Egg yolk phospholipids: a functional food material to generate deep-fat frying odorants

Use of egg yolk phospholipids to improve the thermal-oxidative stability of fatty acids, capsaicinoids and carotenoids in chili oil

Phospholipids can act as antioxidants in food. In this study, egg yolk phospholipids (EPL) and sunflower oil were utilized in making chili oil, and proton nuclear magnetic resonance spectroscopy was employed to quantify the concentrations of fatty acyl groups, carotenoids, capsaicinoids in chili oil according to their specific signals in the spectra. The results showed that the changes in the concentrations of fatty acyl groups in the control samples were greater than those in the EPL-treated samples at the same frying temperature, while the contents of carotenoids and capsaicinoids were significantly lower than those of the EPL-treated samples when fried at 150 °C (p < 0.05). Two-way ANOVA indicated that frying temperature and EPL treatment, as well as their interaction had significant impacts on the thermal-oxidative stability of chili oil (p < 0.05). The results suggest that EPL may act as antioxidants during frying, and EPL can improve the thermal-oxidative stability of chili oil.

The effect of lutein on the oxidation of egg yolk phospholipids in a liposome model

Egg yolk phospholipids (PLs) extracted by organic solvent are prone to oxidation, while they are quite stable in egg yolk. This study was to verify the decisive role of lutein (naturally present in egg yolk) on the oxidative stability of PLs by constructing liposome. The liposome samples were heated at 100 °C for 10 min, and then the oxidation products of the liposome samples were analyzed by 1H NMR and GC-MS. The results showed that the concentrations of most of the oxidation products in the PLs-liposomes sample were significantly higher than those in the PLs&lutein-liposomes sample. Therefore, lutein could protect egg yolk PLs from oxidation, thus inhibiting the formation of lipid-derived volatile compounds. As those lipid-derived volatile compounds are the key fatty note odorants, this study has confirmed that the removal of lutein is the determining factor in using egg yolk PLs as an ideal precursor of fatty note odorants.

Egg yolk phospholipids as an ideal precursor of fatty note odorants for chicken meat and fried foods: A review

Egg yolk phospholipids (PLs) have been demonstrated to generate large quantities of lipid-derived odorants, especially the fatty note odorants. Recently, egg yolk PLs have been successfully used in chicken meat and fried foods to improve aroma. This review comprehensively summarizes the properties of egg yolk PLs as precursors of fatty note odorants, including their classes, extraction, identification, oxidation, decomposition and odorant formation, applications, considerations and future prospects in the food industry. Most likely, phosphatidylcholine (PC) is the most abundant class in egg yolk PLs, and PC is more efficient than phosphatidylethanolamine in generating fatty note odorants; moreover, the predominant polyunsaturated fatty acid is linoleic acid, and its corresponding predominant hydroperoxide is 9-hydroperoxy-10,12-octadecadienoic acid during autoxidation, which is the precursor of 2,4-decadienals and 2,4-nonadienals, the key fatty note odorants. Therefore, egg yolk PLs could be an ideal precursor of fatty note odorants for chicken meat and fried foods.

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.

Effect of Four Extraction Processes with Acetone-Ethanol Protocols on the Properties of Egg Yolk Phosphatidylcholine and the Structure of Residual Protein

In this study, four acetone-ethanol protocols were employed to investigate the effect of extraction processes on the yield and purity of phosphatidylcholine (PC) from dried egg yolk powder and fresh liquid egg yolk, as well as the cholesterol distribution between the oil and PC fraction. Furthermore, the physicochemical (thermo-stability, fatty acid composition, and molecular structure) and emulsifying (zeta potential, particle size, EAI, ESI, and creaming index) properties of the final PC product were also examined. In addition, the structural characteristics of the egg yolk residual protein were highlighted to promote its application in food industries. The results showed that de-oiling with acetone prior to ethanol extraction can achieve high yield (19.92%) and purity (68.62%) of the PC product with low cholesterol content (< 0.12%). The extraction processes exhibited a significant impact on the emulsifying properties of the PC product. The creaming index of PC emulsions was higher than that of egg yolk powder emulsions with high protein concentration, suggesting that PC plays a critical role in the emulsifying stability of egg yolk protein dispersion. The structural characteristics of residual protein, including free sulfhydryl groups and primary, secondary, and ternary structures, showed considerable differentiation related to extraction processes. These findings provide a powerful tool for the dietary utilization of egg yolk PC and protein in future.

Use of egg yolk to imitate meat aroma

Egg yolk contains abundant meat precursors, but its odor is quite different from meat aroma. In this study, the lipids in egg yolk were partly removed by acetone or totally removed by chloroform/methanol, and lutein was removed simultaneously by the solvents. Then, the samples were heated, and the volatiles and aroma profiles were analyzed. The results showed that chicken meat aroma and meat aroma were imitated successfully through the removal of neutral lipids and lutein (acetone-treated) and total lipids and lutein (chloroform/methanol-treated) egg yolk samples, respectively. Finally, additional lutein and tert-butylhydroquinone were employed for validating the inhibiting effects of lutein on lipid oxidation and Maillard reaction, and the results demonstrated that it was lutein rather than lipids or their degradation products that determined the flavor formation. These findings push forward the mechanisms for the formation of meat flavor and provide insights for future manufacturing of meat aroma.