Changes of microstructure characteristics and intermolecular interactions of preserved egg white gel during pickling

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.

Insight into the effect of sesamol on the structural and gel properties of yak myofibrillar proteins

Different concentrations of sesamol (0, 20, 40, 80 and 160 mg/g protein) were incorporated for evaluating the effects of sesamol on the structural and gel properties of yak myofibrillar proteins (MPs). The results manifested that the contents of active thiol and free amine diminished and the carbonyl contents elevated when the MPs modified with sesamol. The intrinsic fluorescence intensity progressively decreased and surface hydrophobic value displayed a down-up trend after binding with the increasement of sesamol. Moreover, the presence of sesamol reduced protein solubility and increased particle size of MPs. For the protein gels, inclusion of sesamol effectively improved water-holding capacity and gel strength but decremented gel whiteness and the proportion of free water, and significantly enhanced the hydrogen bonds, hydrophobic interactions and disulfide bonds in the gel matrix. Microstructure analysis revealed that a more compact microstructure was formed for the MP-sesamol gels. This study suggests that sesamol is capable of improving the functional properties of MPs, and the complexes of MP-sesamol have potential applications in the food industry.

Mechanistic study on the decline of foaming characteristics of egg white under heat stress: Emphasizing apparent phenomena, structure, and intermolecular interactions

Heat stress is a critical step in the processing of liquid egg white; however, this treatment can severely affect its foaming properties. This study aims to elucidate the mechanisms underlying the decline in foaming properties of liquid egg white during heat stress. The research begins by examining the adverse effects of heat stress on the foaming properties of liquid egg whites, where an increase in apparent viscosity, turbidity, and particle size is initially observed, indicating the formation of aggregates. After heat stress, the binding water capacity of the liquid egg white increases, intermolecular forces strengthen, and the secondary structure transforms towards β-sheet and β-turn configurations, while surface hydrophobicity decreases. Heat stress promotes the transition of liquid egg white into a more stable gel state. Additionally, electrophoresis results show the disappearance of bands for ovomucin subunit, ovotransferrin, and lysozyme, while microscopic observations reveal a rougher surface texture of the samples. In summary, this study provides insights and theoretical basis for understanding the mechanisms behind the decline in foaming properties of liquid egg whites under heat stress.

In vitro digestion and functional properties of bovine β-casein: A comparison between adults and infants

Gastrointestinal digestibility behavior, structural and functional characteristics of bovine β-casein (β-CN) were studied in vitro under infant and adult conditions. This direct comparison helps reveal the effects of different physiological stages on the digestive behavior of β-CN. Not only was the degree of hydrolysis (DH) of β-CN analyzed, but also the changes in its digestive morphology, microstructure, and secondary structure during digestion were explored in depth. Meanwhile, we focused on the physicochemical properties of β-CN digesta, including solubility, emulsifying and foaming properties, as well as their functional properties, such as antimicrobial and antioxidant activities. Key results showed that β-CN underwent more extensive hydrolysis in the adult digestion model, with approximately twice the DH compared to the infant model. The adult model exhibited faster digestion kinetics, less protein flocculation, and a more loosened secondary structure, indicating a more efficient digestion process. Notably, the digesta from the adult model displayed significantly improved solubility and emulsifying properties, and also enhanced antioxidant capacities, with significantly better inhibition of two common pathogenic bacteria than the infant model, and an average increase in the diameter of the inhibition zone of approximately 2 mm. These findings underscore the differential digestive behavior and functional potential of β-CN across physiological stages. This comprehensive assessment approach contributes to a more comprehensive insight into the digestive behavior of β-CN. Therefore, we conclude that producing products from unmodified β-CN may be more suitable for the adult population, and that the digesta in the adult model exhibit higher functional properties.

