Associative phase separation involving canola protein isolate with both sulphated and carboxylated polysaccharides

Covalent modulation of zein surface potential by gallic acid to enhance the formation of electrostatic-driven ternary antioxidant complex coacervates with chitosan

Despite existing research on the interaction between zein (Z) and chitosan (CS), the formation and mechanisms of ternary electrostatic coacervates incorporating polyphenols remain unclear. Herein, we covalently and non-covalently modified zein with gallic acid (GA). Comparisons revealed that the covalent coupling of Z with GA (forming Z(GA)) reduced zein's surface potential, enabling them to form tightly bound coacervates with cationic polysaccharide chitosan through electrostatic attraction. Turbidity, ζ-potential, and appearance experiments indicated that the maximum yield of insoluble coacervates was achieved at a Z(GA)/CS mass ratio of 7:1 and pH 6.5. Furthermore, the coacervate properties were evaluated using Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and microscopic structure analysis. Electrostatic attraction between the -COO- groups of Z(GA) and the -NH3+ groups of CS triggered complex coacervation, which induced structural modifications and enhanced thermal stability. This study fosters the efficient encapsulation and controlled release of nutraceuticals, enhancing human absorption.

Phase behavior and interaction of strong polyelectrolyte dextran sulfate and whey protein isolation: Effects of pH, protein/polysaccharide ratio, and salt addition

The strong polyelectrolyte dextran sulfate (DS) is an anionic polysaccharide with a high negative charge, characterized by high stability and pH independence. DS and whey protein isolate (WPI) were selected to study the specific effects of highly negatively charged polysaccharides on the phase behavior and interaction of WPI/DS complexes (1 % w/v) under varying external conditions (pH, WPI:DS ratio, and salt addition). The phase diagrams, zeta potential, and laser confocal scanning microscopy measurements indicated that the WPI/DS complexes did not dissociate even at pH 1 due to the pH independence of DS. The exclusion volume effect of DS promoted WPI self-aggregation at high salt concentrations, which inhibited acidification-induced dissociation. Isothermal titration calorimetry indicated that the WPI/DS interaction is a spontaneous exothermic reaction driven by both enthalpy and entropy changes due to electrostatic interactions. This study provides valuable information on the interactions between highly negatively charged polysaccharides and proteins.

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.

The properties and formation mechanism of ovalbumin-fucoidan complex

The polymeric materials formed by proteins and polysaccharides through molecular interactions have attracted public attention. In this study, a novel binary complex consisting of ovalbumin (OVA) and fucoidan (FUC) was obtained by electrostatic self-assembly. The self-assembly properties and the formation mechanism of the OVA-FUC binary complex were investigated by changing the charging degree and density of complex through altering pH value and polysaccharides proportion. Structural changes during the OVA-FUC electrostatic self-assembly process were investigated by a phase diagram, ζ-potential, and particle size. The optimal conditions for preparing soluble OVA-FUC binary complex were determined by the protein retention rate and insoluble solids content. Results showed that the soluble OVA-FUC binary complex could be obtained at the pH of 3.5 to 5, and the insoluble OVA-FUC binary complex was generated at the pH of 2.5 to 3.5. The OVA-FUC binary complex (19 ± 0.29 mN/m) possessed a medium ability to reduce interfacial tension of the water-oil interface compared with OVA (15 ± 1.13 mN/m) and FUC (24 ± 0.3 mN/m), indicating that OVA-FUC binary complex has good amphiphilicity and can be applied as a potential pH-controlled emulsifier in function food systems for delivering bioactive substances.

Utilization of two plant polysaccharides to improve fresh goat milk cheese: Texture, rheological properties, and microstructure characterization

This study aimed to evaluate the effects of added jujube polysaccharide (JP) and Lycium barbarum polysaccharide (LBP) on the texture, rheological properties, and microstructure of goat milk cheese. Seven groups of fresh goat milk cheese were produced with 4 levels (0, 0.2, 0.6, and 1%, wt/wt) of JP and LBP. The goat milk cheese containing 1% JP showed the highest water-holding capacity, hardness, and the strongest rheological properties by creating a denser and more stable casein network structure. In addition, the yield of goat milk cheese was substantially improved as a result of JP incorporation. Cheeses containing LBP expressed lower fat content, higher moisture, and softer texture compared with the control cheese. Fourier-transform infrared spectroscopy and low-field nuclear magnetic resonance analysis demonstrated that the addition of JP improved the stability of the secondary protein structure in cheese and significantly enhanced the binding capacity of the casein matrix to water molecules due to strengthened intermolecular interactions. The current research demonstrated the potential feasibility of modifying the texture of goat milk cheese by JP or LBP, available for developing tunable goat milk cheese to satisfy consumer preferences and production needs.

