Exploring the role of NaOH in modulating the properties of metal-free preserved egg white gels: physicochemical, rheological, and structural properties - PMC Skip to main content An official website of the United States government Here's how you know Here's how you know Official websites use .gov A .gov website belongs to an official government organization in the United States. Secure .gov websites use HTTPS A lock ( Lock Locked padlock icon ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites. Search Log in Dashboard Publications Account settings Log out Search… Search NCBI Primary site navigation Search Logged in as: Dashboard Publications Account settings Log in Search PMC Full-Text Archive Search in PMC Journal List User Guide PERMALINK Copy As a library, NLM provides access to scientific literature. Inclusion in an NLM database does not imply endorsement of, or agreement with, the contents by NLM or the National Institutes of Health. Learn more: PMC Disclaimer | PMC Copyright Notice Food Chem X . 2026 Apr 2;35:103814. doi: 10.1016/j.fochx.2026.103814 Search in PMC Search in PubMed View in NLM Catalog Add to search Exploring the role of NaOH in modulating the properties of metal-free preserved egg white gels: physicochemical, rheological, and structural properties Pengfei Geng Pengfei Geng a National Research and Development Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China b Wuhan Meeler Biotech Co., Ltd, Wuhan 430000, China Find articles by Pengfei Geng a, b, 1 , Erjiao Li Erjiao Li a National Research and Development Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China Find articles by Erjiao Li a, 1 , Yanli Wang Yanli Wang a National Research and Development Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China Find articles by Yanli Wang a , Yuanyuan Zhang Yuanyuan Zhang a National Research and Development Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China Find articles by Yuanyuan Zhang a , Yi Sun Yi Sun a National Research and Development Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China Find articles by Yi Sun a , Guofeng Jin Guofeng Jin c School of Food and Health, Beijing Technology & Business University (BTBU), Beijing 100048, China Find articles by Guofeng Jin c , Lizhi Lu Lizhi Lu d State Key Laboratory for Managing Biotic and Chemical Treats to the Quality and Safety of Agro-products, Institute of Animal Husbandry and Veterinary Science, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China Find articles by Lizhi Lu d , Zhaoxia Cai Zhaoxia Cai a National Research and Development Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China Find articles by Zhaoxia Cai a, ⁎ , Long Sheng Long Sheng a National Research and Development Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China Find articles by Long Sheng a, ⁎ Author information Article notes Copyright and License information a National Research and Development Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China b Wuhan Meeler Biotech Co., Ltd, Wuhan 430000, China c School of Food and Health, Beijing Technology & Business University (BTBU), Beijing 100048, China d State Key Laboratory for Managing Biotic and Chemical Treats to the Quality and Safety of Agro-products, Institute of Animal Husbandry and Veterinary Science, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China ⁎ Corresponding authors at: College of Food Science and Technology of Huazhong Agricultural University, Wuhan, Hubei Province, China. [email protected] [email protected] [email protected] 1 These authors contributed equally to this work. Received 2025 Nov 16; Revised 2026 Mar 6; Accepted 2026 Apr 1; Collection date 2026 Apr. © 2026 The Authors This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). PMC Copyright notice PMCID: PMC13090318 PMID: 42006654 Abstract Traditional salted egg production relies on metal ions to regulate alkali penetration during processing. However, excessive metal ion intake poses potential health risks, highlighting the urgent need to develop metal-free processing alternatives. In this study, an ex-shell alkali-induced model was used to investigate the effects of different NaOH concentrations on the physicochemical properties, rheological behavior, and microstructure of duck egg white gels. The results showed that when the NaOH concentration was below 1.0%, gel hardness (107.98 g), elasticity (0.958), viscosity (86.51), and water-holding capacity (60.62%) were significantly enhanced ( P < 0.05). Further increasing the NaOH concentration led to obvious gel liquefaction, accompanied by a sharp decline in these properties. FTIR analysis revealed that the ordered gel structure was mainly stabilized by β-sheet structures, together with the continuous transformation of α-helices. The gel formed at 0.8% NaOH exhibited the highest β-sheet content (28%) and excellent structural stability. Rheological measurements indicated that gel viscosity increased with increasing NaOH concentration, and egg white proteins treated with high alkali concentrations showed the earliest flow behavior. Control group comparisons confirmed that simply adjusting the NaOH concentration could produce protein gels with properties comparable to those induced by metal ions. These findings provide important theoretical support and practical guidance for the industrial production of safe, metal-free preserved eggs. Keywords: Preserved eggs, Alkali treatment, Egg white gel, Protein structure Highlights • Appropriate NaOH concentration enhances the hardness and elasticity of gels. • High NaOH concentrations weaken water-protein interactions and promote gel liquefaction. • β-sheet structures promote the formation of a more stable three-dimensional network. • NaOH promotes the formation of a three-dimensional gel network within a brief time. • Alkali-induced gels exhibited properties comparable to metal ion-induced gels. 1. Introduction Preserved eggs are traditional egg products widely consumed in China and many parts of Southeast Asia. Together with salted duck eggs, they are valued for their distinctive sensory attributes and nutritional profile ( Ganesan et al., 2014 ). Unlike salted eggs; preserved eggs are produced by alkaline pickling; during which the egg white and yolk undergo extensive physicochemical changes that ultimately determine product quality. In practice; duck or chicken eggs are typically pickled in alkaline media containing lime; alkali; salt; and/or sodium hydroxide ( Li et al., 2021 ). A defining quality attribute is the formation of a firm, elastic egg white gel; however, gelation and its stability are highly sensitive to alkali intensity and ionic composition. In conventional formulations, metal compounds are often incorporated to regulate alkali penetration, stabilize gel formation, and mitigate quality defects. Historically, lead oxide (PbO, 0.2%–0.4%) was used as an effective regulator of alkali diffusion and maturation, promoting uniform gelation and