Protein Isolate Gels Research Articles

Improving the Gelation Properties of Pea Protein Isolates Using Psyllium Husk Powder: Insight into the Underlying Mechanism

The industrial application of pea protein is limited due to its poor gelation properties. This study aimed to evaluate the effects of psyllium husk powder (PHP) on improving the rheological, textural, and structural properties of heat-induced pea protein isolate (PPI) gel. Scanning electron microscopy (SEM), intermolecular forces analysis, the quantification of the surface hydrophobicity and free amino groups, and Fourier transform infrared spectroscopy (FTIR) were conducted to reveal the inner structures of PPI-PHP composite gels, conformational changes, and molecular interactions during gelation, thereby clarifying the underlying mechanism. The results showed that moderate levels of PHP (0.5–2.0%) improved the textural properties, water holding capacity (WHC), whiteness, and viscoelasticity of PPI gel in a dose-dependent manner, with the WHC (92.60 ± 1.01%) and hardness (1.19 ± 0.02 N) peaking at 2.0%. PHP significantly increased surface hydrophobicity and enhanced hydrophobic interactions, hydrogen bonding, and electrostatic interactions in PPI-PHP composite gels. Moreover, the electrostatic repulsion between anionic PHP and negatively charged PPI in a neutral environment prevented the rapid and random aggregation of proteins, thereby promoting the formation of a well-organized gel network with more β-sheet structures. However, the self-aggregation of excessive PHP (3.0%) weakened molecular interactions and disrupted the continuity of protein networks, slightly reducing the gel strength. Overall, PHP emerged as an effective natural gel enhancer for the production of pea protein gel products. This study provides technical support for the development of innovative plant protein-based foods with strong gel properties and enriched dietary fiber content.

Gelation properties and swallowing characteristics of heat-induced whey protein isolate/chia seed gum composite gels as dysphagia food

Soft gels based on protein-polysaccharide composite systems play a crucial role in the dietary management of people with dysphagia. The effect of chia seed gum (CSG) on the gelling and swallowing properties of heat-induced whey protein isolate (WPI) gels (3.125–75 mg/mL) was investigated. The results showed that adding CSG reduced the gelation concentration of WPI and weak gels could form at 12.5 mg/mL WPI concentration. In addition, the viscoelasticity and water-binding capacity of the WPI/CSG composite gels were gradually enhanced with increasing WPI concentrations. The WPI/CSG composite systems can be classified as level 2–5 dysphagia-oriented foods according to the International Dysphagia Diet Standardization Initiative (IDDSI) framework. The incorporation of CSG promoted the cross-linking of protein aggregates and the formation of compact and continuous network structures, resulting in improved gelling properties of composite systems. This study contributes to the development of novel soft gel-type dysphagia foods with better textural characteristics.

Incorporation of coenzyme Q10-loaded nanoemulsions in soy protein gels and assessment of the effects in their microstructure and bioaccessibility of the bioactive

Coenzyme Q10 (CoQ10) is a potent antioxidant that provides multiple health benefits, but its incorporation into foods is challenging due to its high hydrophobicity. This study aimed to develop soy protein isolate (SPI) gels filled with CoQ10-loaded nanoemulsion. Minimum gelation concentration tests were performed at pH 5, 6 and 7, as well as 11, 13 and 15 (SPI% w/w), to determine the best conditions for gel production. Gels with 15% SPI at pH 7 and various aqueous phase replacements by YNano Q10 (25%–85%) were produced. Uniaxial compression tests indicated that oil droplets were active particles interacting with the microgels of SPI, which structured the protein network. According to the confocal laser scanning microscopy (CLSM) micrographs, the gel structure was formed by microgels, common for SPI gels, and nanodroplets occupied the gels’ pores, possibly interacting with each other and with the protein matrix, forming a type of “emulsion network”; the scanning electron microscopy data corroborated the CLSM results. The stability of CoQ10 was evaluated using instrumental colorimetry and showed that the bioactive was highly stable after 45 days of storage according to instrumental color measurements. Regarding the release of CoQ10 during in vitro static digestion, the bioactive was present in the final digesta of gastric phase (GP) and intestinal phase (IP), indicating that EFGs protected the active against the harsh conditions of the gastrointestinal tract. Notably, the higher the amount of nanoemulsion, the higher the concentration of CoQ10 present in the digesta, and the presence of nanoemulsion droplets did not influence on protein hydrolysis.

