Complex coacervation of pea protein isolate and alginate polysaccharides

Encapsulation of lycopene in Pickering emulsion stabilized by complexes of whey protein isolate fibrils and sodium alginate: Physicochemical property, structural characterization and in vitro digestion property

In present study, whey protein isolate fibrils and sodium alginate complexes (WPIFs-SA) were prepared and further used to stabilize Pickering emulsions for lycopene delivery. The optimal interaction between WPIFs and SA occurred at pH 3.0, with a mass ratio of 2:1. Increasing the oil fractions and the content of WPIFs-SA complexes significantly improved Pickering emulsions' stability, concurrently reducing droplet size and increasing viscoelasticity. Meanwhile, it facilitated the formation of a thicker protective layer and a compact network structure around the oil droplets, offering better protection for lycopene against thermal and photo degradation. In vitro digestion studies revealed that as the oil fractions and complex contents increased, the lipolysis degree decreased. The engineered WPIFs-SA Pickering emulsion could be used as an innovative delivery system for the protection and delivery of lycopene.

Understanding emulsifier influence on complex coacervation: Essential oils encapsulation perspective

The objective of this research was to explore the viability of pea protein as a substitute for gelatin in the complex coacervation process, with a specific focus on understanding the impact of incorporating an emulsifier into this process. The study involved the preparation of samples with varying polymer mixing ratios (1:1, 1:2, and 2:1) and emulsifier content. As core substances, black pepper and juniper essential oils were utilized, dissolved beforehand in grape seed oil or soybean oil, to minimize the loss of volatile compounds. In total, 24 distinct samples were created, subjected to freeze-drying to produce powder, and then assessed for their physicochemical properties. Results revealed the significant impact of emulsifier addition on microcapsule parameters. Powders lacking emulsifiers exhibited higher water solubility (57.10%-81.41%) compared to those with emulsifiers (24.64%-40.13%). Moreover, the emulsifier significantly decreased thermal stability (e.g., without emulsifier, Ton = 137.21°C; with emulsifier, Ton = 41.55°C) and adversely impacted encapsulation efficiency (highest efficiency achieved: 67%; with emulsifier: 21%).

Protein-Based Packaging Films in Food: Developments, Applications, and Challenges

With the emphasis placed by society on environmental resources, current petroleum-based packaging in the food industry can no longer meet people's needs. However, new active packaging technologies have emerged, such as proteins, polysaccharides, and lipids, in which proteins are widely used for their outstanding gel film-forming properties. Most of the current literature focuses on research applications of single protein-based films. In this paper, we review the novel protein-based packaging technologies that have been used in recent years to categorize different proteins, including plant proteins (soybean protein isolate, zein, gluten protein) and animal proteins (whey protein isolate, casein, collagen, gelatin). The advances that have recently been made in protein-based active packaging technology can be understood by describing protein sources, gel properties, molding principles, and applied research. This paper presents the current problems and prospects of active packaging technology, provides new ideas for the development of new types of packaging and the expansion of gel applications in the future, and promotes the development and innovation of environmentally friendly food packaging.

Fabrication and characterization of complex coacervates utilizing gelatin and carboxymethyl starch

BACKGROUND

Modified polysaccharides have greatly expanded applications in comparison with native polysaccharides due to their improved compatibility and interactions with proteins and active compounds in food-related areas. Nonetheless, there is a noticeable dearth of research concerning the utilization of carboxymethyl starch (CMS) as a microcapsule wall material in food processing, despite its common use in pharmaceutical delivery. The development of an economical and safe embedding carrier using CMS and gelatin (GE) holds immense importance within the food-processing industry. In this work, the potential of innovative coacervates formed by the combination of GE and CMS as a reliable, stable, and biodegradable embedding carrier is evaluated by turbidity measurements, thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and rheological measurements.

RESULTS

The results indicate that GE-CMS coacervates primarily resulted from electrostatic interactions and hydrogen bonding. The optimal coacervation was observed at pH 4.6 and with a GE/CMS blend ratio of 3:1 (w/w). However, the addition of NaCl reduced coacervation and made it less sensitive to temperature changes (35-55 °C). In comparison with individual GE or CMS, the coacervates exhibited higher thermal stability, as shown by TGA. X-ray diffraction analysis shows that the GE-CMS coacervates maintained an amorphous structure. Rheological testing reveals that the GE-CMS coacervates exhibited shear-thinning behavior and gel-like properties.

CONCLUSION

Overall, attaining electroneutrality in the mixture boosts the formation of a denser structure and enhances rheological properties, leading to promising applications in food, biomaterials, cosmetics, and pharmaceutical products. © 2023 Society of Chemical Industry.

Simple and complex coacervation in systems involving plant proteins

Plant-based foods are gaining popularity as alternatives to meat and dairy products due to sustainability and health concerns. As a consequence, there is a renewed interest in the phase behaviour of plant proteins and of mixtures of plant proteins and polysaccharides, in particular in the cases where coacervation is found to occur, i.e., liquid-liquid phase separation (LLPS) into two phases, one of which is rich in biopolymers and one of which is poor in biopolymer. Here we review recent research into both simple and complex coacervation in systems involving plant proteins, and their applications in food- as well as other technologies, such as microencapsulation, microgel production, adhesives, biopolymer films, and more.