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.

Preparation of Oxidized Starch/β-Lactoglobulin Complex Particles Using Microfluidic Chip for the Stabilization of Astaxanthin Emulsion

Here, we designed an oxidized starch/β-lactoglobulin (OS/β-lg) complex colloidal particle using a dual-channel microfluidic chip for the stabilization of astaxanthin emulsion. The effect of the mixing ratio, pH, and the degree of substitution (DS) of the oxidized starch on the formation of OS/β-lg complex particles was investigated in detail. The optimal complexation occurred at a pH of 3.6, a mixing ratio of 2:10, and a DS of 0.72%, giving an ideal colloidal particle with near-neutral wettability. With this optimum agent, the astaxanthin-loaded oil-in-water emulsions were successfully prepared. The obtained emulsions showed the typical non-Newton fluid behavior, and the rheological data met the Herschel-Bulkley model. The microscopic images confirmed the dense adsorption of the particle on the oil/water interface. In vitro release and stability studies demonstrated this compact layer contributed to the controlled-release and excellent stability of astaxanthin emulsions facing heat, ultraviolet, and oxidative intervention. This work suggests the potential of microfluidics for the production of food-grade solid emulsifiers.

A Study on the Mechanisms of Nanoparticle-Stabilized High Internal Phase Emulsions Constructed by Cross-Linking Egg White Protein Isolate with Different Transglutaminase Concentrations

There is an increasing interest in the development of high internal phase emulsions (HIPE) stabilized by food-grade nanoparticles due to their potential applications in the food industry. In this study, cross-linked egg white protein isolates (cEPIs) are prepared by adding 10 u/g, 20 u/g, and 40 u/g of transglutaminase (TG), and the impacts of interface properties of cEPIs and emulsifying of HIPEs are investigated. Relative to the native EPI, the cEPIs have more irregular and agglomerated morphology, and the turbidity and hydrophobicity are significantly increased. The particle size and zeta potential of cEPIs considerably varied with the addition of TG. In HIPE, the formation, physical properties, and microstructure are characterized by visual observations, the Turbiscan stability index, and CLSM. The results indicated that stable and gel-like HIPEs are formed by cEPIs at oil internal phase (φ) values of 0.75–0.90. Especially for the enzyme additions of 20 u/g, the cEPIs had the best storage stability and the lowest TSI value (2.50) and formed a gel network structure at φ values of 0.9 microscopically. Overall, this study can enrich the theoretical frame of interface properties by enzyme treatment. Besides, it would be of great importance for the research of HIPE stabilized by cEPIs appropriate to be applied in food formulations.

Complex coacervate formation between hemp protein isolate and gum Arabic: Formulation and characterization

In this study, intermolecular interactions and structure formation between hemp protein isolate (HPI) and gum Arabic (GA) were investigated to unravel their complexation mechanisms. For this purpose, structural transition as a function of pH (2.0-7.0) and protein to polysaccharide ratio (HPI:GA, R = 0.5:1-13:1 w/w) was evaluated via turbidimetric analysis, ζ-potentiometry, state diagram construction and coacervate yield. It was proved that critical phase transition pH shifted to higher values with R increase, until reaching a plateau at ratio 10:1, with complexes to be formed even at pH region where both biopolymers were negatively charged. The shift of pH value, where maximum turbidity was noticed (pH_opt), was well in accordance with net charge neutrality of HPI-GA mixtures found by electrophoretic mobility measurements. Maximum coacervation, occurred at ratio R = 2:1 and pH_opt = 3.5, was depicted by the highest yield (92%), while morphological characteristics of liquid as well as freeze-dried HPI-GA coacervates, obtained through optical and scanning electron microscope measurements, gave a further perception of the associative processes during complex coacervation. Additionally, the molecular interactions between HPI and GA were confirmed by Fourier transform infrared spectroscopy (FTIR) revealing primarily electrostatic interactions with secondary stabilization of hydrogen bonds. Therefore, these findings could provide useful information for the development of HPI - GA coacervates as a potential bioactive encapsulation means.

