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

Investigating the causes of yolk mudding during storage of salted eggs: Water migration accelerates protein and lipid oxidation

In this study, salted egg yolks (SEYs) were subjected to two distinct storage methods: one group was stored as intact whole eggs, and the other was stored as isolated yolks. It was verified that water migration was the root cause of the mudding of SEYs. LF-NMR and MRI analyses revealed a significant decrease in water content in the egg white and a dramatic increase in the salted egg yolk (SEY) during storage. Additionally, the soluble protein content of the salted egg group significantly decreased, while the sulfhydryl content and peroxide value (PV) increased notably. Finally, CLSM and Cryo-SEM analyses identified three stages in the muddying of SEY: yolk particle dispersion, aggregation, and reorganization. This process accelerates protein-lipid oxidation and re-emulsification, ultimately leading to SEY mudding.

Enhancing salt-induced gelation of egg yolk granules through pH-ultrasound combined treatment: A physicochemical and microstructural analysis

Salted duck eggs are a popular food product, but their high salt content and uneven salt distribution can reduce acceptability. This study investigated the effects of pH-high-intensity ultrasound combined treatment on the salt-induced gelation properties of egg yolk granules. The results showed that the pH5 + 150 W treatment group exhibited the best physical and gelation properties, with the smallest particle size (1597.33 nm), optimal dispersibility (PDI 0.29), and good stability. The gelation properties of this group also demonstrated excellent springiness (0.30 mm), cohesiveness (0.56), and gumminess (0.05 N). Furthermore, the pH5 + 150 W group had the highest water holding capacity of 97.42 % and relatively high hydrophobicity (173.39 μg). Notably, it also showed high oil exudation (2.83 %) and good sandiness (62.07 %). The pH5 + 150 W led to a significant redshift of the fluorescence peak at 335 nm and an enhancement of the peak intensity at 562 nm compared to the control group. Structural characterization revealed a more ordered protein structure and a uniform gel structure with enhanced electrostatic repulsion between oil droplets. Secondary structure analysis of the proteins showed a significant reduction in α-helix and β-sheet, while β-turn and random coil increased. In summary, the pH5 + 150 W treatment displayed the best gelation properties, providing theoretical guidance for enhancing the processing performance of yolk and expanding their application in the food industry.

Targeted metabolomics reveals the contribution of degradation and oxidation of lipids and proteins mediated by pH to the formation of characteristic volatiles in preserved egg yolk during pickling

Targeted metabolomics and flavouromics combined with relative odor activity value were performed to explore the effect of degradation and oxidation of matrix mediated by pH on the formation of characteristic volatiles in preserved egg yolk (PEY) during pickling. It was found that the oxidation of proteins and lipids in PEY induced by pH sequentially occurred in early and later periods, and degradation both mainly occurred in early stage. Moreover, 1-octen-3-one, heptanal, trimethylamine, etc., compounds and 5-HETrE, proline, etc., components were confirmed as up-regulated characteristic volatiles and differential metabolites in PEY during pickling. The formation of octanal-M/D and benzeneacetaldehyde-M was attributed to β-oxidation of hydroxyeicosapentaenoic acid and L-isoleucine catalyzed by strong alkali at early period based on correlation network between them, respectively. Meanwhile, the generation of 1-octen-3-one-M/D mainly depended on L-serine and could be promoted by phosphatidylcholines oxidation. At later stage, the formation of heptanal-M/D was primarily attributed to phosphatidylethanolamines oxidation induced by alkali, and the enrichment of heptanal-M/D and nonanal were both enhanced by oxidized lipids. Lastly, trimethylamine was derived from L-lysine under alkaline conditions and promoted by protein oxidation during the whole process. This manuscript provided insight into the differential contribution of oxidation and degradation from matrix regulated by exogenous factors on the formation pathway for characteristic volatiles in foods.

