Molecular forces and gelling properties of heat-induced gel from egg white protein glycated with isomalto-oligosaccharide

An unfolding/aggregation kinetic instructed rational design towards improving graft degree of glycation for myofibrillar protein

Glycation is an effective strategy for the application of myofibrillar protein (MP) in beverage formulas by improving water solubility. In conventional glycation, the efficiency was limited as MP-saccharides conjugates mostly produced at low temperature due to thermosensitivity. This study was aimed to explore unfolding/aggregation kinetics of MP, including aggregate behavior, structural characteristics, and micromorphology, which guided the selection of temperature for glycation. It was shown that 40 °C/47.5 °C were critical temperature for MP unfolding/aggregation, respectively. Accordingly, an innovative technology of glycation (cyclic continuous glycation, CCG) was established by combining such temperatures. The results confirmed that cyclic continuous heating (CCH) inhibited excessive exposure of sulfhydryl and hydrophobic groups impeding protein aggregation. Importantly, it was revealed that rational designed CCG promoted covalent binding of MP to glucose by regulating unfolding-aggregation balance, exhibiting higher glycation degree. Overall, CCG-modified MP is expected to motivate the application of meat proteins in food formulations.

Increasing the pasteurization temperature of liquid egg white by phosphorylation modification: Exploring the mechanism and application

Pasteurization is an effective sterilization technique for the treatment of liquid egg white (LEW), but the pasteurization temperature is generally limited because increased temperature can lead to aggregation of the proteins and affect their processing properties. In this study, phosphorylation modification was used to increase the thermal stability and pasteurization temperature of LEW, aiming to enhance the pasteurization sterilizing effect. The FT-IR results showed that the phosphate groups were successfully grafted into protein molecules, improving the order degree of protein molecules. In this case, the pasteurization temperature of LEW increased from 58 °C to 61 °C, without accompanying thermal aggregation. The molecular structural results suggested that the enhanced thermal stability was attributed to the decreased average particle size and the increased electrostatic repulsion between protein molecules, which largely reduced the turbidity of LEW during pasteurization treatment. Meanwhile, this process was dominated by noncovalent interactions (hydrophobic interactions and hydrogen bonding). Furthermore, the phosphorylation modification can synchronously improve emulsifying and foaming properties of LEW. Therefore, this work suggested that phosphorylation has great potential to improve thermal stability and pasteurization temperature of LEW, which can be utilized to extend its sterilizing effect and shelf life.

Chicken Egg White Gels: Fabrication, Modification, and Applications in Foods and Oral Nutraceutical Delivery

Chicken egg white (EW) proteins possess various useful techno-functionalities, including foaming, gelling or coagulating, and emulsifying. The gelling property is one of the most important functionalities of EW proteins, affecting their versatile applications in the food and pharmaceutical industries. However, it is challenging to develop high-quality gelled foods and innovative nutraceutical supplements using native EW and its proteins. This review describes the gelling properties of EW proteins. It discusses the development and action mechanism of the physical, chemical, and biological methods and exogenous substances used in the modification of EW gels. Two main applications of EW gels, i.e., gelling agents in foods and gel-type carriers for nutraceutical delivery, are systematically summarized and discussed. In addition, the research and technological gaps between modified EW gels and their applications are highlighted. By reviewing the new modification strategies and application trends of EW gels, this paper provides insights into the development of EW gel-derived products with new and functional features.

Study on the gelling properties of egg white/surfactant system by different heating intensities

