Subcritical fluid extraction treatment on egg yolk: Product characterization

Subcritical water hydrolysis of eggshell membrane and its physicochemical characteristics

The insolubility of eggshell membrane (ESM) limits it application. This study utilized a green process subcritical water (SW), to prepare soluble ESM and compared it with acid hydrolysis. The effect of SW temperature on the yields of total protein, free amino acids, and glycosaminoglycan in the hydrolysate was investigated. Hydrolysates generated at 180-210 °C exhibited the highest protein (40.57 ± 2.40 mg/g ESM concentrate), peptides (20.36 ± 0.43 mg/g), hyaluronic acid (8.19 ± 0.34 mg/g), and chondroitin sulfate (11.68 ± 0.76 mg/g) content. Acid hydrolysis exhibited significantly lower protein hydrolysis (p < 0.05) and total free amino acid content than subcritical water hydrolysis. Collagen was observed in the SW hydrolysate, and its secondary structure transformed from the stable α-helix to unstable β-aggregates as the temperature increased. Scanning electron microscopy confirmed the disruption of the ESM fiber. SDS-PAGE analysis further revealed the presence of low-molecular-weight peptides in the hydrolysate. Compared to acid hydrolysates, hydrolysates obtained from SW exhibited higher degree of hydrolysis, and therefore, demonstrated greater free radical scavenging activity. Hence, SW hydrolysates can be used to develop functional foods from ESM. These results provide promising future directions for preparing active ESM.

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.

Comparative analysis on the properties of egg yolk lipids extracted by different extraction methods

Egg yolk lipids are important components in egg yolk. Compared with proteins, minerals, vitamins and pigments in egg yolk, there is a lack of systematic research on extraction methods and characteristics of yolk lipid. Therefore, in this study, the extraction of egg yolk lipids by supercritical CO2 fluid extraction (SFE), subcritical propane extraction (SPE) and ethanol solvent extraction (SE) was studied, and the differences in composition and physicochemical properties of the three yolk lipids were analyzed. The egg yolk lipids extracted by SFE had the advantages of high unsaturated fatty acid content, low saponification value, acid value, peroxide value, and high content of neutral lipids such as triglyceride and cholesterol, but the polar phospholipids were completely retained in the yolk powder. The efficiency of lipid extraction of SPE was the highest among all the three methods, but the extraction capacity to the polar phospholipid was in the middle of the three methods. The efficiency of lipid extraction of SE was low, but the extraction capacity to the polar phospholipid was the highest. Suitable extraction methods could be selected based on the specific application requirements of egg yolk lipids and low-fat egg yolk powders.

Subcritical and Supercritical Fluids to Valorize Industrial Fruit and Vegetable Waste

The valorization of industrial fruit and vegetable waste has gained significant attention due to the environmental concerns and economic opportunities associated with its effective utilization. This review article comprehensively discusses the application of subcritical and supercritical fluid technologies in the valorization process, highlighting the potential benefits of these advanced extraction techniques for the recovery of bioactive compounds and unconventional oils from waste materials. Novel pressurized fluid extraction techniques offer significant advantages over conventional methods, enabling effective and sustainable processes that contribute to greener production in the global manufacturing sector. Recovered bio-extract compounds can be used to uplift the nutritional profile of other food products and determine their application in the food, pharmaceutical, and nutraceutical industries. Valorization processes also play an important role in coping with the increasing demand for bioactive compounds and natural substitutes. Moreover, the integration of spent material in biorefinery and biorefining processes is also explored in terms of energy generation, such as biofuels or electricity, thus showcasing the potential for a circular economy approach in the management of waste streams. An economic evaluation is presented, detailing the cost analysis and potential barriers in the implementation of these valorization strategies. The article emphasizes the importance of fostering collaboration between academia, industry, and policymakers to enable the widespread adoption of these promising technologies. This, in turn, will contribute to a more sustainable and circular economy, maximizing the potential of fruit and vegetable waste as a source of valuable products.

Subcritical low temperature extraction of bioactive ingredients from foods and food by-products and its applications in the agro-food industry

Bioactive ingredients are part of the food chain and are responsible for numerous health benefits. Subcritical low temperature extraction has been employed to acquire bioactive ingredients because of its excellent properties, such as energy conservation, low temperature, elimination of residual solvent, and high extraction yield and quality. This review aims to provide a clear picture of the basics of subcritical-temperature extraction, its bioactive ingredient extraction efficiency, and possible applications in the agro-food industry. This review suggested that the extraction temperature, time, co-solvents, solid-fluid ratio, and pressure impacted the extraction efficiency of bioactive ingredients from foods and food by-products. Subcritical solvents are appropriate for extracting low polar ingredients, while the inclusion of co-solvents could extract medium and high polar substances. Bioactive ingredients from foods and food by-products can be used as antioxidants, colorants, and nutritional supplements. Additionally, this technology could remove pesticide residues in tea, concentrate edible proteins, and reduce cigarette tar. A new trend toward using subcritical low temperature extraction in extracting bioactive ingredients will acquire momentum.