Effect of salting and dehydration treatments on the physicochemical and gel properties of hen and duck egg yolks, plasma and granules

BACKGROUND

Salted hen egg yolks are less oily and less flavorful than salted duck egg yolks. However, hen eggs have a more adequate market supply and have a broader application prospect than duck eggs. In the present study, egg yolks, plasma, and granules were dehydrated by adding 1% NaCl to simulate traditional curing process of salted egg yolk. The changes in the pickling process of hen egg yolks (HEY) and duck egg yolks (DEY) plasma and granules were compared to reveal the gelation mechanism and the underlying causes of quality differences in salted HEY and DEY. Salted HEY can be compared with the changes in DEY during the pickling process to provide a theoretical basis for the quality improvement of salted HEY to salted DEY.

RESULTS

The results showed that both plasma and granules were involved in gel formation, but exhibited different aggregation behaviors. Based on the intermolecular forces, the HEY proteins achieved aggregation mainly through hydrophobic interactions and DEY proteins mainly through covalent binding. According to spin-spin relaxation time, HEY gels immobilized a large amount of lipid and interacted strongly with lipids. DEY gels showed much free lipid and had weak interaction with lipid. The microstructure showed that HEY proteins were easily unfolded to form a homogeneous three-dimensional gel network structure after salting, whereas heterogeneous aggregates were formed to hinder the gel development in DEY. Changes in protein secondary structure content showed that pickling can promote the transformation of the α-helices to β-sheets structure in HEY gels, whereas more α-helices structure was formed in DEY gels.

CONCLUSION

The present study has demonstrated that different gelation behaviors of hen and duck egg yolk proteins (especially in plasma) through salting treatment led to the difference in the quality of salted HEY and DEY. © 2024 Society of Chemical Industry.

The effects of sucrose/NaCl combined pickling on the textural characteristics, moisture distribution, and protein aggregation behavior of egg yolk

Salted egg yolks have a tender, loose, gritty, and oily texture and are commonly employed as fillings in baked goods. This study investigated the formation mechanism of egg yolk gels using three different pickling methods: NaCl, sucrose, and mixed groups. The results revealed that of these pickling methods, egg yolks pickled with the mixture had the lowest moisture content (11.59% at 25°C and 10.21% at 45°C), almost no free water content, and the highest hardness (19.11 N at 25°C and 31.01 N at 45°C). Intermolecular force measurements indicated that pickling with the mixture mitigated the surface hardening effect of sucrose and facilitated protein cross-linking. Moreover, confocal laser scanning microscopy of the egg yolk gels pickled with the mixture displayed macromolecular aggregates and oil exudation, suggesting that this method partially disrupted the lipoprotein structure and notably promoted yolk protein aggregation and lipid release. Overall, egg yolks formed a dense gel via the mixed pickling method owing to the ionic concentration and dehydration effects. These findings show the impact of NaCl and sucrose in pickling egg yolks, providing a crucial foundation for developing innovative and desirable egg yolk products. PRACTICAL APPLICATION: This study introduces a novel pickling strategy that combines sucrose and NaCl for egg yolk processing. The egg yolk pickled using this method exhibited improved quality according to the evaluated textural characteristics, moisture distribution, and protein aggregation behavior. The findings may broaden the use of sucrose as a pickling agent for egg yolk processing and provide new ideas for developing and producing pickled eggs and other food products.

Mechanism of ultrasonic enhancement of the gelling properties of salted ovalbumin-cooked soybean isolate hybrid gels

The influence of ultrasonic processing on the physicochemical characteristics, microstructure, and intermolecular forces of the hybrid gels obtained by heating the mixtures of different ratios of salted ovalbumin (SOVA)-cooked soybean protein isolate (CSPI) was investigated. With the growth of SOVA addition, ζ-potential in absolute value, cohesiveness, water-holding capacity (WHC), surface hydrophobicity, and the content of soluble protein of the hybrid gels decreased (P < 0.05), while the hardness, T2 relaxation time of the hybrid gels increased (P < 0.05). And the compactness of the network structure of the hybrid gel increased with the increase of SOVA addition. After being treated with ultrasound, significant increases (P < 0.05) of ζ-potential in absolute value, cohesiveness, WHC, and surface hydrophobicity of the hybrid gels were observed. In general, ultrasonic processing is one of the effective means to improve the gel properties of SOVA-CSPI hybrid gels.