Effects of different temperatures on the physicochemical characteristics, microstructure and protein structure of preserved egg yolk

To clarify the mechanism of lower temperatures promoted the solidification of preserved egg yolk, the effects of temperature (4 °C, 10 °C and 25 °C) on the physicochemical properties, microstructure and protein structure of preserved egg yolk were studied. Results showed that the exterior egg yolk (EEY) exhibited higher pH, hardness and free sulfhydryl content at low-temperature pickling. The microstructure showed that the EEY gradually formed a denser gel network structure at lower temperatures. Electrophoresis results and Fourier transform infrared spectroscopy (FTIR) indicated that there were different degrees of protein degradation and cross-linking of proteins in the IEY (the interior egg yolk) and EEY and the decrease of β-sheets in the secondary structure was accompanied by an increase of β-turns during the formation of egg yolk gels. These results indicated that egg yolk solidification was faster and denser gel structure at 4 °C and 10 °C.

N-glycoproteomic profiling reveals structural and functional alterations in yellow primary preserved egg white under saline-alkali treatment

The posttranslational N-glycosylation of food proteins is important to their structure and function. However, the N-glycoproteomics of yellow preserved egg white were rarely reported. This study explored the changes of N-glycoproteome in yellow preserved eggs white after salt and alkali treatment. A total of 213 N-glycosites were identified on 102 glycoproteins, revealing prevalent glycosylation motifs and multiple N-glycosites within proteins. Salt and alkali treatment significantly altered the glycosylation patterns, impacting major proteins differently. GO analysis indicated the roles of differentially expressed glycoproteins in responding to stimuli and biological regulation. KEGG analysis emphasized the importance of salivary secretion pathway in enzyme secretion and peptide generation. Protein domain analysis highlighted the downregulation of Serpin. Protein-protein interaction networks revealed Apolipoprotein B as central players. This study provides essential structural information on the glycosylation modifications of egg white proteins, contributing to our understanding of the mechanisms behind the functional properties of preserved eggs.

Regulation of different copper salts on alkali-induced egg white gels: Physicochemical characteristics, microstructure and protein conformation

The effects of different copper salts (CuSO4, CuCl2, Cu(CH3COO)2) on the physicochemical characteristics, microstructure and protein conformation of alkali-induced egg white (EW) gels were investigated. With increasing concentration, three copper salts promoted the aggregation of EW proteins while decreasing the β-sheet content. The three-dimensional gel network was promoted to form, and the water-holding capacity (WHC), texture and solubility of gels were improved by three copper salts at low concentrations. While at high concentrations, the gel deteriorated. The main forces maintaining the alkali-induced EW gels added with copper salts were mainly ionic and disulfide bonds. And the protein component was not affected by ion concentration. Due to the difference in charge density, the three anions had different effects on the stability of proteins, and finally showed different gel characteristics (gel strength, WHC, solubility): CuSO4 > CuCl2 > Cu(CH3COO)2. Therefore, copper salts (especially CuSO4) can be used to improve EW protein aggregation.

Mechanistic insights into gel formation of egg-based yoghurt: The dynamic changes in physicochemical properties, microstructure, and intermolecular interactions during fermentation

This study aimed to elucidate the mechanism of acid-induced gelation in egg-based yoghurt by investigating the dynamic changes in physicochemical properties, texture, rheology, and microstructure of the gel during fermentation, combined with the role of intermolecular forces in gel formation. Results showed that protein aggregation and cross-linking increased as pH decreased during fermentation. Gel hardness increased with fermentation, eventually reaching 11.36 g, while maintaining low fracturability. Water holding capacity (WHC) decreased from 91.77% to 73.13% during fermentation. Rheological testing demonstrated a significant increase in viscosity and dynamic moduli (G' and G''), consistent with the observation of a more compact microstructure by scanning electron microscopy (SEM) and particle size analysis. Furthermore, dynamic changes of surface hydrophobicity, sulfhydryl content, and intermolecular forces suggested that hydrophobic interactions were likely the main driving force for gel formation, as well as that hydrophobic interactions and disulfide bonds played an important role in the maintenance and construction of the gel network structure. Although ionic bonds and hydrogen bonds also had an effect on the gel formation of egg-based yoghurt, their contributions were not significant. The study provided new insights for the development of novel egg-based fermentation foods and the research of acid-induced protein gels, and also contributed to the deep exploitation and utilization of poultry eggs.