Synergistic formulation approach for developing pea protein and guar gum enriched olive oil-in-water emulsion gels as solid fat substitutes: Formulation optimization, characterization, and molecular simulation

This study aimed to optimize the formulation of olive oil-in-water (O/W) emulsion gels by incorporating Pea Protein (PP) and Guar Gum (GG) as alternative options for solid fats. The optimum rheological (consistency index, apparent viscosity, recovery) and texture (firmness) properties of the emulsion gels were obtained using a mixture of 2 % PP, 1 % GG, 60 % Olive Oil (OO), and 37 % Water (W). The blend of PP2/GG1 showed the highest results for recovery and firmness, 111.27 % and 33.89 g, respectively. PP/GG blend emulsion gels exhibited higher absolute ζ-potential values, ranging between -72.3 and -77.4 mV. The polydispersity index (PDI) ranged from 0.185 to 0.535, with the most uniform distributions found in the PP/GG blend emulsion gels. Strong phase separation resistance indicated strong stability of PP-GG complex emulsion gels. Higher PP concentrations decreased emulsion oxidation. FTIR and XRD research showed that PP and GG interact strongly, indicating good compatibility. The free binding energy of the most stable configuration of the molecules was -6.8 kcal mol-1, indicating a high affinity. PP interacted with GG through 9 amino acid residues, with notable residues being Asp 224, Thr 235, Ala 332, Ile 334, and Arg 336, and their respective interaction distances ranged between 2.69 Å and 3.87 Å.

Formation and microstructural characterization of scallop (Patinopecten yessoensis) male gonad hydrolysates/sodium alginate coacervations as a function of pH

Studying the noncovalent interactions between proteins and polysaccharides is quite important mainly due to the wide number of applications such as developing pH-responsive complexes. Scallop Patinopecten yessoensis male gonad hydrolysates‑sodium alginate (SMGHs-SA) was investigated as noncovalent complexes at pH from 1 to 10. The critical pH values pHC (around 6) and pHφ (around 4) were independent of the SMGHs-SA ratio, indicating the formation of soluble and insoluble complexes. The pH response of SMGHs-SA complexes was evaluated by investigating the rheological behavior, moisture distribution, functional group change and microstructure. Compared to the co-soluble and soluble complexes phases, the SMGHs-SA complexes had a higher storage modulus and viscosity as well as a lower relaxation time (T23) in the insoluble complexes phase (pHφ>3). Additionally, the amide I band and COO- stretching vibration peaks were redshifted and the amide A band vibration peaks were blueshifted by acidification. Electrostatic interactions and intermolecular/intramolecular hydrogen bonding led to SMGHs-SA agglomeration at pH 3, forming a uniform and dense gel network structure with strong gel strength and water-retention capacity. This study provides a theoretical and methodological basis for the design of novel pH-responsive complexes by studying SMGHs-SA complex coacervation.

Microencapsulation of Juniper and Black Pepper Essential Oil Using the Coacervation Method and Its Properties after Freeze-Drying

Essential oils are mixtures of chemical compounds that are very susceptible to the effects of the external environment. Hence, more attention has been drawn to their preservation methods. The aim of the study was to test the possibility of using the classical model of complex coacervation for the microencapsulation of essential oils. Black pepper (Piper nigrum) and juniper (Juniperus communis) essential oils were dissolved in grape seed (GSO) and soybean (SBO) oil to minimize their loss during the process, and formed the core material. Various mixing ratios of polymers (gelatin (G), gum Arabic (GA)) were tested: 1:1; 1:2, and 2:1. The oil content was 10%, and the essential oil content was 1%. The prepared coacervates were lyophilized and then screened to obtain a powder. The following analyses were determined: encapsulation efficiency (EE), Carr index (CI), Hausner ratio (HR), solubility, hygroscopicity, moisture content, and particle size. The highest encapsulation efficiency achieved was within the range of 64.09-59.89%. The mixing ratio G/GA = 2:1 allowed us to obtain powders that were characterized by the lowest solubility (6.55-11.20%). The smallest particle sizes, which did not exceed 6 μm, characterized the powders obtained by mixing G/GA = 1:1. All powder samples were characterized by high cohesiveness and thus poor or very poor flow (CI = 30.58-50.27, HR = 1.45-2.01).

Glutaraldehyde-pea protein grafted polysaccharide matrices for functioning as covalent immobilizers

Three polysaccharide matrices (κ-Carrageenan (Carr), gellan gum, and agar) were grafted via glutaraldehyde (GA) and pea protein (PP). The grafted matrices covalently immobilized β-D-galactosidase (β-GL). Nonetheless, grafted Carr acquired the topmost amount of immobilized β-GL (iβ-GL). Thus, its grafting process was honed via Box-Behnken design and was further characterized via FTIR, EDX, and SEM. The optimal GA-PP-Carr grafting comprised processing Carr beads with 10% PP dispersion of pH 1 and 25% GA solution. The optimal GA-PP-Carr beads acquired 11.44 Ug^-1 iβ-GL with 45.49% immobilization efficiency. Both free and GA-PP-Carr iβ-GLs manifested their topmost activity at the selfsame temperature and pH. Nonetheless, the β-GL K_m and V_max values were reduced following immobilization. The GA-PP-Carr iβ-GL manifested good operational stability. Moreover, its storage stability was incremented where 91.74% activity was offered after 35 storage days. The GA-PP-Carr iβ-GL was utilized to degrade lactose in whey permeate with 81.90% lactose degradation efficiency.

