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

Effects of soy protein isolate interaction with brown rice starch on the multiscale structure of brown rice bread

BACKGROUND

Gluten-free bread (GFB) has technical bottlenecks such as hard texture, rough taste and low nutrition in practical production. In order to solve these problems, this study used germinated brown rice starch as the main raw material, and investigated the effects of soybean isolate protein (SPI) on the multiscale structure of germinated brown rice starch and bread quality.

RESULTS

A gluten-free rice bread process simulation system was established, and the interaction between SPI and starch in the simulation system was characterized. The result shows that the interaction forces between SPI and germinated brown rice starch were mainly represented by hydrogen bonds, and with the addition of SPI, the crystallinity of starch showed a downward trend. At the same time, when the amount of SPI was 3%, the appearance quality was the best and the specific volume of bread was 1.08 mL g-1. When the amount of SPI was 6%, the texture quality was the best. Compared with the bread without SPI, the hardness of the bread with 6% SPI was reduced by 0.13 times, the springiness was increased by 0.03 times, the color was the most vibrant, the L* value being 1.02 times the original, and the baking loss was reduced to 0.98 times the original.

CONCLUSIONS

The interaction force between SPI and germinated brown rice starch and its effect on bread quality were clarified, and these results inform choices about providing a theoretical basis for the subsequent development of higher-quality GFB. © 2024 Society of Chemical Industry.

Effect of chitosan molecular weight and protein to polysaccharide ratio on the rheological and physicochemical properties of milk proteins-chitosan complex coacervate

The small amplitude oscillatory shear (SAOS) rheological properties of complex coacervate of milk proteins with high (HMC), medium (MMC), and low (LMC) molecular weight chitosan in the optimal ratios of milk proteins to chitosan (15:1, 10:1, and 5:1, respectively) were measured. In addition, the morphological (SEM), structural (XRD), and thermal (DSC) properties of the complex coacervates were investigated in comparison with the milk protein concentrate. Complex coacervates showed the shear-thinning behavior due to a linear decrease of complex viscosity with increasing frequency. Furthermore, the highest complex modulus and the more compact structure under optimal conditions, in terms of the ratio of protein to chitosan and pH, revealed strong electrostatic bonding between proteins and chitosan. All coacervates showed a G' > G″ (Tanδ<1), indicating the formation of an interconnected gel-like structure that was described by the power law model. The maximum fracture stress was obtained at optimum conditions (R = 15:1, pH =6.7 for HMC; R = 10:1, pH =5.5 for MMC and R = 5:1, pH =4.6 for LMC), indicating the highest intermolecular interaction between milk proteins and chitosan. The coacervates had a completely amorphous structure similar to MPC, and according to DSC results, the ionic bonds between milk proteins and chitosan were not destroyed up to 300 °C. Coacervation leads to purified milk proteins at a low cost. In addition, the coacervates can be used for the encapsulation of heat-sensitive compounds, and also as a stabilizer to improve the texture of food.

Enzymatically produced acylglycerol and glycerin monostearate additives improved the characteristics of gelatin-stabilized omega-3 emulsions and microcapsules

The impacts of enzymatically produced acylglycerol and glycerin monostearate on the characteristics of gelatin-stabilized omega-3 emulsions and microcapsules were investigated. Tuna oil was enzymatically produced and the resulting acylglycerol was mixed with tuna oil at 12.5% (w/w) to prepare a novel oil phase. This oil phase was stabilized by gelatin to prepare oil-in-water emulsions and subsequent microcapsules via complex coacervation. The tuna oil with glycerin monostearate (GMS) at 1 and 2% (w/w) were used as controls. Results showed that both acylglycerol and GMS significantly reduced the emulsion droplet size and zeta potential, while increasing the viscoelasticity and stability. The diacylglycerol/monoacylglycerol were involved in the oil/water interfacial layer formation by lowering interfacial tension and increasing droplet surface hydrophobicity. Overall, the changed emulsion properties promoted the complex coacervation and contributed to the formation of microcapsules with improved oxidative stability. Therefore, enzymatically produced acylglycerol can develop high-quality stable omega-3 microencapsulated novel food ingredients.

