Acid-induced Gelation Research Articles

Enhancing the gel properties of soy protein isolate: the role of oxidized konjac glucomannan in acid-induced gelation.

Soy protein isolate (SPI) gels formed using a single coagulant often have poor water-holding capacity (WHC) and low hardness, making them fragile and unsuitable for transportation and storage. Adding compound coagulants or polysaccharides can improve the gelation properties of SPI gels induced by gluconolactone (GDL). This study explores the impact of oxidized konjac glucomannan (OKGM) on the physicochemical and structural properties of GDL-induced SPI gels, with the aim of evaluating the potential of OKGM for enhancing the overall quality and stability of these gels. In this study, the composite gels demonstrated a significant increase in whiteness (69.02% to 70.59%) compared with the SPI gel (67.41%). Key physicochemical properties, such as water-holding capacity (WHC), textural characteristics, viscoelasticity, and thermal stability, were notably improved. Scanning electron microscopy (SEM) revealed a reduction in the average pore diameter of the composite gels from 70.57 ± 4.13 μm to 37.19 ± 0.24 μm when the oxidation degree of OKGM was kept at or below 60 min, contributing to a more compact and orderly microstructure. Enhanced hydrophobic and electrostatic interactions within the composite gels also accelerated the gelation process, shortening the gelation time from 15.77 ± 0.37 min to 12.45 ± 0.18 min. The results demonstrate that OKGM acts effectively as a gel enhancer, improving the physicochemical and structural properties of SPI gels significantly. © 2024 Society of Chemical Industry.

Strain hardening of acid-induced sodium caseinate gels as a function of pH and temperature

Strain hardening is a type of rheological behaviour that can be observed in large deformation tests of various materials. In oscillatory shear rheometry, it is characterised by an increase in storage and loss modulus ( and ) with increasing oscillation amplitude (i.e, shear strain) until the material fractures and the moduli drop again. Acid-induced caseinate gels were previously shown to exhibit such a strain hardening behaviour. However, it has not been studied in much detailed how the extent of strain hardening is affected by pH and acidification temperature. In this work, the strain hardening of acid-induced caseinate gels was characterised as a function of pH by starting strain sweeps at various time points during acidification with glucono-delta-lactone, and the experiments were conducted at either 20, 30 or 40 °C to investigate the impact of temperature. The results demonstrate that the strain at fracture and the extent by which increases with the strain amplitude change throughout acid-induced gelation of sodium caseinate in a complex manner with characteristic minima and maxima being barely related to the parameters observed in small strain experiments. The findings demonstrate the importance of considering the pH and temperature when characterising the strain hardening of caseinate gels as previous work showed that the strain hardening properties are related to water expression in forced syneresis experiments.

Arabinan branches in the RG-I region of citrus pectin aid acid-induced gelation

Gelation is a critical property of citrus pectin. However, the roles played by neutral sugar side-chains on acid-induced pectin gelation remain poorly understood. Herein, galactan- or/and arabinan-eliminated pectins (P-G, P-A, and P-AG) were used to investigate the effects of side-chains on gelation. The gel hardness values of citrus pectin, P-G, P-A, and P-AG were 42.6, 39.9, 5.3, and 2.1 g, respectively, suggesting that arabinan contributed more to gelation than galactan. We next found that arabinan branches promoted pectin chain entanglement more effectively than arabinan backbones. Destabilizer addition experiments showed that hydrogen bonding, electrostatic interaction, and hydrophobic interaction were the main forces affecting pectin gel networks and strength, which was further validated by molecular dynamic simulations. The total number of hydrogen bonds between the arabinan branches and galactan/HG (65.7) was significantly higher than that between the arabinan backbones and galactan/HG (39.1), indicating that arabinan branches predominated in terms of such interactions. This study thus elucidated the roles played by neutral-sugar side-chains, especially the arabinan branches of acid-induced pectin gels, in term of enhancing high-methoxyl pectin gelation, and offers novel insights into the structure-gelling relationships of citrus pectin.

