Polyphenols Weaken Pea Protein Gel by Formation of Large Aggregates with Diminished Noncovalent Interactions

Formation of pea protein amyloid-like nanofibrils-derived hydrogels mediated by epigallocatechin gallate

This study investigated the interaction between pea protein amyloid-like nanofibril and epigallocatechin gallate, constructed and characterized the novel pea protein nanofibrils-derived hydrogel mediated by epigallocatechin gallate, and researched the functionalities of the hydrogel. Epigallocatechin gallate remodeled the structure of pea protein nanofibrils, and a stable and strong hydrogel was formed at a relatively low protein concentration (4.5%). Additionally, the hydrogels exhibited various surface structures and hydrogel properties dependent on the mass ratio. Strongest gel strength (51 g) was attained at 0.25 epigallocatechin gallate/pea protein nanofibrils mass ratio. Whereas, the hydrogels exhibited the highest water holding capacity (87%) at 0.05 mass ratio. The primary driving forces in the formation and maintaining of the hydrogels were hydrophobic interactions and ionic bonds. Progressive rise of β-sheet content of pea protein nanofibrils occurred increasing epigallocatechin gallate concentration. This hydrogel holds great potential for applications in food processing, targeted delivery of nutraceuticals and biomedicine.

Development and characterization of fibrous high moisture extrudates based on pea protein isolate and whey protein

BACKGROUND

Construction of meat analogs based on pea protein isolate (PPI) alone by high moisture extrusion (HME) is diffocult as a result of the lack of anisotropic structures. In the present study, 0%-15% of whey protein (WP) was introduced to PPI to make hybrid blends, which were used to construct HME extrudates.

RESULTS

WP enhanced the hardness, adhesive, cohesiveness and gumminess of the extrudates and facilitated the formation of a distinct anisotropic structure of PPI. The fibrous degrees of the extrudates containing 10% and 15% WP were around 1.50. The addition of WP, which has more -SH groups, increased the disulfide bonds and hydrogen bonding in the extrudates, leading to a denser cross-linked structure. Particle size distribution and Fourier transform infrared analysis showed that WP induced more compact structured aggregates and more β-sheet structures in the extrudates. Furthermore, the higher hydration capacity of WP may also help form a dilute melt and generate a more pronounced plug flow, assisting the formation of fiber structures of PPI.

CONCLUSION

The present study demonstrates that WP is a potential modifier, which could be used to improve the structure of PPI-based meat analogs. © 2024 Society of Chemical Industry.

Protein-phenolic interactions and reactions: Discrepancies, challenges, and opportunities

Although noncovalent interactions and covalent reactions between phenolic compounds and proteins have been investigated across diverse scientific disciplines, a comprehensive understanding and identification of their products remain elusive. This review will initially outline the chemical framework and, subsequently, delve into unresolved or debated chemical and functional food-related implications, as well as forthcoming challenges in this topic. The primary objective is to elucidate the multiple aspects of protein-phenolic interactions and reactions, along with the underlying overwhelming dynamics and possibilities of follow-up reactions and potential crosslinking between proteins and phenolic compounds. The resulting products are challenging to identify and characterize analytically, as interactions and reactions occur concurrently, mutually influencing each other. Moreover, they are being modulated by various conditions such as the reaction parameters and, obviously, the chemical structure. Additionally, this review delineates the resulting discrepancies and challenges of properties and attributes such as color, taste, foaming, emulsion and gel formation, as well as effects on protein digestibility and allergenicity. Ultimately, this review is an opinion paper of a group of experts, dealing with these challenges for quite a while and aiming at equipping researchers with a critical and systematic approach to address current research gaps concerning protein-phenolic interactions and reactions.

