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

Extraction of egg yolk lipids via salt-induced synergistic heat treatment: Fabrication, characterization and flavor analysis

In this study, the oxidation of egg yolk lipids (EYL) by salt-induced heat and non-heat treatments was investigated for quality and flavor. The correlation between physicochemical properties, lipid oxidation and antioxidant activity was modeled using partial least squares discriminant analysis (PLS-DA). The results indicated that the prolonged salt-induced synergistic heat treatment produced the highest level of lipid oxidation, antioxidant activity and oil exudation, along with the lowest level of polyunsaturated fatty acid content. In addition, higher contents of pyrazines and fewer acid species were detected, which was not the case with the salt-free heat treatment. In total, 14 identical volatile organic compounds (VOCs) were produced, yet their overall flavor profiles determined by the electronic nose would remain dramatically distinguished. Therefore, heat treatment was particularly critical for lipid oxidation and the generation of aromatic compounds, implying that heat-treated EYL induced by salt is a flavor component with good antioxidant potential.

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.

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.

Changes in physicochemical properties and lipid oxidation lead to the formation of mud on salted egg yolks during storage

Salted egg yolk (SEY) becomes easily "muddy" during storage, leading to a decrease in the quality of salted eggs. The mechanism of SEY mudding was studied in this paper. The results showed that SEY hydrogen proton binding decreased, and SEY water and lipid fluidity increased during storage. In addition, the degree of lipid oxidation and monounsaturated fatty acids in salted egg yolk lipids (SEYL) increased, and primary oxidation products and secondary oxidation products were formed. Moreover, the structure of SEY was degraded to release lipids and proteins, and these proteins and lipids were re-emulsified to form new aggregates. Finally, by PLS-DA modeling analysis, it was found that the content of ω-3 polyunsaturated fatty acids and phospholipids changed significantly after SEY became muddy. These results suggest that the muddiness of SEY can primarily be attributed to higher fluidity and protein-lipid re-emulsification, and secondarily to the oxidation of SEYL.

Characterization of physical properties, volatile compounds and aroma profiles of different salted egg yolk lipids

Salted egg yolks (SEY) have a desirable and unique flavor with multiple underlying applications in food processing, and their abundant lipids contribute to a creamy and pleasant aroma. However, it is important to maintain the stability of the SEY flavor, which depends to a large extent on the egg species and the processing method. This study aimed to extract different SEY lipids with conventional solvents, analyze the fatty acid composition, and screen the volatile compounds to elucidate the flavor differences between salted hen eggs and duck eggs. Compared to ethanol extraction, acetone-extracted lipids had lower acid value and viscosity, and almost had no phospholipid content. Fatty acid analysis revealed that the highest content of fatty acid in SEY lipids was oleic acid, followed by palmitic acid and linoleic acid, while there were significant variations of different SEY lipids in the fatty acid profiles. The volatile compounds were identified by headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS), and the overall odor was detected by the electronic nose (E-nose). A total of 27 volatile compounds were analyzed in SEY lipids and divided into 8 chemical classes. The aldehydes, furans and pyrazines were decreased, and the hydrocarbons were increased compared with untreated SEY. The combination of the physical properties and flavor evaluation of SEY lipids could provide a theoretical basis for the extension of the characteristic flavor matrix in SEY.

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.

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.

Rheological and Flow Behaviour of Yolk, Albumen and Liquid Whole Egg from Eggs of Six Different Poultry Species

Liquid egg products are one of the basic raw materials for the food industry. Knowledge of their rheological and flow behaviour in real technical elements is absolutely necessary for the selection of suitable technological equipment for their processing. In this article, the rheological properties of liquid egg products were determined. Eggs from six different species of poultry are used: domestic hen (Gallus gallus domesticus) hybrid Hisex Brown; Japanese quail (Coturnix japonica); German carrier goose (Anser anser f. domestica); domestic ducks (Anas platyrhynchos f. domestica); domestic guinea fowl (Numida meleagris f. domestica); and domestic turkeys (Meleagris gallopavo f. domestica). Liquid egg products showed pseudoplastic behaviour in range of shear strain rates from 0.2 up to 200 s⁻¹ and at the temperature of 18 °C. Thus, the flow curves were constructed using the Ostwald-de Waele rheological model, with respect to the pseudoplastic behaviour of liquid egg products. According to the values of the coefficients of determination (R²), the sum of squared estimate of errors (SSE) and the root mean square error (RMSE), this model was appropriately chosen. Using the consistency coefficient K, the flow index n and the adjusted equations for the flow rate of technical and biological fluids in standard pipelines, the 3D velocity profiles of liquid egg products were successfully modelled. The values of the Reynolds number of the individual liquid egg products were calculated, and the type of flow was also determined. A turbulent flow has been detected for some liquid egg products.