Impact of ozone-induced oxidation on the textural, moisture, micro-rheology and structural properties of egg yolk gels

Redistribution and fusion of protein-lipid assemblies within the egg yolk sphere under slight non-destructive deformation causing a change in thermal gel properties

Egg yolk production processed after separating egg white is a common method to shorten cycle, but its taste quality will change even the vitelline membrane is intact. This might be related to the slight non-destructive deformation causing redistribution and fusion of protein-lipid assemblies within the egg yolk spheres. We investigated the mechanism of the change in thermal gel properties under slight deformation. The results of microscopic structural morphology revealed that the whole boiled egg yolk (WEY) underwent a transition in protein-lipid assembly morphology within yolk spheres, which changed from local aggregation to disordered fusion in shaken boiled egg yolks (SEYs). The spectroscopic and physicochemical properties analysis demonstrated that the redistribution of protein-lipid assemblies gave rise to marked changes in water migration, texture properties, molecular interactions, and oral sensation simulation of egg yolk thermal gels. This is benefit to guide the regulation of the taste quality egg yolk products in industry.

Study on the adsorption and migration rule of Sichuan pepper characteristic volatile compounds during the cooking process in the sea cucumber body wall

The natural flavor of sea cucumber is generally not easily accepted by consumers. In this study, the effect of different cooking conditions on the adsorption of the characteristic flavor of Sichuan pepper by sea cucumber was investigated by response surface methodology, and the optimal cooking conditions were identified. A total of 45 volatiles were identified based on gas chromatography-mass spectrometry, of which 27 were key flavor actives. Low-field nuclear magnetic resonance and textural analysis showed that the addition of Sichuan pepper during the cooking process affected the water migration and the textural properties of sea cucumbers. It was shown that the addition of Sichuan pepper could significantly improve the flavor and other quality characteristics of sea cucumber. This study has important practical guiding significance for the flavor improvement and product innovation of sea cucumber food.

Influence mechanisms of linoleic acid and oleic acid on the gel properties of egg yolk protein

BACKGROUND

Gel property is among the crucial functional properties of egg yolk (EY), which determines the texture and flavor of EY products. In the present study, the effects of two unsaturated fatty acids [monounsaturated fatty acid oleic acid (OA) and diunsaturated fatty acid linoleic acid (LA)] on the gel properties of EY protein were investigated.

RESULTS

Compared with the blank group, the addition of LA and OA (10-50 g kg-1) improved the gel hardness (from 270.54 g to 385.85 g and 414.38 g, respectively) and viscosity coefficient (from 0.015 Pa.sn to 11.892 Pa.sn and 1.812 Pa.sn, respectively). The surface hydrophobicity of EY protein increased to a maximum value of 40 g kg-1 with the addition of both fatty acids (39.06 μg and 41.58 μg, respectively). However, excess unsaturated fatty acids (≥ 50 g kg-1) disrupted the completeness of the gel matrix and weakened the structural properties of the EY gel.

CONCLUSION

Both fatty acids improved the gel properties of EY protein. At the same addition level, OA was superior to LA in improving gel properties. The present study provides a theoretical underpinning for the sensible application of unsaturated fatty acids in improving EY gel properties. © 2024 Society of Chemical Industry.

The effects of sucrose/NaCl combined pickling on the textural characteristics, moisture distribution, and protein aggregation behavior of egg yolk

Salted egg yolks have a tender, loose, gritty, and oily texture and are commonly employed as fillings in baked goods. This study investigated the formation mechanism of egg yolk gels using three different pickling methods: NaCl, sucrose, and mixed groups. The results revealed that of these pickling methods, egg yolks pickled with the mixture had the lowest moisture content (11.59% at 25°C and 10.21% at 45°C), almost no free water content, and the highest hardness (19.11 N at 25°C and 31.01 N at 45°C). Intermolecular force measurements indicated that pickling with the mixture mitigated the surface hardening effect of sucrose and facilitated protein cross-linking. Moreover, confocal laser scanning microscopy of the egg yolk gels pickled with the mixture displayed macromolecular aggregates and oil exudation, suggesting that this method partially disrupted the lipoprotein structure and notably promoted yolk protein aggregation and lipid release. Overall, egg yolks formed a dense gel via the mixed pickling method owing to the ionic concentration and dehydration effects. These findings show the impact of NaCl and sucrose in pickling egg yolks, providing a crucial foundation for developing innovative and desirable egg yolk products. PRACTICAL APPLICATION: This study introduces a novel pickling strategy that combines sucrose and NaCl for egg yolk processing. The egg yolk pickled using this method exhibited improved quality according to the evaluated textural characteristics, moisture distribution, and protein aggregation behavior. The findings may broaden the use of sucrose as a pickling agent for egg yolk processing and provide new ideas for developing and producing pickled eggs and other food products.