Foaming properties are improved by interactions between brewer's spent grain proteins and carrageenans in aqueous solution

BACKGROUND

Foaming properties and macromolecular interactions in solution among brewer's spent grain proteins (CP) and iota and lambda carrageenans (i-CG and l-CG, respectively) as a function of aqueous medium pH (2-6) and protein-polysaccharide ratio, R_CP:CG (1:1, 2:1 and 4:1), were studied. At these conditions, the CP colloidal stability was favored by the formation of soluble electrostatic complexes with CG. Fluorescence (intrinsic and extrinsic) spectroscopy and dynamic light scattering techniques, including particle size and ζ-potential analysis, were applied to know the phase behavior of the biopolymer systems. The bubbling method was used to produce foams, and the foam expansion (%) and half-life time (t_1/2 ) were determined.

RESULTS

Both CG promoted an increased Trp fluorescence emission depending on the pH, suggesting conformational changes in CP. The CG in mixed systems produced a significant decrease in the extrinsic fluorescence intensity, mainly at low pH values, highlighting a reduction in CP surface hydrophobicity. At the examined pH range, the ζ-potential values for mixed-systems were negative, and their magnitudes were intermediate between CP and CG, revealing the associative electrostatic nature of biopolymer interactions, which were dependent on the R_CP:CG . The particle size analysis confirmed the formation of soluble electrostatic complexes in solution. Finally, using i-CG at pH 2 or 3 and 2:1 R_CP:CG , the best foaming properties for mixed systems were observed.

CONCLUSION

The formation of electrostatic complexes with a compact assembly among biopolymers, high negative net charge, and colloidal stability convert the CP-CG mixed solutions into promising biopolymer systems for food foams production. © 2022 Society of Chemical Industry.

Structure and Dynamics of Hybrid Colloid-Polyelectrolyte Coacervates

We develop a scaling theory for the structure and dynamics of "hybrid" complex coacervates formed from linear polyelectrolytes (PEs) and oppositely charged spherical colloids, such as globular proteins, solid nanoparticles, or spherical micelles of ionic surfactants. At low concentrations, in stoichiometric solutions, PEs adsorb at the colloids to form electrically neutral finite-size complexes. These clusters attract each other through bridging between the adsorbed PE layers. Above a threshold concentration, macroscopic phase separation sets in. The coacervate internal structure is defined by (i) the adsorption strength and (ii) the ratio of the resulting shell thickness to the colloid radius, H/R. A scaling diagram of different coacervate regimes is constructed in terms of the colloid charge and its radius for Θ and athermal solvents. For high charges of the colloids, the shell is thick, H ≫ R, and most of the volume of the coacervate is occupied by PEs, which determine its osmotic and rheological properties. The average density of hybrid coacervates exceeds that of their PE-PE counterparts and increases with nanoparticle charge, Q. At the same time, their osmotic moduli remain equal, and the surface tension of hybrid coacervates is lower, which is a consequence of the shell's inhomogeneous density decreasing with the distance from the colloid surface. When charge correlations are weak, hybrid coacervates remain liquid and follow Rouse/reptation dynamics with a Q-dependent viscosity, η _Rouse ∼ Q ^4/5 and η _rep ∼ Q ^28/15 for a Θ solvent. For an athermal solvent, these exponents are equal to 0.89 and 2.68, respectively. The diffusion coefficients of colloids are predicted to be strongly decreasing functions of their radius and charge. Our results on how Q affects the threshold coacervation concentration and colloidal dynamics in condensed phases are consistent with experimental observations for in vitro and in vivo studies of coacervation between supercationic green fluorescent proteins (GFPs) and RNA.

Microstructure, rheological and water mobility behaviour of plant-based protein isolates (pea and quinoa) and locust bean gum mixtures

This work reports the impact of locust bean gum (LBG) in the continuous phase of plant-based proteins, i.e. quinoa protein (QPI) and pea protein isolates (PPI). Experimental measurements such as confocal microscopy, rheological analysis and water mobility via nuclear magnetic resonance (nmr) spin-spin relaxation time (T2) were carried out. The influence of LBG on the rheological properties of QPI and PPI is consistent with an exchange-based nmr interpretation of T2 for biopolymer and water. Addition of LBG increased the viscoelastic properties (storage and loss modulus) and shear viscosities of the mixtures. LBG interacted with both plant proteins, resulting in the formation of more dense protein networks and protein coacervates. A stronger interaction between the PPI and LBG was observed, resulting in higher shear viscosities with lower water mobility as compared to QPI:LBG formulations. Results indicated that the interaction between the protein and polysaccharide played a significant role in the microstructure, its rheological properties and consequently water mobility.