Effect of linear charge density of polysaccharides on interactions with α-amylase: Self-Assembling behavior and application in enzyme immobilization

The co-existence of polysaccharides and enzymes in the food matrix could form complexes that directly influence the catalytic efficacy of enzymes. This work investigated the self-assembly behaviors of α-amylase and charged polysaccharides and fabricated the α-amylase/polysaccharides complex coacervates. The results showed that the linear charge density of polysaccharides had a critical impact on the complex formation, structure, and enzyme protection under acidic conditions. At low pH, α-amylase formed compact and tight coacervates with the λ-carrageenan. However, α-amylase/pectin coacervates dissociated when the pH was lower than 3.0. The optimized binding ratio of α-amylase/λ-carrageenan was 12:1, and α-amylase/pectin was 4:1. Finally, the α-amylase/λ-carrageenan complex coacervates effectively immobilized the enzyme and almost 70% of enzyme activity remained in coacervates after exposure to pH3.0 for 1 h. This study demonstrates that the change in the linear charge density of polysaccharides could regulate the enzyme-catalyzed process in food processing by a simple and fine-controlled method.

Composition, physicochemical properties of pea protein and its application in functional foods

Field pea is one of the most important leguminous crops over the world. Pea protein is a relatively new type of plant proteins and has been used as a functional ingredient in global food industry. Pea protein includes four major classes (globulin, albumin, prolamin, and glutelin), in which globulin and albumin are major storage proteins in pea seeds. Globulin is soluble in salt solutions and can be further classified into legumin and vicilin. Albumin is soluble in water and regarded as metabolic and enzymatic proteins with cytosolic functions. Pea protein has a well-balanced amino acid profile with high level of lysine. The composition and structure of pea protein, as well as the processing conditions, significantly affect its physical and chemical properties, such as hydration, rheological characteristics, and surface characteristics. With its availability, low cost, nutritional values and health benefits, pea protein can be used as a novel and effective alternative to substitute for soybean or animal proteins in functional food applications.

Extraction of orange pectin based on the interaction between sodium caseinate and pectin

The interaction between commercial orange pectin (COP) and sodium caseinate (SC) was studied using FTIR, fluorescence spectroscopy, CD, and LSCM. The effect of different conditions on the formation and separation of COP-SC complex was determined. The extraction of the orange pectin using SC precipitation (SCOP) was performed, and the physicochemical properties of SCOP were determined and compared with the orange pectin extracted by alcohol precipitation (APOP). The results showed that the electrostatic interaction was the main interaction between these two polymers, and it was strongly dependent on pH, COP/SC ratio, and salt concentration. The mixture of COP and SC formed an electrostatic complex in the pH range of 1.5-6.8 with the absence of NaCl. The recovery rate of SCOP and precipitation rate of SC were 89.43% and 98.33% when the ratio was 1:15. The physicochemical properties of SCOP were almost the same as APOP.

Review on plant protein-polysaccharide complex coacervation, and the functionality and applicability of formed complexes

Controlling the interactions between plant proteins and polysaccharides can lead to the development of novel electrostatic complexed structures that can give unique functionality. This in turn can broaden the diversity of applications that they may be suitable for. Overwhelmingly in the literature, work and reviews relating to coacervation have involved the use of animal proteins. However, with the increasing demand for plant-based protein alternatives by industry and consumers, a greater understanding of how they interact with polysaccharides is essential to control structure, functionality and applicability. This review discusses the factors governing the nature of protein-polysaccharide interactions, their functional attributes and industrial applications, with special attention given to plant proteins. © 2018 Society of Chemical Industry.