Study on the mechanism of improving the quality of salted egg yolks by ultrasonic synergistic NaCl dry-curing

The dry separate curing of duck egg yolks was carried out by ultrasonic synergize NaCl (sodium chloride) and NaCl alone. The mechanism of the amelioration of salted egg yolk quality by ultrasonic synergistic NaCl dry-curing was studied. The quality variations of the salted egg yolks were analyzed for the same curing time and NaCl content achieved by ultrasonic synergistic NaCl curing and NaCl curing alone. The results showed that under the same salting time, the NaCl content, oil exudation and chewiness of U48-SEY (ultrasonic for 48 h-salted egg yolk) were higher than those in SEY (salted egg yolk). At the same NaCl content, the oil exudation and chewiness of U44-SEY (ultrasonic for 44 h-salted egg yolk) were still significantly increased. Compared to SEY, the soluble protein content and H0 of U44-SEY and U48-SEY were augmented. Scanning electron microscopy (SEM) indicated that the polyhedral particles in the salted egg yolks prepared by ultrasonic synergistic NaCl dry-curing were closely aligned and evenly distributed, and the salted egg yolks were sandier. Structural analysis revealed that the secondary and tertiary structures of egg yolk protein were changed although the ultrasonic synergistic NaCl dry-curing did not cause the fragmentation or aggregation of the peptide chain structure. The above results suggested that ultrasonic not only perfected the quality of salted egg yolk by promoting NaCl penetration, but also modified the structures of egg yolk protein by the action of ultrasonic itself, which prominently improved the quality of salted egg yolks.

A Novel Approach for the Production of Mildly Salted Duck Egg Using Ozonized Brine Salting

Salted eggs are normally produced by treating fresh duck eggs with a high salt concentration in order to acquire distinctive features and excellent preservation capabilities as a result of a series of physicochemical changes. This method, however, induces a high salt content in the product. The goal of this research was to create a new way of producing mildly salted duck eggs using ozonized brine salting. The brine was made by dissolving NaCl (26% w/v) in water or ozonized water at a concentration of 50 ng ozone/mL (ozonized brine). Compared to brine, ozonized brine resulted in salted eggs with reduced ultimate salt levels in both albumen and yolk (p < 0.05). The Haugh unit of the salted eggs generated by ozonized brine was similar to that of the brine-made salted egg group (p > 0.05), but the salted egg produced by ozonized brine matured and solidified faster because the yolk index (0.62) was higher than that of the brine (0.55) (p < 0.05). The final pH of salted eggs generated with brine and ozonized brine was not different (p > 0.05). Regardless of the salting method, both salted eggs contained low TVB-N content (<10 mg/100 g). Ozonized brine increased the protein carbonyl content in salted albumen, which may be related to albumen protein aggregation and served as a salt diffusion barrier. However, after boiling the salted egg, the protein carbonyl level was comparable to that of fresh albumen. The TBARS levels of boiled salted albumen prepared with brine and ozonized brine were comparable (p > 0.05), and the value was extremely low (~0.1 mg MDA equivalent/kg). The TBARS value of the salted yolk prepared with brine was higher than that of the salted yolk prepared with ozonized brine (p < 0.05), and both salted yolks showed increased TBARS values after cooking (p < 0.05). The albumen and yolk components appeared to be altered similarly by both brine and ozonized brine, according to the FTIR spectra. Furthermore, the appearance and color of the yolk and albumen in salted eggs prepared with brine and ozonized brine were comparable. Boiled salted albumen produced with ozonized brine had a denser structure with fewer voids. This could be attributed to the final salted egg's lower salt content and lower salt diffusion rate, which were likely caused by protein oxidation and, as a result, aggregation when ozonized brine was used.