Optimizing the formation of myosin/high-density lipoprotein composite gels: PH-dependent effects on heat-induced aggregation

This study investigated impact of high-density lipoprotein (HDL) on thermal aggregation and gelling behavior of myosin in relation to varied pHs. Results revealed that HDL modified myosin structure before and after heating, with distinct effects observed at varied pH. Under pH 5.0, both myosin and HDL-MS exhibited larger aggregates and altered microstructure; at pH 7.0 and 9.0, HDL inhibited myosin aggregation, resulting in enhanced solubility, reduced turbidity and particle size. Comparative analysis of surface hydrophobicity, free sulfhydryl groups and secondary structure highlighted distinct thermal aggregation behavior between MS and HDL-MS, with the latter showing inhibitory effects under neutral or alkaline conditions. Gelation behavior was enhanced at pH 7.0 with maximum strength, hardness, water-holding capacity and rheological properties. Under acidic pH, excessive protein aggregation resulted in increased whiteness and rough microstructure with granular aggregates. Under alkaline pH, gel network structure was weaker, possibly due to higher thermal stability of protein molecules. Scanning electron microscopy revealed expanded HDL protein particles at pH 7.0, accounting for decreased gel strength and altered rheological properties compared with myosin gel. Overall, the results indicated a positive role of HDL at varied pH in regulating thermal aggregation of myosin and further impacting heat-induced gel characteristics.

Effects of cholesterol removal treatment on the flavor and physicochemical properties of hot gel egg yolk

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.

Tracking transformation behavior of soluble to insoluble components in liquid egg yolk under heat treatment and the intervention effect of xylitol

The heat sensitivity of egg yolk limits its application, and xylitol can improve its thermal stability. The soluble and insoluble components of egg yolk and egg yolk containing xylitol treated at different temperatures were explored from the aspects of thermal instability behavior characterization and structure property. Magnetic resonance imaging and low field nuclear magnetic resonance showed that increased temperature induced liberation and transfer of hydrogen protons. Meanwhile, the apparent viscosity of soluble components increased, while that of insoluble components decreased. Microstructure showed that heat treatment induced aggregation and lipid transfer. SDS-PAGE showed that heat treatment induced aggregation and transformation of γ-livetin and apo-LDL. The change in crystal structure, Raman spectroscopy, and 3D fluorescence spectra showed that heat treatment resulted in the unfolding of yolk proteins, especially plasma proteins. Xylitol could alleviate transformation of components by stabilizing protein structure, alleviating the damage in protein integrity and elevation in aggregation size.

Study on the Mechanism of Modified Cellulose Improve the Properties of Egg Yolk gel

Natural fiber is not suitable for modifying yolk gel as a modifier because of its large size and high compactness. In this study, two kinds of modified cellulose were selected to improve the thermal gel properties of yolk. The results showed that the two kinds of cellulose promoted the formation of ordered structure in yolk gel. The ordered gel network not only improved the texture properties and rheological properties, but also improved the water retention of yolk gel significantly. CMC and CNFC at the same concentration, the modification effect of CMC on yolk gel was better than CNFC because of its excellent dispersion. However, high concentration of CNFC (1.20-1.60%) disrupted the cross-linking and ordered structure formation of yolk protein, and the quality of gel was significantly reduced.