Effect of preserved eggs on the health of SD rats, and anti-tumor action of HT-29 cells

Preserved eggs are traditional alkali-pickled food in China and have been enjoyed by consumers and extensively studied by researchers for their nutritional tastes and their anti-tumor, anti-inflammatory, antioxidant, lipid-lowering, and blood pressure-lowering properties. To study the anti-tumor effects of preserved eggs, this project observed the health on rats, and anti-tumor effects and separated anti-tumor active components on HT-29 cells. SD rats fed for 80 days showed that preserved eggs had no significant effect on weight, food intake, blood pH, liver tissues, or organ indices. Preserved eggs significantly increased blood levels of oxidative stress markers SOD and CAT, decreased MDA levels by 0.46, 0.23, and 0.25 times. Moreover, they also increased the level of IL-2 from 1233 to 1340 pg/mL. Two water-soluble bioactive peptide fractions, B1 and B2, with molecular weights ≥10 kDa were further obtained from preserved eggs by ultrafiltration and Superdex Peptide 10/300 GL. The potential mechanism of B1 and B2 is to activate the internal mitochondrial apoptotic pathway and induce apoptosis by up-regulating the expression of the pro-apoptotic factors cytochrome C, caspase-3, and caspase-9 mRNA in HT-29 cells.

Influence of rose anthocyanin extracts on physicochemical properties and in vitro digestibility of whey protein isolate sol/gel: Based on different pHs and protein concentrations

Protein-polyphenol interactions can improve the physicochemical properties of proteins. The objective of this study was to investigate the influence of rose anthocyanin extracts (RAEs) on the physicochemical properties and digestibility of whey protein isolate (WPI) sol/gel at different pHs and protein concentrations. Hydrophobicity interaction and ionic bonding were the main forces for the formation of acidic WPI and WPI-RAEs sol/gel. When pH was higher than 2.4, sol/gel became unstable, which may be related to hydrophobicity, ζ-potential value, total sulfhydryl and free sulfhydryl content changes. In addition, RAEs had positive effects on the color and water distribution of all WPI sol/gel. Moreover, RAEs improved the viscoelasticity of WPI sol/gel with protein content ≥ 12 % (w/v) at pH 2.4. More importantly, the addition of RAEs could reduce the digestibility of WPI sol/gel. We hope our works can provide promising strategies for developing WPI-RAEs foods.

Quantitative proteomics study on the changes of egg white of yellow preserved primary chicken eggs soaked in alkali solution

In order to investigate the changes of egg white of primary chicken eggs after being soaked in alkali solution, the tandem mass tags (TMT)-labeled quantitative proteomic technology combined with bioinformatics was conducted in this study. The results indicated that 100 differentially expressed proteins (DEPs) in yellow preserved primary egg white (YPPEW), 75 of which were highly and significantly correlated with the quality traits of YPPEW (| r | ≥ 0.9000, P < 0.01). Most of DEPs were involved in cellular processes by binding in extracellular space. Six pathways revealed the potential anti-inflammatory, anti-virus, anti-cancer and neuromodulatory mechanism of YPPEW. The current research provided a theoretical basis for the further study on YPPEW.

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.

Exploring the influence of ultrasound on the antibacterial emulsification stability of lysozyme-oregano essential oil

A lysozyme-oregano essential oil (Lys-OEO) antibacterial emulsion was developed via ultrasonic treatment. Based on the general emulsion materials of ovalbumin (OVA) and inulin (IN), the addition of Lys and OEO successfully inhibited the growth of E. coli and S. aureus, two representatives of which were Gram-negative and Gram-positive bacteria respectively. The emulsion system in this study was designed to compensate for the limitation that Lys could only act on Gram-positive bacteria, and the stability of the emulsion was improved using ultrasonic treatment. The optimal amounts among OVA, Lys and OEO were found to be the mass ratio of 1:1 (Lys to OVA) and 20% (w/w) OEO. The ultrasonic treatment at the power of 200, 400, 600, and 800 W and time length of 10 min improved the stability of emulsion, in which the surface tension was below 6.04 mN/m and the Turbiscan stability index (TSI) did not exceed 10. The multiple light scattering showed that sonicated emulsions were less prone to delamination; salt stability and pH stability of emulsions were improved, CLSM image showed emulsion as oil-in-water type. In the meantime, the particles of the emulsions were found to become smaller and more uniform with ultrasonic treatment. The best dispersion and stability of the emulsion were both achieved at 600 W with a zeta potential of 7.7 mV, the smallest particle size and the most uniform particle distribution.