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.

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.

Study on functional improvement of freeze-thaw egg yolk pellet by enzymatic hydrolysis

Freeze-thaw egg yolk pellet (FYP) could be produced as a by-product in the process of egg yolk immunoglobulin (IgY) extraction. The FYP contained many superior nutritional components like fresh egg yolk, but it has poor functionalities because of protein denaturation resulted from freezing treatment during IgY extraction. For the purpose of comprehensive utilization of egg yolk resources, FYP was subjected to enzymatic hydrolysis with alcalase to produce FYP hydrolysates (FYPh) with four enzyme concentrations of 250, 500, 1000 and 2000 U/g for improved functional properties. And then FYPh was spray dried to obtain hydrolyzed egg yolk pellet powder (HYP). Solubility, emulsifying property and surface hydrophobicity of HYP were investigated. The results showed that enzymatic hydrolysis could lead to noticeable changes in surface hydrophobicity, microstructure, solubility and emulsifying properties of HYP compared with the control group without enzymatic hydrolysis treatment. Solubility and emulsification stability index generally increased from 19 g/100 g, 12.33 to 87 g/100 g, 76.63 with increasing degree of hydrolyze, respectively. This study demonstrated that the functional properties of FYP could be effectively improved when the enzyme addition amount reached 1000 U/g. HYP prepared under this condition owes desirable solubility and emulsification, and has the potential of application in food industry.

A review on recent advances of egg byproducts: Preparation, functional properties, biological activities and food applications

The rapid development of egg industries produced vast byproducts that have not been effectively used. In this paper, the comprehensive utilization of egg byproducts was reviewed. Protein extraction and enzymatic hydrolysis were the main used ways for recycle of egg byproducts. The fact that eggshell membrane could accelerate would healing and improve facial skin of healthy people for 12 weeks was found. However, salted egg white had poor functional properties owing to high salt and ultrafiltration was an effective technology to remove 92.93% of salt. Moreover, Defatted yolk protein had the great potential to be used as food additives and functional foods. Other egg byproducts such as egg inhibitor and eggshells also were discussed. The novel applications of egg byproducts in the food field included food additives, feeds, food packaging materials and nutraceuticals based on current knowledge, but the proportion needed to be improved. This paper would provide a new insight for comprehensive utilization of egg byproducts.

Effect of a SO2 Rich Atmosphere on Tempera Paint Mock-Ups. Part 1: Accelerated Aging of Smalt and Lapis Lazuli-Based Paints

The behavior of historic tempera paints exposed to pollutant gases is an important issue when developing conservation strategies. In this work, binary tempera paint mock-ups that were made with either smalt or lapis lazuli pigments mixed with either rabbit glue or egg yolk binders were exposed to an SO2 accelerated aging test in order to find out more about the forms and mechanisms of alteration resulting from pigment-binder interaction. To this end, spectrophotometry, hyperspectral image analysis, and profilometry were used to study macro-scale, physical changes taking place on the surface of the paints, affecting color, gloss, reflectance, and roughness. Likewise, chemical and mineralogical changes were evaluated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (ATR-FTIR), polarized light microscopy (PLM), and scanning electron microscopy with micro-analysis (SEM-EDS), which was also used to visualize micro-texture changes in the paints. The smalt-based tempera showed a higher degree of deterioration than the lapis lazuli-based tempera, in particular a notable whitening related to the precipitation of sulfate-rich salts and to binder and pigment chemical alterations. Moreover, whereas aged egg yolk-based paints showed visible color change due to damage to the oily binder and the pigments, the most evident change in rabbit glue-based paints was binder loss. The alteration suffered by the pigments varied in line with their composition; thus, smalt (blue cobalt-containing glass) grains were more sensitive to SO2 exposure than lapis lazuli-(Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)]-crystals. In the smalt grains, the SO2 test caused K+ leaching from the glass matrix, which was detected by means of K/Co ratios, but the lazurite crystals (main component of lapis lazuli) were unaffected (regardless of the binder used in the tempera). The most likely source of the crystallized sulfate rich salts were the impurities that were detected in association with the natural lapis lazuli pigment, i.e., calcite and diopside. Indeed, the precipitation of efflorescences is the main cause of the optical changes found in the smalt- and lapis lazuli-based tempera, in addition to the physical-chemical damage to the binders. The information reported here would be useful for preventive conservation, as well as for art restorers, who are planning work on paintings in which paints of this kind were used.