Effect of limited proteolysis and CaCl2 on the rheology, microstructure and in vitro digestibility of pea protein-carboxymethyl cellulose mixed gel

Limited proteolysis, CaCl2 and carboxymethyl cellulose (CMC) have individually demonstrated ability to increase the gel strength of laboratory-extracted plant proteins. However, the syneresis effects of their combination on the gelling capacity of commercial plant protein remains unclear. This was investigated by measuring the rheological property, microstructure and protein-protein interactions of gels formed from Alcalase hydrolyzed or intact pea proteins in the presence of 0.1 % CMC and 0-25 mM CaCl2. Sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed the molecular weight of pea protein in the mixture were < 15 kDa after hydrolysis. The hydrolysates showed higher intrinsic fluorescence intensity and lower surface hydrophobicity than the intact proteins. Rheology showed that the storage modulus (G') of hydrolyzed pea protein (PPH)-based gels sightly decreased compared to those of native proteins. 5-15 mM CaCl2 increased the G' for both PP and PPH-based gels and decreased the strain in the creep-recovery test. Scanning electron microscopy (SEM) showed the presence of smaller protein aggregates in the PPH-based gels compared to PP gels and the gel network became denser, and more compact and heterogenous in the presence of 15 and 25 mM CaCl2. The gel dissociation assay revealed that hydrophobic interactions and hydrogen bonds were the dominant forces to maintain the gel structure. In vitro digestion showed that the soluble protein content in PPH-based gels was 10 ∼ 30 % higher compared to those of the PP counterpart. CaCl2 addition reduced protein digestibility with a concentration dependent behavior. The results obtained show contrasting effects of limited proteolysis and CaCl2 on the gelling capacity and digestibility of commercial pea proteins. These findings offer practical guidelines for developing pea protein-based food products with a balanced texture and protein nutrition through formulation and enzymatic pre-treatment.

Structural evolution of pea-derived albumins during pH and heat treatment studied with light and X-ray scattering

Pea albumins are found in the side stream during the isolation of pea proteins. They are soluble at acidic pH and have functional properties which differ from their globulin counterparts. In this study, we have investigated the aggregation and structural changes occurring to pea albumins under different environmental conditions, using a combination of size-exclusion chromatography coupled with multi-angle laser light scattering (SEC-MALS) and small-angle X-ray scattering (SAXS). Albumins were extracted from a dry fractionated pea protein concentrate by precipitating the globulin fraction at acidic pH. The albumins were then studied at different pH (3, 4, 4.5, 7, 7.5, and 8) values. The effect of heating at 90 °C for 1, 3, and 5 min on their structural changes was investigated using SAXS. In addition, size exclusion of the albumins showed 4 distinct populations, depending on pH and heating conditions, with two large aggregates peaks (∼250 kDa): a dimer peak (∼24 kDa) containing predominantly pea albumin 2 (PA2), and a monomer peak of a molar mass of about 12 kDa (PA1). X-ray scattering intensities as a function of q were modeled as polydisperse spheres, and their aggregation was followed as a function of heating time. Albumins was most stable at pH 3, showing no aggregation during heat treatment. While albumins at pH 7.5 and 8 showed aggregation after heating, solutions at pH 4, 4.5, and 7 already contained aggregates even before heating. This work provides new knowledge on the overall structural development of albumins under different environmental conditions, improving our ability to employ these as future ingredients in foods.

Fabrication and characterization of soy protein isolation-ferulic acid antioxidant hydrogels

BACKGROUND

Soy protein gel products are prone to direct oxidation by reactive oxygen during processing and transportation, thus reducing their functional properties and nutritional values. A covalent complex was prepared with soy protein isolate (SPI) and ferulic acid (FA) catalyzed by laccase (LC). The complex was further treated with microbial transglutaminase (TGase) to form hydrogels. The structural changes of the covalent complex (SPI-FA) and the properties and antioxidant stability of hydrogel were investigated.