Characterization of the Dynamic Gastrointestinal Digests of the Preserved Eggs and Their Effect and Mechanism on HepG2 Cells

Preserved eggs, an alkaline-fermented food, have been widely searched for their anti-inflammatory activity. Their digestive characteristics in the human gastrointestinal tract and anti-cancer mechanism have not been well explained. In this study, we investigated the digestive characteristics and anti-tumor mechanisms of preserved eggs using an in vitro dynamic human gastrointestinal-IV (DHGI-IV) model. During digestion, the sample pH dynamically changed from 7.01 to 8.39. The samples were largely emptied in the stomach with a lag time of 45 min after 2 h. Protein and fat were significantly hydrolyzed with 90% and 87% digestibility, respectively. Moreover, preserved eggs digests (PED) significantly increased the free radical scavenging activity of ABTS, DPPH, FRAP and hydroxyl groups by 15, 14, 10 and 8 times more than the control group, respectively. PED significantly inhibited the growth, cloning and migration of HepG2 cells at concentrations of 250-1000 μg/mL. Meanwhile, it induced apoptosis by up/down-regulating the expression of the pro-apoptotic factor Bak and the anti-apoptotic gene Bcl-2 in the mitochondrial pathway. PED (1000 μg/mL) treatment resulted in 55% higher ROS production than the control, which also led to apoptosis. Furthermore, PED down-regulated the expression of the pro-angiogenic genes HIF-1α and VEGF. These findings provided a reliable scientific reference for the study of the anti-tumor activity of preserved eggs.

Flame atomic absorption spectrometry combined with surface-modified magnetic mesoporous silica microspheres by polyethyleneimine for enrichment, isolation and determination of Cu2+ in preserved eggs after high-temperature digestion

A new efficient magnetic solid-phase extractant based on a surface-modified magnetic mesoporous silica microsphere referred as MMSM-PEI was synthesised and used for the enrichment and isolation of copper ions (Cu²⁺) in preserved eggs. The physicochemical properties and morphology of MMSM-PEI were characterized by X-ray diffraction (XRD) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), vibration sample magnetometry (VSM), scanning electron microscopy (SEM) and thermos-gravimetric analyses (TGA). The concentrations of trace Cu²⁺ in the preserved egg were determined by flame atomic absorption spectroscopy (FAAS). The effects of important parameters were examined. The most suitable pH values and temperature for adsorbing Cu²⁺ were 6.5 and 25 °C, respectively. According to the determination of Cu²⁺ in egg white, egg yolk and the outer coating mixture (TOCM) of preserved eggs, the spiked recovery and RSD were 94.1-103.8% and 0.96-4.35%, respectively. The limit of detection (LOD) and the limit of quantitation (LOQ) were 0.14 mg/kg and 0.46 mg/kg, respectively. The developed method improved the sensitivity and accuracy of FAAS for the determination of Cu²⁺ and it could be applied to the determination of trace Cu²⁺ in real samples.

