Effects of temperature on quality of preserved eggs during storage

Investigation on appearance, texture, and molecular structure of heat-alkali synergistically induced egg white gel

To investigate the effect of heat-alkali synergistical induction on egg white gels, the gels formed from fresh duck egg whites were induced by heating in a water bath at 50 °C, 55 °C, 60 °C and 65 °C for 10 min, followed by the addition of NaOH at concentrations of 4.5 %, 5.0 %, 5.5 %, and 6 % were investigated at the level of appearance, texture, and molecular structure in this study. The appearance, physical and chemical character, textural properties, and molecular structure comprehensive investigation concluded that alkali induction caused heat-induced egg white protein to continue to be denatured, the degree of transparency was increased, part of the free water was converted to bound water, the intermolecular repulsion increased, the microscopic pores increased. The proteins in egg white continued to be crosslinked to form a three-dimensional network structure, creating a stable gel structure.

Evaluation of Physicochemical Changes in Hard-Boiled Eggs Stored at Different Temperatures

Eggs that have been hard-boiled are frequently used as ready-to-eat food. Refrigerated and frozen storage of hard-boiled eggs causes issues, such as customer rejection owing to textural changes. The objective of this research is to ascertain how storage temperature affects hard-boiled eggs' alteration in texture over time. Medium-sized brown shell eggs were acquired from a local market, boiled at 100°C for 15 min, and then stored at room temperature (25°C), refrigeration (4°C), and freezing (-18°C) conditions for 0, 12, 24, and 48 h. Fourier transform infrared spectroscopy (FTIR), texture profile, visual observation using a gemological microscope, free amino acid content, and color were measured. Freezing had a substantial impact on the eggs' hardness, gumminess, chewiness, and cohesiveness (p<0.05). The FTIR spectrums confirmed the textural changes in bonds of amide A (3,271 cm-1), amide I (1,626.2 cm-1), amide II (1,539.0 cm-1), C=O stretch of COO- (1,397 cm-1), asymmetric PO2- stretch (1,240 cm-1). Microscopic images confirmed structural changes in eggs stored at -18°C. The free amino acid content was lower in fresh and frozen eggs than in the rest (p<0.05). However, there was no discernible variation in the egg white's color when eggs were kept at 4°C (p>0.05). Salmonella spp. was found exclusively in eggs kept at room temperature. In conclusion, hard-boiled eggs did not exhibit structural or chemical changes when stored at 4°C for up to 48 h compared to freezing and room temperature conditions.

Development of an antimicrobial fungal egg tray containing orange oil and smoke for eggs preservation at room temperature

The prevention and controlled growth of pathogenic bacteria on eggs during storage and distribution at room temperature is important to ensure commercial eggs and egg products are safe for consumer. This study investigated the combined effects of orange oil (0.001%-0.004% v/w) and smoke for 10 min in paper egg tray packaging produce from the fungal pulp of Trametes versicolor. Eggs were kept in the developed paper egg tray at room temperature (30 ± 2°C). The mechanism of the combined antibacterial effects against Escherichia coli, Salmonella Typhimurium, and Staphylococcus aureus and egg quality were investigated. The combination of orange oil (0.004%) and smoke delayed all bacteria and suppressed changes in weight loss and the quality factor of eggs (Haugh unit, yolk index, albumen index) for at least 14 d. It was found that the volatile orange oil smoke in the egg tray could be passed through the structure of the cell wall and membrane of bacteria, giving rise to loss of cell viability by irreversibly damaging the cell membranes of all the bacteria in this test. Moreover, higher antioxidant activity was found on the eggs than on the eggshells, which is linked to greater shelf-life of treated eggs. The study demonstrates an improved paper egg tray packaging system and the possibility of combining released essential oils and smoke, which can be extended to egg products. Smoke can also be modified on the surface of paper egg trays easily, which shows potential in functionalizing implanted materials with antibacterial properties.

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.

Development of novel green methods for preparation of lead-free preserved pidan (duck egg)

Pidan, a pickled duck egg, is a traditional Chinese cuisine and generally produced by soaking in metal ion containing strong alkaline solution such as NaOH solution. However, nowadays consumers possess negative perception for using strong alkali in food processing. Therefore, the objective of the current study was to determine the potential of incinerated eggshell powder and alkaline electrolyzed oxidized (EO) water for pidan production rather than harmful NaOH use. This study aims to obtain the optimal physicochemical and sensory qualities of pidan. Various dosing (1-5%) of the incinerated eggshell powder solution or alkaline EO water was used as a basic pickling solution. Duck eggs were pickled at 25-27 °C for 15-30 days with 3 days of an observation interval. Actual commercial process commonly undergoes for 14 days of ripening, after 25 days of picking process with incinerated eggshell powder or EO water. Results showed that physicochemical and sensory attributes of pidan obtained by incinerated eggshell powder solution and alkaline EO water were not significantly different (P < 0.05) from the commercial product. This study reports a cost-effective and green alternative method for pidan processing by replacing costly NaOH without compromising their physico-chemical and sensory attributes.

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.

