Preserved Eggs Research Articles

Differential contribution of Cu2+ and OH− to the formation of Nε-carboxymethyllysine and Nε-carboxyethyllysine in preserved egg white during pickling

In this study, the relationship between advanced glycosylation end products (AGEs) in preserved egg white (PEW) with protein oxidation and precursors induced by OH− and Cu2+ were performed to clarify the differential contribution of OH− and Cu2+ on the formation of AGEs during pickling. It was found that AGEs were more easily formed in PEW rather than yolk, and the accumulation of Nε-carboxymethyllysine (CML) could be promoted through protein oxidation related to carbonyl compounds, tryptophan induced by Cu2+ at early stage, while carbonyl compounds were more conducive to form Nε-carboxyethyllysine (CEL) under synergistic action of Cu2+ and OH−. At later period, Schiff base promoted the formation of CEL and CML in the presence of Cu2+. Meanwhile, the enrichment of CEL and CML could both be promoted by α-dicarbonyl compounds in presence of Cu2+ and/or OH−. This manuscript will provide theoretical guidance for reducing and limiting hazardous compounds in preserved eggs.

Alkali‐induced aggregation behaviour of tea polyphenols and its gel strengthening mechanism to alkali‐induced egg white

SummaryThe effect of black and green tea extracts with different alkali induction degrees on gel properties of alkali‐induced egg white gels (EWGs) was evaluated. Results indicate that, with the increase in alkali induction time, the concentration of soluble polyphenols gradually decreases while their relative polymerisation degree increases, especially for black tea polyphenols. The addition of tea extracts, especially induced by alkaline treatment for 6, 12, and 24 h, can promote the coagulation and browning and inhibit the ‘alkali injury liquefaction’ of alkali‐induced EWGs. Additionally, under alkali‐induced conditions, polyphenols in tea, especially black tea, can enhance the textural properties and thermal stability of alkali‐induced EWGs, this enhancement reaches its peak at 12 h of alkali induction and is consistent with protein secondary structure and interaction forces results. This research provides theoretical support for selection and induction of tea in high‐gel‐strength preserved eggs and other alkali‐induced protein gel food processing.

Multi-staged temperature control of the gelling properties and flavor quality of preserved eggs

The gelling properties and flavor quality of preserved eggs are affected by temperature reached during pickling. In response, this study investigates the effects of different temperature-controlled techniques on the gelling properties and flavor quality of preserved eggs. The results show that compared with an overall constant temperature and a two-stage temperature-controlled technique, the P-12–18–30 °C three-stage temperature-controlled pickling model produced the best texture properties of the preserved egg white gel, as further verified by LF NMR and SEM analysis. The results of amino acid analysis also show that the taste intensity of free amino acids in the P-12–18–30 °C group was significantly increased, especially for umami amino acids. In addition, the results of the electronic noise show that the volatile components of preserved eggs subjected to different temperature-controlled pickling techniques were similar, mainly consisting of short-chain alkanes; alcohols, aldehydes, ketones, and some aromatic compounds; long-chain alkane aliphatic groups; and inorganic sulfides, and there was no significant difference in the content of each flavor substance. In conclusion, this study offers theoretical basis for temperature-controlled pickling of preserved egg with better gel quality.

A Non-Destructive Detection and Grading Method of the Internal Quality of Preserved Eggs Based on an Improved ConvNext.

As a traditional delicacy in China, preserved eggs inevitably experience instances of substandard quality during the production process. Chinese preserved egg production facilities can only rely on experienced workers to select the preserved eggs. However, the manual selection of preserved eggs presents challenges such as a low efficiency, subjective judgments, high costs, and hindered industrial production processes. In response to these challenges, this study procured the transmitted imagery of preserved eggs and refined the ConvNeXt network across four pivotal dimensions: the dimensionality reduction of model feature maps, the integration of multi-scale feature fusion (MSFF), the incorporation of a global attention mechanism (GAM) module, and the amalgamation of the cross-entropy loss function with focal loss. The resultant refined model, ConvNeXt_PEgg, attained proficiency in classifying and grading preserved eggs. Notably, the improved model achieved a classification accuracy of 92.6% across the five categories of preserved eggs, with a grading accuracy of 95.9% spanning three levels. Moreover, in contrast to its predecessor, the refined model witnessed a 24.5% reduction in the parameter volume, alongside a 3.2 percentage point augmentation in the classification accuracy and a 2.8 percentage point boost in the grading accuracy. Through meticulous comparative analysis, each enhancement exhibited varying degrees of performance elevation. Evidently, the refined model outshone a plethora of classical models, underscoring its efficacy in discerning the internal quality of preserved eggs. With its potential for real-world implementation, this technology portends to heighten the economic viability of manufacturing facilities.

