Formation and pH-stability of whey protein fibrils in the presence of lecithin

The non-covalent and covalent interactions of whey proteins and saccharides: influencing factor and utilization in food

During the application of Whey proteins (WPs), they often have complex interactions with saccharides (Ss), another important biopolymer in food substrate. The texture and sensory qualities of foods containing WPs and Ss are largely influenced by the interactions of WPs-Ss. Moreover, the combination of WPs and Ss is possible to produce many excellent functional properties including emulsifying properties and thermal stability. However, the interactions between WPs-Ss are complex and susceptible to some processing conditions. In addition, with different interaction ways, they can be applied in different fields. Therefore, the non-covalent interaction mechanisms between WPs-Ss are firstly summarized in detail, including electrostatic interaction, hydrogen bond, hydrophobic interaction, van der Waals force. Furthermore, the existence modes of WPs-Ss are introduced, including complex coacervates, soluble complexes, segregation, and co-solubility. The covalent interactions of WPs-Ss in food applications are often formed by Maillard reaction (dry or wet heat reaction) and occasionally through enzyme induction. Then, two common influencing factors, pH and temperature, on non-covalent/covalent bonds are introduced. Finally, the applications of WPs-Ss complexes and conjugations in improving WP stability, delivery system, and emulsification are described. This review can improve our understanding of the interactions between WPs-Ss and further promote their wider application.

Study on the interaction mechanism of whey protein isolate with phosphatidylcholine: By multispectral methods and molecular docking

The elucidation of the interaction mechanism between phospholipids and milk proteins within emulsions is pivotal for comprehending the properties of infant formula fat globules. In this study, multispectral methods and molecular docking were employed to explore the relationship between phosphatidylcholine (PC) and whey protein isolate (WPI). Observations indicate that the binding constant, alongside thermodynamic parameters, diminishes as temperature ascends, hinting at a predominantly static quenching mechanism. Predominantly, van der Waals forces and hydrogen bonds constitute the core interactions between WPI and PC. This assertion is further substantiated by Fourier transform infrared spectroscopy, which verifies PC's influence on WPI's secondary structure. A detailed assessment of thermodynamic parameters coupled with molecular docking reveals that PC predominantly adheres to specific sites within α-lactalbumin, β-lactoglobulin, and bovine serum albumin, propelled by a synergy of hydrophobic interactions, hydrogen bonding, and van der Waals forces, with binding energies noted at -5.59, -6.71, and -7.85 kcal/mol, respectively. An increment in PC concentration is observed to amplify the emulsification properties of WPI whilst concurrently diminishing the zeta potential. This study establishes a theoretical foundation for applying the PC-WPI interaction mechanism in food.

Fabrication of bovine serum albumin nanofibrils: Physicochemical characteristics, emulsifying and foaming activities

Bovine serum albumin nanofibrils (BSNs) were fabricated under thermal treatment (85 °C) at acidic condition (pH 2.0) and the incubation time on the structural, and physicochemical characteristics were probed. The formation and development of BSNs have been detected and confirmed by Thioflavin T (ThT) fluorescence and circular dichroism (CD) measurements. The structural alterations of bovine serum albumin (BSA) have also been investigated using intrinsic fluorescence and Congo red (CGR) UV-vis spectroscopy. Atomic force microscopy (AFM) outcomes displayed the morphologies of BSNs at varied time, with a diameter of about 3 nm and a contour length of about 200 nm at 24 h. The apparent viscosities of BSNs at three different pH were in the following order: pH 3.0 > pH 5.0 > pH 7.0. Emulsifying and foaming properties of BSA were pronouncedly enhanced through fibrillation, which was highly correlated with the interfacial properties and structural characteristics. Highest EAI 54.2 m2/g was attained at 48 h and no pronounced alterations were observed for EAI at 24 h and 48 h. Maximum value of FC was obtained at 48 h for BSA. This study will provide some useful information in understanding the formation of BSNs and broaden their application in food systems as functional food ingredients.