The aim of this study was to elucidate the different effects and difference mechanism of gelling properties among egg white (EW) treated with different heating intensities and the composite addition of rhamnolipid and soybean lecithin. Particle size analyzer, potentiometric analyzer, surface hydrophobicity method, and Fourier transform infrared spectroscopy techniques were used to determine the physicochemical properties and molecular structure, respectively. Low-field nuclear magnetic resonance, magnetic resonance imaging, texture profile analysis, and scanning electron microscopy techniques were used to analyze the gelling properties and gel structure, respectively. And we illuminate the different mechanisms in the gelling properties of the EW with various treatments and key internal factors that play important roles in improving gelling properties by establishing the link between the gelling properties and relevant characteristics by mixed effects model and visual network analysis. The results indicate raising the content of rhamnolipid decreased the migration of immobilized water in the EW gel and the free water content. At the heating intensities of 55 °C/3.5, 65 °C/2.5, and 67 °C/1.5 min, with an increase in rhamnolipid, the gel's cohesiveness, gumminess, and chewiness gradually increased. The mixed effects model indicated that heating intensities and composite ratios have a 2-way interaction on zeta potential, the relaxation time of bound water (T21), the content of bound water (P21), the content of immobilized water (P22), and fractal dimension (df) attributes (P < 0.05). The visual network analysis showed that the protein solubility, the relaxation time of immobilized water (T22), surface hydrophobicity, zeta potential, average particle size (d43) and the relaxation time of free water (T23) are critical contributors to the different gelling properties of EW subjected to various treatments and the improvement of gelling properties. This study will provide theoretical guidance for the development of egg white products and the expansion of egg white's application scope in the egg product processing industry.

Impact of soybean protein isolate concentration on chitosan-cellulose nanofiber edible films: Focus on structure and properties

Chitosan and cellulose nanofiber films are frequently employed as biodegradable materials for food packaging. However, many exhibit suboptimal hydrophobicity and antioxidant properties. To address these shortcomings, we enhanced the performance by adding different concentrations of soybean protein isolate (SPI) to chitosan-cellulose nanofiber (CS-CNF) films. As SPI concentration varied, the turbidity, particle size, and ζ-potential of the film-forming solutions initially decreased and subsequently increased. This suggests that 1 % SPI augments the electrostatic attraction and compatibility. Rheological analysis confirmed a pronounced apparent viscosity at this concentration. Analyses using Fourier transform infrared spectra, Raman spectra, X-ray diffraction, and Scanning electron microscope revealed the presence of hydrogen bonds and electrostatic interactions between SPI and CS-CNF, indicative of superior compatibility. When SPI concentration was set at 1 %, notable enhancements in film attributes were observed: improvements in tensile strength and elongation at break, a reduction in water vapor permeability by 8.23 %, and an elevation in the contact angle by 18.85 %. Furthermore, at this concentration, the ABTS+ and DPPH scavenging capacities of the film surged by 61.53 % and 46.18 %, respectively. Meanwhile, the films we prepare are not toxic. This research offers valuable insights for the advancement and application of protein-polysaccharide-based films.

Correlationship between self-assembly behavior and emulsion stabilization of pea protein-high methoxyl pectin complexes treated with ultrasound at pH 2.0

This study investigated the effects of ultrasound on the self-assembly behavior of pea protein (PP)-high methoxyl pectin (HMP) complexes at pH 2.0 through transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and intrinsic fluorescence analysis. The emulsion stabilization mechanism of PP-HMP treated with ultrasound (PP-HMP-US) was also elucidated. The results indicated that ultrasound increased the emulsifying activity index (EAI) and emulsifying stability index (ESI) of PP-HMP. Moreover, PP-HMP-US-based emulsions formed small, dispersed oil drops, which were stable during storage. PP-HMP- and PP-HMP-US-based emulsions did not demonstrate any creaming. The TEM results revealed that ultrasound can regulate the self-assembly behavior of PP and HMP to form spherical particles with a core-shell structure. This structure possessed low turbidity, a small particle size, and high absolute zeta potential values. The FTIR and intrinsic fluorescence spectra demonstrated that ultrasound increased the α-helix and β-sheet contents and exposed the tryptophan groups to more hydrophilic environments. Ultrasound also promoted the PP-HMP self-assembly through electrostatic interaction and improved its oil-water interfacial behavior, as indicated by the EAI and ESI values of PP-HMP-US-based emulsions. The current results provide a reference for the development of an innovative emulsifier prepared by ultrasound-treated protein-pectin complexes at low pH.

