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Egg yolk will undergo gelation when it is stored below −6 °C due to protein denaturation and aggregation. In this study, the cryoprotective effects of sugar alcohols with various molecular weights (erythritol, xylitol, mannitol and maltitol) on egg yolks stored at −18 °C were compared, and the corresponding mechanism was elucidated. The rheological and textural properties showed that small molecular weight sugar alcohol could greatly increase the fluidity of frozen-thawed yolk and weaken the gel strength. Smaller molecule sugar alcohol, such as erythritol, had better efficiency in inhibiting the aggregation of proteins during freezing, due to the restricted growth of ice crystals, which was verified by the decrease in the loss of immobile water and crystallization enthalpy. In addition, the dominant interaction between protein molecules changed from hydrophobic interactions to electrostatic interactions in the presence of erythritol. It could be concluded that, small molecule sugar alcohols especially erythritol could more effectively protect proteins from aggregation by inhibiting the denaturation caused by ice crystal growth and hindering intermolecular hydrophobic interactions. • Small molecule sugar alcohol can effectively improve fluidity of frozen egg yolk. • The improved fluidity of frozen egg yolk was related to the reduced aggregation and ice crystal formation. • Erythritol addition could restrict inter-molecular hydrophobic interaction between frozen egg yolk proteins. • The gelation and emulsifying properties of frozen egg yolk were significantly improved. [ABSTRACT FROM AUTHOR]

BACKGROUND: Egg yolk granules (EYGs)‐soy lecithin (SL) complex is a newly developed delivery system that is effective for improving the storage stability of hydrophobic bioactive compounds. However, the formation mechanism of EYGs and SL complex and its effect on the gastrointestinal fate of lutein‐loaded emulsions needs to be investigated further. RESULTS: Adding SL greatly improved the surface activity of the EYGs, as evidenced by reduced surface tension and an increased adsorption rate to the oil/water interface. Hydrophobic interaction was the dominant force in the formation of EYG‐SL complex, with hydrogen and ionic bonds playing complementary roles. Using the EYG‐SL complex, stable oil‐in‐water emulsions were formed and exhibited an enhanced retention ratio and bioaccessibility of lutein after simulated digestion. Correlation analysis demonstrated that the additional anti‐oxidant activity as a result of EYGs was responsible for the high retention of lutein, whereas low surface tension facilitated the micellization of bioaccessible lutein. CONCLUSION: The present study shows that the EYG and SL have a synergistic effect with respect to improving the retention ratio and bioaccessibility of lutein in emulsions stabilized by EYG‐SL complex after digestion and this will guide the development of value‐added oil‐in‐water emulsion products using protein‐lecithin complex as a promising nutrient delivery vehicle. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The effects of three different enzyme treatments on the structure and volatile compounds of egg yolk protein were investigated. The secondary and tertiary structures, as well as volatiles, were characterized using ultraviolet spectroscopy (UV), fourier transform infrared (FTIR) spectroscopy, free sulfhydryl group analysis, and gas chromatography-mass spectrometry (GC-MS). FTIR analysis revealed a decrease in the contents of intermolecular, intramolecular, and intermolecular antiparallel β-sheets while an increase in random coils was observed. The contents of α-helices and β-turns did not show significant changes, indicating a reduction in protein compactness. Enzymatic treatment led to an increase in hydrophobic interaction, electrostatic interaction, and hydrogen bond formation within the egg yolk hot gel (EYG). Structural characterization demonstrated that EYG formed large uniform air chamber cavities after lipase hydrolysis (LEYG), while EYG hydrolyzed by papain (PEYG) and by flavor protease (FEYG) exhibited more compact structures. In addition, the binding of proteins to flavor substances inhibited the release of volatile flavor compounds. These findings provide insights into enhancing the flavor and texture of egg yolk by modulating its protein structure. [Display omitted] • The enzyme treatment induced a significant alteration in the secondary structure, resulting in increased flexibility. • The flavor components potentially formed hydrophobic interactions with egg yolk, thereby improving their flavor profile. • The alteration of free sulfhydryl group could potentially result in a reduction in gel strength. • The interrelation among protein structure, gel texture, and flavor was investigated through diverse analytical approaches. [ABSTRACT FROM AUTHOR]

• Freeze-thaw treatment is helpful for removing lipoprotein and lipid; • Freeze-induced yolk gelation is helpful for improving the purity of Immunoglobulins; • Freeze triggers aggregation of lipoprotein with mobility of boundary water decrease; • Hydrophobic and electrostatic interactions are the dominant forces in yolk gelation; In this study, the effect of freeze–thaw treatment on isolation of IgY was investigated, with macrograph, protein concentration, solid content, and transmittance evaluated. The results showed that higher refrigeration power (at −18 °C for more than 4 h and −40 °C for more than 2 h) caused yolk gelation and was helpful for removing heteroproteins. To reveal the mechanism of freeze-induced gelation assisting isolation of IgY, the properties of yolk frozen at −5°C, −18 °C and −40 °C for 8 h were determined, with SDS-PAGE, rheology property, low field NMR and interactions between proteins evaluated. As the results showed, the purity of separated IgY increased obviously (frozen at −18 °C and −40 °C), corresponding to the removal of LDL which aggregated during freezing. LDL aggregation may be triggered by hydrophobic interaction during boundary water crystallization. Therefore, freeze-induced yolk gelation is beneficial for IgY isolation by keeping LDL in dense gel structure while releasing IgY to the supernatant. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cholesterol removal treatment (CRT) can reduce the off-odor of EY. • The effect of CRT on the flavor of EY is evaluated by E-nose and GC–MS. • The texture, color, and taste of EY are not affected. • CRT reduces the degree of lipid oxidation by reducing the content of PUFA. The aim of this study was to investigate effects of cholesterol removal treatment (CRT) on the flavor, taste, texture, color, and nutritional value of hot gel egg yolk (EY). The off-odor, volatile components and taste of EY treated with CRT were studied by electronic nose (E-nose), gas chromatography-mass spectrometry (GC–MS) and electronic tongue (E-tongue). The effect of CRT on the nutritional value of EY was studied by amino acid and fatty acid analysis. The CRT significantly reduced the content of hexanal, 2-amyl-furan, 1-octene-3-ol, styrene and heptanal in EY1-EY4, also decreased its bitter taste without affecting other taste and elasticity. In addition, the CRT did not affect the essential amino acids (EAA) content and L*, a* and b* values of EY1-EY4, but it led to the reduction in polyunsaturated fatty acids (PUFA) content. In general, the CRT is an effective way to reduce the off-odor of EY without affecting consumer acceptance. [ABSTRACT FROM AUTHOR]