Effects of ovotransferrin-chitosan composite coating agent on the storage quality of heavy metals-free preserved eggs

Heavy metals-free preserved eggs (HMFPEs) are prepared by adjusting the sodium hydroxide and temperature during the pickling process, without heavy metals such as copper and zinc compared with traditional methods in the pickling solution. Due to the absence of plugging effect by heavy metals, there is a sharp drop in quality during storage. In order to guarantee the quality of HMFPEs during storage, a unique blend of ovotransferrin-chitosan composite coating solution was evenly spread over the shells, and the changes of physicochemical, sensory, and microbial properties during different storage periods were studied. The results showed that after 182 days of storage at 25 °C, coating group with citric acid as crosslinker could effectively prevent moisture loss, lipid oxidation and microbial growth, and consequently maintain desirable color and flavor of HMFPEs.

DNAzyme amplified dispersion state change of gold nanoparticles and its dual optical channels for ultrasensitive and facile detection of lead ion in preserved eggs

A dual-mode sensing platform for Pb2+ was constructed based on the dual optical channels of Au NPs system with the amplification of DNAzyme, and it was successfully applied for Pb2+ determination in preserved egg with satisfactory results. The presence of Pb2+ activated the DNAzyme and induced the dispersion change of Au NPs in high salt concentration. The sequent absorption change of Au NPs was translated to the fluorescence change of carbon dots through FRET, and the scattering change was transferred to grey value of images involving the Tyndall effect. Thus, a sensing platform based on fluorescence and colorimetric dual-technique was achieved for Pb2+ detection, under the optimized conditions. With the assistance of DNAzyme, the linear range of fluorometric and colorimetric method were 2.0 × 10-14 ∼ 8.0 × 10-10 mol/L and 2.4 × 10-13 ∼ 9.5 × 10-9 mol/L, respectively. The dual-mode sensing platform demonstrated its promising application in the environmental monitoring and food safety field.

Non-destructive determination and visualization of gel springiness of preserved eggs during pickling through hyperspectral imaging

The gel springiness of preserved egg during pickling is an important indicator of the maturity and gel quality of preserved eggs (PEs), for which there are no validated rapid means of detection. This work, hyperspectral imaging was used to non-destructively detect the gel springiness of preserved eggs (PEs) at different maturity levels during the curing period. Firstly, principal component analysis was used to explain the characteristics of the changes in gel springiness during the curing process of PEs of different maturity levels. Secondly, based on two-dimensional correlation spectroscopy(2DCOS), the 427–843 nm band range was explored as the optimal study region for gel springiness when gel springiness was used as a perturbation factor. In turn, spectral factors representative of the change in gel springiness are stripped in this band region. Comparing three different variable selection methods (SPA、CARS and UVE), it was found that the UVE-PLSR model had the highest detection accuracy: The predicted coefficient of determination Rp2 and the predicted standard deviation SEp of the predicted gel springiness are 0.846 and 1.526, with a residual prediction deviation RPD of 2.35. Finally, the above optimal prediction model is applied to the pixel spectrum to calculate the springiness value of each pixel point on the hyperspectral image and is supplemented by a pseudo-color technique to visualize the prediction of the spatial distribution of the gel springiness value. The results show that using hyperspectral imaging can detect the gel springiness value of the PE during the curing process, which will provide a theoretical basis for future determination of the ripeness of the PE as well as high-throughput online sorting.

Combined effects of NaOH, NaCl, and heat on the characteristics of ovalbumin gel and the exploration of the mechanism of transparent gel formation

Salted preserved eggs are made using poultry eggs under the combined action of NaOH, NaCl, and heat. To elucidate the main basis and mechanism of the formation of salted preserved egg white, the effects of NaOH (0.5–2.5%), NaCl (0–1.2%), and heat (72–100 °C) on the properties of ovalbumin (the most abundant protein in poultry egg whites) gel were studied. With increasing NaOH addition, the pH and the absolute value of zeta potential (TAV-ZP) increased, the opacity and Hunter whiteness decreased, and the relaxation time (T2) initially decreased and then increased. With increasing NaCl addition and heating temperature, the pH and TAV-ZP decreased, the opacity and Hunter whiteness increased, and T2 decreased first and then increased. In addition, the hardness and cohesiveness of the ovalbumin gel were greatly modified by NaOH, NaCl, and heat. NaOH contributed to the formation of the gel network structure. In addition, the surface hydrophobicity (H0) analysis result indicated that the tertiary structure of the ovalbumin had changed during the formation of the ovalbumin gel. The correlation analysis results showed that electrostatic repulsion played a vital role in the formation of the transparent ovalbumin gel, and the transparent ovalbumin gel possessed the following characteristics: low aggregation degree, high cross-linking degree, high immobilized water content, gel network structure, and the fully unfolded structure of ovalbumin molecules. In general, the ovalbumin formed a unique gel under the combined action of NaOH, NaCl, and heat. This study could provide theoretical guidance for the processing and control of salted preserved eggs and a reference for highly transparent egg white gel products.