Rheological and physicochemical properties of heat-induced ovalbumin gels in presence of sodium carboxymethyl cellulose

In this study, the effect of sodium carboxymethylcellulose (CMC-Na) on the rheological and physicochemical properties of heat-induced ovalbumin (OVA) gels was evaluated. The OVA/CMC-Na composite gels were prepared by heat-induced (85 °C, pH 7.0) a mixture of CMC-Na (0, 0.2, 0.4, 0.8 and 1%) and OVA. The results revealed that the addition of CMC-Na dramatically reduced the springiness and hardness of the composite gels, while slightly enhancing the intermolecular hydrogen bonding interactions, which facilitated the improvement of the softness of the gels. It can be observed by SEM that the added CMC-Na was stacked on the surface of the OVA, resulting in visible "linear bumps". All gel samples exhibited shear-thinning behavior. The apparent viscosity of the composite gels increased with the addition of CMC-Na, and the OVA gel with 1% CMC-Na showed the highest apparent viscosity and the lowest storage modulus (G'). Additionally, low field nuclear magnetic resonance (LF-NMR) measurements indicated that the increasing CMC-Na boosted the water mobility of the composite gel. This study offers a novel approach to the development of ovalbumin-based soft gel foods, especially for certain populations with swallowing difficulties.

Changes in structural, rheological, and gel properties of egg white protein induced by preheating in the dry state

The knowledge of fundamental rheological concepts is essential to understand the gelling process of egg white proteins (EWP), which can be used to further manipulate the gel performance with desired sensorial attributes. In this study, the rheological and gel properties of EWP as influenced by heating in the dry state were investigated. The structural changes in dry heated EWP (DEWP) were also characterized in terms of morphology, protein stability, and protein microenvironment. The results showed that moderate dry heating induced linear aggregation of DEWP and decreased the denaturation temperature (Td) and enthalpy of denaturation (ΔH). Furthermore, the cross-linking on protein surface led to nonpolar microenvironment of hydrophobic groups, which lays the foundation of improved gel properties. The specific outcomes include the increase in the G'max and the G''max values, k'/k'' values of DEWP dispersions, gel hardness and gumminess of DEWP gels and a decrease in gelation temperature of DEWP dispersions. However, few changes were found in the springiness and cohesiveness of the DEWP gels with increasing dry heating time. Notably, gels prepared with DEWP also had better digestibility. Overall, these results can provide theoretical basis for quality control and sensory evaluation of DEWP in the food industry.

Thermal gelation and digestion properties of hen egg white: Study on the effect of neutral and alkaline salts addition

In this study, the thermal gelation and digestion properties of hen egg white (hen EW) proteins with different salts were investigated. Results show that the addition of neutral salt - sodium chloride (NaCl) decreased the gel hardness/resilience, increased gel lightness, aggregated particle size and digestibility of hen EW proteins significantly. In contrast, alkaline salts - phosphate and carbonate addition increased the gel resilience and strain tolerance as well as reduced the aggregated particle size and gel lightness of hen EW proteins due to the increase of solution pH and negative charge. Correlation analysis shows that the digestibility of hen EW gels was affected by gel viscoelasticity, molecule forces and texture. In conclusion, thermal gelation properties of hen EW proteins could be modulated by salts with different pH/ionic strength, and thus affected the protein digestion and peptide released.

Efficient Degradation for Raffinose and Stachyose of a β-D-Fructofuranosidase and Its New Function to Improve Gel Properties of Coagulated Fermented-Soymilk

A novel β-D-fructofuranosidase gene was identified via database mining from Leptothrix cholodnii. The gene was chemically synthesized and expressed in Escherichia coli, resulting in the production of a highly efficient enzyme known as LcFFase1s. The enzyme exhibited optimal activity at pH 6.5 and a temperature of 50 °C while maintaining stability at pH 5.5-8.0 and a temperature below 50 °C. Furthermore, LcFFase1s exhibited remarkable resistance to commercial proteases and various metal ions that could interfere with its activity. This study also revealed a new hydrolysis function of LcFFase1s, which could completely hydrolyze 2% raffinose and stachyose within 8 h and 24 h, respectively, effectively reducing the flatulence factor in legumes. This discovery expands the potential applications of LcFFase1s. Additionally, the incorporation of LcFFase1s significantly reduced the particle size of coagulated fermented-soymilk gel, resulting in a smoother texture while maintaining the gel hardness and viscosity formed during fermentation. This represents the first report of β-D-fructofuranosidase enhancing coagulated fermented-soymilk gel properties, highlighting promising possibilities for future applications of LcFFase1s. Overall, the exceptional enzymatic properties and unique functions of LcFFase1s render it a valuable tool for numerous applications.