RESULTS

The SPI-FA complexes were demonstrated to be covalently bound by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and they had the least hydrophobic and free sulfhydryl groups at a 1.0 mg mL-1 FA concentration. The α-helix of complexes increased from 11.50% to 27.39%, and random coil dropped from 26.06% to 14.44%. The addition of FA caused SPI fluorescence quenching and redshift. The hydrogel was formed after the complex was induced with TGase, and its hardness and water holding capacity was increased by 50.61% and 26.21%, respectively. Scanning electron microscopy showed that a layered and ordered gel structure was formed. After in vitro digestion, the complex hydrogels maintained stable antioxidant activity, and the free radical scavenging rates of DPPH and ABTS reached 87.65% and 84.45%, respectively.

CONCLUSION

SPI-FA covalent complexes were prepared under laccase catalysis, and complex hydrogels were formed by TGase. Hydrogels have stable antioxidant activity, which provides application prospects for the antioxidant development of food. © 2023 Society of Chemical Industry.

Gallic acid: design of a pyrogallol-containing hydrogel and its biomedical applications

Polyphenol hydrogels have garnered widespread attention due to their excellent adhesion, antioxidant, and antibacterial properties. Gallic acid (GA) is a typical derivative of pyrogallol that is used as a hydrogel crosslinker or bioactive additive and can be used to make multifunctional hydrogels with properties superior to those of widely studied catechol hydrogels. Furthermore, compared to polymeric tannic acid, gallic acid is more suitable for chemical modification, thus broadening its range of applications. This review focuses on multifunctional hydrogels containing GA, aiming to inspire researchers in future biomaterial design. We first revealed the interaction mechanisms between GA molecules and between GA and polymers, analyzed the characteristics GA imparts to hydrogels and compared GA hydrogels with hydrogels containing catechol. Subsequently, in this paper, various methods of integrating GA into hydrogels and the applications of GA in biomedicine are discussed, finally assessing the current limitations and future development potential of GA. In summary, GA, a natural small molecule polyphenol with excellent functionality and diverse interaction modes, has great potential in the field of biomedical hydrogels.

Gallic acid-functionalized soy protein-based multiple cross-linked hydrogel: Mechanism analysis, physicochemical properties, and digestive characteristics

Herein, carbodiimide hydrochloride/N-hydroxysuccinimide was used to mediate the grafting of gallic acid (GA) (0.005, 0.0015, and 0.025 wt%) with soybean protein isolate (SPI) in the preparation of SPI-GA conjugates and hydrogels. The modified materials were primarily joined via the CN bonds and exhibited excellent antioxidant properties. In addition, spectral analysis revealed that the grafting of GA increased the flexibility of the SPI structure. The SPI-GA hydrogel is fabricated through covalent/non-covalent cross-linking mechanisms, including Schiff base, Michael addition, and hydrogen bonding. Furthermore, the microstructure, rheological properties, thermal stability, and textural properties of the hydrogel were affected by the amount of GA grafted. The SPI-GA hydrogel exhibited the best performance when the amount of GA graft was 0.015 wt%. Furthermore, the tightly cross-linked structure of SPI-GA prevented premature degradation of the protein by pepsin. In conclusion, these capabilities provide numerous possibilities for the development of multifunctional and active substance delivery carriers.

Spontaneous gelation behaviors and mechanism of Ficus awkeotsang Makino pectin

Ficus awkeotsang Makino (jelly fig) can produce edible gels by rubbing its seeds in water at room temperature in which pectin is considered as the main gelling component. However, the spontaneous gelation mechanism of Ficus awkeotsang Makino (jelly fig) pectin (JFSP) is still unclear. This study aimed to reveal the structure, physicochemical properties, and spontaneous gelation behaviors and mechanism of JFSP. JFSP was first obtained by water extraction and alcohol precipitation method, with a pectin yield of 13.25 ± 0.42 % (w/w), weight-average molar mass (Mw) of 111.26 kDa, and methoxylation degree (DM) of 26.8 %. Analysis of monosaccharide compositions showed that JFSP was composed of 87.8 % galactose acid, indicating a high percentage of galacturonic acid blocks. Measurement on the gelling capacity suggested that JFSP gels can be easily formed by simply dispersing the pectin in water at room temperature without adding any co-solutes or metal ions. Gelation force analysis indicated that hydrogen bonding, hydrophobic interactions, and electrostatic interactions were the main factors contributing to gel formation. At 1.0 % (w/v) of pectin concentration, JFSP gels exhibited relatively high gel hardness (72.75 ± 1.15 g) and good thermal and freeze-thawing stability. Overall, these findings highlight the potential application of JFSP as a promising commercial pectin resource.