Effect of curdlan on the gel properties and interactions of whey protein isolate gels

This study investigated the influence of curdlan on the gel properties of whey protein isolate (WPI). Results demonstrated that curdlan significantly improved the water-holding capacity, gel strength and rheological properties of the WPI gels. Moreover, it promoted the unfolding of the molecular structures of WPI, which was manifested by the transition from α-helix to β-sheet, an increase in free sulfhydryl content and a decrease in surface hydrophobicity. Furthermore, 4 % curdlan promoted the formation of WPI with uniform and compact elastic gel network structures, primarily attributed to disulphide bonds, hydrogen bonds and hydrophobic interactions. However, when the addition of curdlan exceeds 4 %, excessive entanglement of curdlan chains and steric hindrance effects hinder the unfolding and folding of protein structures, weaken their interaction, result in a loose network structure and affect the gel properties. In conclusion, this study demonstrates that curdlan can effectively improve the gelling properties of WPI, suggesting its potential application in low-calorie gel-based dairy products.

Incorporation of Locust Bean Gum and Solid Lipid Microparticles as Strategies to Improve the Properties and Stability of Calcium-Rich Soy Protein Isolate Gels.

The present study aimed to investigate the properties of calcium-rich soy protein isolate (SPI) gels (14% SPI; 100 mM CaCl2), the effects of incorporating different concentrations locust bean gum (LBG) (0.1-0.3%, w/v) to the systems and the stability of the obtained gels. Also, the incorporation of solid lipid microparticles (SLMs) was tested as an alternative strategy to improve the system's stability and, therefore, potential to be applied as a product prototype. The gels were evaluated regarding their visual aspect, rheological properties, water-holding capacities (WHCs) and microstructural organizations. The CaCl2-induced gels were self-supported but presented low WHC (40.0% ± 2.2) which was improved by LBG incorporation. The obtained mixed system, however, presented low stability, with high syneresis after 10 days of storage, due to microstructural compaction. The gels' stability was improved by SLM incorporation, which decreased the gelled matrices' compaction and syneresis for more than 20 days. Even though the rheological properties of the emulsion-filled gels (EFGs) were very altered due to the ageing process (which may affect the sensory perception of a future food originated from this EFG), the incorporation of SLMs increased the systems potential to be applied as a calcium-rich product prototype.

Effects of pH and temperature on the properties of acid-induced commercial soy protein isolate gel

The goals of this study were to investigate the effect of preheating conditions on the formation of thermal aggregates of commercial soy isolate protein (SPI) and to characterize the textural properties and microstructure of acid-induced SPI gels. SPI was subjected to preheating treatments at different temperatures (85 °C, 95 °C) and pH values (7.0, 7.5, 8.5, 9.5), and the treated SPI was then used to form acid-induced gels. Characterization of the different gels showed that lower temperatures and pH values favored protein aggregation and the formation of larger aggregates, while higher temperatures and pH values led to a lower degree of aggregation and the formation of smaller aggregates. The lowest average particle size (340.77 nm) and turbidity (0.063), and the highest solubility (81.79 %) were obtained when the preheating temperature of the thermal aggregates was 95 °C and the pH was 9.5. Higher preheating temperature and pH values caused the unfolding of SPI’s tertiary structure, decreased the content of β-sheet structure, and increased the exposure of hydrophobic groups and free sulfhydryl groups. These exposed groups facilitated protein–protein interactions during network assembly, resulting in denser and stronger gel networks. Notably, SPI subjected to higher temperatures and pH values exhibited greater binding capacity for water molecules, higher water holding capacity, and gel strength. Overall, the results showed that modification of preheating temperature and pH can control the formation state of SPI thermal aggregates, ultimately impacting the properties of SPI acid-induced gels.