Unaided efficient transglutaminase cross-linking of whey proteins strongly impacts the formation and structure of protein alginate particles

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Microbial transglutaminase (MTG) cross-linked >70% β-lactoglobulin (β-Lg) at pH 8.5.

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Initial MTG catalyzed isopeptide bond formation caused partial unfolding of β-Lg.

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>75% of whey protein cross-linked, forming hetero-polymers containing β-Lg.

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50% less alginate is needed to form particles with cross-linked than with native β-Lg.

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Cross-linked β-Lg and alginate formed suspendable hydrophobically driven particles.

There is a dogma within whey protein modification, which dictates the necessity of pretreatment to enzymatic cross-linking of β-lactoglobulin (β-Lg). Here microbial transglutaminase (MTG) cross-linked whey proteins and β-Lg effectively in 50 mM NaHCO₃, pH 8.5, without pretreatment. Cross-linked β-Lg spanned 18 to >240 kDa, where 6 of 9 glutamines reacted with 8 of 15 lysines. The initial isopeptide bond formation caused loss of β-Lg native structure with t_1/2 = 3 h, while the polymerization occurred with t_1/2 = 10 h. Further, cross-linking effects on protein carbohydrate interaction have been overlooked, leaving a gap in understanding of these complex food matrices. Complexation with alginate showed that β-Lg cross-linking decreased onset of particle formation, hydrodynamic diameter, stoichiometry (β-Lg/alginate) and dissociation constant. The complexation was favored at higher temperatures (40 °C), suggesting that hydrophobic interactions were important. Thus, β-Lg was cross-linked without pretreatment and the resulting polymers gave rise to altered complexation with alginate.

Complex coacervation of soy protein isolate-limited enzymatic hydrolysates and sodium alginate: Formation mechanism and its application

The complex coacervation of soybean protein isolate and polysaccharide has been widely applied for preparing biopolymer materials like microcapsule. In this study, hydrolytic soy protein isolate (HSPI) was prepared by mild hydrolysis of soy protein isolate (SPI) with fungal protease 400 (F400). The degree of hydrolysis (DH) for the enzymatic products was controlled at 1%-5%. Emulsification, oxidation resistance, and thermal stability were used to evaluate the performances of HSPI with different DH. The results showed that the HSPI with the hydrolysis degree of 2% had the optimal property. Subsequently, the complex polymer of HSPI/SA was prepared by the coalescence reaction of HSPI and sodium alginate (SA). The turbidity curves manifested the optimal complex coacervation occurred at the ratio of 7:1 (HSPI:SA). Fourier transform infrared spectroscopy (FTIR) presented that the reaction involved electrostatic interactions between -NH₃ ⁺ in HSPI and -COO^- in SA. Isothermal titration calorimetry experiments indicated that the complex coacervation reactions of HSPI and SA arose spontaneously. The microencapsulation by complex coacervation of HSPI and SA was further produced for embedding sweet orange oil. The thermogravimetric analysis (TGA) result revealed that the microencapsulation system of HSPI/SA had a better heat resistance than that using the SPI/SA complex polymer.

In situ exopolysaccharides from Lactobacillus helveticus MB2-1 in Sayram ketteki yoghurt: Set yoghurts properties and interactions with sodium caseinate

The effects of high exopolysaccharides (EPS) - producing Lactobacillus helveticus MB2-1 on the structure and storage stability of set yoghurts, and the interactions between its EPS (molecular weight 9.34 × 10⁴ Da) from Sayram ketteki yoghurt (SKY) and sodium caseinate (CAS) were studied. The rheology, microstructure, texture and storage stability of the three set yoghurts including control yoghurt (Control), adding-probiotic yoghurt (APY) and SKY were investigated, which showed that the SKY exhibited less shear thinning than the Control and APY, and the textural indexes and storage stability of the SKY were significantly better than that of other two yoghurts (p < 0.05). Moreover, the increased turbidity, decreased ζ potential and surface hydrophobicity of EPS/CAS complex coacervation were determined at EPS/CAS mass ratio of 3 (corresponding to 0.33 g/L of CAS and 1 g/L of EPS), mainly owing to the electrostatic attraction of the two biopolymers to form aggregates. Besides, the higher sizes and more aggregation of EPS/CAS complexes were formed at pH 3.5. Taken together, the results indicated that the high EPS-producing characteristic of L. helveticus MB2-1 could positively influence the qualities of set yoghurts, and the EPS/CAS complex coacervation in dairy products was closely related to the EPS/CAS mass ratio and pH condition.

Unraveling the phase behavior of cricket protein isolate and alginate in aqueous solution

The associative phase behavior of cricket protein isolate (CPI) and sodium alginate (AL) in aqueous solutions was explored using turbidimetry, methylene blue spectroscopy, zeta potentiometry, dynamic light scattering, and confocal microscopy as a function of pH, biopolymer ratio, total biopolymer concentration (C_T), and ionic strength. When both biopolymers had net-negative charges, soluble complexes formed between pH 6.0 and 8.0, however when both biopolymers had opposing net charges, insoluble complexes formed as complex coacervates below pH 5.5, defined as pH_φ1, followed by precipitates below another critical pH 3.0 (pH_p). Increasing the CPI:AL weight ratio or C_T facilitated complex formation, and the addition of salts (NaCl/KCl) had a salt-enhancement and salt-reduction impact at low and high salt concentrations, respectively. Ionic interactions between oppositely charged CPI and AL were mainly responsible for the formation of their insoluble complexes, while hydrogen bonding and hydrophobic interactions also played significant roles.