Waste to Wealth Approach: Improved Antimicrobial Properties in Bioactive Hydrogels through Humic Substance-Gelatin Chemical Conjugation

Exploring opportunities for biowaste valorization, herein, humic substances (HS) were combined with gelatin, a hydrophilic biocompatible and bioavailable polymer, to obtain 3D hydrogels. Hybrid gels (Gel HS) were prepared at different HS contents, exploiting physical or chemical cross-linking, through 1-ethyl-(3-3-dimethylaminopropyl)carbodiimide (EDC) chemistry, between HS and gelatin. Physicochemical features were assessed through rheological measurements, X-ray diffraction, attenuated total reflectance (ATR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and scanning electron microscopy (SEM). ATR and NMR spectroscopies suggested the formation of an amide bond between HS and Gel via EDC chemistry. In addition, antioxidant and antimicrobial features toward both Gram(-) and Gram(+) strains were evaluated. HS confers great antioxidant and widespread antibiotic performance to the whole gel. Furthermore, the chemical cross-linking affects the viscoelastic behavior, crystalline structures, water uptake, and functional performance and produces a marked improvement of biocide action.

Effect of ultrasound treatment on interactions of whey protein isolate with rutin

Rutin is a biologically active polyphenol, but its poor water solubility and low bioavailability limit its application to the food industry. We investigated the effect of ultrasound treatment on the properties of rutin (R) and whey protein isolate (WPI) using spectral and physicochemical analysis. The results revealed that there was covalent interaction between whey protein isolate with rutin, and the binding degree of whey isolate protein with rutin increased with ultrasound treatment. Additionally, solubility and surface hydrophobicity of WPI-R complex improved with ultrasonic treatment, and a maximum solubility of 81.9 % at 300 W ultrasonic power. The ultrasound treatment caused the complex to develop a more ordered secondary structure, resulting in a three-dimensional network structure with small and uniform pore sizes. This research could provide a theoretical reference for studying protein-polyphenol interactions and their applications in food delivery systems.

Controlling the assembly of soy β-conglycinin to fabricate heat-stable particles for high protein liquid systems

BACKGROUND

Recently, there is a growing interest in developing protein-fortified liquid systems, which are formulated to provide special nutrient combinations to those with special dietary needs. The fabrication of heat-stable protein for protein-fortified liquid systems relies heavily on precise control of the edible protein-building process.

RESULTS

Results suggested that heat-stable 7S protein particles (7SPPs) could be obtained by preheating at 100 °C for an extended time, whereas 7S proteins with better gelling properties were discovered after preheating at lower temperatures. According to the findings of the protein conformational and morphological characterization, the 7SPPs showed rather stable tertiary and secondary structures as well as size distributions, which might be responsible for their heat stability. Additionally, during the reheating test, suspensions of 7SPPs showed no signs of gelation and had a low viscosity even though the protein content was as high as 120 mg mL^-1 . However, 7S proteins with improved gelling properties were found to show rising aggregate size, higher susceptibility and larger conformational structure changing rates upon reheating treatment.

CONCLUSION

Soy β-conglycinin (7S) proteins with tunable heat stability were successfully prepared by preheating 10 mg mL^-1 protein dispersions at various temperatures (80-120 °C) and durations (15-120 min). These findings provide fundamental insights for developing 7S-based protein-fortified systems. © 2023 Society of Chemical Industry.