Stability of protein particle based Pickering emulsions in various environments: review on strategies to inhibit coalescence and oxidation

The emerging research interests in fabrication of protein particles as soft-particle emulsifiers show the prospective potential of using protein particles in novel poly-phase dispersing food systems. This review first provides a comprehensive summary and analysis on the dominant role of key physicochemical properties of protein particles including wettability, morphology, surface charge and protein concentration on their emulsifying abilities to construct Pickering emulsions. It was found that the constructed emulsions showed high sensitivity to changes in pH, ionic strength and temperature (thermal and freeze-thaw treatment). Moreover, oxidation remains as a challenge for protein particle based Pickering emulsions during prolonged storage, reducing their acceptance in food products. Current strategies for improving the stability of these emulsions to variable aqueous conditions and variable temperatures, and restricting oxidation event are summarized. In summary, an "ideal" protein particle-based Pickering emulsion system is proposed, encompassing aspects of interfacial property, emulsion network and texture, and antioxidant enrichment, thus promoting industrial translation into novel food and nutraceutical products.

Quantitative proteomics provides insights into the mechanism of the differences in heat-induced gel properties for egg white proteins with different interior quality during ageing in laying hens

The purpose of this study was to investigate the mechanism for the differences in heat-induced gel properties of egg white proteins with different interior quality during ageing in laying hens. Quantitative proteomic analysis revealed that the abundance of ovotransferrin, avidin, mucin 5B, and clusterin increased with decreasing Haugh units (HU), leading to the transition from disorder to order in the secondary and tertiary structure of egg white proteins, with the burial of hydrophobic groups and a reduction in the negative charge on the protein surface, rendering the egg white protein solution aggregated. These changes would accelerate the rate of aggregation of egg white proteins during heating, resulting in the loss of orientation of the molecular chains, forming coarse and porous gel structures and poor gel properties. This research provides a new idea for improving the gelling properties of egg whites from lower interior quality during ageing in laying hens.

Changes in partial properties of glycosylated egg white powder during storage

BACKGROUND

Glycosylation is an effective method to modify protein. However, there is a lack of research on the property changes of glycosylated protein during storage. In the present study, the changes in the physicochemical, functional, and structural properties of xylo-oligosaccharide (XOS) glycosylated egg white powder (EWP) (XOS-EWP conjugates) prepared with different glycosylation conditions (XOS/EWP ratio and reaction time) were investigated when stored at 25 °C and 60% relative humidity.

RESULTS

In the 12 weeks of storage, the degree of grafting, browning, and the formation of Maillard reaction products of XOS-EWP conjugates increased. The increase in XOS/EWP ratio and reaction time led to an increase in protein aggregation, though a decrease in solubility, due to increased degree of glycosylation and structural changes. Furthermore, improved gel hardness of XOS-EWP conjugates deteriorated, while improved emulsification ability was kept stable during storage. For the sample with a lower XOS/EWP ratio and reaction time, the gel hardness and emulsifying properties underwent little or no deterioration even improving during storage. The results could be attributed to the limited degree of glycosylation, further unfolding of the protein structure, increased surface hydrophobicity of protein, and improved thermal characteristics.

CONCLUSION

During storage, the Maillard reaction would continue to occur in the glycosylated EWP, further affecting the performance of modified EWP. Modified EWP prepared under different glycosylation conditions performed differently during storage. Modified EWP with a larger XOS/EWP ratio and reaction time meant it was harder to maintain good performance. Modified EWP with a smaller XOS/EWP ratio and reaction time changed significantly to better performances. © 2022 Society of Chemical Industry.