Production, Processing, and Protection of Microalgal n-3 PUFA-Rich Oil

Microalgae have been increasingly considered as a sustainable “biofactory” with huge potentials to fill up the current and future shortages of food and nutrition. They have become an economically and technologically viable solution to produce a great diversity of high-value bioactive compounds, including n-3 polyunsaturated fatty acids (PUFA). The n-3 PUFA, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), possess an array of biological activities and positively affect a number of diseases, including cardiovascular and neurodegenerative disorders. As such, the global market of n-3 PUFA has been increasing at a fast pace in the past two decades. Nowadays, the supply of n-3 PUFA is facing serious challenges as a result of global warming and maximal/over marine fisheries catches. Although increasing rapidly in recent years, aquaculture as an alternative source of n-3 PUFA appears insufficient to meet the fast increase in consumption and market demand. Therefore, the cultivation of microalgae stands out as a potential solution to meet the shortages of the n-3 PUFA market and provides unique fatty acids for the special groups of the population. This review focuses on the biosynthesis pathways and recombinant engineering approaches that can be used to enhance the production of n-3 PUFA, the impact of environmental conditions in heterotrophic cultivation on n-3 PUFA production, and the technologies that have been applied in the food industry to extract and purify oil in microalgae and protect n-3 PUFA from oxidation.

Complex Coacervation and Precipitation Between Soluble Pea Proteins and Apple Pectin

Complex formation (leading to either coacervation or precipitation) offers a tool to generate plant-based novel food structures and textures. This study investigated the formation of complexes between soluble pea proteins and apple pectin upon varying the protein-to-pectin ratio (r = 2:1 to 10:1), pH (3–7), and temperature (25 and 85 °C) with a total biopolymer concentration set to 1% (w/w). The results showed that predominantly soluble biopolymer complexes were formed at pH 5, and at low ratio (r = 2:1), whereas lowering the pH to more acidic condition, and to higher ratios (r = 4:1–10:1) induced the formation of more insoluble biopolymer complexes. In general, the mean particle sizes of the biopolymer complexes ranged between approximately 20 and 100 μm. Upon heating to 85 °C, the amount of insoluble biopolymer complexes increased at pH 3–5 at all ratios, except at r = 2:1. In addition, the complex sizes became somewhat larger at r = 2:1 to 6:1 upon heat treatment, whereas only trivial size changes were observed at higher ratios (r = 8:1 to 10:1). Overall, electrostatic and hydrophobic interactions played a major role in the complex formation between the soluble pea proteins and apple pectin. These findings are important for designing solely plant-based food structures.

Thermodynamic compatibility of gelatin and tragacanth gum in aqueous systems

The influence of total concentration, biopolymer mixing ratio, and ionic strength on the association of tragacanth gum (TG) and gelatin (G) in the aqueous system during acidification was investigated. The onset of soluble complex formation appeared at pH_c, where both biopolymers carried a negative charge. Insoluble complexes were formed at pH_φ1 by a further pH decrease, owing to increased interactions between the polymers. The complexes formed at pH_φ1 still had partly high negative surface charge. Complex coacervation was observed at pH_opt due to the growing size and number of insoluble complexes. The ζ value of the G- TG significantly decreased at pH_opt, which was subjected to phase separation. Turbidity decreased at pH_φ2 as a result of complex decomposition. The maximum efficiency of complex formation was at the salt-free samples. NaCl reduced critical pHs and complex formation efficiency by screening the ionized groups on the biopolymers.

Modulating Role of Co-Solutes in Complexation between Bovine Serum Albumin and Sodium Polystyrene Sulfonate

The action of three types of co-solutes: (i) salts (NaCl, NaBr, NaI), (ii) polymer (polyethylene glycol; PEG-400, PEG-3000, PEG-20000), and (iii) sugars (sucrose, sucralose) on the complexation between bovine serum albumin (BSA) and sodium polystyrene sulfonate (NaPSS) was studied. Three critical pH parameters were extracted from the pH dependence of the solution’s turbidity: pHc corresponding to the formation of the soluble complexes, pHΦ corresponding to the formation of the insoluble complexes, and pHopt corresponding to the charge neutralization of the complexes. In the presence of salts, the formation of soluble and insoluble complexes as well as the charge neutralization of complexes was hindered, which is a consequence of the electrostatic screening of attractive interactions between BSA and NaPSS. Distinct anion-specific trends were observed in which the stabilizing effect of the salt increased in the order: NaCl < NaBr < NaI. The presence of PEG, regardless of its molecular weight, showed no measurable effect on the formation of soluble complexes. PEG-400 and PEG-3000 showed no effect on the formation of insoluble complexes, but PEG-20000 in high concentrations promoted their formation due to the molecular crowding effect. The presence of sugar molecules had little effect on BSA-NaPSS complexation. Sucralose showed a minor stabilizing effect with respect to the onset of complex formation, which was due to its propensity to the protein surface. This was confirmed by the fluorescence quenching assay (Stern-Volmer relationship) and all-atom MD simulations. This study highlights that when evaluating the modulatory effect of co-solutes on protein-polyelectrolyte interactions, (co-solute)-protein interactions and their subsequent impact on protein aggregation must also be considered.