Enzymatic hydrolysis of soy and chickpea protein with Alcalase and Flavourzyme and formation of hydrogen bond mediated insoluble aggregates

Food applications involving plant proteins require modification of their functionality to mimic the unique properties of animal proteins. Enzymatic hydrolysis is commonly used to alter the functionality of plant proteins, particularly to improve their solubility near the isoelectric point. Current methodological approaches mostly indicate improved solubility upon hydrolysis. However, published methods include the removal of insoluble material before analysis, and calculations are based on only the solubilized material as a percentage of the filtered protein. This approach artificially increases solubility estimation and gives an incorrect assessment of the efficacy of hydrolysis. By using the total amount of protein, this study aims to determine the effect of two microbial proteases, Flavourzyme and Alcalase, on the solubility and structural and thermal properties of soy and chickpea proteins. Protein isolates were first extracted from soy and chickpea flour and hydrolyzed from 0 to 3 h. Then, their degree of hydrolysis and solubility at a range of pHs were determined using the o-phthaldialdehyde (OPA) and Lowry methods, respectively. Proteins' electrophoretic mobility, protein-protein interactions, thermal properties, and protein secondary structures were also determined. Solubility decreased over time though the solubility of the hydrolysate improved near the isoelectric point. Soy Flavourzyme hydrolysates remained the most soluble and chickpea Flavourzyme hydrolysates showed the least solubility. Thermal data suggested that Alcalase reduced the protein denaturation temperature, leading to a loss of solubility upon thermal enzyme inactivation. The loss of solubility of hydrolysates was strongly associated with hydrogen bonding, which may result from the formation of polar peptide termini. These results challenge commonly accepted beliefs that hydrolysis inevitably improves solubility of plant proteins. Instead, it is shown that hydrolysis causes structural changes that result in aggregation, thus potentially limiting the application of enzymatic hydrolysis without the addition of further processing methods.

A review of the structure, function, and application of plant-based protein-phenolic conjugates and complexes

Interactions between plant-based proteins (PP) and phenolic compounds (PC) occur naturally in many food products. Recently, special attention has been paid to the fabrication of PP-PC conjugates or complexes in model systems with a focus on their effects on their structure, functionality, and health benefits. Conjugates are held together by covalent bonds, whereas complexes are held together by noncovalent ones. This review highlights the nature of protein-phenolic interactions involving PP. The interactions of these PC with the PP in model systems are discussed, as well as their impact on the structural, functional, and health-promoting properties of PP. The PP in conjugates and complexes tend to be more unfolded than in their native state, which often improves their functional attributes. PP-PC conjugates and complexes often exhibit improved in vitro digestibility, antioxidant activity, and potential allergy-reducing activities. Consequently, they may be used as antioxidant emulsifiers, edible film additives, nanoparticles, and hydrogels in the food industry. However, studies focusing on the application of PP-PC conjugates and complexes in real foods are still scarce. Further research is therefore required to determine the structure-function relationships of PP-PC conjugates and complexes that may influence their application as functional ingredients in the food industry.

Recent advances in structural characterization of biomacromolecules in foods via small-angle X-ray scattering

Small-angle X-ray scattering (SAXS) is a method for examining the solution structure, oligomeric state, conformational changes, and flexibility of biomacromolecules at a scale ranging from a few Angstroms to hundreds of nanometers. Wide time scales ranging from real time (milliseconds) to minutes can be also covered by SAXS. With many advantages, SAXS has been extensively used, it is widely used in the structural characterization of biomacromolecules in food science and technology. However, the application of SAXS in charactering the structure of food biomacromolecules has not been reviewed so far. In the current review, the principle, theoretical calculations and modeling programs are summarized, technical advances in the experimental setups and corresponding applications of in situ capabilities: combination of chromatography, time-resolved, temperature, pressure, flow-through are elaborated. Recent applications of SAXS for monitoring structural properties of biomacromolecules in food including protein, carbohydrate and lipid are also highlighted, and limitations and prospects for developing SAXS based on facility upgraded and artificial intelligence to study the structural properties of biomacromolecules are finally discussed. Future research should focus on extending machine time, simplifying SAXS data treatment, optimizing modeling methods in order to achieve an integrated structural biology based on SAXS as a practical tool for investigating the structure-function relationship of biomacromolecules in food industry.