Physicochemical Properties, Stability, and Functionality of Non-Covalent Ternary Complexes Fabricated with Pea Protein, Hyaluronic Acid and Chlorogenic Acid

The aim of this study was to prepare and characterize stable non-covalent ternary complexes based on pea protein (PP, 0.5%), hyaluronic acid (HA, 0.125%), and chlorogenic acid (CA, 0~0.03%). The ternary complexes were comprehensively evaluated for physicochemical attributes, stability, emulsifying capacities, antioxidant properties, and antimicrobial efficacy. PP-HA binary complexes were first prepared at pH 7, and then CA was bound to the binary complexes, as verified by fluorescence quenching. Molecular docking elucidated that PP interacted with HA and CA through hydrogen bonding, hydrophobic and electrostatic interactions. The particle size of ternary complexes initially decreased, then increased with CA concentration, peaking at 0.025%. Ternary complexes demonstrated good stability against UV light and thermal treatment. Emulsifying activity of complexes initially decreased and then increased, with a turning point of 0.025%, while emulsion stability continued to increase. Complexes exhibited potent scavenging ability against free radicals and iron ions, intensifying with higher CA concentrations. Ternary complexes effectively inhibited Staphylococcus aureus and Escherichia coli, with inhibition up to 0.025%, then decreasing with CA concentration. Our study indicated that the prepared ternary complexes at pH 7 were stable and possessed good functionality, including emulsifying properties, antioxidant activity, and antibacterial properties under certain concentrations of CA. These findings may provide valuable insights for the targeted design and application of protein-polysaccharide-polyphenol complexes in beverages and dairy products.

Salt reduction in myofibrillar protein gel via inhomogeneous distribution of sodium-containing encapsulated fish oil coacervate: Mucopenetration ability of sodium carboxymethyl cellulose

The potential application of fish oil microcapsules as salt reduction strategies in low-salt myofibrillar protein (MP) gel was investigated by employing soy protein isolates/carboxymethyl cellulose sodium (SPI-CMC) coacervates enriched with 25 mM sodium chloride and exploring their rheological characteristics, taste perception, and microstructure. The results revealed that the SPI-CMC coacervate phase exhibited the highest sodium content under 25 mM sodium level, albeit with uneven distribution. Notably, the hydrophilic and adhesive properties of CMC to sodium facilitated the in vitro release of sodium during oral digestion, as evidenced by the excellent wettability and mucopenetration ability of CMC. Remarkably, the fish oil microcapsules incorporating SPI-CMC as the wall material, prepared at pH 3.5 with a core-to-wall ratio of 1:1, demonstrated the highest encapsulation efficiency, which was supported by the strong hydrogen bonding. Interestingly, the presence of SPI-CMC coacervates and fish oil microcapsules enhanced the interaction between MPs and strengthened the low-salt MP gel network. Coupled with electronic tongue analysis, the incorporation of fish oil microcapsules slightly exacerbated the non-uniformity of sodium distribution. This ultimately contributed to an enhanced perception of saltiness, richness, and aftertaste in low-salt protein gels. Overall, the incorporation of fish oil microcapsules emerged as an effective salt reduction strategy in low-salt MP gel.

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.

Interactions between paramyosin and actin greatly improve their thermostability and gel properties

BACKGROUND

Myofibrillar proteins, the main contributors to the quality of meat products, are the main structural protein component of muscle and have functional properties such as the formation of a 3D protein gel network and water binding. The susceptibility of meat-derived proteins to heat-induced aggregation is the functional constraint that hinders their applications in industry, and so establishing an effective but simple method to improve their thermostability of the proteins is of great importance.

RESULTS

In the present study, we describe an easy approach to perform high colloidal thermostability of both paramyosin and actin by mixing them at low ionic strength. The improvement in thermal stability was found to be derived from intermolecular interactions between these two different proteins through non-covalent binding with each other. Consequently, such interactions protected each of them from thermal-induced degradation compared to individual components. Notably, this binary native protein mixture rather than single paramyosin or actin component has the ability to form protein hydrogels with a shear-thinning and reversible sol-gel transformation behavior, which is markedly different from most of reported heat-induced, denatured protein hydrogels.