desirable texture ( Huang et al., 2019 ). Owing to concerns regarding lead toxicity; lead-free and heavy-metal-free preserved egg technologies have been actively developed ( Ge & Liu, 2020 ). Nevertheless, many current approaches still depend on added metal salts or complex formulations, and achieving consistent gel quality without any metal salts remains challenging. Alkali treatment is pivotal in preserved egg manufacture because it governs the denaturation, aggregation, and network formation of egg white proteins. Sodium hydroxide induces pronounced changes in egg white, including color development and gelation; denatured proteins assemble into fibrous networks that immobilize water and impart mechanical strength ( Zhao et al., 2016 ). Alkaline conditions may also contribute to product safety and shelf-life by degrading aflatoxins; inactivating pathogenic microorganisms; and improving storage stability ( Gharbi & Labbafi, 2018 ). These effects are strongly concentration-dependent: insufficient NaOH may not induce adequate solidification of the egg white and yolk; whereas excessive alkalinity can cause “alkali damage;” manifested by reduced elasticity; network disruption; and progressive quality deterioration; and may ultimately lead to complete liquefaction of the egg white ( Gao et al., 2020 ; X. Zhang et al., 2023 ). Such liquefaction severely compromises appearance and sensory acceptance and represents a major source of industrial production losses. Substantial efforts have been made to elucidate how alkaline environments modulate egg white protein assembly. Microstructural evolution and changes in intermolecular interactions during pickling have been linked to gel maturation, indicating that alkaline conditions reorganize protein networks and water distribution over time ( Zhao et al., 2016 ). At the formulation level; the coupled presence of alkali and salt is widely recognized as a key determinant of gelation behavior; for example; NaOH/NaCl pickling has been reported to alter heat-induced gelation and the resulting network properties ( Huang et al., 2019 ). Moreover; an alkali-induced sol–gel–sol transformation has been proposed as an intrinsic behavior of egg white proteins under sufficiently strong alkaline exposure; providing a mechanistic basis for the liquefaction defect ( Gao et al., 2020 ). However, the independent contribution of alkali intensity—particularly the controllable NaOH concentration window that balances gel strengthening against liquefaction—remains insufficiently defined for metal-salt-free processing. To reduce diffusion-related variability and isolate the direct role of alkali from confounding factors, shell-free (ex-shell) systems provide a controllable platform for evaluating the effect of NaOH concentration on egg white gelation. Such a model also enables assessment of whether metal-salt-free regulation via NaOH adjustment can achieve gel properties comparable to those obtained using conventional metal-containing formulations, thereby informing formulation simplification. Accordingly, this study established a shell-free, alkali-induced duck egg white model to systematically investigate the direct effects of NaOH concentration on gel formation and alkali-induced liquefaction. The physicochemical properties, rheological behavior, and structural characteristics of egg white gels prepared at different NaOH levels were comprehensively evaluated. In addition, traditional copper- and zinc-containing preserved egg formulations were included as references, and NaCl-matched controls were used to distinguish NaOH-specific effects from ionic-strength effects. Collectively, these results provide evidence supporting the feasibility of heavy-metal-free preserved egg processing and offer mechanistic insights for developing safer preserved egg products and related protein gel-based foods. 2. Materials and methods 2.1. Materials Fresh duck eggs (weight 70 ± 5 g) were sourced from a local supermarket (Wuhan, China). The sodium chloride, sodium hydroxide, potassium bromide, phosphate buffer, anhydrous ethanol, glycine and urea were obtained from Sinopharm Chemical Reagent Co., Ltd. (Beijing, China). Other chemicals used in this study were of analytical grade. 2.2. Preparation of egg white liquid Fresh duck eggs stored at 4 °C were washed and manually broken to separate the egg whites from the yolks. After removing the ties from the egg whites, the egg whites were stirred for 2 h at 4 °C using a magnetic stirrer to obtain a homogeneous sample of egg white liquid. 2.3. Preparation of egg white alkali-induced gel model A mixed solution of NaOH and NaCl at a specific concentration was prepared and blended with egg white liquid in a beaker at a ratio of 1:2. The preparation of NaCl concentration of 0.6%, NaOH concentration of 0.6%, 0.8%, 1.0%, 1.2%, 1.4% of composite egg white samples (through the pre-experiment found that, when the concentration of NaOH <0.5% the egg white could not solidify to form a gel). The control group was NaCl (0.6%, w / v ), NaOH (0.8%, w/v), 5 mg/kg CuSO 4 , 15 mg/kg ZnSO 4 composite egg white samples. The subsequent indexes were measured after equilibration at 4 °C for 12 h. 2.4. Texture profile analysis (TPA) The TPA of egg white gels were determined using a texture analyzer (Stable Micro Systems, Surrey, England) according to the method described by Xu et al. (2019) . Egg white gel samples were trimmed into 1 cm × 1 cm × 1 cm cubes and subjected to TPA using a P/36R probe. The test parameters were set as follows: trigger force of 5.0 g, pre-test speed of 5.0 mm/s, test speed of 1.0 mm/s, post-test speed of 5.0 mm/s, time interval between two compression cycles of 5 s, and compression strain of 60%. Hardness, springiness, adhesiveness, chewiness, resilience, and cohesiveness were recorded. 2.5. Determination of water-holding capacity (WHC) The WHC was determined according to the method of Ai et al. (2022) with some modifications. Gel samples (approximately 5.0 g) were accurately weighed, and the mass was recorded as M₁. Each gel sample was wrapped in three layers of filter paper and placed in a 50 mL centrifuge tube. Subsequently, the samples were centrifuged at 5000 rpm for 20 min, and the mass of the gel was recorded as M₂. The WHC of the gel was calculated using the following equation: WHC % = M 2 M 1 × 100 (1) 2.6. Low-field nuclear magnetic resonance (LF-NMR) analysis Transverse (T 2 ) relaxation times were measured using a LF-NMR instrument (MesoMR23-060H-I, Niumag Analytical Instrument Co. Ltd., China), following the method of Sheng et al. (2018) with appropriate modifications. Gel samples were cut into cylindrical shapes (1 cm × 1 cm × 1.2 cm) using a gel sampler and then placed into nuclear magnetic resonance (NMR) tubes. The operating parameters of the LF-NMR instrument were set as follows: proton resonance frequency, 21 MHz; measurement temperature, 32 °C; τ value, 150 μs; number of scans, 16; repetition time, 4000 ms; and number of echoes collected, 4500. The Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence was used to acquire the exponential decay curve, which was then fitted to obtain the T₂ relaxation spectrum and further determine the T₂ relaxation times. All measurements were performed in triplicate for each sample under the same experimental conditions. 