Effects of different copper salts on the physicochemical properties, microstructure and intermolecular interactions of preserved egg white

This study was conducted to investigate the effects of different copper salts on the physicochemical properties, microstructure and intermolecular interactions of preserved egg white (PEW) during pickling. With increased pickling time, the alkalinity of the pickling solution and the moisture of PEW pickled by three copper salts (CuSO4, CuCl2 and Cu(CH3COO)2) gradually decreased, while the pH showed dynamic trends. During the early stage of pickling, the viscosity of PEW changed dynamically. With the progress of pickling, the hardness and springiness of PEW increased gradually and the α-helix structure gradually transformed into a more stable β-structure. The main forces that maintained PEW gel were ionic and disulfide bonds. In the early stage of pickling, the alkali penetration rate of CuCl2 pickled preserved eggs was faster, and better gel strength and network structure were observed, followed by CuSO4 and Cu(CH3COO)2, while there were no significant differences in the later stage of pickling.

The role of metal compounds in dynamically regulating alkali infiltration during pickling of preserved eggs

This study was conducted to investigate the dynamic regulation of alkali infiltration by different metal compounds during the pickling of preserved eggs. With the increased pickling time, the alkalinity of the pickling solution decreased, while the pH of preserved egg white increased firstly, then decreased, and finally increased again. The metal ions corresponding to the added metal compounds (CuSO4, CuSO4/ZnSO4 and PbO) underwent a complex migration with pickling time, and their content gradually increased in eggshell and yolk, but showed complex changes in egg white. The addition of metal compounds could produce a plugging effect. The main components of the black spots on eggshells of preserved eggs pickled by CuSO4, CuSO4/ZnSO4, and PbO were Cu2S, Cu2S/ZnS and PbS, respectively. In short, different metal compounds were combined with H2S to form insoluble compounds to block eggshell stomata, mesh pores and corrosion pores, thereby dynamically regulating the penetration of alkali.

The changes of umami substances and influencing factors in preserved egg yolk: pH, endogenous protease, and proteinaceous substance.

The study investigated the changes of nucleotides, succinic acid, and free amino acids amounts in yolk and the causes leading to the changes after pickling to uncover the fundamental umami component of preserved egg yolk. The findings demonstrated that while the contents of 5′-adenosine monophosphate (AMP), 5′-cytidine monophosphate (CMP), 5′-guanosine monophosphate (GMP), 5′-uridine monophosphate (UMP), and succinic acid increased after slightly decreasing aspartic acid (Asp) content in preserved egg yolk increased gradually. The contents of 5′-inosine monophosphate (IMP) and other free amino acids were gradually decreased. Comparing the taste activity value (TAV), it was found that the single umami substance, succinic acid, played a key role in inducing the umami taste. In combination with the Spearman correlation analysis, it was shown that the proteinaceous substance, which is the most significant umami component in preserved egg yolk, tended to condense first and subsequently disintegrate in an alkaline environment. The orthogonal partial least squares analysis (OPLS) found that pH was also affected by the changes in proteinaceous substance. These findings offer suggestions for enhancing the pickling procedure and investigating the optimal pickling period for preserved eggs.

Preparation and characterization of an alkali‐pickled preserved egg white heat‐induced gel

AbstractIn recent years, heavy‐metal salts for pickling preserved eggs and the long production period have affected its acceptability and industrialization. In this study, we used the method of short‐term pickling of no‐heavy‐metal salts to obtain gels by alkali‐picked and heat induced. The physicochemical properties, secondary structure and free amino acid composition of egg whites during pickling were determined. Furthermore, the texture and chromatic characters of the preserved egg white gels after heating were analyzed. After 7 days of pickling, the pH and free alkalinity can reach the level of preserved eggs, presenting the value of 11.48 and 184.03 mg/100 g respectively. The α‐helix content decreased from 36.01% to 32.39%. On the other hand, the β‐turns increased from 16.98% to 18.82%, and the Random coils increased from 26.31% to 28.76%. The free sulfhydryl content of preserved egg white increased gradually, whereas the total sulfhydryl content, the Td value, and free amino acid content decreased during the pickling process. The hardness and springiness of the gel remained largely unchanged during the pickling time (5–8 days). The gel's appearance, chromatic, and texture reached the level of traditional preserved egg in a relatively short pickling time, providing a new idea for the rapid picking of preserved egg white gel. The treatment in this study is important for improving the efficiency of industrial production of preserved egg white gels.Practical applicationsHeat treatment is a standard method in food processing, helping improve the texture and quality of products. After heat treatment, the physicochemical properties of the alkali‐pickled eggs can reach the state of traditionally preserved egg whites. Therefore, the method described in this study can help shorten the pickling time of preserved egg white products and provide theoretical support for developing new preserved egg products.