Delineating the dynamic transformation of gluten morphological distribution, structure, and aggregation behavior in noodle dough induced by mixing and resting

To understand the formation of gluten network and its regulation on noodle qualities upon mixing and resting, the dynamic distribution and molecular transformation of gluten were tracked and quantified. Confocal laser scanning microscopy and scanning electron microscopy images showed that appropriate mixing (8 min) and resting (60 min) induced a compact gluten network with higher gluten junctions. Both height and width of protein molecular chains were increased by hydration during mixing and reduced after excessive resting (90 min). According to the size exclusion/reversed phase-HPLC profiles, mixing induced slight depolymerization of large glutenin polymer, and α-gliadin subunits were more susceptible to polymerization after appropriate mixing and resting. Increased mixing time was accompanied by the strengthening of ionic and hydrogen bonds, and the weakening of hydrophobic interaction. PCA and correlation analysis revealed the accurate regulation of mixing and resting induced dynamic distribution and evolution of gluten on the macroscopic noodle qualities.

Formation mechanism of high-viscosity gelatinous egg white among "Fenghuang Egg": Phenomenon, structure, and substance composition

"Fenghuang Egg" is a special egg product incubated for 12 days by fertilized hen eggs. Its egg white contains high-viscosity and excellent thermal gel strength. A comparative study on the differences in gel properties, structure, and substance composition between fresh egg white (FEW) and "Fenghuang egg" gelatinous egg white (GEW) was carried out. Experimental results showed GEW had better apparent viscosity, as well as the hardness, cohesiveness and water holding capacity (WHC) of thermal gel; the content and size of aggregate structure increased significantly in GEW, and a fibrous dense network composed of numerous spherical nanoparticles connected in series was formed after heating. In addition, it also discovered that more water molecules in GEW existed in the form of bound water. A total of 41 proteins changed significantly in FEW and GEW, Mucin 6 might be the main reason for the enhanced viscosity of GEW, and OVA might be the dominant protein differentiating the thermal gel properties between FEW and GEW. This study revealed that the differences in gel properties and structures between FEW and GEW were closely related to the content of highly glycosylated globular proteins, laying a theoretical foundation for the application of high-viscosity egg whites.

High intensity ultrasound-assisted quality enhancing of the marinated egg: Gel properties and in vitro digestion analysis

In this study, high intensity ultrasonication (HIU) was employed as an efficient tool to improve the gel property and in vitro digestibility of marinated egg (ME). The effects of HIU treatment at 100 W and 200 W for a series of time periods (0.5 h, 1 h, and 2 h) on the textural profiles, structural changes, and microstructures were also studied. After HIU treatment, the springiness and gumminess of ME white were enhanced. The water holding capacity reached the highest point (66.6%) when 0.5 h 200 W HIU was used. It was observed that 100 W HIU led to the highest zeta potential (-12.0 mV) and hydrophobicity (175.35 μg) of ME, indicating a high degree of electrostatic repulsion prevented agglomeration. HIU treatment at 100 W affected the dynamic rheological behaviors by boosting non-covalent bonds, which maintains the gel network's homogeneity. Meanwhile, the decreasing formation of α-helix, in contrast to β-turn, altered the aggregation behaviors of egg white gel. The microstructure of the 200 W HIU treated samples had porous colloidal network structures, and the in vitro digestibility (>75%) was increased after HIU. This work demonstrated that HIU could be a green and cost-effective tool for processing the egg product with high quality.

Effects of different curing methods on edible quality and myofibrillar protein characteristics of pork

This study aimed to investigate the effects of standing curing (SC), tumbling curing (TC), vacuum tumbling curing (VTC) and ultrasonic-assisted curing (UAC) on the edible quality of black pork and property of myofibrillar proteins (MPs) extracted from black pork. The results showed that all curing methods could improve the marinating absorptivity and the gel water retention of black pork, the solubility and surface hydrophobicity of myofibrillar proteins, and reduce the cooking loss and shear force of black pork, the hydrogen bond content of myofibrillar proteins and the gel whiteness compared with the control group (SC). The result of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the concentration of protein bands by VTC treatment was decreased obviously. In addition, the result of the scanning electron microscope (SEM) presented that tumbling and ultrasound treatment would destroy the structure of muscle fibers and make them loose and disordered.