Plant protein-based fibers: Fabrication, characterization, and potential food applications

Proteins from plants have been considered as safer, healthier, and more sustainable resources than their animal counterparts. However, incomplete amino acid composition and relatively poor functionality limit their applications in foods. Structuring plant proteins to fibrous architectures enhances their physicochemical properties, which can favor various food applications. This review primarily focuses on fabrication of fibers from plant proteins via self-assembly, electrospinning, solution blow spinning, wet spinning, and high-temperature shear, as well as on several applications where such fibrous proteins assemble in quality foods. The changes of protein structure and protein-protein interactions during fiber production are discussed in detail, along with the effects of fabrication conditions and protein sources on the morphology and function of the fibers. Self-assembly requires proteolysis and subsequent peptide aggregation under specific conditions, which can be influenced by pH, salt and protein type. The spinning strategy is more scalable and produces uniformed fibers with larger length scales suitable for encapsulation, food packaging and sensor substrates. Significant progress has been made on high-temperature shear (including extrusion)-induced fibers responsible for desirable texture in meat analogues. Structuring plant proteins adds values for broadened food applications, but it remains challenging to keep processes cost-effective and environmentally friendly using food grade solvents.

Effect of pH and Pea Protein: Xanthan Gum Ratio on Emulsions with High Oil Content and High Internal Phase Emulsion Formation

Electrostatic interaction between protein and polysaccharides could influence structured liquid oil stability when emulsification is used for this purpose. The objective of this work was to structure sunflower oil forming emulsions and High Internal Phase Emulsions (HIPEs) using pea protein (PP) and xanthan gum (XG) as a stabilizer, promoting or not their electrostatic attraction. The 60/40 oil-in-water emulsions were made varying the pH (3, 5, and 7) and PP:XG ratio (4:1, 8:1, and 12:1). To form HIPEs, samples were oven-dried and homogenized. The higher the pH, the smaller the droplet size (Emulsions: 15.60-43.96 µm and HIPEs: 8.74-20.38 µm) and the oil release after 9 weeks of storage at 5 °C and 25 °C (oil loss < 8%). All systems had weak gel-like behavior, however, the values of viscoelastic properties (G' and G″) increased with the increment of PP:XG ratio. Stable emulsions were obtained at pHs 5 and 7 in all PP:XG ratios, and at pH 3 in the ratio 4:1. Stable HIPEs were obtained at pH 7 in the ratios PP:XG 4:1, 8:1, and 12:1, and at pH 5 at PP:XG ratio 4:1. All these systems presented different characteristics that could be exploited for their application as fat substitutes.

Interactions of the molecular assembly of polysaccharide-protein systems as encapsulation materials. A review

Studying the interactions of biopolymers like polysaccharides and proteins is quite important mainly due to the wide number of applications such as the stabilization and encapsulation of active compounds in complex systems. Complexation takes place when materials like proteins and polysaccharides are blended to promote the entrapment of active compounds. The interaction forces between the charged groups in the polymeric chains allow the miscibility of the components in the complex system. Understanding the interactions taking place between the polymers as well as between the wall material and the active compound is important when designing delivery systems. However, some features of the biopolymers like structure, functional groups, or electrical charge as well as extrinsic parameters like pH or ratios might affect the structure and the performance of the complex system when used in encapsulation applications. This work summarizes the recent progress of the polysaccharide/protein complexes for encapsulation and the influence of the pH on the structural modifications during the complexation process.

Effects of Salts on Structural, Physicochemical and Rheological Properties of Low-Methoxyl Pectin/Sodium Caseinate Complex

The addition of salts is an effective way to improve the properties of polysaccharide/protein complexes for use in foods. However, there is no comparative study on the effects of different ions on the complex system of low methoxyl pectin (LMP)/ sodium caseinate (CAS) complex. The effects of different concentrations of three salt ions (Na⁺, K⁺, Ca²⁺) on the physicochemical and rheological properties of the LMP/CAS complex were determined in this study, and the structure of LMP/CAS complex was characterized. The results showed that the addition of these three salt ions affected zeta potential, particle size, and turbidity of the LMP/CAS complex, and lead the LMP/CAS complex to form a more regular and uniform network structure, which helped improve its stability, solubility, and rheological properties. The particle size and turbidity value of the complex achieved with Ca²⁺ were higher than those obtained using Na⁺ and K⁺. Moreover, the secondary structure of the proteins in the complex changed to adding high concentrations of Ca²⁺. Our study provides valuable information for the application of the LMP/CAS complex in the food industry.