2.7. Magnetic resonance imaging (MRI) measurement MRI of hydrogen protons in the gels was conducted according to the method of Wu et al. (2024) with appropriate modifications. MRI measurements were performed using an instrument (MesoMR23-060H-I, Suzhou Niumag Analytical Instrument Co., Ltd., China) under the following conditions: proton resonance frequency, 21.25 MHz; measurement temperature, 32 °C; number of scans, 4; repetition time, 800 ms; and echo time, 18.2 ms. MRI imaging was conducted with three slices, each with a thickness of 2.0 mm and an interlayer gap of 0.5 mm. The obtained images were processed using MRI imaging software and displayed in pseudo-color. 2.8. Fourier transform infrared spectroscopy (FTIR) measurement FTIR spectroscopy was performed according to previously reported methods with minor modifications ( Gan et al., 2025 ; Pang et al., 2025 ). FTIR spectra of the samples were collected using a FTIR spectrometer (Nicolet Nexus 470, Thermo Electron, USA) via the KBr pellet method. Egg white composite gels were frozen at −20 °C overnight and then freeze-dried. The resulting sample powder was mixed with KBr powder at a ratio of 1:100. The mixture was pressed into a thin pellet and then analyzed by FTIR. The instrumental parameters were set as follows: scanning range of 4000–400 cm −1 , resolution of 4 cm −1 , and 32 scans. Each sample was analyzed in triplicate. The obtained spectra were normalized, and protein secondary structure analysis was performed using PeakFit 4.12 software. Second derivatives of the amide I band were deconvoluted into α-helix (1658–1650 cm −1 ), β-sheet (1640–1615 cm −1 ), β-turn (1670–1660 cm −1 ), and random coil (1650–1640 cm −1 ). The peak area of each component was calculated based on Gaussian fitting. 2.9. Determination of free sulfhydryl (SH) content The content of free SH groups was determined according to the method of Y. Zhang et al. (2024) with minor modifications. Briefly, 3 g of egg white gel sample was mixed with 27 mL of phosphate-buffered saline (pH 8.0), homogenized at 3000 rpm for 2 min, and then centrifuged at 4000 rpm for 20 min. Then, 0.2 mL of the supernatant was transferred into a tube containing 2.8 mL of buffer (0.10 mol/L Tris, 0.10 mol/L glycine, 4.00 mmol/L EDTA, pH 8.0) and 0.02 mL of Ellman's reagent (4 mg/mL DTNB dissolved in Tris-glycine buffer). After mixing thoroughly, the absorbance of the mixture at 412 nm was measured using a UV–visible spectrophotometer. The calculation of the free SH group is as follows: free SH μmol / g = 75.53 × A 412 × D / C (2) where A 412 is the absorbance at 412 nm, C is the protein content in mg/ mL and D is the dilution factor. 2.10. Dynamic rheological characterization The linear and nonlinear rheological properties of alkali-induced egg white gels were determined using a rheometer (Bohlin Gemini 2, Malvern Instruments Ltd., UK) equipped with a parallel plate fixture (PP-40, diameter 40 mm, gap 1 mm), according to the method of Yang et al. (2023) . An appropriate amount of egg white gel was placed at the center of the lower plate, and the gap was adjusted to 1 mm. Excess sample was carefully removed, and a thin layer of silicone oil was applied around the sample to prevent water evaporation during measurement. 2.10.1. Time scan The measurement method described by Xi et al. (2019) was adopted with slight modifications. Changes in the storage modulus (G'), loss modulus (G"), and loss factor (tan δ) during gelation were monitored by time sweep over a period of 3600 s. For each measurement, egg white and alkaline solution were mixed rapidly and immediately loaded onto the rheometer plate to start the test. 2.10.2. Frequency scan At 25 °C, the following parameters used: a fixed strain of 0.5% (determined from the amplitude sweep test), and a frequency sweep range of 0.1–100 Hz. The changes in G' and G" of the gel as functions of strain were recorded, and the tan δ was calculated as the ratio of G"/G'. The dependence of G' on angular frequency for alkali-induced egg white gels was fitted using the power law equation: G ′ = K ′ • ω n ′ (3) where G′ is storage modulus; ω is the angular frequency; k' is the power law constant; n' is frequency exponents. 2.11. Scanning electron microscope (SEM) SEM was performed according to the method of Lv et al. (2024) with appropriate modifications. The prepared composite gels were cut into small pieces and fixed with 2.5% ( v /v) glutaraldehyde solution at 4 °C for 3 h. Subsequently, the samples were rinsed with 0.01 mol/L phosphate buffer (pH 7.4) and dehydrated in a graded ethanol series (60%, 70%, 80%, 90%, and 100% v/v). The treated gels were frozen at −20 °C for 2 h and then freeze-dried. Before observation, the sample surfaces were sputter-coated with gold, and the microstructures were observed using a scanning electron microscope (S-4800, Hitachi Ltd., Tokyo, Japan) at 200× magnification. It should be noted that the freeze-drying process may slightly alter the gel morphology compared with the original weak gel state. Pore size was quantified from gel micrographs using ImageJ software. 2.12. Statistical analysis All experiments were conducted in 3 parallel groups, and the results were expressed as the mean ± standard deviation. The data were processed using SPSS Statistics 26 software (IBM Corporation, New York, USA). One-way analysis of variance (ANOVA) and Duncan test were used for multiple comparisons between groups. Different between groups with p<0.05 were considered statistically significant. The results were plotted using Origin 2023 software (Origin Lab Corp., Northampton, Massachusetts, USA). 