Interventional effect of compound sugar and salt on the thermal instability behavior of liquid egg yolk

In this study, the influence of compound sugar (glucose, sucrose, trehalose, and arabinose) and compound sugar and salt (glucose, sucrose, trehalose, arabinose, and NaCl) on the thermal stability of heat-treated liquid egg yolk was explored. The results showed that the addition of 4% compound sugar or 4% compound sugar salt could significantly enhance the heat resistance of liquid egg yolk and increase the denaturation temperature of liquid egg yolk to above 77°C. Moreover, the addition of sugar and salt could improve the functional properties of liquid egg yolk to varying degrees, allowing it to maintain excellent emulsification and soluble protein content after heat treatment. Further analysis using Fourier transform infrared spectroscopy showed that the increase in α-helix content in liquid egg yolk treated with sugar salt also contributes to improving the thermal stability of egg yolk. The method of inhibiting egg yolk aggregation caused by heat treatment provided in this study provides a selective method and theoretical basis for the commercial production of heat-resistant liquid egg yolk.

Effect of continuous instant pressure drop treatment on the rheological properties and volatile flavor compounds of whole highland barley flour

Continuous instant pressure drop (CIPD) treatment effectively reduces microbial contamination in whole highland barley flour (WHBF). Base on it, this study further investigated its effects on flour properties (especially rheological properties) and volatile compounds (VOCs) profile of WHBF, and compared it with that of ultraviolet-C (UV-C), ozone and hot air (HA) treatments. The results showed that the damaged starch content (6.0%) of CIPD-treated WHBF was increased, leading to a rough surface and partial aggregation of starch particle, thereby increasing the particle size (18.06 μm of D10, 261.46 μm of D50 and 534.44 μm of D90). Besides, CIPD treatment exerted a positive influence on the structure and rheological properties of WHBF, including an elevation in pasting temperature and viscosity. Notably, CIPD-treated WHBF exhibited higher storage modulus and loss modulus compared to the other three groups of sterilization treatments, contributing to the formulation of a better-defined and stable gel strength (tan δ = 0.38). UV-C and ozone, as cold sterilization techniques, also induced alterations in specific characteristics of WHBF. UV-C treatment led to changes in WHBF's crystallinity, while ozone treatment caused modifications in the secondary protein structure of WHBF. A total of 68 VOCs were identified in raw WHBF (including 3 acids, 19 alcohols, 25 aldehydes, 1 alkene, 8 esters, 2 ethers, 3 furans, and 7 ketones). The maximum flavor-contributing VOC in CIPD-treated WHBF remained dimethyl sulfide monomer (cabbage aroma), consistent with the raw WHBF. Conversely, in HA-treated WHBF, the maximum flavor-contributing VOC shifted to 2-furanmethanethiol monomer (roasted coffee aroma), altering the initial flavor presentation. These findings will provide strong support for the application of CIPD technology in the powdery foods industry.

Unexpected variations in the effects of ultrasound-assisted myofibrillar protein processing under varying viscosity conditions

The efficient synthesis of myofibrillar protein(MRN)-gallic acid (GAD) complex in ultrasound (UID)-assisted processing is a challenging problem in food manufacturing. In this investigation, the effect of viscosity characteristics on the efficiency of UID processing in MRN-based beverages was analyzed. Both viscosity and surface tension can increase sono-physico-chemical effects on the degradation of terephthalic acid and crystal violet, with surface tension having a more significant effect (negative correlation, R2 = 0.99) than viscosity (positive correlation, R2 = 0.79). The structural indicators and microstructure demonstrated that the reaggregation and refolding of the MRN structure during the modification procedure occurred with relatively small three-dimensional dimensions. Compared to the MRN/GAD4 group, the water contact angle of the MRN/GAD7 system enhanced by 129.44%, leading to greater system stability. The ABTS-scavenging capacity of the system increased by approximately 19.45% due to the increase in viscosity of these two categories.