Physicochemical and Structural Properties of Gluten-Konjac glucomannan Conjugates Prepared by Maillard Reaction

Gluten (Glu) is important to wheat products by forming a three-dimensional matrix. This study aimed to investigate the physicochemical and structural properties of gluten after conjugation with konjac glucomannan (KGM) through the Maillard reaction. The study revealed that the degree of graft increased with the prolonged reaction time. The Glu-KGM conjugates were possessed of increased β-sheet but decreased α-helix and β-turn, as well as unfolding and loose tertiary structures as the reaction proceeded. Among three different proportions, the Glu-KGM 1:1 conjugate was proved to have the most excellent foaming and emulsifying properties, and could form more rigid and firm gelation structures, which could be related to the decreased particle size and increased zeta potential of the conjugate. Overall, the physicochemical and structural properties of gluten were significantly related to the KGM ratios as well as the reaction period.

Study on gel properties of lysozyme-free egg white before and after Lactiplantibacillus plantarum fermentation

BACKGROUND

Isolation of lysozyme from egg white (EW) using ion exchange resin adsorption method generates large quantities of lysozyme-free egg white (LFEW) with poor gelling property. To maximize the applications of LFEW, the effect of Lactiplantibacillus plantarum fermentation on the gel properties of LFEW was investigated in this study.

RESULTS

The fermentation efficiency of LFEW with lysozyme removed was significantly improved, and the sugar removal rate (2 g kg^-1 Lactiplantibacillus plantarum, 37 °C, 7 h) was more than 90%. Removal of lysozyme resulted in increased stability and surface hydrophobicity of EW. After Lactiplantibacillus plantarum fermentation, the stability of EW decreased, and the average particle size and surface hydrophobicity increased. In addition, by comparing the gel properties of EW and LFEW before and after fermentation at different pH, it was found that the hardness, elasticity, and water holding capacity (WHC) of EW gel increased significantly. The removal of lysozyme effectively improved the WHC and springiness of the EW gel and promoted the formation of a denser network structure with smaller pores. After Lactiplantibacillus plantarum fermentation treatment, LFEW gel hardness decreased, with loose and porous network structure, no browning occurred after autoclaving.

CONCLUSION

This study provided the direction and theoretical basis for producing a fermented LFEW gel with pleasing texture and appearance. © 2022 Society of Chemical Industry.

Preparation and characterization of W1 /O/W2 emulsions stabilized by glycated and heat-modified egg white proteins

BACKGROUND

Water-in-oil-in-water (W₁ /O/W₂ ) emulsions stabilized by protein-carbohydrate complexes were prepared from an inner water phase (W₁ ), an oil phase (O) and an outer water phase (W₂ ). The complexes consisted of heat-induced aggregates (HIAs) of isomalto-oligosaccharide/egg white protein Maillard conjugates. The effects of polyglycerol ester of polyricinoleic acid (PGPR) concentration, HIA concentration, W₁ -to-O volume ratio and W₁ /O-to-W₂ volume ratio on the properties of the W₁ /O/W₂ emulsions were systematically investigated.

RESULTS

At sufficiently high PGPR concentrations (>2%), the emulsions possess a high negative charge (≈-44 mV). The encapsulation efficiency of the emulsions, which was determined by incorporating a hydrophilic yellow dye in the inner water phase prior to homogenization, was relatively high (up to 93%) and did not change significantly during 14-day storage at 4 °C. All emulsions were fluids that exhibited shear thinning behavior.

CONCLUSION

Overall, this study shows that nature-derived emulsifiers can be used to create W₁ /O/W₂ emulsions suitable for application in the food industry. In addition, we provided a viable strategy to encapsulate water-soluble nutrients. © 2022 Society of Chemical Industry.

Tremella fuciformis polysaccharides as a fat substitute on the rheological, texture and sensory attributes of low-fat yogurt

The potential of Tremella fuciformis polysaccharides (TFPS) as a fat substitute in low-fat yogurt was evaluated in this study. The effects of adding different concentrations of TFPS solution on the physical and chemical properties, texture, rheology, microstructure and sensory properties of low-fat yogurt were evaluated. Compared with control, the addition of TFPS not only increased the solid content and water holding capacity of yogurt, but also reduced syneresis losses in low-fat yogurt. In fact, the addition of TFPS did not affect the color of yogurt but had a positive effect on the texture and sensory of yogurt. In terms of rheology, all low-yogurt samples exhibited rheological to the weak gel-like structures (G' > G″), and the storage modulus and loss modulus of the yogurt added with TFPS were higher than those of the low-fat yogurt control group. Compared with the low-fat yogurt control group, yogurt added TFPS makes the cross-linking of polysaccharides and casein more compact. In conclusion, TFPS has potential as a fat substitute in dairy products.