3. Results and discussion 3.1. Texture analysis TPA analysis simulates human oral chewing behavior to comprehensively characterize food texture properties. Hardness is a key indicator for evaluating the quality of gel products ( Li et al., 2018 ). The degree of gel structure disruption during the initial compression stage is affected by its elasticity; higher elasticity reflects better retention of gel network integrity ( Zhu & Zhong, 2024 ). Fig. 1 shows the changes in gel texture properties at different NaOH concentrations. No significant differences in texture parameters were observed between gels treated with 0.6% and 0.8% NaOH ( p > 0.05). However; when the NaOH concentration exceeded 1.0%; the hardness; resilience; stickiness; and chewiness of the gel decreased significantly; whereas adhesiveness increased markedly ( P < 0.05). This phenomenon may be attributed to the continuous penetration of alkaline solution into the egg system; leading to sustained structural changes of the gel under alkaline conditions. The stable gel texture becomes difficult to maintain; and partial proteins are degraded into peptides and amino acids; resulting in the gradual collapse of the three-dimensional network structure ( Kaewmanee et al., 2011 ). Similar observations were reported by Gao et al. (2021) , who used ovalbumin as a model system to investigate the effect of NaOH on ovalbumin gel properties. Fig. 1. Open in a new tab Effect of different NaOH concentration treatments on the texture characteristics of duck egg white gel. A, Changes in hardness of duck egg white gel; B, Changes in springiness of duck egg white gel; C, Changes in resilience of duck egg white gel; D, Changes in gumminess of duck egg white gel; E, Changes in chewiness of duck egg white gel; F, Changes in adhesiveness of duck egg white gel. Groups with different lowercase letters indicate significant differences ( P < 0.05) among samples. The texture parameters including hardness, elasticity, viscosity, and adhesiveness of the control group showed no significant differences compared with the 0.8% NaOH-treated group ( P > 0.05). These results indicate that the cross-linking degree between protein molecules is closely related to the hardness and network integrity of the gel samples. Nevertheless, the resilience and chewiness of the control group significantly decreased. This might be explained by the fact that metal ions compete with protein molecules for water molecules, disrupt the surface water film, and reduce the hardness and elasticity of the gel, which is unfavorable to the self-supporting structure of the gel system ( Tian et al., 2022 ). From an edible-quality perspective, these texture changes are directly relevant to consumer perception and oral processing. Decreases in hardness, resilience, and chewiness typically indicate a weaker “bite” and reduced elastic recovery during mastication, yielding a softer, more fragile gel that fractures readily and lacks the springy mouthfeel associated with high-quality preserved egg whites. In contrast, the pronounced increase in adhesiveness suggests a greater tendency for the gel to adhere to teeth and oral surfaces, which is commonly perceived as an undesirable sticky or pasty sensation and may reduce overall palatability. Collectively, the deterioration of these TPA parameters at NaOH concentrations >1.0% indicated a transition from a firm, elastic gel to a less cohesive and more adhesive texture, consistent with the onset of alkali-induced structural failure. 3.2. WHC analysis WHC reflects the ability of a gel network to absorb and immobilize water, and serves as a key indicator for evaluating gel properties. Gels with a well-organized structure usually exhibit high water retention via electrostatic interactions and capillary forces within the gel matrix ( Khemakhem et al., 2019 ). Fig. 2 shows the effect of different NaOH concentrations on the WHC of duck egg white gels. The WHC first increased and then decreased with increasing NaOH concentration ( P < 0.05); reaching a maximum value of 60.63% at 0.8% NaOH. These results suggest that excessively high NaOH concentrations were negatively correlated with WHC. Meanwhile; a strong positive correlation was observed between gel hardness and WHC; implying that a compact and well-developed three-dimensional network structure contributes to improved water retention ( Urbonaite et al., 2015 ). When the NaOH concentration further increased to 1.2%; the WHC of the egg white gel decreased to 37.38%; indicating obvious deterioration of the gel structure. During gel formation; the protein network gradually densified; thus enhancing the ability to entrap free water. However; under long-term exposure to high-alkali conditions; excessive protein-protein interactions weakened the gel structure; causing the release of water immobilized within the gel matrix ( Gao et al., 2021 ). The WHC of the control sample was slightly lower than those of the 0.6% and 0.8% NaOH-treated samples, but no significant difference was detected ( P > 0.05). Fig. 2. Open in a new tab Effect of different NaOH concentration treatments on the water holding of duck egg white gel. Groups with different lowercase letters indicate significant differences ( P < 0.05) among samples. 3.3. LF-NMR and MRI analysis Two water components, designated T 21 and T 22 , were identified in the gel samples. T 21 (1–50 ms) corresponds to bound water that is tightly associated with macromolecules, whereas T 22 (within 1100 ms) represents free water (Y. Zhang et al., 2023 ). Fig. 3 B shows the effects of NaOH concentration on the LF-NMR T 2 relaxation times of duck egg white gels. As shown in Fig. 3 B, T 22 accounted for the dominant proportion, indicating that free water was the predominant water component in the alkaline-induced egg white gel system. With increasing NaOH concentration, the relative proportion of T 21 gradually increased, suggesting that alkaline treatment facilitated the formation of a stable protein network structure, thus restricting the mobility of water molecules. In contrast, the proportion of T 22 first increased and then decreased, with the highest value observed in the 0.8% NaOH group. These results are consistent with those obtained from WHC analysis, confirming that appropriate alkaline treatment can densify the protein gel network, whereas excessive high-concentration alkaline exposure causes structural fragility via excessive protein-protein interactions and consequently promotes water release. Furthermore, as the NaOH concentration increased, the T 21 and T 22 peaks of the gel shifted gradually to the right, indicating enhanced mobility of water molecules. This phenomenon may be attributed to the disruption of the ordered spatial structure upon protein denaturation, which weakens the interactions between water molecules and protein chains. Fig. 3. Open in a new tab A, Effect of different NaOH concentration treatments on the hydrogen proton density of duck egg white gel. B, Effect of different NaOH treatment concentrations on the LF-NMR T 2 relaxation time in duck egg white gel. MRI is a non-invasive imaging technique that provides a complete image of a sample without damage. Hydrogen proton density imaging allows visualization of the water distribution within the sample. A redder pseudo-color indicates higher hydrogen density and greater moisture content, whereas a bluer pseudo-color signifies lower density and less moisture. Fig. 3 A shows pseudo-color images of samples with different NaOH concentrations, illustrating the differences in water distribution among the samples. Overall, the red regions in the pseudo-color maps gradually decreased with increasing NaOH concentration. When the NaOH concentration reached 1.2%, the red areas in the gel pseudo-color map were significantly reduced and unevenly distributed compared with the sample at 1.0%, indicating that the gel network structure became more porous and the WHC decreased. The addition of NaOH to egg white induced protein sol–gel transformation. This process involved protein denaturation, structural unfolding, and cross-linking, ultimately leading to the formation of a three-dimensional gel network. During hydration, water molecules interacted with proteins and became immobilized within the protein network ( Li et al., 2024 ). When the alkali concentration was within an appropriate range; hydrogen bonds between protein molecules were broken; weakening intramolecular interactions and promoting binding with water molecules ( Cai et al., 2021 ). 