Improving the gel properties of salted egg white/cooked soybean protein isolate composite gels by ultrasound treatment: Study on the gelling properties and structure

In this study, the effects of ultrasound treatment on the texture, physicochemical properties and protein structure of composite gels prepared by salted egg white (SEW) and cooked soybean protein isolate (CSPI) at different ratios were investigated. With the increased SEW addition, the ζ-potential absolute values, soluble protein content, surface hydrophobicity and swelling ratio of composite gels showed overall declining trends (P < 0.05), while the free sulfhydryl (SH) contents and hardness of exhibited overall increasing trends (P < 0.05). Microstructural results revealed that composite gels exhibited denser structure with the increased SEW addition. After ultrasound treatment, the particle size of composite protein solutions significantly decreased (P < 0.05), and the free SH contents of ultrasound-treated composite gels were lower than that of untreated composite gels. Moreover, ultrasound treatment enhanced the hardness of composite gels, and promoted the conversion of free water into non-flowable water. However, when ultrasonic power exceeded 150 W, the hardness of composite gels could not be further enhanced. FTIR results indicated that ultrasound treatment facilitated the composite protein aggregates to form a more stable gel structure. The improvement of ultrasound treatment on the properties of composite gels was mainly by promoting the dissociation of protein aggregates, and the dissociated protein particles further interacted to form denser aggregates through disulfide bond, thus facilitating the crosslinking and reaggregation of protein aggregates to form denser gel structure. Overall, ultrasound treatment is an effective approach to improve the properties of SEW-CSPI composite gels, which can improve the potential utilization of SEW and SPI in food processing.

A review on the development of pickled eggs: rapid pickling and quality optimization

Pickled eggs enjoy a long processing history with unique flavor and rich nutrition but suffer from long pickling cycle due to the limitations of traditional processing methods. In terms of quality, salted egg whites have the disadvantage of high sodium content, and salted egg yolks have problems such as hard core and black circle around outer layer. Likewise, the quality of preserved eggs is challenged by the black spots (dots) on the eggshells and the high content of heavy metals in the egg contents. The sustainable development of traditional pickled eggs are hindered by these defects and extensive research has been carried out in recent years. Based on the elaboration of the quality formation mechanism of salted eggs and preserved eggs, this paper reviewed the processing principles and applications of rapid pickling technologies like ultrasonic technology, magnetoelectric-assisted technology, water cycle technology, vacuum decompression technology, and pulsed pressure technology, as well as the quality optimization methods such as controlling the sodium content of the salted egg whites, improving the quality of salted egg yolks, promoting the quality of lead-free preserved eggs, and developing heavy metal-free preserved eggs. In the end, the future development trend of traditional pickled eggs was summarized and prospected in order to provide theoretical guidance for the actual production.

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.

Effects of different metal ions on the physicochemical properties and microstructure of egg white gel

BACKGROUND

To ameliorate egg white gel's salinity and undesirable texture characteristics during curing, different metal ions (K⁺ , Mg²⁺ , Ca²⁺ , Zn²⁺ ) were used to replace sodium chloride (NaCl) to simulate salted eggs partially. The effects of these ions on the physicochemical properties, microstructure, and gel characteristics of egg white protein were studied.

RESULTS

Low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) analysis showed that adding K⁺ , Mg²⁺ , Ca²⁺ , and Zn²⁺ could decrease immobile water content and increase free water content in egg white gel. Circular dichroism/fluorescence spectrophotometry (CD/FL) analysis showed that substitutive addition of K⁺ , Mg²⁺ , Ca^2+, and Zn²⁺ changed the conformational structure of the protein, which was not conducive to the formation of the three-dimensional mesh gel structure. Differential scanning calorimetry (DSC) results show that the addition of four metal ions could reduce the thermal denaturation temperature of egg white gel. Scanning electron microscopy (SEM) showed that the gel structure of egg white in the zinc chloride (ZnCl₂ ) group was rougher and more chaotic, the crosslinking degree was worse, so it was not suitable for low sodium salted egg preparations. The gel strength of the calcium chloride (CaCl₂ ) group was significantly higher than other groups (P < 0.05), while the gel strength of the potassium chloride (KCl) group was similar to the NaCl group (P > 0.05).