Effects of moderate electric fields on the structural and gelling properties of soybean protein isolate gel induced by glucono-δ-lactone

To investigate the effects of moderate electric fields (MEF) treatment on the gelling properties of soybean protein isolate (SPI) gels induced by glucono-δ-lactone (GDL), SPI was treated by applying different electric field intensities (EFI) before GDL-induced gelation. The structure of SPI (4% and 6%, w/v) was characterized via particle size distribution, ζ-potential, fluorescence spectra, and total free sulfhydryl content. The effects of MEF treatment on the acidification pH, rheological properties, water-holding capacity (WHC), textural properties, intermolecular forces, and microstructure of GDL-induced SPI gels were investigated. The results revealed that the SPI gels treated with EFI 4 V/cm aggregated faster during acidification, with higher storage modulus, stronger gel texture, and better deformation resistance. The WHC of the gel was enhanced, and the gel network was finer and more uniform. The results suggested that MEF treatment can improve the characteristics of vegetable protein gels.

Transglutaminase-crosslinked cold-set pea protein isolate gels modified by pH shifting: Properties, structure and formation mechanisms

The poor gelation properties of pea protein isolate (PPI) limit their use in food industries. In the present study, PPI was modified by pH-shifting combined with heat treatment, followed by cold-set gelation of PPI gels induced by transglutaminase. Both pH 2–3 and pH 10–12 promoted the unfolding of PPI molecules and the transformation of secondary structures from ordered to disordered. In particular, PPI molecules with pH 12-shifting tended to expand and unfold, which resulted in the exposure of internal active groups and improvement in surface hydrophobicity. Accordingly, after the addition of 50 U/g transglutaminase, PPI gels with pH 12-shifting and heating treatment exhibited homogeneous and dense gel network with high cross-linking degree (88.12 ± 1.80%) and water holding capacity (92.13 ± 2.40%), since pH 12-shifting and heating treatment promoted the conversion of random coils and β-turns to β-folds and α-helices in PPI gels. However, with pH 10 and 11-shifting, the PPI molecules was partially unfolded and the PPI gels had a high non-network protein content, resulting in low-strength gel networks of PPI gels with rough and loose microstructures and a low WHC. These results showed that TGase-crosslinked cold-set PPI gels after pH 12-shifting and heat treatment could promote the formation of homogeneous and dense gel network structure, so that improved the PPI gelation properties, which had great potential to be used as gelling agents or nutraceutical delivery systems for thermal sensitive bioactive compounds in food and non-food fields.

Hyaluronic acid modulates techno-functional and digestion properties of heat-induced ginkgo seed protein isolate gel

The industrial application of ginkgo seed protein isolated (GSPI) is limited by its poor gel performance. This study investigated the effects of pH (3.0, 5.0, 7.0) and molecular weight (50, 500, 1500 kDa) of hyaluronic acid (HA) on the physicochemical properties, textural characteristics, microstructure, and in vitro gastrointestinal digestion of heat-induced GSPI gels. The results indicate that gels formed at pH 3.0 may be suitable for individuals with dysphagia with storage and loss moduli lower than 15.8 Pa. The highest gel hardness was achieved by incorporating high molecular weight HA at pH 5.0 (100.4 g). At pH 7.0, GSPI gels with medium molecular weight HA exhibited the highest storage (28005 Pa) and loss moduli (8395 Pa). Fourier-transform infrared spectrum analysis revealed that increased pH fostered hydrogen bond formation, and interactions between protein molecules intensified with increasing HA molecular weight. HA promoted a more stable and compact network structure. In addition, the incorporation of HA accelerated the in vitro digestion rate by up to 70%. In summary, adjusting pH and utilizing HA with different molecular weights enables easy manipulation of the texture and digestibility of GSPI gels. These findings can provide a theoretical basis for the application of HA as a gel modifier in food and expand the application of GSPI in food processing.

Impact of Oil Bodies on Structure, Rheology and Function of Acid-Mediated Soy Protein Isolate Gels.