A new insight into the influence of pH on the adsorption at oil-water interface and emulsion stability of egg yolk protein

This study investigated the impact of varied pH treatments on the structural, emulsification, and interfacial adsorption properties of egg yolk. The solubility of egg yolk proteins decreased and then increased in response to pH changes, with a minimum value (41.95 %) observed at pH 5.0. The alkaline condition (pH 9.0) significantly impacted the secondary/tertiary structure of egg yolk, with the yolk solution displaying the lowest surface tension value (15.98 mN/m). Emulsion stability was found to be optimal when egg yolk was used as the stabilizer at pH 9.0, which corresponded to the more flexible diastolic structure, smaller emulsion droplets, increased viscoelasticity, and enhanced resistance to creaming. At pH 9.0, proteins exhibited a maximum solubility (90.79 %) due to their unfolded conformation, yet the protein adsorption content at the oil-water interface showed relatively low (54.21 %). At this time, electrostatic repulsion between the droplets and the spatial site barrier made by proteins that were unable to efficiently adsorb at the oil-water interface kept the emulsion stable. Moreover, it was found that different pH treatments could effectively regulate the relative adsorption contents of various protein subunits at the oil-water interface, and all proteins except livetin displayed good interfacial adsorption capacity at the oil-water interface.

Impact of emerging food processing technologies on structural and functional modification of proteins in plant-based meat alternatives: An updated review

In the past decade, the plant-based meat alternative industry has grown rapidly due to consumers' demand for environmental-friendly, nutritious, sustainable and humane choices. Consumers are not only concerned about the positive relationship between food consumption and health, they are also keen on the environmental sustainability. With such increased consumers' demand for meat alternatives, there is an urgent need for identification and modification of protein sources to imitate the functionality, textural, organoleptic and nutritional characteristics of traditional meat products. However, the plant proteins are not readily digestible and require more functionalization and modification are required. Proteins has to be modified to achieve high quality attributes such as solubility, gelling, emulsifying and foaming properties to make them more palatable and digestible. The protein source from the plant source in order to achieve the claims which needs more high protein digestibility and amino acid bioavailability. In order to achieve these newer emerging non-thermal technologies which can operate under mild temperature conditions can reach a balance between feasibility and reduced environmental impact maintaining the nutritional attributes and functional attributes of the proteins. This review article has discussed the mechanism of protein modification and advancements in the application of non-thermal technologies such as high pressure processing and pulsed electric field and emerging oxidation technologies (ultrasound, cold plasma, and ozone) on the structural modification of plant-based meat alternatives to improve, the techno-functional properties and palatability for successful food product development applications.

A Novel Approach for the Production of Mildly Salted Duck Egg Using Ozonized Brine Salting

Salted eggs are normally produced by treating fresh duck eggs with a high salt concentration in order to acquire distinctive features and excellent preservation capabilities as a result of a series of physicochemical changes. This method, however, induces a high salt content in the product. The goal of this research was to create a new way of producing mildly salted duck eggs using ozonized brine salting. The brine was made by dissolving NaCl (26% w/v) in water or ozonized water at a concentration of 50 ng ozone/mL (ozonized brine). Compared to brine, ozonized brine resulted in salted eggs with reduced ultimate salt levels in both albumen and yolk (p < 0.05). The Haugh unit of the salted eggs generated by ozonized brine was similar to that of the brine-made salted egg group (p > 0.05), but the salted egg produced by ozonized brine matured and solidified faster because the yolk index (0.62) was higher than that of the brine (0.55) (p < 0.05). The final pH of salted eggs generated with brine and ozonized brine was not different (p > 0.05). Regardless of the salting method, both salted eggs contained low TVB-N content (<10 mg/100 g). Ozonized brine increased the protein carbonyl content in salted albumen, which may be related to albumen protein aggregation and served as a salt diffusion barrier. However, after boiling the salted egg, the protein carbonyl level was comparable to that of fresh albumen. The TBARS levels of boiled salted albumen prepared with brine and ozonized brine were comparable (p > 0.05), and the value was extremely low (~0.1 mg MDA equivalent/kg). The TBARS value of the salted yolk prepared with brine was higher than that of the salted yolk prepared with ozonized brine (p < 0.05), and both salted yolks showed increased TBARS values after cooking (p < 0.05). The albumen and yolk components appeared to be altered similarly by both brine and ozonized brine, according to the FTIR spectra. Furthermore, the appearance and color of the yolk and albumen in salted eggs prepared with brine and ozonized brine were comparable. Boiled salted albumen produced with ozonized brine had a denser structure with fewer voids. This could be attributed to the final salted egg's lower salt content and lower salt diffusion rate, which were likely caused by protein oxidation and, as a result, aggregation when ozonized brine was used.