Antidiabetic activities of glycoprotein from pea (Pisum sativum L.) in STZ-induced diabetic mice

Polysaccharides have hypoglycemic activity and pea protein has high nutritional value. The purified pea glycoprotein PGP2 has been shown to inhibit the activity of α-glucosidase and α-amylase in previous studies. To study the mechanism of PGP2-induced blood glucose lowering in vivo, this paper established a diabetic mouse model by intraperitoneal injection of STZ and high-fat diet, and evaluated the blood-glucose-lowering activity of the pea component PGP2 at different doses. The results showed that intragastric administration of PGP2 could effectively reduce diabetic weight loss and polyphagia symptoms, reduce fasting blood glucose levels in mice, and improve oral glucose tolerance levels in mice. PGP2 could promote insulin secretion and had a protective effect on mouse organs. After intragastric administration of PGP2 in mice, the serum levels of total cholesterol, triglycerides and low-density lipoprotein decreased. PGP2 up-regulated the gene expression of insulin receptor substrates IRS-1 and IRS-2 in liver tissues, thereby reducing insulin resistance. Based on the above experimental results, PGP2 had good hypoglycemic activity and was expected to be developed as a natural medicine for the treatment of type II diabetes.

Effect of heat treatment on the structure and stability of Grass pea (Lathyrus sativus) protein isolate/Alyssum homolocarpum seed gum nanoparticles

In the present study, Grass pea protein isolate (GPPI)- Alyssum homolocarpum seed gum (AHSG) complex nanoparticles were formed through two fabrication methods and their physicochemical properties, structure and stability against sodium chloride and different pHs were investigated. Type 1 particles were formed by creating GPPI nanoparticles, and then coating them with AHSG; while Type 2 particles were fabricated through the heat treatment of GPPI-AHSG complexes at 85 °C for 15 min. The preparation methods did not influence the magnitude of electrical charges on biopolymer particles. The particle size analysis revealed that Type 2 particles had lower mean diameter (d = 360.20 nm) compared to Type 1 particles (d = 463.22 nm). Structural properties of Type 1 and Type 2 particles were determined using Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD), Differential scanning calorimetry (DSC), Atomic force microscopy (AFM), and transmission electron microscopy (TEM). Hydrogen bonding, electrostatic and hydrophobic interactions were the main driving forces contributed to the formation of both GPPI-AHSG complex particles. Assessments of morphological and structural properties also indicated that both Type 1 and 2 particles had spherical shapes and heat treatment increased the ordered intermolecular structures in biopolymer particles. Type 2 particles had higher denaturation temperature and better pH and salt stability when compared to Type 1 particles. These results indicate that thermal treatment was effective for the fabrication of stable GPPI-AHSG complex nanoparticles.

Complex coacervation of pea albumin-pectin and ovalbumin-pectin assessed by isothermal titration calorimeter and turbidimetry

BACKGROUND

This study investigates the complexation of a pea albumin-rich fraction and ovalbumin with pectin of different degrees of esterification (DE) and blockiness (DB) as a function of pH and biopolymer mixing ratio by turbidimetric titration and isothermal titration calorimetry (ITC).

RESULTS

Turbidimetric analysis found maximum complexation occurred at a mixing ratio of 4:1 for pea albumin with high methoxy pectin, 8:1 for pea albumin with low methoxy pectin, and 8:1 for ovalbumin with low methoxy pectin. In the case of ovalbumin with high methoxy pectin, interactions were very weak. The pectin with high levels of esterification and blockiness displayed greater interactions with the pea albumin in both turbidimetry and ITC. However, low methoxy pectin imparted better interactions with ovalbumin and displayed higher optical density values than high methoxy pectin.

CONCLUSIONS

The current study indicated that the different thermodynamic parameters of PA-pectin complexes can be tuned by controlling the structural characteristics (DB, DE, and d-galacturonic acid) of the pectin. © 2020 Society of Chemical Industry.

Impact of Alginate Mannuronic-Guluronic Acid Contents and pH on Protein Binding Capacity and Complex Size

Alginates, serving as hydrocolloids in the food and pharma industries, form particles at pH < 4.5 with positively charged proteins, such as β-lactoglobulin (β-Lg). Alginates are linear anionic polysaccharides composed of 1,4-linked β-d-mannuronate (M) and α-l-guluronate (G) residues. The impact of M and G contents and pH is investigated to correlate with the formation and size of β-Lg alginate complexes under relevant ionic strength. It is concluded, using three alginates of M/G ratios 0.6, 1.1, and 1.8 and similar molecular mass, that β-Lg binding capacity is higher at pH 4.0 than at pH 2.65 and for high M content. By contrast, the largest particles are obtained at pH 2.65 and with high G content. At pH 4.0 and 2.65, the stoichiometry was 28-48 and 3-10 β-Lg molecules bound per alginate, respectively, increasing with higher M content. The findings will contribute to the design of formation of the desired alginate-protein particles in the acidic pH range.