Modulation of acid-induced pea protein gels by gellan gum and glucono-δ-lactone: Rheological and microstructural insights

This study investigated the effect of gellan gum (GG) and glucono-δ-lactone (GDL) on the acid-induced gel properties of pea protein isolate (PPI) pretreated with media milling. The inclusion of GG substantially enhanced the gel hardness of PPI gel from 18.69 g to 792.47 g though slightly reduced its water holding capacity (WHC). Rheological analysis showed that GG increased storage modulus (G’) and decreased damping factor of gels in the small amplitude oscillatory shear region and transformed its strain thinning behavior into weak strain overshoot behavior in the large amplitude oscillatory shear region. SEM revealed that GG transformed the microstructure of gel from a uniform particle aggregate structure to a chain-like architecture composed of filaments with small protein particles attached. Turbidity and zeta potential analysis showed that GG promoted the transformation of PPI from a soluble polymer system to an insoluble coagulant during acidification. When GG content was relatively high (0.2 %-0.3 %), high GDL content increased the electrostatic interaction between PPI and GG molecules, causing their rapid aggregation into a dense irregular aggregate structure, further enhancing gel strength and WHC. Overall, GG and GDL can offer the opportunity to modulate the microstructure and gel properties of acid-induced PPI gels, presenting potential for diversifying food gel design strategies through PPI-GG hybrid systems.

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.

Influence of Heating Temperature and pH on Acid Gelation of Micellar Calcium Phosphate-Adjusted Skim Milk.

Micellar calcium phosphate (MCP) plays an important role in maintaining the structure and stability of the casein micelle and its properties during processing. The objective of this study was to investigate how heating (10 min at 80 or 90 °C) at different pH levels (6.3, 6.6, 6.9, or 7.2) impacted the acid-induced gelation of MCP-adjusted milk, containing 67 (MCP67), 100 (MCP100), or 113 (MCP113) % of the original MCP content. The unheated sample MCP100 at pH 6.6 was considered the control. pH acidification to pH 4.5 at 30 °C was achieved with glucono delta-lactone while monitoring viscoelastic behaviour by small-amplitude oscillatory rheology. The partitioning of calcium and proteins between colloidal and soluble phases was also examined. In MCP-depleted skim milk samples, the concentrations of non-sedimentable caseins and whey proteins were higher compared to the control and MCP-enriched skim milk samples. The influence of MCP adjustment on gelation was dependent on pH. Acid gels from sample MCP67 exhibited the highest storage modulus (G'). At other pH levels, MCP100 resulted in the greatest G'. The pH of MCP-adjusted skim milk also impacted the gel properties after heating. Overall, this study highlights the substantial impact of MCP content on the acid gelation of milk, with a pronounced dependency of the MCP adjustment effect on pH variations.

Lactiplantibacillus plantarum enhances the texture of fermented milk by facilitating protein gelatinization through the action of a novel coagulation-promoting protease

Enzymatic modification can effectively improve the gel properties of protein-based food matrices. However, how bacterial proteases influence milk gels has been rarely reported. In the current study, the proteases isolated from two strains of Lactiplantibacillus plantarum, namely YM13–8.1 and YN22–3.1, demonstrated significant improvement in the textural properties of acid-induced gels characterized by increased hardness and a more compact, dense and fine-pored structure. The inclusion of milk-coagulating proteases resulted in a significant augmentation of hydrophobic interactions and disulfide bonds within the protein gels. Furthermore, both proteases exhibited rennet-like characteristics through κ-casein hydrolysis, with key hydrolysis sites identified as Tyr25-Ile26, Ala65-Ala66 and Lys112-Asn113. By utilizing MALDI-TOF-MS, whole genome sequencing and RT-qPCR analysis, we successfully identified the gene responsible for encoding the proteases as prtA, which has not been previously characterized. In conclusion, our findings demonstrate that the newly characterized protease prtA exerts a positive influence on milk gelling.

Acid-induced gels from mixtures of micellar casein and pea protein: Effect of protein ratio and preheating route