Effect of the degree of esterification and blockiness on the complex coacervation of pea protein isolate and commercial pectic polysaccharides

The complex coacervation of pea protein isolate (PPI) with commercial pectic polysaccharides [high methoxy citrus pectin (P90, 90 representing DE), apple pectin (P78) sugar beet pectin (P62), low methoxy citrus pectin (P29)] of different degrees of esterification (DE) [and galacturonic acid content (GalA)] and blockiness (DB), was investigated. The maximum amount of coacervates formed at a biopolymer weight mixing ratio of 4:1 for all PPI-pectin mixtures, with the exception of PPI-P29 where maximum coacervation occurred at the 10:1 mixing ratio. The pH at which maximum interactions occurred was pH 3.4-3.5 (PPI: P90/P78) and 3.7-3.8 (PPI: P62/P29). PPI complexed with pectins with high levels of DE (low levels of GalA) and DB displayed greater interactions at optimal mixing conditions compared to pectin having lower levels of esterification and blockiness. The addition of P78 to PPI greatly increased protein solubility at pH 4.5.

Heteroprotein complex coacervates of ovalbumin and lysozyme: Formation and thermodynamic characterization

The formation of heteroprotein coacervates obtained by the interaction of ovalbumin (Ova) and lysozyme (Lys) was investigated using turbidimetric analysis and the zeta potential at different protein ratios, pH values and concentrations of NaCl. The complexes were formed over a wide pH range with a 1:1 (Ova:Lys) ratio and the highest turbidity was observed at pH 7.5, which optimal biopolymer interactions occurring. The addition of NaCl disfavored formation, even at low concentrations, and suppressed it at 300mM. The complex coacervate formation occurred in the region between the isoelectric points (pI) of the proteins, predominantly by electrostatic interactions but with participation of hydrogen bonds. The structures formed had an average size of ∼2μm, which was well above the isolated proteins, and microscopic analysis revealed that the complexes had a globular structure. The interaction was exothermic and spontaneous with a favorable entropic and unfavorable entropic contribution during interaction.

Deciphering the interactions of fish gelatine and hyaluronic acid in aqueous solutions

The interactions of fish gelatine (FG) with hyaluronic acid (HA) are studied in an aqueous environment at 25°C by turbidimetric titration, confocal scanning laser microscopy, dynamic light scattering, zeta potentiometry, spectrophotometry with methylene blue, and construction of state diagrams. FG forms soluble complexes with HA above a boundary pH (pH_φ1), where both biopolymers are net-negatively charged, but develop insoluble complexes as liquid-state complex coacervates below pH_φ1, where the two biopolymers are oppositely charged. The insoluble complexes are continuously aggregated with further acid titration, followed by immediate visible phase-separation when another boundary pH (pH_p) is reached. The complex formation is mainly driven by electrostatic attractions rather than hydrogen bonding or hydrophobic interactions. The complex formation is promoted by increasing FG-to-HA weight ratio or total biopolymer concentration, or at a low ionic strength, but significantly suppressed in the presence of high ionic strength.

Nature of protein-protein interactions during the gelation of canola protein isolate networks

The nature of interactions involved during the gelation of a canola protein isolate was investigated using rheology and fractal imaging at neutral pH as a function of protein concentration (5.0-9.0% w/w). The onset of denaturation and the denaturation temperature by differential scanning calorimetry for canola protein isolate (CPI; 98.2% protein) was 78.6°C and 87.1°C, respectively. Rheological testing determined the gelation temperature (T_gel) to be ~87-90°C for all concentrations. The log % strain at break increased from 1.70 to 1.80 as CPI concentration increased from 5.0 to 7.0% (w/w). Rheological testing of CPI in the presence of destabilizing agents, NaCl (0.1 and 0.5M), urea (0.1, 0.5, 1 and 5M) and 2-β-mercaptoethanol (0.1 and 2%), was performed. Samples with NaCl and urea (0.1-1M) had similar temperature profiles and T_gel values to CPI alone whereas no gel was formed with the addition of 5M urea and 2-β-mercaptoethanol reduced the strength of the gel network. Fractal dimension and lacunarity was analyzed using CLSM imaging. The fractal dimension value for all CPI concentrations was ~1.5. The lacunarity of the gel decreased from 0.62 to 0.41 as the concentration of CPI increased from 5 to 7% (w/w). Mechanistic understanding of CPI aggregation and network formation will enable the food industry to better tailor food structure when CPI is present as ingredient.