CONCLUSION

CaCl₂ and KCl could be used as partial NaCl substitutes to study the addition level and ratio further and improve salted egg white quality. © 2021 Society of Chemical Industry.

Impact of Different Sugar Types and Their Concentrations on Salted Duck Egg White Based Meringues

Meringues were prepared with salted duck egg white and different sugars (granulated white, cane, palm, and coconut) at various concentrations (25, 50, 75, and 100%). The prepared meringues were subjected to analyses of functional and physicochemical properties and antioxidant activities. The results showed that the type and concentration of sugar influenced the meringue quality. Foam properties such as the whipping index, the index of foam durability, and specific density gradually increased with sugar concentration. On the other hand, the overrun and air phase values were stable without significant differences. The color attributes whiteness and the chroma hue of meringues decreased with the sugar concentration regardless of the sugar type. Moisture, water activity, and pH decreased, while weight loss during baking, meringue volume, and hardness gradually increased with sugar concentration. The addition of sugar increased the meringue’s weight, while its height and diameter did not change much. Protein content in the meringue decreased with increased sugar levels, while carbohydrate and ash levels increased. Antioxidant activities increased with the sugar concentration, and unrefined sugars influenced the radical scavenging activities differently from refined sugars. In general, meringue made with coconut sugar at 75% showed preferable qualities over the other sugar types or concentrations.

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.

Effects of salt and heat treatment on the physicochemical properties, microstructure, secondary structure, and simulated in vitro gastrointestinal digestion of duck egg white

BACKGROUND

The texture and structure of the duck egg white (DEW) gel under salt and heat treatment are crucial to its digestibility. Specifically, the structural changes of food protein gels have been recognized for their potential to regulate in vitro digestion. In this study, the effects of gel characteristics and simulated in vitro gastrointestinal digestion of DEW under combined salt and heat treatment were investigated.

RESULTS

With the increase in salting time and temperature, a porous opaque gel with large particles was formed, the moisture content of DEW showed a downward trend, and the same was true for hardness changes. The microstructure suggested that, with the penetration of NaCl, DEW proteins were denatured, and the protein molecules gradually unfolded and then aggregated after 7 days. The secondary structure revealed that, as the salting time and temperature increased, the proportion of intermolecular β-sheets and α-helices decreased. In terms of in vitro digestion, the highest digestibility was obtained at 14 days of salting combined with 100 °C heat treatment, and the digestibility was the lowest when marinated for 7 days at 121 °C. Liquid chromatography and tandem mass spectrometry (LC-MS/MS) indicated that the number of different types of peptides and specific peptides was positively correlated with the salting time and temperature of the DEW at the end of gastric digestion.

CONCLUSIONS

Heat treatment at 100 °C has a higher in vitro digestibility than at 121 °C. Gels with low hardness, large pores, and rough textures are easier to digest by pepsin and release more peptides. © 2021 Society of Chemical Industry.

Salted duck eggs: the source for pathogens and antibiotic resistant bacteria

Salted duck eggs as a convenient food are very popular in China and Southeast Asia. Generally, they are produced by traditional curing methods. Here we used traditional methods to profile the bacterial community of salted duck eggs purchased from markets to systematically investigate their microbiological safety. 77 bacteria belonging to 14 genera were isolated. Bacillus related to flavor formation of salted duck eggs were the dominant genus. However, there existed some clinical pathogens which can cause food poisoning, such as Klebsiella pneumoniae, Staphylococcus aureus, and Aeromonas hydrophila. Moreover, PCA analysis showed that the composition of bacteria was related to the source and storage time rather than sampling sites. Besides, bacteria in the shell, intima and egg white of salted duck eggs were cross-linked. In addition, antimicrobial susceptibility testing indicated that resistant bacteria reached to 47.9%. And there was also no significant difference in bacterial resistance with sampling sites. Consequently, it's necessary to strengthen the food quality of salted duck eggs and improve personal dietary habit.