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TFPS with Medicine Food Homology can be used as a fat substitute for low-fat yogurt.

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TFPS significantly improved the physical and chemical properties of low-fat yogurt.

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0.025% TFPS in low-fat yoghurt was most acceptable in the sensory score.

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Polysaccharide-protein interactions enhanced protein network structure.

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TFPS improved overall organoleptic quality of low-fat yogurt.

Effect of glycation degree on the structure and digestion properties of ovalbumin: A study of amino acids and peptides release after in vitro gastrointestinal simulated digestion

Glycation can improve the functional properties of protein. However, in vitro and animal studies have shown that glycation induced lysine blockage and impaired protein digestibility. This study aimed to explore the effects of different glycation degree on the structure and digestive characteristics of ovalbumin. The results showed that glycation decreased the turbidity and hydrophobicity of the protein and changed the protein structure. Moreover, the results of in vitro simulated digestion revealed that glycation reduced the contents of essential amino acids and total amino acids after digestion. Glycation changed the amino acids and peptides release from the protein by resisting the digestion of digestive enzymes, especially trypsin. In conclusion, this work links glycation, protein digestibility, and the release of amino acids and peptides. This emphasizes the importance of the balance between improving properties and ensuring the digestibility of proteins during food processing.

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.

Inhibition of the liquefaction of alkali-induced egg white gel by sodium ascorbate

Effects of sodium ascorbate (1%, 2%, 3%) on the liquefaction of alkali-induced egg white gel (EWG) were investigated. Results showed hardness and water holding capacity (WHC) gradually decreased at 1%. However, hardness and WHC declined and then rose at 2% and 3%. Microstructural changes further confirmed the effects of sodium ascorbate on hardness and WHC. Electrophoresis showed sodium ascorbate caused the cross-linking between proteins, which was more resistant to degradation. Fourier transform infrared spectroscopy (FTIR) and surface hydrophobicity indicated sodium ascorbate significantly changed protein structure, especially at 2% and 3% resulted in protein reaggregation, increasing β-sheet, and decreasing surface hydrophobicity in the later stage. In general, sodium ascorbate didn't inhibit the liquefaction of alkali-induced EWG at 1%, but did effectively at 2% and 3%. Therefore, high concentrations of sodium ascorbate possess the potential to inhibit the "alkali injury liquefaction" of preserved egg whites without heavy metals.

Effect of ultrasound assisted konjac glucomannan treatment on properties of chicken plasma protein gelation

The effect of ultrasound assisted konjac glucomannan treatment on the properties of chicken plasma protein gelation was investigated in this study. There were four gelation groups as follows: untreated plasma protein gelation (Control), gelation added konjac glucomannan (KGG), gelation by ultrasound treatment alone (UG) and gelation added konjac glucomannan combined with ultrasound treatment (KGUG). The data showed that the gelation strength and water-holding capacity of the treated groups were significantly increased compared with those of Control. The strongest bonding water was present in KGUG, followed by KGG and UG in low-field nuclear magnetic resonance. The storage energy (G') and loss energy modulus (G″) of KGUG showed the largest rheological properties, and the G' value was higher than that of G″. Furthermore, the elastic and gelatinous properties of UG, KGG and KGUG played a dominant role in viscoelasticity. After konjac glucomannan addition, the particle size of KGG increased significantly. Compared with that of the Control and KGG, the average particle size of UG and KGUG decreased significantly after ultrasound treatment. The hydrophobicity and disulfide bonds mainly affected the formation of heat-induced gelation in these four groups. Furthermore, KGUG with the highest hydrophobicity and disulfide bonds revealed the best stability. Therefore, the gelation of chicken plasma protein by ultrasound assisted konjac glucomannan treatment had excellent gelling properties.

