, viscosity, ion concentrations (that is, Na(+), K(+)), total nitrogen, and color were significantly affected by the input voltage and the salt-removal level.