SUPPLEMENTARY INFORMATION

Supplementary information accompanies this paper at 10.1007/s13197-020-04962-w.

Effect of partial substitution of sodium salt on the quality of salted quail eggs

To improve the quality of salted quail eggs and solve the problem of excessive sodium content in salted eggs, we selected substitutes (K₂ CO₃ , CaCl₂ , MgCl₂ , ZnCl₂ , and FeC₆ H₅ O₇ ) to partially replace NaCl and study its effect on water migration, physicochemical properties, and textural characteristics. The low-field nuclear magnetic resonance technology (LF-NMR) was used to qualitatively analyze the moisture and proton content of quail eggs during the pickling process. The results showed that the relaxation curves of ZnCl₂ and FeC₆ H₅ O7 groups were significantly different from those of other groups. The bound water content of the ZnCl₂ group increased significantly, and FeC₆ H₅ O₇ made the binding degree of water closer. The Na⁺ of different substitute groups was determined by atomic absorption spectrometry; it was found that the permeation rate of NaCl in the curing process was in the following order: K₂ CO₃ > control group > MgCl₂ > FeC₆ H₅ O₇ > CaCl₂ > ZnCl₂ . Through the electronic tongue study and comparing the ripening period of salted quail eggs, it was found that the flavor and ripening time of salted quail eggs cured by ZnCl₂ and FeC₆ H₅ O₇ were not suitable for low-sodium pickling preparation. At the same time, CaCl₂ and MgCl₂ were suitable for low-sodium pickling and could improve the product quality. When using K₂ CO₃ , the substitution ratio can be reduced and two or more compound-curing agents can be formed with CaCl₂ and MgCl₂ , thus reducing the content of sodium salt in salted eggs. PRACTICAL APPLICATIONS: We simulated the metallic elements contained in the traditional black ash-salted eggs and salt mud coatings. By partial substitution of sodium chloride (NaCl) with different metal salts (K₂ CO₃ , CaCl₂ , MgCl₂ , ZnCl₂ , and FeC₆ H₅ O₇ ), we studied the effects of these metal salts on the physical and chemical properties, texture, and microstructure of quail eggs during the pickling process. Several suitable low-sodium substitutes were screened out to provide a theoretical foundation for the process optimization of low-sodium-salted quail eggs.

A review on recent advances of egg byproducts: Preparation, functional properties, biological activities and food applications

The rapid development of egg industries produced vast byproducts that have not been effectively used. In this paper, the comprehensive utilization of egg byproducts was reviewed. Protein extraction and enzymatic hydrolysis were the main used ways for recycle of egg byproducts. The fact that eggshell membrane could accelerate would healing and improve facial skin of healthy people for 12 weeks was found. However, salted egg white had poor functional properties owing to high salt and ultrafiltration was an effective technology to remove 92.93% of salt. Moreover, Defatted yolk protein had the great potential to be used as food additives and functional foods. Other egg byproducts such as egg inhibitor and eggshells also were discussed. The novel applications of egg byproducts in the food field included food additives, feeds, food packaging materials and nutraceuticals based on current knowledge, but the proportion needed to be improved. This paper would provide a new insight for comprehensive utilization of egg byproducts.

Effect of κ-carrageenan addition on protein structure and gel properties of salted duck egg white

BACKGROUND

Salted duck egg white (SDEW) is a major by-product during salted egg yolk manufacturing. Due to the high salt concentration, SDEW has not been efficiently utilized. Moreover, functional properties of SDEW are altered by salt during pickling. To improve the functional properties, the effect of κ-carrageenan (κ-CAR) addition on the protein structure and gel properties of SDEW was investigated in this study.