Enhancing the sustainability of dairy products through the partial substitution of dairy proteins with plant proteins requires exploring formulation and processing strategies. This study investigates the gluconic-δ-lactone (GDL)-induced hybrid gels from commercial micellar casein isolate (M) and pea protein isolate (P) dispersions (5% w/w protein content). Variations in the M/P ratios (3:1, 2:2, and 1:3) and preheating routes (Route 1: preheating M and P dispersions together; Route 2: preheating them separately) impacted the physical/conformational properties of protein dispersions as well as the rheological/structural features of resulting gels. Small and large amplitude oscillatory shear (SAOS and LAOS) tests revealed that lower M/P ratio led to earlier gelling points and increased the stiffness and elasticity of hybrid gels in the linear viscoelastic (LVE) region. All gels transitioned from elastic to plastic behavior in the non-linear viscoelastic (NLVE) region, with lower M/P ratio showing reduced stretchability and faster structural breakdown. Regardless of routes, the preheating step (95 °C, 30 min) disintegrated inherent aggregates/agglomerates in these commercial protein ingredients, leading to smaller particle size, but higher protein solubility, surface hydrophobicity, and |ζ-potential|. Pea proteins formed soluble aggregates during preheating, but the presence of micellar caseins (Route 1) hindered this process. Consequently, mixtures with lower M/P ratio and from preheating route 2, possessed higher quantities of pea protein soluble aggregates, forming a compact gel network with low water mobility, as observed by CLSM, STED, and LF-NMR. These findings show the potential for using pea proteins in acid-induced gel foods like yogurt and paneer-type cheeses.

Development of a stable fermented creamy structure from hazelnut in the scope of plant-based food production

A hazelnut-based fermented creamy structure was developed from whole hazelnut kernels in the scope of plant-based food production. Firstly, heat-induced and acid-induced gelation of aqueous slurries of raw or roasted hazelnut kernels were investigated. The final structure was formed by heat treatment and fermentation by yoghurt culture along with supplementary sucrose. A stabilizer mixture of locust bean gum and xanthan gum was needed to prevent phase separation. Roasting treatment of hazelnuts reduced the temperature and increased the pH at which gelation started; however, a weak gel was obtained. On the other hand, fermentation of raw hazelnuts resulted in a gel structure with higher strength, yield stress, flow point and spreadability. Phase separation was not observed in the structures during storage. Viable lactic acid bacteria count was above 6 log cfu/g in the samples and a slight decrease was observed after storage at 4°C. Soluble protein content in the samples was reduced by roasting and fermentation but increased after storage. Roasting enhanced allergenicity of the water-soluble fraction while fermentation decreased it by about 70%. Raw hazelnuts are recommended for preparation of stable fermented gel structures with reduced allergenicity towards plant-based food production.

Effect of Latilactobacillus sakei and Staphylococcus xylosus on the textural characteristics of dry fermented sausages

This study examined the effect of inoculating Latilactobacillus sakei R7 and Staphylococcus xylosus A2 on the textural characteristics of fermented sausages. The results showed that, at the end of ripening, the sausages inoculated with L. sakei increased hardness, springiness, cohesiveness and chewiness (P < 0.05), but the inoculation of the sausages with S. xylosus did not affect these textural characteristics (P > 0.05). L. sakei reduced the pH of the fermented sausages through acid production, causing protein denaturation and the subsequent exposure of hydrophobic groups. Consequently, the cross-linking between meat proteins was enhanced. Hydrophobic interaction was found to be the main force that maintained the three-dimensional gel network of the L. sakei-inoculated sausage. The uniform and dense gel network structure led to the enhanced springiness and cohesiveness of the fermented sausage. Simultaneously, the sausages inoculated with L. sakei exhibited an increase in moisture loss and a decrease in water activity owing to the closeness of the pH to the isoelectric point of the myofibrillar protein, which also increased the hardness of the sausages. This study further elucidates the formation of acid-induced gel and provides a theoretical basis for understanding the effect of inoculation on the textural characteristics of fermented sausages.

Acid-Induced Gelation of Carboxymethylcellulose Solutions.

The present work offers a comprehensive description of the acid-induced gelation of carboxymethylcellulose (CMC), a water-soluble derivative of cellulose broadly used in numerous applications ranging from food packaging to biomedical engineering. Linear viscoelastic properties measured at various pH and CMC contents allow us to build a sol-gel phase diagram and show that CMC gels exhibit broad power-law viscoelastic spectra that can be rescaled onto a master curve following a time-composition superposition principle. These results demonstrate the microstructural self-similarity of CMC gels and inspire a mean-field model based on hydrophobic interchain association that accounts for the sol-gel boundary over the entire range of CMC content under study. Neutron scattering experiments further confirm this picture and suggest that CMC gels comprise a fibrous network cross-linked by aggregates. Finally, low-field NMR measurements offer an original signature of acid-induced gelation from a solvent perspective. Altogether, these results open avenues for the precise manipulation and control of CMC-based hydrogels.

Tannic Acid-Induced Gelation of Aqueous Suspensions of Cellulose Nanocrystals.