Rheological and textural properties of acid-induced soybean protein isolate gel in the presence of soybean protein isolate hydrolysates or their glycosylated products

Enzymatic hydrolysis and glycosylation were successively applied to modify soybean protein isolate (SPI) and rheological and textural properties of acid-induced SPI gel added with the obtained SPI hydrolysates and their glycosylated products were then investigated. The incorporation of SPI hydrolysates decreased the elastic modulus (G') and hardness of SPI gel, which might be related to the random aggregation between SPI hydrolysates and native SPI molecules via hydrophobic interactions. In addition, as the molecular weight of SPI hydrolysates decreased, the reduction in G' and hardness became more significant. Although glycosylation of SPI hydrolysates weakened the adverse effects of hydrolysates on the SPI gel formation to some extent, the glycosylated SPI hydrolysates were still unable to improve the gel quality compared with the control. However, results of this research may provide important information for understanding the influencing mechanism of SPI hydrolysates and their glycosylated products on the formation of SPI gel.

Effect of processing technologies on the digestibility of egg proteins

Egg and egg products are a rich source of highly bioavailable animal proteins. Several processing technologies can affect the structural and functional properties of these proteins differently and can influence their fate inside the gastrointestinal tract. The present review examines some of the processing technologies for improving egg protein digestibility and discusses how different processing conditions affect the digestibility of egg proteins under gastrointestinal digestion environments. To provide up-to-date information, most of the studies included in this review have been published in the last 5 years on different aspects of egg protein digestibility. Digestibility of egg proteins can be improved by employing some processing technologies that are able to improve the susceptibility of egg proteins to gastrointestinal proteases. Processing technologies, such as pulsed electric field, high-pressure, and ultrasound, can induce conformational and microstructural changes that lead to unfolding of the polypeptides and expose active sites for further interactions. These changes can enhance the accessibility of digestive proteases to cleavage sites. Some of these technologies may inactivate some egg proteins that are enzyme inhibitors, such as trypsin inhibitors. The underlying mechanisms of how different technologies mediate the egg protein digestibility have been discussed in detail. The proteolysis patterns and digestibility of the processed egg proteins are not always predictable and depends on the processing conditions. Empirical input is required to tailor the optimization of processing conditions for favorable effects on protein digestibility.

Heat-induced gel properties and gastrointestinal digestive properties of egg white produced by hens fed with selenium-enriched yeast

The aim of this study was to investigate the effect of selenium enrichment on the gel properties and gastrointestinal digestive properties of egg white. Results of texture profile analysis, scanning electron microscopy and differential scanning calorimetry showed that the heat-induced gel of selenium-enriched egg white (EW-2) exhibited higher gel strength, smoother microstructure, and higher thermal denaturation temperature than ordinary egg white (EW-1), which might be due to the change of ovomucin and ovotransferrin content. The gastrointestinal digestive products of the EW-2 protein contained a higher proportion of small peptides and more free amino acids than those of EW-1. Results of oxygen radical absorbance capacity and cellular antioxidant activity assays indicated that digestive products of the EW-2 protein exhibited stronger antioxidant activity than those of the EW-1 protein. In summary, Se enrichment improved heat-induced gel properties of egg white, and promoted the gastrointestinal digestion of egg white protein.

Effect of dry heating on egg white powder influencing water mobility and intermolecular interactions of its gels

BACKGROUND

Dry heat processing remains the most promising and simple approach for achieving better gelling properties of spray-dried egg white powder (EWP). Water mobility and intermolecular interactions in gels derived from EWP were investigated after subjecting EWP to various dry heating times (0-21 days).

RESULTS

The gel hardness and water-holding capacity significantly increased with an increase in dry heating time (P < 0.05), and both parameters were positively correlated with gel transparency. In contrast to the coarser structure of untreated EWP gel, the gel of EWP corresponding to 15 days of dry heating time had a fine-stranded and orderly network structure with smaller pores. An increase in the binding force between the gel and water was observed with an increase in dry heating time due to the formation of more 'protein-water' hydrogen bonds. Increasing the dry heating time resulted in an increase in the contribution of disulfide bonds, which in turn made a significant contribution to the rigidity of the EWP gels. By contrast, a decrease in the contribution of ionic bonds and hydrophobic interactions upon increasing the dry heating time promoted the formation of orderly networks.