RESULTS

The surface hydrophobicity and free sulfhydryl content of SDEW protein increased, while total sulfhydryl content decreased significantly with the addition of κ-CAR (0.02-0.10%). Fourier-transform infrared spectroscopy analysis revealed that the relative content of α-helix and β-turn decreased, β-sheet and random coil increased, indicating the variation tendency of protein structure from order to disorder. As κ-CAR addition increased, the texture profiles including hardness, gumminess, chewiness, springiness, cohesiveness and resilience of SDEW gel were all improved. Water holding capacity increased significantly by 32.33% in the presence of 0.10% κ-CAR addition. The scanning electron microscopy indicated that the microstructure of SDEW/κ-CAR mixed gel was more smooth and compact.

CONCLUSION

The results suggested that adding κ-CAR can be an effective method to improve gel quality of SDEW. This study is expected to provide theoretical basis for modification of SDEW protein, as well as preparation of food ingredients with better gel properties from SDEW. © 2020 Society of Chemical Industry.

Gelation behavior of egg yolk under physical and chemical induction: A review

Gelation is one of the most important functional properties of egg yolk. High content and rich variety of protein and lipid in egg yolk are the material basis of gel formation. The natural structure of proteins in egg yolk is unfolded under treatments such as heat, alkali, salt, etc., thus causing the interactions between protein-protein and protein-lipid and forming the gel. Under different methods of induction, egg yolk is solidified to form different three-dimensional network structures. Different inducing methods exhibit different gel formation mechanisms. In this paper, the gelation behavior of egg yolk and its internal molecular agglomeration mechanism induced by heat, alkali, salt, freezing, high pressure, and salt-heating synergy were reviewed to provide a reference for further studies on the formation mechanisms and product development of egg yolk gel.

Changes in physicochemical properties, gel structure and in vitro digestion of marinated egg white gel during braising

In this paper, changes in physicochemical properties, gel structure and in vitro digestion of marinated egg with spice or tea during braising were investigated. Results indicated that the moisture content and surface hydrophobicity of marinated egg white showed an overall decreased trend. The springiness of marinated egg white showed an increased trend, and the hardness in the late stage showed an increased trend. Microstructure showed that compact gel structures formed many holes during the braising. Intermolecular forces showed that ionic bonds and disulfide bonds played a dominant role in the marinated egg white. Secondary structure showed that the β-turn showed a decreased trend, contrary to that of random coils and α-helices. Appropriate braising increased the digestibility of marinated egg white, but excessively long-time braising could reduce it. Both spice and tea braising could improve the gel strength of protein, and the tea braising was also slightly better than spice braising.

The sol-gel-sol transformation behavior of egg white proteins induced by alkali

In the current study, we found an interesting phenomenon that fresh egg white (EW) undergo the sol-gel-sol transition with alkali treatment. The transformation behavior at different alkalinity (1.5%, 2.0%, and 2.5%) was investigated. As the gel formed, the hardness, lightness, surface hydrophobicity and the total number of identified peptides increased, and then, remarkable reduction when the gel collapsed. Rheological behavior indicated that the viscosity varied with shear rate. Fourier transform infrared spectroscopy (FTIR) showed that β-sheets gradually decreased as the α-helices increased during gel-sol transformation. The quantification of EW peptides analysis revealed that there was no dramatic correlation between the number of identified peptides and alkalinity. It was concluded that the sol-gel-sol transition was strongly dependent on alkali levels, moreover, high concentration promoted gel formation as well as liquefaction. The EW transformation behavior induced by alkali had a significant effect on protein aggregation and denaturation, and further changed physicochemical properties.