3.4. FTIR analysis Fig. 4 A shows the FTIR spectra of egg white gels treated with different concentrations of sodium hydroxide. The characteristic absorption peak near 3296 cm −1 is mainly attributed to O—H stretching vibrations, and peak shifts reflect the disruption and formation of hydrogen bonds. The characteristic absorption peaks at approximately 2962 cm −1 and 2875 cm −1 correspond to symmetric and asymmetric stretching vibrations of methyl or methylene groups, whose variations are associated with changes in hydrophobic interactions ( Li et al., 2023 ). As observed in the figure, the overall FTIR spectral profiles under different NaOH concentrations show no obvious differences, and the characteristic protein absorption peaks appear at almost identical wavenumber ranges. Fig. 4. Open in a new tab Infrared spectra (A) and relative content of protein secondary structures (B) of duck egg white gels under different NaOH concentration treatment conditions. In addition, the Amide I and Amide II bands are closely related to the secondary structure of the protein backbone and are therefore widely used for protein secondary structure analysis. The Amide I band (1700–1600 cm −1 ) arises from the C Created by potrace 1.16, written by Peter Selinger 2001-2019 O stretching vibration of amide groups, while the Amide II band (1480–1580 cm −1 ) originates from the in-plane bending vibration of NH groups. Fig. 4 B presents the changes in protein secondary structure of samples treated with different NaOH concentrations. Li et al. (2022) reported that prolonged pickling time of preserved eggs leads to an increase in β-structure content. The elevated β-sheet and reduced α-helix content promote protein aggregation and enhance the stability of the gel structure (P. Zhang et al. (2024) ). As shown in the figure; the proportion of β-turn first decreases and then increases with increasing NaOH concentration; reaching a minimum value of 35.95% at 0.8% NaOH. In contrast; the β-sheet content initially increases and then decreases sharply; reaching a maximum of 27.72% at the same 0.8% NaOH concentration. This phenomenon may be attributed to the hydration interaction between proteins and water at low NaOH concentrations; which facilitates the formation of a more stable three-dimensional network gel structure (X. Zhang et al.; 2023). Above the threshold concentration; protein degradation is intensified; resulting in the dissolution of soluble proteins or peptides and a reduction in the protein content within the gel network. Meanwhile; the increased ionic strength of the composite gel affects the ionization state and electrostatic charge distribution of protein molecules; altering the intermolecular attractive and repulsive forces and thus reducing the ordered secondary structure of the gel ( Zhang et al., 2015 ). The relative secondary structure content of the metal-added control group was like that of the sample treated with 1.0% NaOH. Furthermore; Gao et al. (2020) reported a positive correlation between β-sheet content and gel hardness, which is consistent with the results obtained in the present study. 3.5. Free SH content analysis Protein denaturation can be reflected by the content of free SH groups, which represent the exposed SH groups after protein unfolding. This parameter plays a crucial role in determining the functional properties of proteins. Fig. 5 shows the free SH content of gel samples prepared under different NaOH concentrations. During gel formation, free SH groups can be oxidized to form disulfide bonds, which further affect the structure and strength of the gel network ( Li et al., 2021 ). As natural covalent cross-links in proteins; disulfide bonds are essential for maintaining the stability of the protein spatial structure ( Wang et al., 2024 ). At low NaOH concentrations; the free SH content in the samples was relatively low. With increasing alkali concentration; however; the free SH content increased significantly ( P < 0.05). This phenomenon can be partially explained by the fact that alkali treatment induced protein denaturation; causing a large number of buried SH groups inside the molecules to become exposed; thus impairing the gel structure ( Ai et al., 2020 ). On the other hand; excessively high alkali concentrations may also destroy the newly exposed SH groups; further reducing the stability of the gel system ( Deng et al., 2020 ). Fig. 5. Open in a new tab Effect of different NaOH concentration treatments on the content of free sulfhydryl groups in the egg white gel of duck eggs. Groups with different lowercase letters indicate significant differences ( P < 0.05) among samples. 3.6. Rheological properties analysis The effect of NaOH concentration on the gelation behavior and strength development of egg white gels was investigated using dynamic rheological analysis. Time-scan measurements at a fixed frequency were applied to characterize the rate and extent of gel formation. Fig. 6 A and B show the changes in storage modulus (G'), loss modulus (G"), and loss tangent (tan δ) during the time sweep. G' represents the elastic (solid-like) behavior of the gel, G" reflects the viscous (liquid-like) behavior, and variations in tan δ provide a sensitive indicator of gel formation, stability, and structural disruption. Fig. 6. Open in a new tab Effect of different NaOH treatments on free sulfhydryl groups in duck egg white gels. A, and B, variation of G', G", and tan δ during the time scanning process, respectively; C, and D, changes in G' as well as tan δ with increasing frequency for different egg white composite gels; K, degree of elasticity of viscoelastic systems; n, frequency index, respectively. As shown in Fig. 6 A, G‘and G" for all samples increased sharply within the initial 1000 s, with G' increasing more rapidly than G", indicating the formation of a gel network. Moreover, the rate of increase in G' during the early reaction stage accelerated with increasing NaOH concentration, suggesting that higher NaOH levels promoted faster formation of a stable gel network. As illustrated in Fig. 6 B, tan δ decreased rapidly during gelation and gradually stabilized at approximately 0.2, indicating the transition of egg white from a liquid sol to an elastic gel. At 1.4% NaOH, tan δ was significantly higher than in other groups, suggesting increased viscosity and