CONCLUSION

The present study not only presents a facile and effective strategy for improvement of the thermal stability and gel properties of a binary paramyosin and actin mixture, but also enhances our understanding of how mutual interactions of protein components affect their physicochemical and functional properties. © 2023 Society of Chemical Industry.

Conformational and Structural Changes in Chickpea Proteins Caused by Simulated Salivary Alterations in the Elderly

The impact of salivary alterations on chickpea protein structure in the elderly has not been well documented. This study aimed to understand the role of simulated salivary alterations in the conformational properties and secondary structure of the chickpea protein isolate (CPI). Whey protein isolate (WPI) was used as the reference. Protein dispersions (10%) were subjected to in vitro oral processing under simulated salivary conditions in both the elderly and adult subjects. Proteins and their oral counterparts were characterized in terms of their composition, charge, size, solubility, water absorption, molecular weight (MW), and secondary structure (Circular Dichroism and Raman spectroscopy). Under condition of simulated oral digestion in the elderly population, the ordered secondary protein structure was significantly affected, decreasing α-helix by ~36% and ~29% in CPI and WPI compared to the control (adult) population, respectively. An increase in the unordered random coil state was observed. These results could be attributed to an increase in electrolytes in the salivary composition. The structure of CPI is more stable than that of WPI because of its higher MW, more rigid structure, less charged surface, and different amino acid compositions. This study is meaningful in understanding how alterations in the elderly oral system affect protein conformation and is expected to improve the understanding of plant-based protein digestibility.

Rheological Characteristics of Soluble Cress Seed Mucilage and β-Lactoglobulin Complexes with Salts Addition: Rheological Evidence of Structural Rearrangement

Functional, physicochemical, and rheological properties of protein-polysaccharide complexes are remarkably under the influence of the quality of solvent or cosolute in a food system. Here, a comprehensive description of the rheological properties and microstructural peculiarities of cress seed mucilage (CSM)-β-lactoglobulin (Blg) complexes are discussed in the presence of CaCl₂ (2-10 mM), (CSM-Blg-Ca), and NaCl (10-100 mM) (CSM-Blg-Na). Our results on steady-flow and oscillatory measurements indicated that shear thinning properties can be fitted well by the Herschel-Bulkley model and by the formation of highly interconnected gel structures in the complexes, respectively. Analyzing the rheological and structural features simultaneously led to an understanding that formations of extra junctions and the rearrangement of the particles in the CSM-Blg-Ca could enhance elasticity and viscosity, as compared with the effect of CSM-Blg complex without salts. NaCl reduced the viscosity and dynamic rheological properties and intrinsic viscosity through the salt screening effect and dissociation of structure. Moreover, the compatibility and homogeneity of complexes were approved by dynamic rheometry based on the Cole-Cole plot supported by intrinsic viscosity and molecular parameters such as stiffness. The results outlined the importance of rheological properties as criteria for investigations that determine the strength of interaction while facilitating the fabrication of new structures in salt-containing foods that incorporate protein-polysaccharide complexes.

Interactions between Soybean Trypsin Inhibitor and Chitosan in an Aqueous Solution

Supramolecular structures obtained from protein-polysaccharide association may be applied to encapsulate bioactive compounds or to improve the physical stability and texture properties of colloid-based products. In this study, the interaction of 0.1 wt% soybean trypsin inhibitor (STI) with different concentrations of chitosan (CS) in aqueous solutions was investigated under different pH by the analysis of state diagram, turbidity, zeta potential, spectroscopy, and microstructure; the protective effect of STI-CS complex coacervates on STI stability in simulated gastric juice was also discussed. The results suggested that interactions between STI and CS could form soluble/insoluble complexes mainly through hydrophobic interactions (pH 4.0) or electrostatic interactions (pH 6.0). The CD spectra showed that the secondary structure of STI did not change significantly when CS with the same charge was mixed with STI, and the secondary structure of STI was slightly changed when CS with the opposite charge was mixed with STI. Simulated gastric digestion experiments showed that the complex formed by non-covalent bonding had a protective effect on the active protein. This study provides information about the effect of different CS concentrations and pH values on the formation of complexes of CS and STI in an aqueous solution and provides theoretical references for the construction of supramolecular-structured carrier substances based on CS and STI.