Effects of manual washing with three alkaline sterilizing agent solutions on egg quality during storage

This study aimed to investigate the abundance of microorganisms and quality of eggs washed with different washings (tap water, 0.03% calcium hypochlorite solution, 0.25% hydrogen peroxide solution, or 1% sodium percarbonate solution) and unwashed for 28-day storage. The results showed that the washing significantly decreased the abundance of microorganisms in all cases. Washing with one of the three alkaline sterilizing agent solutions significantly inhibited the deterioration of egg quality (evidenced by lower weight loss, air cell depth, albumen pH, yolk pH, and total volatile base nitrogen, but higher Haugh unit and yolk index) during storage, while washing with tap water showed opposite effects. The texture profile analysis and high-resolution scanning electron microscopy observation showed that all washings had slight negative effects on eggshell quality (eggshell breaking strength and microstructure), and washing with the alkaline sterilizing agent solution had no additional effects. The results might be attractive to egg preservation industry.

Quality of free-range and commercial eggs subjected to different storage periods and temperatures

Abstract The objective was to evaluate the internal quality of eggs from commercial laying hens and free-range hens subjected to different storage periods and temperatures. For the experiment, 280 eggs were randomly distributed into different treatments, adopting a completely randomized design, in a 2 x 7 factorial arrangement of two temperatures, seven storage periods, totaling 14 treatments with 10 replications. The treatments consisted of two storage conditions: under refrigeration (6 ± 1.0ºC) and at room temperature (26.6 ± 1.0ºC). Eggs were analyzed for 30 days, with evaluations in different storage periods (0, 5, 10, 15, 20, 25 and 30 days). For each storage condition, 140 eggs were separated, 70 commercial eggs and 70 free-range eggs. There was a linear increase in egg weight loss, yolk weight, albumen pH, yolk pH, length and width of albumen and yolk of commercial and free-range eggs, as the storage period increased. There was a linear reduction in weight, height and albumen index and in the yolk index of commercial and free-range eggs as the storage period increased, with more pronounced responses for eggs stored at room temperature (P<0.05). Albumen percentage was linearly reduced only for commercial eggs (P<0.05). Eggs kept at room temperature reduce their quality after 15 days of storage, and the storage under refrigeration for 30 days is recommended to preserve the shelf life of the egg for consumption.

Egg Freshness Evaluation Using Transmission and Reflection of NIR Spectroscopy Coupled Multivariate Analysis

This work presents a novel work for the detection of the freshness of eggs stored at room temperature and refrigerated conditions by the near-infrared (NIR) spectroscopy and multivariate models. The NIR spectroscopy of diffuse transmission and reflection modes was used to compare the quantitative and qualitative investigation of egg freshness. It was found that diffuse transmission is more conducive to the judgment of egg freshness. The linear discriminant analysis model (LDA) for pattern recognition based on the diffuse transmission measurement was employed to analyze egg freshness during storage. NIR diffuse transmission spectroscopy showed great potential for egg storage time discrimination in normal atmospheric conditions. The LDA model discrimination rated up to 91.4% in the prediction set, while only 25.6% of samples were correctly discriminated among eggs in refrigerated storage conditions. Furthermore, NIR spectra, combined with the synergy interval partial least squares (Si-PLS) model, showed excellent ability in egg physical index prediction under normal atmospheric conditions. The root means square error of prediction (RMSEP) values of Haugh unit, yolk index, and weight loss from predictive Si-PLS models were 4.25, 0.031, and 0.005432, respectively.

Changes in lipid properties of duck egg yolks under extreme processing conditions

The changes in lipid properties of duck egg yolks during processing may affect the quality of egg yolks. In this paper, various physicochemical and instrumental methods were used to study the changes of lipid characteristics of duck egg yolks under extreme processing conditions such as high salt, high salt-heat synergy and strong alkali. The results showed that both the high salt and high salt-heat treatments resulted in the decrease of the moisture content and the increase of the oil exudation of egg yolks. The iodine value of the lipid extracted from salted egg yolks with or without heat treatment decreased. However, strong alkali treatment increased the moisture content of egg yolks, and the oil exudation increased at first and then decreased. The iodine value of the lipid obtained from preserved egg yolks showed an overall trend with first increase and then decrease, and the saponification value of the lipid got from preserved egg yolks was lower than the lipid got from the raw salted egg yolks. According to the conjugated diene acid value and thiobarbituric acid value, the lipid of egg yolks was oxidized to different degrees under the three processing conditions. At the end of pickling, the fatty acid content of the lipid acquired from egg yolks all increased. Therefore, all three extreme treatments significantly changed the lipid properties of duck egg yolks.

Effect of Cladosporium cladosporioides on the Composition of Mycoflora and the Quality Parameters of Table Eggs during Storage

The eggshells of 120 experimental one-day-old table eggs were contaminated with the spore suspension of Cladosporium cladosporioides, divided into three groups (A–C) and stored at three different temperatures (3 °C, 11 °C and 20 °C) for 28 days. Visible growth of molds on/in experimental eggs was not observed within the entire storage period. No significant differences in the numbers of molds were found between particular groups of eggs. However, the composition of egg mycoflora was greatly influenced by storage conditions. Three mold genera were identified using the PCR method. The highest mold numbers were determined on Day 14 (Groups A and C) and Day 21 (Group B) when the maximum relative humidity and dew point temperature were recorded. On the same days, the dominance of Penicillium spp. and the minimum eggshell firmness were observed. Noticeable changes in egg quality were observed in eggs stored at 20 °C, and most of these eggs were downgraded at the end of storage period. The growth ability differed significantly among three mold genera. Penicillium spp. and Fusarium spp. showed better growth intensity at increased values (0.91–0.94) of water activity (aw) indicating a possible risk associated with the occurrence of mycotoxins in the egg contents.

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.