Nanocellulose hydrogels are a crucial category of soft biomaterials with versatile applications in tissue engineering, artificial extracellular matrices, and drug-delivery systems. In the present work, a simple and novel method, involving the self-assembly of cellulose nanocrystals (CNCs) induced by tannic acid (TA), was developed to construct a stable hydrogel (SH-CNC/TA) with oriented porous network structures. The gelation process is driven by the H-bonding interaction between the hydroxyl groups of CNCs and the catechol groups of TA, as substantiated by the atoms in molecules topology analysis and FTIR spectra. Interestingly, the assembled hydrogels exhibited a tunable hierarchical porous structure and mechanical moduli by varying the mass ratio of CNCs to TA. Furthermore, these hydrogels also demonstrate rapid self-healing ability due to the dynamic nature of the H-bond. Additionally, the structural stability of the SH-CNC/TA hydrogel could be further enhanced and adjusted by introducing coordination bonding between metal cations and TA. This H-bonding driven self-assembly method may promote the development of smart cellulose hydrogels with unique microstructures and properties for biomedical and other applications.

Interplay between microstructure, mechanical properties, macrostructure breakdown and in vitro gastric digestion of whey protein gels

Gastric digestion of proteins is influenced by multiple factors including microstructure, mechanical properties and structure breakdown during mastication. The interplay between these factors affects protein digestion but is underexplored. This study aimed to investigate the contribution of microstructure, mechanical properties and macrostructure breakdown on in vitro whey protein gastric digestion. Whey protein isolate (WPI) was mixed with different types of polysaccharides (κ-carrageenan, ι-carrageenan, pectin) at various concentrations to obtain heat- or acid-induced gels with distinct microstructures (homogeneous, coarse stranded, protein continuous and bi-continuous) and Young's moduli (E, 19–165 kPa). Structural breakdown during mastication was mimicked crudely by cutting single gel cylinders into several smaller cubes to increase the total surface area by a factor of 2.65. In vitro gastric digestion was measured using the INFOGEST 2.0 protocol with minor modifications. Homogeneous heat-induced WPI/κ-carrageenan gels showed the highest digestion rate followed by protein continuous, coarse stranded and bi-continuous heat-induced WPI/κ-carrageenan gels with similar E. A 1.47-fold increase in E decreased the digestion rate of acid-induced homogeneous WPI/ι-carrageenan gels by a factor of 0.22. In contrast, a 1.13–1.83-fold increase in E barely changed the digestion rate of acid-induced protein continuous WPI/pectin gels. A 2.65-fold increase in total surface area increased the digestion rate of all gels by a factor of 1.35–2.54 depending on microstructure and mechanical properties. We conclude that the microstructure of protein gels affects in vitro protein gastric digestion and the impact of Young's modulus on in vitro protein gastric digestion depends strongly on the microstructure of protein gels.

Insights into the Acid-Induced Gelation of Original Pectin from Potato Cell Walls by Gluconic Acid-δ-Lactone.

The acid-induced gelation of pectin in potato cell walls has been gradually recognized to be related to the improvement in the cell wall integrity after heat processing. The aim of this study was to characterize the acid-induced gelation of original pectin from a potato cell wall (OPP). Rheological analyses showed a typical solution-sol-gel transition process of OPP with different additions of gluconic acid-δ-lactone (GDL). The gelation time (Gt) of OPP was significantly shortened from 7424 s to 2286 s. The complex viscosity (η*) of OPP gradually increased after 4000 s when the pH was lower than 3.13 and increased from 0.15 to a range of 0.20~6.3 Pa·s at 9000 s. The increase in shear rate caused a decrease in η, indicating that OPP belongs to a typical non-Newtonian fluid. Furthermore, a decrease in ζ-potential (from -21.5 mV to -11.3 mV) and an increase in particle size distribution (from a nano to micro scale) was observed in OPP after gelation, as well as a more complex (fractal dimension increased from 1.78 to 1.86) and compact (cores observed by cryo-SEM became smaller and denser) structure. The crystallinity of OPP also increased from 8.61% to 26.44%~38.11% with the addition of GDL. The above results call for an investigation of the role of acid-induced OPP gelation on potato cell walls after heat processing.