CONCLUSIONS

Overall, gel corresponding to EWP dry heating for 15 days had better gel properties, the highest transparency and water-holding capacity, as well as a fine-stranded and orderly network structure. These results provide more information on improvement of the gel properties of EWP through dry heat treatment. © 2020 Society of Chemical Industry.

Effect of pullulan concentration and pH on the interactions between whey protein concentrate and pullulan during gelation

BACKGROUND

Whey protein concentrate (WPC)/pullulan (PUL) hydrogel is applied as a microencapsulation wall material to protect probiotics. However, the interactions between WPC and PUL during gelation have not been clarified. In the present study, the effects of PUL concentration and pH on the interactions between WPC and PUL during gelation were evaluated with respect to appearance, zeta-potential, sulfhydryl group amount, surface hydrophobicity and infrared spectroscopy measurements. The rheological properties of WPC/PUL gels were also determined.

RESULTS

The results obtained showed that a proper concentration (0.40 g mL^-1 ) of PUL could improve the gel by enhancing the strength of hydrogen bonding, electrostatic interactions and exposure of hydrophobic groups, whereas too much PUL inhibited the formation of disulfide bonds. Furthermore, hydrophobic interactions, disulfide bonds and hydrogen bonds were destroyed in varying degrees under an alkaline environment. The rheological results also demonstrated a similar effect of PUL concentration and pH on the storage modulus (G') of WPC/PUL gels.

CONCLUSION

When the WPC/PUL gel was formed at PUL concentration of 0.40 g mL^-1 and pH 7.0, the interaction between WPC and PUL could be enhanced, which is beneficial for the future application of WPC/PUL gels in the food industry. © 2020 Society of Chemical Industry.

Effect of glycation degree on the in vitro simulated gastrointestinal digestion: A promising formulation for egg white gel with controlled digestibility

The mechanism between food gelation and its digestibility has attracted increasing attention over the past few decades. This study aimed to evaluate the effect of glycation degree on the gelation and digestibility of egg white gel (EWG) using an in vitro model and a multi-scale characterization of gel structure. Results showed that EWG glycated with increasing d-ribose by covalent bonds exhibited better gelling properties and lower in vitro digestibility according to the appearance of soluble proteins and peptides. Besides, glycation preference for ovotransferrin at lysine might be important for regulating gel structure and proteolysis accessibility via the ratio of fibrous and granular aggregates. Moreover, gel structure was predominant over amino acids modification for digestibility. Binding disorder and steric hindrance could ascribe to the lower digestibility of gels. These findings are enlightening for the formulation and production of food matrix with controlled digestibility through glycation in food and related pharmaceutical fields.

Sweet potato starch addition together with partial substitution of tilapia flesh effectively improved the golden pompano (Trachinotus blochii) surimi quality

In order to improve the gel performance and edible quality of surimi for sustainable manufacture, the present study explored the feasibility of four kinds of starchs (potato, corn, sweet potato, and wheat) and fresh water fish tilapia as additives for golden pompano based surimi production. Sweet potato starch stood out as the most appropriate additive for golden pompano surimi due to the highest gel strength, lowest expressible moisture content and more compact microstructure. When the tilapia flesh substitution ratio reached 30%, best gel property of tilapia-golden pompano compound surimi with best texture property and whiteness value was achieved. Moreover, addition of 5% sweet potato starch to the golden pompano-tilapia (7:3) compound surimi comparatively obtained the optimal effect. Namely, it was observed that the texture parameters with hardness (3.62 N), gumminess (2.74 N), chewiness (17.35 mJ), cohesiveness (4.918), and springiness (0.872) being biggest values. On the other hand, the gel strength and expressible moisture content were 2,137.31 g. mm and 3.52%, respectively, which were overwhelming than other levels. Simultaneously, the whiteness of 5% addition group was 74.75, which was also a little higher than other groups. In summary, partial substitution of tilapia and proper addition of sweet potato starch effectively improved the gel performance and quality of golden pompano-based surimi products, which has potential applications in the industry of surimi.