enhanced fluidity, which implied partial disruption of the gel network. These results are consistent with texture profile analysis (TPA) and water-holding capacity (WHC) measurements, both of which identified 0.8% NaOH as the optimal concentration for forming a compact and stable gel network. Moderate alkalinity enhanced gel viscoelasticity, whereas excessive NaOH destroyed the internal network structure. Fig. 6 C and D present the frequency-scan profiles of G' and tan δ, respectively. Within the frequency range of 0.1–100 Hz, G' was consistently higher than G" for all samples with no crossover observed, demonstrating typical elastic gel characteristics. G' increased with increasing frequency, and tan δ remained below 1, confirming that all samples behaved as weak gels stabilized by physical interactions. With increasing NaOH concentration, G' first increased and then decreased, while tan δ showed a continuous upward trend. The highest G' value was observed at 0.8% NaOH, indicating the strongest elastic network and the highest resistance to deformation at this concentration. The viscoelastic properties were further evaluated by frequency-dependent fitting of G', and the corresponding parameters K and n are presented in Fig. 6 E. The constant K represents the elastic strength of the system, where higher K values indicate greater gel hardness. The exponent n reflects the frequency dependence; a lower n value suggests stronger intermolecular interactions and cross-linking within the gel network. All samples exhibited n < 1, confirming that the gel structure was formed via physical intermolecular cross-linking ( Razi et al., 2018 ). With increasing NaOH concentration, n first decreased and then increased. The n value was 0.076 at 0.6% NaOH and 0.074 at 0.8% NaOH, with no significant difference between these two groups ( P > 0.05). The K and n values of the control group were lower than those of the 0.8% NaOH group. At 1.4% NaOH, n increased significantly to 1.28 ( P < 0.05), indicating remarkably enhanced frequency dependence. Meanwhile, the tan δ value was notably higher than in other groups, reflecting increased viscosity and fluidity. The K value first increased and then decreased with rising NaOH concentration, reaching a maximum of 749.14 at 0.8% NaOH and decreasing to 74.66 at 1.4% NaOH. These results demonstrate that low to moderate NaOH concentrations favor the formation of highly elastic gel networks with strong intermolecular cross-linking ( Huang et al., 2024 ); whereas small changes within the low concentration range have negligible effects on gel quality. However; above a critical concentration (1.0%); NaOH causes severe structural damage; resulting in weak and fragile gels with low elasticity. This finding aligns with the results reported by Ai and Jiang (2021) . These rheological findings are consistent with TPA analysis, WHC, LF-NMR, free SH group analysis, and SEM, all confirming that excessive alkali disrupts protein conformation, weakens intermolecular interactions, and destroys the three-dimensional gel network. 3.7. SEM analysis SEM was employed to observe the microstructure of protein gels and characterize their spatial network arrangement. Fig. 7 presents the SEM micrographs of egg white composite gels prepared with different NaOH concentrations. For clarity, the representative porous regions in each micrograph were highlighted using red boxes, and the pore sizes were quantified using ImageJ; the pore-size distributions and characteristic pore diameter (D, mean ± SD) are shown in the Fig. 7 . All gel samples displayed a linear fibrous network structure. At a NaOH concentration of 0.6%, the three-dimensional gel network was not fully developed, showing an irregular porous architecture with a relatively broad pore-size distribution (D = 53.29 ± 23.35 μm). In contrast, at 0.8% NaOH, a more uniform, ordered, and regular three-dimensional fibrous network was established, accompanied by the smallest average pore size among all groups (D = 47.25 ± 21.49 μm), which is consistent with a denser network stabilized by disulfide bonds, ionic interactions, hydrogen bonds, and hydrophobic interactions ( Ai et al., 2019 ). This compact microstructure explains the superior textural properties (e.g., higher hardness and elasticity) observed at this concentration. When the NaOH concentration increased to 1.0%, the pore size remained comparable (D = 49.57 ± 16.46 μm), whereas a further increase in alkali concentration led to a progressive loosening of the network. Specifically, at 1.2% NaOH, the porous structure became more open (D = 62.76 ± 18.19 μm), and at 1.4% NaOH, the microstructure exhibited obvious fusion, collapse, and markedly enlarged voids with the largest pore size and the widest distribution (D = 90.53 ± 51.04 μm). These observations indicate that high-concentration NaOH severely disrupted the gel microstructure, ultimately inducing a “liquefaction” tendency. This interpretation is supported by the increased relaxation times of both bound water and free water in the LF-NMR T₂ relaxation analysis. Meanwhile, these findings confirm that gel hardness and cohesiveness were significantly reduced under high-alkali conditions, consistent with the TPA and rheological results. For comparison, the control gel exhibited an intermediate pore size (D = 59.91 ± 21.56 μm), further supporting that 0.8–1.0% NaOH favors a denser and more regular network, whereas excessive alkalinity promotes pore coalescence and network failure. Fig. 7. Open in a new tab Effect of different NaOH concentration treatments on the microstructure of duck egg white gel. 4. Conclusion This study employed a shell-less duck egg white protein model to investigate the alkaline-induced liquefaction behavior of duck egg white gels, specifically the sol-gel-sol transition, under varying NaOH concentrations. The results demonstrated a biphasic response: during the initial gelation phase, textural properties including hardness, elasticity, viscosity, and WHC were enhanced. However, as the NaOH concentration exceeded a critical threshold, the gel network collapsed, and these functional properties underwent significant deterioration. FTIR spectroscopy revealed that during the gel-sol transition, the content of β-sheets gradually decreased alongside a concomitant increase in α-helices, indicating a rearrangement of the protein secondary structure. Rheological analysis confirmed a strong shear-rate dependence of viscosity, reflecting the structural breakdown under high alkaline conditions. SEM micrographs further validated that low alkali concentrations facilitated the formation of a regular, ordered three-dimensional gel network, whereas excessive alkalinity led to structural disruption and collapse. Collectively, these findings indicate that NaOH modulates gel properties primarily by altering the intermolecular interactions and conformational structure of egg white proteins. Notably, modulating the NaOH