Hen egg yolk (EY) has a variety of techno-functionalities, including emulsifying, gelling, and film-forming properties. However, the application of native EY and its fractions is still limited due to the insufficient functionalities. Thus, various modification treatments have been used to improve the functionalities. In addition, there has been increasing research interest to explore the potential of modified EY and its fractions for applications in developing value-added food products. This review provides a brief introduction of EY structures, fractions, and components and focuses on discussing a wide range of existing modification methods and the mechanism of each method to change the structure and improve the desirable functionality of EY and its fractions. Three emerging applications of EY in food formulation industry, i.e. nutrient encapsulation and delivery system, unmodified EY substitutes, and edible films, are finally highlighted. Recent studies have shown that pre-treatment of EY and its fractions are often needed using enzymatic hydrolysis, complexing with polysaccharides, or other chemical, physical, and fermentation methods. The purpose of the pre-treatment is to dissociate the aggregated EY protein state, modify solution characteristics (such as solubility, hydrophobicity, and surface charge), so that the functionality is greatly improved, leading to more stable emulsion systems or other novel EY-based food products. By reviewing the new modification technology and application trends of EY, this review provides expert opinions of future research directions for the development of value-added EY derived food products. • Modification techniques for the functional enhancement of egg yolk are summarized. • Egg yolk derived emulsions or micro-capsules are attractive delivery systems. • Low cholesterol egg yolk fractions are new alternatives for unmodified egg yolk. • Egg yolk components are important candidates in the preparation of edible films. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phospholipids had a major influence on the physical properties of SEY lipids. • There were marked differences in the distribution of fatty acid profiles. • Furans and pyrazines were highly reduced in the extracted SEY lipids. • Phospholipids contribute little to the characteristic flavor of SEY 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. [ABSTRACT FROM AUTHOR]

This study investigated the effects of subcritical fluid extraction on lipid removal and the physicochemical properties of egg yolk powder. In addition, two-step enzymatic hydrolysis was used to improve the physicochemical properties. The content of total lipids and cholesterol decreased to 30.2% and 10.5 mg/g after subcritical propane-butane extraction, respectively, while phospholipids were retained. Protein solubility, surface hydrophobicity and total sulfhydryl results showed that this partial defatting avoided further quality deterioration of egg yolk powder. Scanning electron microscopy and confocal microscopy showed that the surface morphology and distribution of proteins and lipids changed with defatting degree. After two-step enzymatic hydrolysis, protein solubility of subcritical propane-butane extraction egg yolk powder significantly increased to 31.4% and soluble peptides with an average molecular weight lower than 1000 Da accounted for 70.0%. The improved defatted egg yolk powder is rich in protein, peptides and phospholipids and has great potential as a nutritional supplement. [Display omitted] • Subcritical extraction selectively removed triglycerides and cholesterol in yolk. • Phospholipids were retained after subcritical propane and butane extraction. • Part defatting avoided further quality deterioration of defatted egg yolk powder. • Surface morphology and components distribution changed with defatting degree. • Two steps enzymatic hydrolysis improved quality of defatted egg yolk powder. [ABSTRACT FROM AUTHOR]

Egg yolk powder is a widely used functional food ingredient due to its beneficial physicochemical and nutritional properties. However, its utilization in food can be limited due to its relatively high lipid content and low water-solubility. To address this issue, a two-step processing method utilizing enzymatic treatment combined with subcritical fluid extraction was investigated in this study. This method effectively reduced lipid content and improved water-solubility of egg yolk powder. An alcalase enzyme concentration of 500 U/g, extraction temperature of 313.15 K, extraction time of 120 min and a solid-liquid ratio of 1:9 (g:mL) produced powder with 20% lipid content and 71% water-solubility. Enzymatic hydrolysis clearly enhanced subcritical fluid extraction efficiency. This was attributed to hydrolysis disrupting the structure of egg yolk particles and facilitating the release of enclosed lipid molecules and was confirmed by scanning electron microscopy and laser confocal microscopy. [Display omitted] • Low-fat (20%) egg yolk powder with high water solubility (71%) was developed. • Enzymatic hydrolysis combined with subcritical fluid extraction was used. • Enzymatic hydrolysis improved the water solubility. • The highest oil extraction efficiency was achieved using 500 U/g alcalase. • Disruption in egg yolk structure promoted oil release. [ABSTRACT FROM AUTHOR]