Development and test of a smart multisensory device for preserved eggs

Preserved eggs have exceptional sensory quality traits such as pine-needle-like flowers on the surface, reddish-brown and elastic albumen, dark green umami and runny yolk, ammonia smell, and so forth. In this work, a smart multisensory device equipped with a raspberry Pi, a camera, and visual sensor arrays for odor and taste perception was developed to assist in the evaluation of preserved eggs sensory quality. The feasibility of the device to nondestructively detect the maturation stages of preserved eggs during curing was conducted on preserved eggs with five different maturation stages, yielding an accuracy of 95.00%. To further increase the accuracy of identifying preserved egg brands, this study incorporated three types of intelligent sensory data. The three parts of data were combined into a two-dimensional matrix, normalization and principal component analysis were carried out, and the linear discriminant analysis (LDA) model was finally established, achieving 91.67% accuracy for brand recognition. The results demonstrated that the device could be employed to provide rapid and accurate characterization of the sensory qualities of preserved eggs, as well as provide useful reference for smart sensory characterization of other food products. Practical Applications Processors prioritize food safety and quality, which is why producers of preserved eggs frequently face complex and time-consuming workflows, such as the appointment of sensory evaluators to assess the quality of preserved eggs. The sensory panel, on the other hand, is prone to fatigue. This study presents a smart multi-sensory device that can collect and analyze sensory data trends from preserved eggs at a speed and interconnectedness that human sensory panels cannot match. The device has an easy-to-use interface that allows for the real-time collection of critical information about consumer acceptance of preserved eggs. The results showed that the device could be used by preserved egg producers to provide rapid and accurate sensory characterization of preserved eggs, as well as a useful reference for smart sensory characterization of other food products.

Identification of preserved egg white protein glycation and insight into the bioactivity

AbstractPreserved eggs have been reported to possess anti‐inflammatory and antioxidant bioactivities, which are enhanced after protein glycation. However, it is still unknown which proteins are glycated during pickling process of preserved eggs and whether the glycated proteins are related to the bioactivity of preserved eggs. In this study, UPLC‐ESI‐MS/MS was used to identify glycation of proteins in preserved egg white (PEW) and duck egg white (DEW). Altogether, 142 sites on 53 glycated proteins were detected in PEW while 9 sites on 2 glycated proteins were found in DEW. Bioinformatic analysis suggested that the glycation of PEW proteins (e.g. Ovalbumin, Ovotransferrin, Albumin) were supposed to be connected with allergenicity reduction, and the enhancement of antibacterial and antioxidant bioactivities. These findings provide some indications for the future studies on the detailed bioactivities of glycated proteins in PEW, and pave the way for applied research on glycation and the development of functional foods.

High-Throughput Online Visual Detection Method of Cracked Preserved Eggs Based on Deep Learning

Cracked preserved eggs can easily decay, emit a peculiar smell, and cause cross-infection. The identification of cracked preserved eggs during production suffers from low efficiency and high cost. This paper proposes an online detection and identification method of cracked preserved eggs to address this issue. First, the images of preserved eggs are collected online. Then, each collected image is cut into a single image of the preserved egg, and the images of different surfaces of the same preserved egg are respectively spliced by the sequential splicing scheme and the matrix splicing scheme. Finally, the data sets obtained by the two stitching methods are exploited to establish a deep learning detection model. The experimental results indicate that the MobileNetV3_egg model, an improved version of the MobileNetV3_large model, achieves the best recognition ability for cracked preserved eggs by using the matrix splicing scheme. The accuracy reaches 96.3%, and the detection time for 300 images is only 4.267 s. The proposed method can meet the needs of actual production, and the application of this method will make the identification of cracked preserved eggs more automated and intelligent.

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.

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.

Application of volatile and spectral profiling together with multimode data fusion strategy for the discrimination of preserved eggs

The maturity level of eggs during pickling is conventionally assessed by choosing few eggs from each curing batch to crack open. Yet, this method is destructive, creates waste and has consequences for financial losses. In this work, the feasibility of integrating electronic nose (EN) with reflectance hyperspectral (RH) and transmittance hyperspectral (TH) data for accurate classification of preserved eggs (PEs) at different maturation periods was investigated. Classifier models based solely on RH and TH with EN achieved a training accuracy (93.33%, 97.78%) and prediction accuracy (88.89%; 93.33%) respectively. The fusion of the three datasets, (EN + RH + TH) as a single classifier model yielded an overall training accuracy of 98.89% and prediction accuracy of 95.56%. Also, 52 volatile compounds were obtained from the PE headspace, of which 32 belonged to seven functional groups. This study demonstrates the ability to integrate EN with RH and TH data to effectively identify PEs during processing.