concentration in this shell-less model yielded gel properties comparable to those prepared via traditional metal salt-induced gelation, with no significant differences in overall quality-despite distinct underlying mechanisms. Traditional metal ions (e.g., Cu 2+ , Zn 2+ ) mainly promote gelation through electrostatic interactions and chelation with protein functional groups, while appropriate NaOH treatment induces protein unfolding, exposes hydrophobic groups and sulfhydryl groups, and facilitates the formation of intermolecular cross-links to construct a compact 3D network. This research provides significant implications for the industrial production of heavy-metal-free preserved eggs, as it simulates the sol-gel-sol transition behavior of egg white protein in the absence of heavy metal compounds, while systematically characterizing the physicochemical and structural changes involved. Future research should focus on clarifying the behavioral patterns and underlying mechanisms of alkaline-induced damage and liquefaction in protein gels within the context of the traditional in-shell pickling model. CRediT authorship contribution statement Pengfei Geng: Writing – original draft, Investigation, Data curation. Erjiao Li: Writing – review & editing, Writing – original draft, Software, Data curation, Conceptualization. Yanli Wang: Software, Investigation, Data curation. Yuanyuan Zhang: Investigation, Data curation. Yi Sun: Supervision, Data curation. Guofeng Jin: Supervision, Data curation. Lizhi Lu: Supervision, Investigation. Zhaoxia Cai: Supervision, Funding acquisition, Conceptualization. Long Sheng: Writing – review & editing, Validation, Supervision, Funding acquisition, Conceptualization. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This research was supported by the fund of HZAU-AGIS Cooperation Fund (No. SZYJY2023023). Contributor Information Zhaoxia Cai, Email: [email protected]. Long Sheng, Email: [email protected], [email protected]. Data availability Data will be made available on request. References Ai M., Jiang A. Phosphorylation modification affects the gelation behavior of alkali-induced duck egg white gels. Food Chemistry. 2021;340 doi: 10.1016/j.foodchem.2020.128185. [ DOI ] [ PubMed ] [ Google Scholar ] Ai M., Xiao N., Zhou Q., Tian X., Guo S., Chen W., Jiang A. The relationship between acylation degree and gelling property of NaOH-induced egg white gel: Efficient is better? Food Research International. 2022;160 doi: 10.1016/j.foodres.2022.111668. [ DOI ] [ PubMed ] [ Google Scholar ] Ai M., Zhou Q., Guo S., Fan H., Cao Y., Ling Z.…Jiang A. Characteristics of intermolecular forces, physicochemical, textural and microstructural properties of preserved egg white with ca(OH)2 addition. Food Chemistry. 2020;314 doi: 10.1016/j.foodchem.2020.126206. [ DOI ] [ PubMed ] [ Google Scholar ] Ai M., Zhou Q., Guo S., Ling Z., Zhou L., Fan H.…Jiang A. Effects of tea polyphenol and ca(OH)2 on the intermolecular forces and mechanical, rheological, and microstructural characteristics of duck egg white gel. Food Hydrocolloids. 2019;94:11–19. doi: 10.1016/j.foodhyd.2019.03.002. [ DOI ] [ Google Scholar ] Cai Y., Huang L., Chen B., Zhao X., Zhao M., Zhao Q., Van der Meeren P. Effect of alkaline pH on the physicochemical properties of insoluble soybean fiber (ISF), formation and stability of ISF-emulsions. Food Hydrocolloids. 2021;111 doi: 10.1016/j.foodhyd.2020.106188. [ DOI ] [ Google Scholar ] Deng C., Shao Y., Xu M., Yao Y., Wu N., Hu H., Zhao Y., Tu Y. Effects of metal ions on the physico-chemical, microstructural and digestion characteristics of alkali-induced egg white gel. Food Hydrocolloids. 2020;107 doi: 10.1016/j.foodhyd.2020.105956. [ DOI ] [ Google Scholar ] Gan N., Song Y., Li Y., Liu P., Chen S., He Y.…Wu D. Characterization of the effects of bridging linker on the β-lactoglobulin binding mechanism on the nanoscale metal-organic frameworks. Food Chemistry. 2025;464 doi: 10.1016/j.foodchem.2024.141715. [ DOI ] [ PubMed ] [ Google Scholar ] Ganesan P., Kaewmanee T., Benjakul S., Baharin B.S. Comparative study on the nutritional value of pidan and salted duck egg. Korean Journal for Food Science of Animal Resources. 2014;34(1):1–6. doi: 10.5851/kosfa.2014.34.1.1. [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] Gao X., Yao Y., Wu N., Xu M., Zhao Y., Tu Y. The sol-gel-sol transformation behavior of egg white proteins induced by alkali. International Journal of Biological Macromolecules. 2020;155:588–597. doi: 10.1016/j.ijbiomac.2020.03.209. [ DOI ] [ PubMed ] [ Google Scholar ] Gao X., Yao Y., Wu N., Xu M., Zhao Y., Tu Y. The underlying mechanism of alkali-induced ovalbumin gel transforms to sol: Physicochemical properties, structure and quantitative protein degradation analysis. Food Hydrocolloids. 2021;120 doi: 10.1016/j.foodhyd.2021.106954. [ DOI ] [ Google Scholar ] Ge L., Liu H. Engineering grey nanosystem as activatable ratio-colorimetric probe for detection of lead ions in preserved egg. Analytical Sciences. 2020;36(11):1407–1413. doi: 10.2116/analsci.19P458. [ DOI ] [ PubMed ] [ Google Scholar ] Gharbi N., Labbafi M. Effect of processing on aggregation mechanism of egg white proteins. Food Chemistry. 2018;252:126–133. doi: 10.1016/j.foodchem.2018.01.088. [ DOI ] [ PubMed ] [ Google Scholar ] Huang X., Li J., Chang C., Gu L., Su Y., Yang Y. Effects of NaOH/NaCl pickling on heat-induced gelation behaviour of egg white. Food Chemistry. 2019;297 doi: 10.1016/j.foodchem.2019.06.006. [ DOI ] [ PubMed ] [ Google Scholar ] Huang X., Li X., Li S., Ding Y., Li X., Huang Y., Huang Q., Geng F., Wu Y. A study to reveal the synergistic bacteriostatic potential of egg white lysozyme with carvacrol at the molecular level. International Journal of Biological Macromolecules. 2024;283 doi: 10.1016/j.ijbiomac.2024.138000. [ DOI ] [ PubMed ] [ Google Scholar ] Kaewmanee T., Benjakul S., Visessanguan W. Effect of NaCl on thermal aggregation of egg white proteins from duck egg. Food Chemistry. 2011;125(2):706–712. doi: 10.1016/j.foodchem.2010.09.072. [ DOI ] [ Google Scholar ] Khemakhem M., Attia H., Ayadi M. The effect of pH, sucrose, salt and hydrocolloid gums on the gelling properties and water holding capacity of egg white gel. Food Hydrocolloids. 2019;87:11–19. doi: 10.1016/j.foodhyd.2018.07.041. [ DOI ] [ Google Scholar ] Li A., Wang Y., Zhang D., Liu S., Ye Y. Formation of high-elasticity and high-strength semitransparent ovalbumin gel induced by alkali-heat treatment. International Journal of Food Properties. 2022;25(1):907–923. doi: 10.1080/10942912.2022.2070201. [ DOI ] [ Google Scholar ] Li C.-H., Hsieh C.-H., Hung C.-C., Cheng C.-W. Nondestructive detection of the gel state of preserved eggs based on dielectric impedance. Foods. 2021;10(2):2–13. doi: 10.3390/foods. [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] Li J., Zhang Y., Fan Q., Teng C., Xie W., Shi Y., Su Y., Yang Y. Combination effects of NaOH and NaCl on the rheology and gel characteristics of hen egg white proteins. Food Chemistry. 