Ionic Strength Dependence of the Complex Coacervation between Lactoferrin and β-Lactoglobulin

Heteroprotein complex coacervation is an assembly formed by oppositely charged proteins in aqueous solution that leads to liquid-liquid phase separation. The ability of lactoferrin and β-lactoglobulin to form complex coacervates at pH 5.5 under optimal protein stoichiometry has been studied in a previous work. The goal of the current study is to determine the influence of ionic strength on the complex coacervation between these two proteins using direct mixing and desalting protocols. The initial interaction between lactoferrin and β-lactoglobulin and subsequent coacervation process were highly sensitive to the ionic strength. No microscopic phase separation was observed beyond a salt concentration of 20 mM. The coacervate yield decreased drastically with increasing added NaCl from 0 to 60 mM. The charge-screening effect induced by increasing the ionic strength is attributed to a decrease of interaction between the two oppositely charged proteins throughout a decrease in Debye length. Interestingly, as shown by isothermal titration calorimetry, a small concentration of NaCl around 2.5 mM promoted the binding energy between the two proteins. These results shed new light on the electrostatically driven mechanism governing the complex coacervation in heteroprotein systems.

Brush-Structured Chitosan/PolyHEMA with Thymine and Its Synergistic Effect on the Specific Interaction with ssDNA and Cellular Uptake

Cationic polymers are known to attach on an anionic cell surface and favor gene transportation/transfection into the cells. However, when the positive charges accumulate, they tend to cause cell damage and delivery failure. Chitosan (CS) is a potential cationic bio-derived polymer whose chemical structures can be modified to fine-tune the charges as well as the add-on functions. The present work demonstrates (i) the decoration of a nucleic acid sequence-like brush structure on CS to allow the specific interaction with DNA and (ii) delivery into the cell. By simply applying mercaptoacetic acid as the chain transfer agent, the grafting of poly(hydroxyethyl methacrylate) (PHEMA) containing Thy (P(HEMA-Thy)) on CS is possible. The brush-like P(HEMA-Thy) leads Thy moieties to be in sequences. The Thy sequences perform as poly[T] for the specific interaction with ssDNA. The synergistic effect of CS and Thy sequences, i.e., electrostatic and base pairing interactions, results in an effective and efficient binding with ssDNA as well as significant delivery, especially in cellular uptake and cell viability. The use of CS in combination with Thy sequences in brush-like structures on CS is a model for other polysaccharides to be conjugated with the as-designed nucleic acid sequences for potential gene delivery.

Pickering emulsions stabilized by pea protein isolate-chitosan nanoparticles: fabrication, characterization and delivery EPA for digestion in vitro and in vivo

The work aimed to prepare pea protein isolate-chitosan (PPI-CS) nanoparticles, fabricate PPI-CS nanoparticles stabilized Pickering emulsions (PPI-CS Pickering emulsions) and deliver EPA for digestion in vitro and in vivo. The nanoparticles were characterized by scanning electron microscopy (SEM), and PPI-CS Pickering emulsions were characterized by physicochemical and rheological properties. The results showed that the size of PPI-CS nanoparticles was 194.22 ± 0.45 nm. Rheological measurement showed that the PPI-CS Pickering emulsions possessed a gel-like network. EPA encapsulated Pickering emulsions (EPA-PE, φ = 0.6) exhibited a high retention rate (93%) during storage and performed a lower release rate compared with EPA-PE (φ = 0.4) in vitro digestion. The area under the curve of EPA concentration of EPA-PE group and EPA-emulsions (EPA-Em) group was 1.71 and 1.48, respectively. It demonstrated that PPI-CS Pickering emulsions provided the possibility to deliver EPA for digestive absorption.