Oil bodies (OBs) are naturally occurring pre-emulsified oil droplets that have broad application prospects in emulsions and gels. The main purpose of this research was to examine the impact of the OB content on the structure and functional aspects of acid-mediated soy protein isolate (SPI) gel filled with OBs. The results indicated that the peanut oil body (POBs) content significantly affected the water holding capacity of the gel. The rheological and textural analyses showed that POBs reduced the gel strength and hardness. The scanning electron and confocal laser scanning microscopy analyses revealed that POBs aggregated during gel formation and reduced the gel network density. The Fourier transform infrared spectrum (FTIR) analysis demonstrated that POBs participated in protein gels through hydrogen bonds, steric hindrance and hydrophobic interactions. Therefore, OBs served as inactive filler in the acid-mediated protein gel, replaced traditional oils and provided alternative ingredients for the development of new emulsion-filled gels.

Effect of glycosylation on soy protein isolate–sodium carboxymethyl cellulose conjugates heat-induced gels and their applications as carriers of riboflavin

The objective of this study was to improve the rheological properties and riboflavin delivery ability of soy protein isolate (SPI) gels by incorporating sodium carboxymethyl cellulose (CMC) through glycosylation. The investigation focused on the structural and gel properties of SPI–CMC conjugates at different Maillard reaction times (30, 60, 90, 120, and 150 min). The results showed that the degree of grafting initially increased and then decreased as the Maillard reaction times increased, reaching its peak at 90 min (25.52%). The changes in the structure and conformation of the SPI–CMC conjugates were verified by Fourier transform infrared spectroscopy and surface hydrophobicity. An appropriate Maillard reaction reduced the content of highly ordered α-helix and β-sheet while increasing the content of disordered random coil and β-turn. This secondary structural change led to protein unfolding, exposure of surface hydrophobic groups, and orderly aggregation, forming a dense cross-linked gel network. When the Maillard reaction times increased, especially for 90 min, the gel strength and water-holding capacity of the SPI–CMC conjugate gels were significantly increased, along with a denser microstructure. Compared with the SPI and SPI–CMC mixture, SPI–CMC conjugate gels with 60 and 90 min reaction times exhibited notably increased viscosity and storage modulus (G′), as well as better structural recovery characteristics. The above physicochemical property improvements markedly enhanced the riboflavin encapsulation efficiency and riboflavin delivery ability of SPI–CMC conjugate gels, improving the ability to protect riboflavin from photodegradation and slowly releasing riboflavin in the simulated intestinal environment. Hence, SPI–CMC conjugate gels have significant potential for the delivery of nutrients.

Gelation behaviour of Auricularia polytricha polysaccharides-whey protein isolate

The thermal gelling behaviour and formation mechanism of Auricularia polytricha polysaccharides-whey protein isolate (APP-WPI) gel was studied by moisture migration, conformation transformation and microstructure. Electrostatic repulsion between APP and WPI limited the rapid or random aggregation of WPI aggregate, leading to establishment of a more ordered structure. The conformation transformation from α-helix to β-sheet and strong hydrophobic interaction in WPI gelation process promoted the formation of stable three-dimension (3D) gel network, as proved by the increase in crystallinity and thermal stability. The composite gel had decreased T23 and PT23 values which indicated restricted water mobility within the gel resulting in dense water cavity via APP's high-water absorption. Furthermore, 0.25–1.00% APP concentration improved gel hardness, water holding capacity, storage modulus (G′) and loss modulus (G″) of WPI gel. This study demonstrated that APP played a vital role in regulating ideal physicochemical and structural characteristics of WPI-based gel products.

Enhancing soy protein isolate gels: Combined control of pH and surface charge for improved structural integrity and gel strength

The application of sophisticated technologies to enhance soy protein isolate (SPI) gelation in the industry faces limitations due to high costs and technical intricacies. This investigation examined how different combinations of pH pretreatment and NaCl concentration affect the gel properties of SPI. Decreasing pH and increasing NaCl concentration caused soy protein particle sizes to increase in the solution due to reduced electrostatic repulsion. Additionally, decreasing pH and increasing NaCl concentration reduced the absolute zeta potential, promoting particle collisions and aggregation in SPI solutions and influencing gel strength. Rheological studies showed that lowering pH levels decreased gelation temperatures and increased gel strength. However, extreme pH levels compromised gel integrity, impacting water-holding capacity and microstructure. Supplementing SPI pretreated at pH 6.0 with 100 mM NaCl notably boosted the gel strength compared to other pretreatment methods. Further solvent analyses revealed that interactions governing gel strength-hydrogen bonding and hydrophobic interactions emerged as crucial contributors. This comprehensive investigation sheds light on the intricate interplay of factors influencing SPI gel formation, providing crucial insights for future industrial-scale applications.