Study on the mechanism of enhanced gel strength of heat-induced egg white by shikimic acid braising

This study evaluated the effects and mechanism of shikimic acid braising on the gelling characteristics of heat-induced egg white gel (HEWG). The results indicated that, during braising, soluble protein and hardness showed an overall increasing trend. The absolute Zeta potential value showed a decreasing trend; however, T₂ and free sulfhydryl group showed an increasing trend first and decreasing trend later, and surface hydrophobicity showed a decreasing trend. Microstructure analysis showed that protein gel aggregation increased and that holes and cracks formed first, and then the cracks decreased. Fourier transform infrared spectrometry showed that shikimic acid could strengthen the polarity of HEWG, and a mutual transformation occurred between intramolecular β-sheets, intermolecular β-sheets, and intermolecular antiparallel β-sheets, as well as a slight blue-shift, in the α-helices. In general, the addition of shikimic acid could alter the HEWG structure and improve its gel strength, polarity, and aggregation. Moreover, the higher the concentration of shikimic acid, the greater the influence on HEWG. Therefore, shikimic acid could be used as a new type of gel enhancer for the modification of egg white gel.

Inhibition of the liquefaction of alkali-induced egg white gel by sodium ascorbate

Effects of sodium ascorbate (1%, 2%, 3%) on the liquefaction of alkali-induced egg white gel (EWG) were investigated. Results showed hardness and water holding capacity (WHC) gradually decreased at 1%. However, hardness and WHC declined and then rose at 2% and 3%. Microstructural changes further confirmed the effects of sodium ascorbate on hardness and WHC. Electrophoresis showed sodium ascorbate caused the cross-linking between proteins, which was more resistant to degradation. Fourier transform infrared spectroscopy (FTIR) and surface hydrophobicity indicated sodium ascorbate significantly changed protein structure, especially at 2% and 3% resulted in protein reaggregation, increasing β-sheet, and decreasing surface hydrophobicity in the later stage. In general, sodium ascorbate didn't inhibit the liquefaction of alkali-induced EWG at 1%, but did effectively at 2% and 3%. Therefore, high concentrations of sodium ascorbate possess the potential to inhibit the "alkali injury liquefaction" of preserved egg whites without heavy metals.

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.

Real-Time Gauging of the Gelling Maturity of Duck Eggs Pickled in Strong Alkaline Solutions

Although many ultraviolet-visible-near-infrared transmission spectroscopy techniques have been applied to chicken egg studies, such techniques are not suitable for duck eggs because duck eggshells are much thicker than chicken eggshells. In this study, a high-transmission spectrometer using an equilateral prism as a dispersive element and a flash lamp as a light source was constructed to nondestructively detect the transmission spectrum of duck eggs and monitor the pickling of eggs. The evolution of egg transmittance was highly correlated with the albumen during pickling. The transmittance exponentially decays with time during this period, and the decay rate is related to the pickling rate. The colors of the albumen and yolk remain almost unchanged in the first stage. A multiple linear regression analysis model that realizes a one-to-one association between the days of pickling and the transmission spectra was constructed to determine the pickling duration in the second stage. The coefficient of determination reached 0.88 for a single variable, wavelength, at 590 nm. This method can monitor the maturity of pickled eggs in real time and does not require the evolution of light transmittance.

Effect of processing technologies on the digestibility of egg proteins

Egg and egg products are a rich source of highly bioavailable animal proteins. Several processing technologies can affect the structural and functional properties of these proteins differently and can influence their fate inside the gastrointestinal tract. The present review examines some of the processing technologies for improving egg protein digestibility and discusses how different processing conditions affect the digestibility of egg proteins under gastrointestinal digestion environments. To provide up-to-date information, most of the studies included in this review have been published in the last 5 years on different aspects of egg protein digestibility. Digestibility of egg proteins can be improved by employing some processing technologies that are able to improve the susceptibility of egg proteins to gastrointestinal proteases. Processing technologies, such as pulsed electric field, high-pressure, and ultrasound, can induce conformational and microstructural changes that lead to unfolding of the polypeptides and expose active sites for further interactions. These changes can enhance the accessibility of digestive proteases to cleavage sites. Some of these technologies may inactivate some egg proteins that are enzyme inhibitors, such as trypsin inhibitors. The underlying mechanisms of how different technologies mediate the egg protein digestibility have been discussed in detail. The proteolysis patterns and digestibility of the processed egg proteins are not always predictable and depends on the processing conditions. Empirical input is required to tailor the optimization of processing conditions for favorable effects on protein digestibility.