Physicochemical characteristics and gel-forming properties of mandarin fish (Siniperca chuatsi) protein during the fish fermentation with Lactobacillus sake SMF-L5: The formation of garlic-cloves shaped protein gel

Mandarin fish (Siniperca chuatsi) during fermentation presents a unique elastic texture. In this investigation, the physicochemical and gel-forming properties of fish proteins were evaluated to explain the formation of elastic characteristics. During fermentation, the combined effects of acidification by Lactobacillus sake SMF-L5, increased sodium chloride, and decreased moisture content in the fish protein generated a suitable microenvironment for gelation. The mass transfer of sodium chloride was accompanied by NMR relaxation of the immobilized water. The ripening fermented fish had a functionally available MHC, a higher fractal dimension, and a stable α-helical structure. Also, it exhibited excellent gel-forming performances, mainly including garlic-cloves shaped protein gel, stronger springiness, and enhanced L* and whiteness. Correlation analysis showed that the gel's physical properties were differently related to the protein's physicochemical characteristics except for total free amino acids. These results could lay a theoretical foundation for the gel formation mechanism of fermented mandarin fish.

Effect of yolk spheres as a key histological structure on the morphology, character, and oral sensation of boiled egg yolk gel

This study explored the effect of yolk sphere on gel state and taste differences between whole boiled egg yolk (WBEY) and stirred boiled egg yolks (SBEYs). Optical microscopy, scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM) indicated that the WBEY was formed via the accumulation of yolk spheres, whereas the SBEY was a gel with a tight and ordered microstructure. The stirring disrupted the yolk sphere structure, leading to a homogeneous distribution of proteins and lipids in SBEYs, and a cross-linked network in gel was established with higher hardness and springiness. In the oral sensation simulation, WBEY had a higher saliva adsorption capacity and frictional force to oral soft tissue during swallowing than SBEY. This work contributes to a deeper understanding of the gel structure and taste of egg yolk, and provides a theoretical basis for the research on the formation of the gritty taste of egg yolks.

Characterization of four thermogelled egg yolk varieties based on moisture and protein content

There are obvious differences between egg yolks of different varieties. Additionally, boiled eggs, which are widely liked and consumed globally, are nutrient rich. However, they absorb water in the esophagus during swallowing, and this result in an uncomfortable sensation. Here, we determined the moisture content and distribution as well as the protein contents and properties of 4 varieties of thermogelled egg yolks. Among the varieties, Green Shelled thermogelled egg yolk showed the highest protein content and solubility. Additionally, the ionic, hydrogen, and disulfide bonds corresponding to Rhode Island Red thermogelled egg yolk samples were the weakest, while the hydrophobic interaction force corresponding to the Hetian Dahei (HD) egg yolk samples was the weakest. Further, the distribution of the moisture contents of the 4 varieties was significantly different (P < 0.05). HD egg yolk showed the highest moisture content, and its bound and immobile moisture contents were significantly higher than those of the other 3 varieties. Egg yolk moisture content also affected free amino acid content, which was the highest for HD egg yolk. Therefore, owing to its high moisture content, HD egg yolk was conducive for chewing and swallowing and given its high free amino acid content, it also had a more suitable taste and flavor. The results of this study provide a theoretical basis for the application of egg yolks in food processing.

An Efficient Processing Strategy to Improve the Flavor Profile of Egg Yolk: Ozone-Mediated Oxidation

This study investigated the effect of ozone treatment on egg yolk volatiles and fatty acids. The composition and content of volatile substances and the fatty acid content of the egg yolk were changed significantly after ozonation. With proper ozone treatment (30 min), the aldehyde content in the egg yolk increased from 78.08% to 94.63%, and the relative content of dibutyl amine decreased from 1.50% to 0.00%. There were no significant differences among the types of fatty acids in the egg yolks after being treated with ozone, but there were differences in their relative contents. The results of SDS-PAGE showed no significant difference in yolk protein composition and contents among the groups. SEM results showed that moderate ozone treatment (20 min and 30 min) led to a regular and dense network structure of egg yolk. These results provided a theoretical basis for expanding the application of ozone technology in the egg yolk processing industry.