Fermented camel milk influenced by soy extract: Apparent viscosity, viscoelastic properties, thixotropic behavior, and biological activities

During fermentation, camel milk forms a fragile, acid-induced gel, which is less stable compared with the gel formed by bovine milk. In this study, camel milk was supplemented with different levels of soy extract, and the obtained blends were fermented with 2 different starter culture strains (a high acidic culture and a low acidic culture). The camel milk-soy extract yogurt treatments were evaluated for pH value, acidity, total phenolic compounds, antioxidant capacities, degree of hydrolysis, α-amylase and α-glucosidase inhibition, angiotensin-converting enzyme inhibition, antiproliferative activities, and rheological properties after 1 and 21 d of storage at 4°C. The results revealed that some of the investigated parameters were significantly affected by the starter culture strain and storage period. For instance, the effect of starter cultures was evident for the degree of hydrolysis, antioxidant capacities, proliferation inhibition, and rheological properties because these treatments led to different responses. Furthermore, the characteristics of camel milk-soy extract yogurt were also influenced by the supplementation level of soy extract, particularly after 21 d of storage. This study could provide valuable knowledge to the dairy industry because it highlighted the characteristics of camel milk-soy yogurt prepared with 2 different starter culture strains.

Mechanistic insights into gel formation of egg-based yoghurt: The dynamic changes in physicochemical properties, microstructure, and intermolecular interactions during fermentation

This study aimed to elucidate the mechanism of acid-induced gelation in egg-based yoghurt by investigating the dynamic changes in physicochemical properties, texture, rheology, and microstructure of the gel during fermentation, combined with the role of intermolecular forces in gel formation. Results showed that protein aggregation and cross-linking increased as pH decreased during fermentation. Gel hardness increased with fermentation, eventually reaching 11.36 g, while maintaining low fracturability. Water holding capacity (WHC) decreased from 91.77% to 73.13% during fermentation. Rheological testing demonstrated a significant increase in viscosity and dynamic moduli (G' and G''), consistent with the observation of a more compact microstructure by scanning electron microscopy (SEM) and particle size analysis. Furthermore, dynamic changes of surface hydrophobicity, sulfhydryl content, and intermolecular forces suggested that hydrophobic interactions were likely the main driving force for gel formation, as well as that hydrophobic interactions and disulfide bonds played an important role in the maintenance and construction of the gel network structure. Although ionic bonds and hydrogen bonds also had an effect on the gel formation of egg-based yoghurt, their contributions were not significant. The study provided new insights for the development of novel egg-based fermentation foods and the research of acid-induced protein gels, and also contributed to the deep exploitation and utilization of poultry eggs.

Transglutaminase, glucono-δ-lactone, and citric acid–induced whey protein isolation–milk fat emulsion gel embedding lutein and its application in processed cheese

In this study, transglutaminase (TG), glucono-δ-lactone (GDL), and citric acid (CA) were used to induce the formation of whey protein isolate (WPI)-milk fat emulsion gels to embed lutein, and the emulsion gels induced in different ways were used for the preparation of processed cheese. The protective effect of emulsion gels induced in different ways on lutein was investigated, and the stability of lutein in emulsion gels and processed cheese was analyzed. The results showed that the acidification rate of CA was higher than that of GDL, which was the key step in acid-induced gels, and that the difference in acidification rate led to differences in gel structure. Compared with the 2 acid inducers (GDL and CA), TG exhibited greater potential for forming gel structures with high strength. The TG-induced emulsion gels showed the best physical stability and the highest embedding efficiency for lutein. After heat treatment (85°C), the GDL-induced emulsion gels had higher retention rate of lutein and showed good thermal stability compared with the CA-induced emulsion gels. The processed cheese added with the TG-induced emulsion gel had higher hardness and springiness compared with the processed cheese added with the other 2 kinds of emulsion gels, whereas the processed cheese added with the CA-induced emulsion gel had a lower density of network structure, showing porosity and a larger aggregated structure, but the highest bioavailability of lutein. These results provide valuable information for the formation of cold-set emulsion gel and provide the possibility for the application of emulsion gel embedding active substances in processed cheese.