Development of a heatable duck egg white translucent jelly: an evaluation of its physicochemical properties and thermal stability

Though nutritional, the remaining separated duck egg white in duck egg processing plants presents challenges for its transportation and use, as it spoils easily and has a strong odor. Uses for the excess egg white are of paramount concern for agricultural resource reuse. The purpose of this study was to increase its value and use efficiency. Duck egg white was mixed with sodium hydroxide to produce translucent alkali-induced egg white jelly similar to that in preserved egg whites. To develop a heatable translucent egg white jelly, their physiochemical properties and thermal stabilities were investigated. A gel prepared with 150 mM sodium hydroxide at 25°C had optimal bloom strength and the densest microstructure. Storing the jelly at 5°C helped maintain its disulfide bonds and delayed liquefaction. Although heating decreased its bloom strength and total disulfide bond content as temperature increased (P < 0.05), scanning electron microscopy of the heated jelly revealed that the protein network structure was denser than that of unheated jelly. Heating caused parts of the structure to shrink and even dehydrate, leading to a wrinkled surface. However, no signs of liquefaction or collapse were observed, and the free alkali released during heating was lower than that from the white of existing preserved eggs. These results confirmed the thermal stability of the jelly and its potential to be served hot or used in food processing. Furthermore, in addition to disguising the odor and special flavor attributable to the alkaline treatment, adding ginger juice or turmeric to the preparation yielded higher bloom strength, resulted in lower free alkalinity, and delayed liquefaction, thus improving the jelly's thermal stability. Like preserved eggs on the market that can be served in hot congee, the proposed egg white jelly is rich in proteins and suitable for hot or instant serving. These findings may help address the problem of excessive remaining duck egg white created during food processing by diversifying duck egg processing and boosting its value.

Effects of packaging methods on the quality of heavy metals-free preserved duck eggs during storage

Preserved eggs without adding heavy metals in the pickling solution (heavy metals–free preserved eggs) have been developed, but it was found that the undesirable phenomenon such as dry shrinkage and fading occurred when they were not packaged and stored at room temperature. In this study, the effects of 5 packaging methods on the quality of heavy metals-free preserved eggs during storage were systematically studied. These methods included storage at room temperature and 4°C without packaging, wrapping with plastic bags, paraffin coating, and vacuum package. Through adopting these 5 packaging methods, the results showed that the moisture content and pH of the albumen decreased continuously, the mass loss rate increased continuously, the content of total volatile basic nitrogen increased firstly and then decreased, and the albumen hardness increased continuously. No microorganisms were detected in all samples with the 5 packaging methods during storage. Among them, the uncoated preserved eggs suffered the most serious moisture loss and mass loss, and the pH dropped at the fastest rate, followed by the preserved eggs wrapped in plastic bags. Preserved eggs stored at low temperature tended to turn yellow during storage, and the albumen showed higher hardness. The packaging method of paraffin coating performed the best in preventing the moisture loss of the albumen and the weight loss, which only decreased by 0.34 and 1.24%, respectively, after 3 mo. The best springiness, the darkest color, and the highest sensory score were found in the vacuum-packed preserved eggs after 3 mo of storage. It was concluded that paraffin coating and vacuum packing had better effect, while plastic bag packing showed the worst preservation performance for heavy metals–free preserved eggs.