Effects of temperature on quality of preserved eggs during storage

The effects of storage temperature (4°C, 25°C, and 35°C) on sensory quality, physicochemical properties, texture, molecular forces, flavor, and microbial indexes of preserved eggs were studied. The results showed that the sensory quality, weight loss rate, pH, and color of preserved eggs were significantly different at different storage temperatures (P < 0.05). Compared with high temperature and normal temperature storage, low temperature storage reduced weight loss rate by 55.15 and 64.1%, respectively, improved the sensory score (P < 0.05), inhibited the reduction of pH and the increase of total volatile base nitrogen (P < 0.05), and decreased the change of color (P < 0.05). During storage, there was no difference in the springiness of preserved egg white stored at different temperatures (P > 0.05). Hardness and chewiness at 3 different temperatures increased first and then decreased, and low temperature significantly inhibited the progress of these changes to a certain extent (P < 0.05). The content of ionic bond in egg white first decreased and then increased, and content of disulfide bond increased first and then decreased. Content of ionic bond in yolk decreased all the time, and high temperature could promote this change. Whatever the temperature was, the content of free amino acids in preserved egg white and yolk increased first and then decreased, and the total content of amino acids stored at different temperatures was significantly different (P < 0.05). The content of free fatty acids in yolk decreased. At the end of storage, no microorganisms were detected in 3 temperatures during the storage period of 84 D. The results showed that low temperature storage is more conducive for preservation of preserved eggs.

Formation mechanism of low-density lipoprotein gel induced by NaCl

Salted eggs, which are a traditional Chinese egg product, are favored by Chinese consumers and have become very popular in other Asian countries due to their unique features such as "fresh, fine, tender, loose, gritty and oily texture." In order to illuminate the forming process of salted egg, the gelation behavior and mechanism of low-density lipoprotein (LDL) induced by NaCl were investigated using marinated model outside the eggshell. Results showed that as the salting proceeded, the moisture content exhibited a decreasing trend. The NaCl content, oil exudation, hardness, and surface hydrophobicity showed constantly increasing trends. In the early stages of salting, the size of the LDL particles, soluble protein content, and T21 increased, whereas T21 (with D2O), T22, and the free sulfhydryl content declined. In the later stages of salting, LDL formed a multiple composite aggregate gel structure with filamentous apoproteins and non-spherical lipid particles intertwined with each other. The soluble protein content and T23 (without D2O) decreased, whereas T21 (with D2O), T22 and the free sulfhydryl content increased. Fourier transform infrared spectroscopy revealed that the fresh LDL mainly consisted of α-helix and β-sheet structures. After the gel becomes hardened, the LDL secondary structure was changed remarkably, characterized by the decrease of α-helix elements and increase of β-sheet elements. The results suggested that the oil exudation of salted LDL gels was mainly due to LDL destruction and the release of components (apoproteins, phospholipids, and neutral lipids) facilitated by increased interactions between apoproteins and lipids.

Assessment of different proteases on degree of hydrolysis, functional properties and radical scavenging activities of salted duck egg white hydrolysate

The impact of different proteases (alcalase, ficin, protamex, and neutrase) on the hydrolyzation, foaming and radical scavenging potency of salted duck egg white was studied. Egg white without protease hydrolyzation served as control. Regarding the degree of hydrolysis, neutrase and protamex were more capable of hydrolyzing duck egg white than the others. The α-amino nitrogen content in the egg whites was highly correlated with hydrolysis ability of the enzymes, and it had gradually increased with curing. Foam stability, capacity and emulsion stability were significantly influenced by proteases and curing period. However, the solubility of the egg white hydrolysate was not much affected by curing but showed significant differences between hydrolyzed and control samples. Emulsion stability of hydrolysate decreased with curing times. Neutrase and alcalase hydrolysates gave the best foaming and emulsion properties. Moreover, neutrase and protamex hydrolysates showed good scavenging potency against the DPPH radicals, hydroxyl radicals, hydrogen peroxide, and ferrous ion radicals. Overall, the hydrolysate from neutrase hydrolyzed duck egg white showed the highest foaming and radical scavenging capacities among the other hydrolysis treatments in this study.

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.