Acid-induced Poria cocos alkali-soluble polysaccharide hydrogel: Gelation behaviour, characteristics, and potential application in drug delivery

Poria cocos alkali-soluble polysaccharide (PCAP), a water-insoluble β-glucan, is the main component of the total dried sclerotia of Poria cocos. However, its gelation behaviour and properties have yet to be comprehensively studied. In this study, an acid-induced physical hydrogel based on natural PCAP is fabricated. The acid-induced gelation in PCAP is explored with respect to the pH and polysaccharide concentration. PCAP hydrogels are formed in the pH range of 0.3–10.5, and the lowest gelation concentration is 0.4 wt%. Furthermore, dynamic rheological, fluorescence, and cyclic voltammetry measurements are performed to elucidate the gelation mechanism. The results reveal that hydrogen bonds and hydrophobic interactions play a dominant role in gel formation. Subsequently, the properties of the PCAP hydrogels are investigated using rheological measurements, scanning electron microscopy, gravimetric analysis, free radical scavenging, MTT assays, and enzyme-linked immunosorbent assays. The PCAP hydrogels exhibit a porous network structure and cytocompatibility, in addition to good viscoelastic, thixotropic, water-holding, swelling, antioxidant, and anti-inflammatory activities. Furthermore, using rhein as a model drug for encapsulation, it is demonstrated that its cumulative release behaviour from the PCAP hydrogel is pH dependent. These results indicate the potential of PCAP hydrogels for application in biological medicine and drug delivery.

Development of Hydrophobically Modified Casein Derivative-Based Delivery System for Docosahexaenoic Acids by an Acid-Induced Gelation.

Although omega-3 fatty acids including docosahexaenoic acid (DHA) contain various health-promoting effects, their poor aqueous solubility and stability make them difficult to be induced in dairy foods. The aims of this research were to manufacture casein derivative-based delivery system using acid-induced gelation method with glucono-σ-lactone and to investigate the effects of production variables, such as pH and charged amount of linoleic acid, on the physicochemical properties of delivery systems and oxidative stability of DHA during storage in model milk. Covalent modification with linoleic acid resulted in the production of casein derivatives with varying degrees of modification. As pH was reduced from 5.0 to 4.8 and the charged amount of linoleic acid was increased from 0% to 30%, an increase in particle size of casein derivative-based delivery systems was observed. The encapsulation efficiency of DHA was increased with decreased pH and increased charged amount of linoleic acid. The use of delivery system for DHA resulted in a decrease in the development of primary and secondary oxidation products. An increase in the degree of modification of casein derivatives with linoleic acid resulted in a decrease in the formation of primary and secondary oxidation products than of free DHA indicating that delivery systems could enhance the oxidative stability of DHA during storage in model milk. In conclusions, casein derivatives can be an effective delivery system for DHA and charged amount of linoleic acid played a key role determining the physicochemical characteristics of delivery system and oxidative stability of DHA.

Gel properties of acid-induced gels obtained at room temperature and based on common bean proteins and xanthan gum

This work investigates the effect of pH (4.0, 4.5) and the protein-polysaccharide ratio (1:1–5:1) on the intermolecular interactions and gel properties of food hydrogels based on bean protein isolate (BPI) and xanthan gum (XG). Mixed hydrogels induced by acidification with glucone-δ-lactone (GDL) were obtained at room temperature, without the use of crosslinking agents, and using 1% (w/v) of total biopolymer content. The studies on intermolecular forces by a protein solubility assay and FTIR analyses showed that BPI promotes electrostatic associations with XG that depend on pH and ratio. Interestingly, hydrophobic interactions were predominant at ratios 1:1 and 2:1 even when no denaturing heat treatment was employed. In addition, the absence of heating throughout the gelation process caused no changes in the secondary structure of bean proteins as demonstrated by Raman spectroscopy. Concerning gel properties, hydrogels at pH 4.5 showed higher water holding capacity (up to 98.09%) than gels at pH 4.0 (up to 95.65%). Despite this observation, more compact and stronger gel structures were assembled at pH 4.0 as shown by SEM, dynamic oscillatory measurements, and texture profile analysis. Regarding the effect of ratio, the lowest ratios showed the best performance on the evaluated gel properties highlighting that almost all the gels with the 1:1–3:1 ratio exhibited the typical rheological behavior of strong gels. These results indicate that acidification with GDL of BPI:XG systems at ratios 1:1–3:1 at pH 4.0/4.5 and room temperature produce promising mixed hydrogels for functional foods. • Hydrogels were obtained through slow acidification of BPI:XG mixtures. • Mixed hydrogels were obtained at room temperature and without crosslinking agents. • Electrostatic and hydrophobic interactions drove the formation of mixed hydrogels. • Gels at low ratios (1:1–3:1) and both pH 4 and 4.5 showed strong-gel-character. • The food gels obtained exhibited excellent rheological and textural properties.