Characterization and Cellular Uptake of Peptides Derived from In Vitro Digestion of Meat Analogues Produced by a Sustainable Extrusion Process

Whether proteins in meat analogues (MAs) have the ability to provide equivalent nutrition as those in animal meat remains unknown. Herein, a MA was produced by high-moisture extrusion using soy and wheat proteins. The physicochemical properties, in vitro digestion, and cellular uptake of the released peptides were systematically compared between the MA and the chicken breast (CB). The MA showed a higher hardness but a lower degree of texturization than the CB. After simulated digestion, soluble peptides in the MA had a higher molecular weight and higher hydrophobicity. No observable cytotoxicity or inflammatory response to Caco-2 cells was found for both MA and CB digests. The former exhibited less permeability of peptides across Caco-2 cells. Liquid chromatography with tandem mass spectrometry found that the identified peptides in MA and CB digests contained 7-30 and 7-20 amino acid residues, respectively, and they became shorter after cellular transportation. The amino acid composition showed fewer essential and non-essential amino acids in the MA permeate than in the CB permeate.

Functional, textural, and rheological properties of mixed casein micelle and pea protein isolate co-dispersions

In the midst of rising consumer health and environmental concerns, pea protein has increased in popularity as an alternative to animal-origin proteins. However, the use of pea protein in food systems is largely hindered by its poor functionality, including low solubility. The objective of this study was to measure the textural, functional, and rheological properties of a mixed plant- and animal-based protein system. Caseins, the major protein in bovine milk, are a known animal-based protein with optimal functional properties and high sensory acceptability. Through cold-temperature homogenization, insoluble pea proteins were incorporated with casein micelles in a stable, mixed, colloidal dispersion. Three blends with various casein-to-pea ratios (90:10, 80:20, 50:50) were prepared and analyzed. We hypothesized that incorporation with casein micelles would improve the poor functional properties of pea protein, and thus increase its potential uses in the food industry as a functional ingredient. The protein blend successfully underwent chymosin coagulation, a key ability of caseins, and formed protein gels with textures similar to commercial queso fresco and hard tofu. The 50% casein micelle:50% pea protein blend had better emulsification properties than pea protein alone. In contrast, this blend had the same foaming properties as pea protein alone. The mixed protein blends had similar rheological properties to skim milk, thus increasing their potential applications in the food industry. These results serve as a starting point to begin fully understanding the interactions between pea protein isolate and casein micelles combined via low-temperature homogenization and the effect on their techno-functional properties.

Adding Humic Acids to Gelatin Hydrogels: A Way to Tune Gelation

Exploring the chance to convert biowaste into a valuable resource, this study tests the potential role of humic acids (HA), a class of multifunctional compounds obtained by oxidative decomposition of biomass, as physical agents to improve gelatin's mechanical and thermal properties. To this purpose, gelatin-HA aqueous samples were prepared at increasing HA content. HA/gelatin concentrations changed in the range 2.67-26.67 (wt/wt)%. Multiple techniques were employed to assess the influence of HA content on the gel properties and to unveil the underlying mechanisms. HAs increased gel strength up to a concentration of 13.33 (wt/wt)% and led to a weaker gel at higher concentrations. FT-IR and DSC results proved that HAs can establish noncovalent interactions through H-bonding with gelatin. Coagulation phenomena occur because of HA-gelatin interactions, and at concentrations greater than 13.33 (wt/wt)%, HAs established preferential bonds with water molecules, preventing them from coordinating with gelatin chains. These features were accompanied by a change in the secondary structure of gelatin, which lost the triple helix structure and exhibited an increase in the random coil conformation. Besides, higher HA weight content caused swelling phenomena due to HA water absorption, contributing to a weaker gel. The current findings may be useful to enable a better control of gelatin structures modified with composted biowaste, extending their exploitation for a large set of technological applications.