Effect of sodium chloride on the thermodynamic, rheological, and microstructural properties of field pea protein isolate/chitosan complex coacervates

The effect of increasing sodium chloride concentration (c_NaCl, 0-0.4 M) on the formation and rheological and microstructural properties of field pea protein isolate (FPPI)/chitosan (Ch) complex coacervates was investigated. The maximum turbidity and zeta potential of FPPI/Ch mixtures consistently decreased with the increasing c_NaCl. The tertiary conformation of FPPI was altered to facilitate the aggregation of FPPI/Ch complexes via hydrophobic interactions. Changes in thermodynamic parameters during the titration of FPPI with Ch confirmed the addition of NaCl could cause the inhibition of electrostatic complexation and the induction of non-Coulombic interactions. FPPI/Ch complex coacervates exhibited first enhanced and then weakened viscoelastic properties and an initially tightened and then a loosened microstructure as the c_NaCl increased. In summary, appropriate c_NaCl favors the formation of FPPI/Ch complex coacervates with improved functionalities via the coordination of promoted hydrophobic interactions and inhibited electrostatic attractions, facilitating the application of this protein ingredient in food development.

The interaction between sodium alginate and myofibrillar proteins: The rheological and emulsifying properties of their mixture

The interaction between sodium alginate (SA) and turbot myofibrillar proteins (TMP) and the effects of SA concentration (0.1%-0.5%) on the rheological and emulsifying properties of the mixture at neutral pH were investigated. TMP and SA formed complexes through electrostatic repulsion and hydrophobic interaction. The FT-IR analysis indicated that hydrogen bonding was also related to the interaction. With the addition of SA, the electrostatic repulsion between molecules enhanced, which prevented protein aggregation and improved the stability of dispersions. The TMP/SA mixture showed non-Newtonian shear-thinning behavior. The viscosity gradually increased with the increasing SA concentration. TMP and SA formed an interconnected gel-like network structure with a predominant elastic behavior. The strength of network increased due to the strong repulsion between the two biopolymers. Both EAI and ESI of TMP significantly increased after SA addition. The addition of SA reduced droplet size of emulsions. The emulsions also showed pseudoplastic behavior. Addition of SA increased stability of emulsions by increasing viscosity of continuous phase. Complexation with SA effectively improved the rheological and emulsifying properties of fish myofibrillar proteins. These results contributed to the efficient utilization of marine fish proteins as functional ingredients in food products.

Addition of Selected Plant-Derived Proteins as Modifiers of Inulin Hydrogels Properties

The aim of the study was to determine the effects of pea and soy protein addition (1, 3, 6 g/100 g) on inulin hydrogels properties. Inulin hydrogels (20 g/100 g) were obtained by thermal induction. It was stated that tested plant protein might be used as a modifier of inulin hydrogels properties. The addition of pea and soy protein to inulin hydrogels resulted in networks with more a compact and homogeneous structure. The increase of the protein concentration caused the structure of the hydrogels to get smoother, more cohesive, and less granular. Pea and soy protein addition (3-6 g/100 g) to hydrogels allowed to obtain higher values of yield stress, texture (firmness, adhesiveness) and spreadability parameters. At a protein concentration of 6 g/100 g, the firmness of inulin hydrogels was seven times higher for those with pea protein (1.87 N) and ten times higher for those with soy protein (2.60 N) compering to the control hydrogel (0.24 N). The transmission profiles of hydrogels with incorporated 6 g/100 g of soy proteins showed the slowest motion of the particles, which indicates the highest stability of gel. As the concentration of protein addition increased, a reduction in the lightness was observed.

Binary Solutions of Hyaluronan and Lactose-Modified Chitosan: The Influence of Experimental Variables in Assembling Complex Coacervates

A miscibility study between oppositely charged polyelectrolytes, namely hyaluronic acid and a lactose-modified chitosan, is here reported. Experimental variables such as polymers' weight ratios, pH values, ionic strengths and hyaluronic acid molecular weights were considered. Transmittance analyses demonstrated the mutual solubility of the two biopolymers at a neutral pH. The onset of the liquid-liquid phase separation due to electrostatic interactions between the two polymers was detected at pH 4.5, and it was found to be affected by the overall ionic strength, the modality of mixing and the polymers' weight ratio. Thorough Dynamic Light Scattering (DLS) measurements were performed to check the quality of the formed coacervates by investigating their dimensions, homogeneity and surface charge. The whole DLS results highlighted the influence of the hyaluronic acid molecular weight in affecting coacervates' dispersity and size.

Development of high methoxyl pectin-surfactant-pea protein isolate ternary complexes: Fabrication, characterization and delivery of resveratrol

The purpose of this study was to fabricate ternary complexes composed of pea protein isolate (PPI), high methoxyl pectin (HMP) and individual surfactants including rhamnolipid (Rha), tea saponin (TS) and Ethyl lauroyl arginate (LAE), for the delivery of resveratrol (Res). A combination of electrostatic attraction and hydrophobic interaction was dominantly responsible for the formation of HMP-surfactant-PPI complexes. The physicochemical properties of the ternary complexes were affected by surfactant types as well as mass ratios of individual surfactant to PPI. HMP-Rha-PPI_1:1, HMP-TS-PPI_1:1 and HMP-LAE-PPI_1:25 complexes had higher denaturation temperatures of 82.78 ± 0.31, 80.21 ± 0.02 and 79.98 ± 0.86 ℃, respectively. The HMP-Rha-PPI_1:1 ternary complex could be an effective delivery system, which were effective to retard photo- and thermal- degradation of Res as well as delayed the release of Res in in vitro digestion.