Identification of candidate genomic regions for thermogelled egg yolk traits based on a genome-wide association study

Egg yolk texture is an important indicator for evaluating egg yolk quality. Genetic markers associated with economic traits predict genomes and facilitate mining for potential genes. Numerous genome-wide association studies have been conducted on egg traits. However, studies on the genetic basis of thermogelled yolk texture are still lacking. The aim of the present study was to find significant single nucleotide polymorphism (SNP) sites and candidate genes related to thermogelled yolk texture in Hetian Dahei chicken (HTHD) flocks that can be used as genetic markers. Five traits, including hardness, cohesiveness, gumminess, chewiness, and resilience, had low heritability (0.044-0.078). Ten genes, including U6, FSHR, PKDCC, SLC7A11, TIMM9, ARID4A, PSMA3, ACTR10, EML4, and SLC35F4 may control the hardness of the thermogelled egg yolks. In addition, 12 SNPs associated with cohesiveness were identified. RELCH located on GGA2 participates in cholesterol transport. The candidate gene LRRK2, which is associated with gumminess, influences the concentrations of very low-density lipoprotein in blood. Eight SNPs associated with resilience were identified, mainly on GGA3 and GCA28. In total, 208 SNPs associated with chewiness were identified, and 159 candidate genes, which were mainly involved in proteasome-mediated ubiquitin-dependent protein catabolic process, negative regulation of transport, lipid droplet organization, and vehicle docking involved in exocytosis, were found near these regions. Thermogel egg yolk texture is a complex phenotype controlled by multiple genes. Based on heritability assays and GWAS results, there is a genetic basis for the texture of thermogelled egg yolks. We identified a series of SNPs associated with yolk texture and candidate genes. Our result provides a theoretical basis for breeding high-quality egg yolk using molecular marker-assisted selection and could facilitate the development of novel traits.

Modification methods and applications of egg protein gel properties: A review

Egg protein (EP) has a variety of functional properties, such as gelling, foaming, and emulsifying. The gel characteristics provide a foundation for applications in the food industry and research on EP. The proteins denature and aggregate to form a dense three-dimensional gel network structure, with a process influenced by protein concentration, pH, ion type, and strength. In addition, the gelation properties of EP can be altered to varying degrees by applying different treatment conditions to EP. Currently, modification methods for proteins include physical modification (heat-induced denaturation, freeze-thaw modification, high-pressure modification, and ultrasonic modification), chemical modification (glycosylation modification, phosphorylation modification, acylation modification, ethanol modification, polyphenol modification), and biological modification (enzyme modification). Pidan, salted eggs, egg tofu, and other egg products have unique sensory properties, due to the gel properties of EP. In accessions, EP has also been used as a new ingredient in food packaging and biopharmaceuticals due to its gel properties. This review will further promote EP gel research and provide guidance for its full application in many fields.

Gel properties of heat-induced transparent hydrogels from ovalbumin by acylation modifications

In this paper, the effects of acylation modification on the gel behavior of ovalbumin (OVA) under heating induction have been investigated. From the obtained results, the acylated OVA hydrogels exhibited superior gelation properties than the native OVA hydrogels (NOVA-G) in terms of light transmission, gel hardness, resilience and water holding capacity. SEM revealed acylation modifications effectively promoted the formation of uniform and dense network structure of OVA hydrogels. The main intermolecular forces of the acylation-modified OVA hydrogels were hydrophobic interactions and hydrogen bonding. FTIR showed that acylation modifications caused 26.2% decrease in α-helix and 59.2% increase in β-sheet content compared to NOVA-G. Furthermore, in-vitro release experiments showed that the release rate of curcumin from acylated OVA hydrogels was significantly delayed. Moreover, the above results have shown that acylation modifications can be considered as an effective method to improve the gelation as well as drug release properties of protein hydrogels.