Nondestructive Detection of the Gel State of Preserved Eggs Based on Dielectric Impedance

After completing the production of preserved eggs, traditionally, the degree of gelling is judged by allowing workers to tap the preserved eggs with their fingers and sense the resulting oscillations. The amount of oscillation is used for the quality classification. This traditional method produces varying results owing to the differences in the sensitivity of the individual workers, who are not objective. In this study, dielectric detection technology was used to classify the preserved eggs nondestructively. The impedance in the frequency range of 2–300 kHz was resolved into resistance and reactance, and was plotted on a Nyquist diagram. Next, the diagram curve was fitted in order to obtain the equivalent circuit, and the difference in the compositions of the equivalent circuits corresponding to gelled and non-gelled preserved eggs was analyzed. A preserved egg can be considered an RLC series circuit, and its decay rate is consistent with the decay rate given by mechanical vibration theory. The Nyquist diagrams for the resistance and reactance of preserved eggs clearly showed that the resistance and reactance of gelled and non-gelled eggs were quite different, and the classification of the eggs was performed using Bayesian network (BN). The results showed that a BN classifier with two variables, i.e., resistance and reactance, can be used to classify preserved eggs as gelled or non-gelled, with an accuracy of 81.0% and a kappa value of 0.62. Thus, a BN classifier based on resistance and reactance demonstrates the ability to classify the quality of preserved egg gel. This research provides a nondestructive method for the inspection of the quality of preserved egg gel, and provides a theoretical basis for the development of an automated preserved egg inspection system that can be used as the scientific basis for the determination of the quality of preserved eggs.

Effect of dry heating on egg white powder influencing water mobility and intermolecular interactions of its gels

BACKGROUND

Dry heat processing remains the most promising and simple approach for achieving better gelling properties of spray-dried egg white powder (EWP). Water mobility and intermolecular interactions in gels derived from EWP were investigated after subjecting EWP to various dry heating times (0-21 days).

RESULTS

The gel hardness and water-holding capacity significantly increased with an increase in dry heating time (P < 0.05), and both parameters were positively correlated with gel transparency. In contrast to the coarser structure of untreated EWP gel, the gel of EWP corresponding to 15 days of dry heating time had a fine-stranded and orderly network structure with smaller pores. An increase in the binding force between the gel and water was observed with an increase in dry heating time due to the formation of more 'protein-water' hydrogen bonds. Increasing the dry heating time resulted in an increase in the contribution of disulfide bonds, which in turn made a significant contribution to the rigidity of the EWP gels. By contrast, a decrease in the contribution of ionic bonds and hydrophobic interactions upon increasing the dry heating time promoted the formation of orderly networks.

CONCLUSIONS

Overall, gel corresponding to EWP dry heating for 15 days had better gel properties, the highest transparency and water-holding capacity, as well as a fine-stranded and orderly network structure. These results provide more information on improvement of the gel properties of EWP through dry heat treatment. © 2020 Society of Chemical Industry.

Gelatin-Based Nanocomposite Film with Bacterial Cellulose–MgO Nanoparticles and Its Application in Packaging of Preserved Eggs

Preserved eggs are prone to lose water during storage, which causes the preserved eggs to shrink and have poor taste, bad flavor, and reduced quality. By studying a degradable coating agent and applying it to preserved eggs, we explored its effect on the quality of preserved eggs during storage. In this paper, the structure and performance of gelatin film (GF), gelatin–bacterial cellulose film (GBF), and gelatin–bacterial cellulose–MgO nanocomposite film (GBMF) were explored by adding bacterial cellulose (BC) and MgO nanoparticles to gelatin. The results showed that the BC solution increased the particle size and absolute value of the zeta potential. The cross-sectional microstructure of the film showed fewer and smaller pores. The water vapor permeability (WVP) decreased, and the elongation at break (EB) increased significantly. The addition of MgO nanoparticles increased the particle size and reduced the absolute value of the zeta potential. The cross section of the film became denser and more uniform by adding MgO nanoparticles, and the surface hydrophobicity of the film increased, and the EB decreased. After coating the preserved eggs with these films, the weight loss rate, the content of total volatile base nitrogen (TVB-N), and the hardness were lower than that of uncoated preserved eggs. The pH of the uncoated preserved eggs also dropped faster than the coated preserved eggs. Moreover, the preserved egg coated with GBMF had the lowest weight loss rate and the highest sensory score. It can be seen that these three films had a certain preservation effect on preserved eggs, and the GBMF had the best preservation effect.