2018;250:1–6. doi: 10.1016/j.foodchem.2018.01.031. [ DOI ] [ PubMed ] [ Google Scholar ] Li Q., Jin H., Zhang X., Hu G., Lei C., Sun H., Sheng L., Jin Y., Huang X., Lu L., Cai Z. Effect of salt penetration and water migration on cooked salted egg yolk gel during storage: Physicochemical properties, structural characteristics and flavor changes. Food Chemistry. 2023;404 doi: 10.1016/j.foodchem.2022.134510. [ DOI ] [ PubMed ] [ Google Scholar ] Li X., Wu Y., Liu F., Duan W., Chen L., Cheng L., Huang Y., Li X., Ai C., Huang Q. Egg yolk lecithin delivery system constructed by ovalbumin-fucoidan (OVA-FUC) binary complex: Storage stability, release yield and in vitro digestion characteristics. LWT-Food Science and Technology. 2024;209 doi: 10.1016/j.lwt.2024.116727. [ DOI ] [ Google Scholar ] Lv X., Jin H., Fu X., Lv J., Chen R., Shi M., Lv Y., Jin Y. Egg white fermentation by lactic acid bacteria: Effects on gel characteristics and preliminary investigation of suitable genera. Food Bioscience. 2024;61 doi: 10.1016/j.fbio.2024.104582. [ DOI ] [ Google Scholar ] Pang J., Song Y., Chen L., Li Y., Geng F., Gan N., Wang X., Wang Q., Zeng T., Wu D. Multispectral methods combined with computer simulation to explore the binding mechanism of the azo pigment allure red to hemoglobin and myoglobin. LWT. 2025;221 doi: 10.1016/j.lwt.2025.117603. [ DOI ] [ Google Scholar ] Razi S., Motamedzadegan A., Shahidi A., Rashidinejad A. The effect of basil seed gum (BSG) on the rheological and physicochemical properties of heat-induced egg albumin gels. Food Hydrocolloids. 2018;82:268–277. doi: 10.1016/j.foodhyd.2018.01.013. [ DOI ] [ Google Scholar ] Sheng L., Li P., Wu H., Liu Y., Han K., Gouda M., Tong Q., Ma M., Jin Y. Tapioca starch-pullulan interaction during gelation and retrogradation. LWT-Food Science and Technology. 2018;96:432–438. doi: 10.1016/j.lwt.2018.05.064. [ DOI ] [ Google Scholar ] Tian Y., Jin H., Guo S., Lin S., Bao Z. Effects of different metal ions on the physicochemical properties and microstructure of egg white gel. Journal of the Science of Food and Agriculture. 2022;102(8):3308–3315. doi: 10.1002/jsfa.11677. [ DOI ] [ PubMed ] [ Google Scholar ] Urbonaite V., de Jongh H., van der Linden E., Pouvreau L. Water holding of soy protein gels is set by coarseness, modulated by calcium binding, rather than gel stiffness. Food Hydrocolloids. 2015;46:103–111. doi: 10.1016/j.foodhyd.2014.12.010. [ DOI ] [ Google Scholar ] Wan Z., Xiao N., Guo S., Tian X., Ai M. Synergistic effects of tea polyphenols and phosphorylation on the gelation behavior of egg white proteins. Food Hydrocolloids. 2024;149 doi: 10.1016/j.foodhyd.2023.109530. [ DOI ] [ Google Scholar ] Wu Y., Xu X., Sheng L. Effects of different plant proteins on the quality and characteristics of heat induced egg white protein gel under freezing conditions. Food Hydrocolloids. 2024;146 doi: 10.1016/j.foodhyd.2023.109281. [ DOI ] [ Google Scholar ] Xi Z., Liu W., McClements D., Zou L. Rheological, structural, and microstructural properties of ethanol induced cold-set whey protein emulsion gels: Effect of oil content. Food Chemistry. 2019;291:22–29. doi: 10.1016/j.foodchem.2019.04.011. [ DOI ] [ PubMed ] [ Google Scholar ] Xu L., Zhao Y., Xu M., Yao Y., Wu N., Du H., Tu Y. Changes in physico-chemical properties, microstructure, protein structures and intermolecular force of egg yolk, plasma and granule gels during salting. Food Chemistry. 2019;275:600–609. doi: 10.1016/j.foodchem.2018.09.078. [ DOI ] [ PubMed ] [ Google Scholar ] Yang Y., Jin H., Jin Y., Jin G., Sheng L. A new insight into the influence of pH on the adsorption at oil-water interface and emulsion stability of egg yolk protein. International Journal of Biological Macromolecules. 2023;246 doi: 10.1016/j.ijbiomac.2023.125711. [ DOI ] [ PubMed ] [ Google Scholar ] Zhang P., Liu L., Huang Q., Li S., Geng F., Song H., An F., Li X., Wu Y. Mechanism study on the improvement of egg white emulsifying characteristic by ultrasound synergized citral: Physicochemical properties molecular flexibility, protein structure. Ultrasonics Sonochemistry. 2024;111 doi: 10.1016/j.ultsonch.2024.107104. [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] Zhang X., Huang Z., An D., Zhang H., Wang J., Xia N., Ma Y., Han S., Wei A. Effect of ultrasound and alkali-heat treatment on the thermal gel properties and catechin encapsulation capacity of ovalbumin. Food Hydrocolloids. 2023;145 doi: 10.1016/j.foodhyd.2023.109069. [ DOI ] [ Google Scholar ] Zhang Y., Wang Q., Jin H., Yang Y., Chen B., Sheng L. Enhancement of foaming properties and storage stability of pasteurized liquid egg white through ultrasound modification. Food Hydrocolloids. 2024;146 doi: 10.1016/j.foodhyd.2023.109282. [ DOI ] [ Google Scholar ] Zhang Y., Zhao J., Gu Y., Zhang Y., Chen Y., Song P., Yang T. A methodology study on the optimal detection of oil and moisture content in soybeans using LF-NMR and its 2D T1-T2 nuclear magnetic technology. Agronomy-Basel. 2023;13(4):1102. doi: 10.3390/agronomy13041102. [ DOI ] [ Google Scholar ] Zhang Z., Yang Y., Tang X., Chen Y., You Y. Chemical forces and water holding capacity study of heat-induced myofibrillar protein gel as affected by high pressure. Food Chemistry. 2015;188:111–118. doi: 10.1016/j.foodchem.2015.04.129. [ DOI ] [ PubMed ] [ Google Scholar ] Zhao Y., Chen Z., Li J., Xu M., Shao Y., Tu Y. Changes of microstructure characteristics and intermolecular interactions of preserved egg white gel during pickling. Food Chemistry. 2016;203:323–330. doi: 10.1016/j.foodchem.2016.02.044. [ DOI ] [ PubMed ] [ Google Scholar ] Zhu P., Zhong Z. Analysis of the Mullins effect in buckling instability of double-network hydrogel beams under swelling equilibrium. International Journal of Solids and Structures. 2024;288 doi: 10.1016/j.ijsolstr.2023.112627. [ DOI ] [ Google Scholar ] Associated Data This section collects any data citations, data availability statements, or supplementary materials included in this article. Data Availability Statement Data will be made available on request. Articles from Food Chemistry: X are provided here courtesy of Elsevier ACTIONS View on publisher site PDF (6.2 MB) Cite Collections Permalink PERMALINK Copy RESOURCES Similar articles Cited by other articles Links to NCBI Databases Cite Copy Download .nbib .nbib Format: AMA APA MLA NLM Add to Collections Create a new collection Add to an existing collection Name your collection * Choose a collection Unable to load your collection due to an error Please try again Add Cancel Follow NCBI NCBI on X (formerly known as Twitter) NCBI on Facebook NCBI on LinkedIn NCBI on GitHub NCBI RSS feed Connect with NLM NLM on X (formerly known as Twitter) NLM on Facebook NLM on YouTube National Library of Medicine 8600 Rockville Pike Bethesda, MD 20894 Web Policies FOIA HHS Vulnerability Disclosure Help Accessibility Careers NLM NIH HHS USA.gov Back to Top