Optimizing texture and mechanical properties: The impact of pH-modulated metal-phenolic networks on soy protein isolate gels

This study presents the initial exploration of utilizing metal-phenolic networks (MPN) to augment the structure of soy protein isolate (SPI) gels. By employing EGCG and zinc ions to create MPN at varying pH levels (5, 7, and 9), the research investigates the impact of MPN on the texture, mechanical properties, and microstructure of SPI gels. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy demonstrated that MPN binds to SPI through hydrogen bonding and electrostatic interactions. The findings indicate that the incorporation of MPN significantly enhances the structure of SPI gels. It is noteworthy that the MPN at pH 5 is the most effective in enhancing rheological properties, showing a 4 to 5-fold increase in the storage modulus. Conversely, the MPN at pH 7 excels in strengthening the 3D network, which boosts the mechanical properties, leading to a 1.88-fold increase in compressive stress. Furthermore, the addition of MPN enhances the structural integrity, thermal stability, and water retention of SPI gels, showcasing the potential of MPN as an innovative reinforcement method for food protein gels.

Reinforcement of heat-set whey protein gels using whey protein nanofibers: Impact of nanofiber morphology and pH values

Traditional whey protein isolate (WPI) gels require relatively high protein concentrations and prolonged heating to prepare. They exhibit a limited range of physicochemical attributes. To overcome these disadvantages, in this study, we examined the impact of incorporating whey protein isolate nanofibers (WPIFs) on the properties of heat-set WPI gels. Initially, WPIFs with different morphologies were prepared by varying the time they were exposed to acid heating (pH 2.0, 95 °C). Then, the effects of these WPIFs on the texture, rheology, microstructure, and fluid holding properties of WPI-WPIF composite gels were studied under acidic (pH 2.0) and neutral (pH 7.0) conditions. At both pH values, the gel strength and water holding capacity of the composite gels was significantly higher (P < 0.05) than for simple WPI gels. Moreover, the gelation time was shortened from around 30 min to 14.3 and 8.3 min at pH 2.0 and 7.0, respectively. WPI-WPIF composite gels prepared at pH 7.0 had the highest hardness (3120 Pa), storage modulus (10 kPa), and water holding capacity (94%). Cryo-SEM indicated that these gels had highly porous honeycomb structures with a pore size around 1–2 μm. Hydrophobic, hydrogen, and disulfide bonds played a crucial role in the formation of the composite gels at pH 7.0, but only hydrophobic and hydrogen bonds played a crucial role at pH 2.0. The impact of the WPIFs on the properties of the composite gels depended on their morphologies. The novel composite gels created in this study may have applications in the food and other industries.

Effect of polysaccharide concentration on heat-induced Tremella fuciformis polysaccharide-soy protein isolation gels: Gel properties and interactions

The formation of a single soybean protein isolate (SPI) gel is limited by the processing conditions, and has the disadvantages of poor gel property, and it is usually necessary to add other biomacromolecules to improve its property. In this study, we investigated the effects of polysaccharide concentration on gel properties and interaction mechanisms of Tremella fuciformis polysaccharide (TFP)-SPI complexes. It was found that (1) the rheological properties, texture properties, water-holding properties, and thermal stability of TFP-SPI composite gels were improved with the addition of TFP (0.25–2.0 %, w/v) in a concentration-dependent manner; (2) hydrogen bond, the electrostatic interaction, hydrophobic interaction, and disulfide bond in the gel system increased with the increase of TFP concentration; (3) the electrostatic and hydrophobic interactions played an important role in the formation of the TFP-SPI composite gel while hydrogen bond formation was the least contributor to the binary composite gel network. Overall, TFP is not only a critical health food but also a promising structural component for improving the gel properties of SPI.

Development of soy protein isolate gels added with Tremella polysaccharides and psyllium husk powder as 3D printing inks for people with dysphagia.

The aim of this study was to investigate the feasibility of soy protein isolate (SPI) gels added with Tremella polysaccharides (TPs) and psyllium husk powder (PHP) as 3D printing inks for developing dysphagia-friendly food and elucidate the potential mechanism of TPs and PHP in enhancing the printing and swallowing performance of SPI gels. The results indicated that the SPI gels with a TP : PHP ratio of 3 : 7 could be effectively used as printing inks to manufacture dysphagia-friendly food. The addition of TPs increased the free water content, resulting in a decrease in the viscosity of the SPI gels, which, in turn, reduced the line width of the 3D-printed product and structural strength of the gel system. The addition of PHP increased disulfide bond interactions and excluded volume interactions, which determined the mechanical strength of SPI gels and increased the line width of the printed product. The synergistic effects between TPs and PHP improved the printing precision and structural stability. This study presents meaningful insights for the utilization of 3D printing in the creation of dysphagia-friendly food using protein-polysaccharide complexes.

Effects of Dextran on the Gel Properties of Faba Bean Protein Isolates Prepared Using Different Processes.

The properties of faba bean (Vicia faba L.) protein isolate (FPI) gels depend on their starting protein material and can be modulated by the addition of polysaccharides. In order to investigate the interplay between these two factors, commercial FPI (FPI1) and FPI prepared in-house (FPI2) were used to fabricate glucono-delta-lactone-induced gels, with or without dextran (DX) addition. FPI1 exhibited lower solubility in water and a larger mean particle size, likely because it experienced extensive degradation due to the intense conditions involved in its preparation. The FPI1 gel showed a similar water-holding capacity as the FPI2 gel; however, its hardness was lower and viscoelasticity was higher. After DX addition, the hardness of both FPI gels decreased, while their water-holding capacity increased. Interestingly, DX addition decreased the viscoelasticity of the FPI1 gel but enhanced the viscoelasticity of the FPI2 gel. The microstructural analysis demonstrated that the density of the aggregation network decreased in the FPI1 gel after DX addition but increased in the FPI2 gel. This was consistent with the changes observed in the dominant protein interaction forces in these gels after DX addition. Overall, these findings have the potential to guide ingredient selection for the tailored preparation of FPI gels.

Improvement in texture and color of soy protein isolate gel containing capsorubin and carotenoid emulsions following microwave heating.

The effects of microwave heating on the properties and pigment release of soybean protein isolate (SPI) emulsion gel and hydrogel were investigated. The properties of the samples were analyzed by rheology and texture. The results showed that the hardness of the emulsion gel was lower than that of the hydrogel, but the cohesiveness was the opposite. The hydrogen bonding and electrostatic interaction between SPI and soybean soluble polysaccharide (SSPS) enhanced the thermal stability of the gel, and the enthalpy values were the lowest. In addition, a chroma meter was used to assess the slow-release effect of pigment, with results indicating that the emulsion gel was more red and yellow than the hydrogel; the values of a* and b* were reduced with the extension of heating time, indicating that the emulsion had a good protective effect on carotenoids and capsorubin, which was helpful to the application of the pigment in food.

Entrapment of curcumin in hydrogels of whey peptides and its release during static in vitro gastrointestinal digestion

The suitability of a whey peptide hydrogel for entrapping curcumin compared with a whey protein isolate (WPI) gel was investigated. In addition, the release of curcumin entrapped in the peptide and protein gels was evaluated during static in vitro gastrointestinal digestion. The peptide hydrogel showed a 91% entrapment efficiency of curcumin compared with 99.9% for the WPI gel and at the end of intestinal digestion curcumin retention was close to 98% in the peptide hydrogel, whereas it was only 90% for the WPI gel. The preservation of the gel microstructure and, consequently, peptide-curcumin hydrophobic interactions during intestinal digestion could explain why curcumin release from the peptide hydrogel was lower than from the WPI gel. This work provides innovative results regarding the potential of using food-derived peptide hydrogels as an entrapment system for curcumin and its preservation during digestive conditions.