Effects of molecular weight of hydrolysate on the formation of soy protein isolate hydrolysate nanofibrils: Kinetics, structures, and interactions

Enzymatic hydrolysis prior to protein fibrillation was an effective way to facilitate the formation of nanofibrils. This study aimed to investigate the effects of molecular weights of hydrolysate on the kinetics, structures, and interactions of soy protein isolate (SPI) hydrolysate nanofibrils. The results showed that hydrolysate with molecular weight > 10 kDa showed a distinct fibrillation kinetics curve and a higher apparent rate constant (27.72) during fibrillation, indicating their vital role in determining the fibrillation. Hydrolysate with molecular weight > 10 kDa could form nanofibrils with higher radius gyration (17.11 ± 0.77 Å) due to stronger hydrophobic interaction, showing a stronger fibrillation ability. Hydrolysate with molecular weight within 5-10 kDa exhibited enhanced π-π stacking interactions during fibrillation, thereby promoting the extension of nanofibrils, and contributing to the formation of more nanofibrils. Hydrolysate with molecular weight < 5 kDa tended to randomly aggregate during fibrillation, resulting in a significant loss of cross-β structures in nanofibrils. Therefore, hydrolysate with different molecular weights exhibited synergistic effects during fibrillation.

Milk Whey Protein Fibrils-Effect of Stirring and Heating Time

Milk whey proteins, which are derived from skim milk through membrane filtration, exhibit valuable functional properties when transformed into a fibrillar form. This conversion enhances their suitability for various applications, including thickening, gelling, emulsification, and foaming. However, reported fibrillation methods have longer heating times, which may not be economical for the dairy industry. To address these challenges, the current study was undertaken with the objective of reducing the time required for fibril formation. In this study, 2% milk whey protein isolate (mWPI) solution at pH 2 was heated with static and stirring heating conditions at 80 °C for 20 h to convert milk whey proteins into fibrils. Fibrils were observed using the thioflavin T value, transmission electron microscopy, Tricine SDS-PAGE, rheology, and protein oxidation. Results suggest that stirring heating conditions with 14 h heating time produced fibrils with good morphology compared to static heating, showing a 6 h reduction compared to an earlier reported 80 °C for 20 h heating time. Also, stirring heating produced a uniform and homogeneous fibril solution compared to the static heating method. Gentle stirring during heating can also help to scale up fibril production in an industrial setup. The fibrillation method with processing intervention will help to produce fibrils with enhanced functionality at the pilot and industrial scales.

Production and functional evaluation of nonfat dry milk with whey proteins as fibrils

Commercial manufacturing of dairy products involves the addition of dairy ingredients (such as nonfat dry milk and milk protein concentrates), as well as nondairy additives (such as gums, stabilizers, emulsifiers, and texture modifiers) to get the best product appearance, maintain the product quality, and extend shelf life. Though these nondairy additives are not harmful, consumers do not prefer them in dairy food formulations. Therefore, the dairy industry is working on improving the inherent functionality of dairy ingredients using different processes. Recently, fibrillation emerged as a new technique to convert globular proteins such as whey proteins into fibrils, which provide enhanced viscosity, foaming, and emulsification capacity. Therefore, skim milk was subjected to microfiltration followed by ultrafiltration of microfiltration permeate to fractionate whey proteins. Then, whey proteins were selectively fibrillated and mixed back with other streams of microfiltration and ultrafiltration to get fibrillated skim milk. Fibrillated skim milk was spray-dried to get fibrillated nonfat dry milk (NDM). Visible whey protein fibrils were observed in reconstituted fibrillated NDM, which showed survival of fibrils in fibrillated NDM. Fibrillated NDM showed significantly higher viscosity than control NDM. Fibrillated NDM also showed higher emulsification capacity, foaming capacity, and stability than the control NDM but lower gel strength. Considering the improved functionality of fibrillated NDM, they can be used in product formulations such as ice cream mix, where the thickening of a solution, good emulsification, and foaming properties are required.

Ultrasonic and homogenization: An overview of the preparation of an edible protein-polysaccharide complex emulsion

Emulsion systems are extensively utilized in the food industry, including dairy products, such as ice cream and salad dressing, as well as meat products, beverages, sauces, and mayonnaise. Meanwhile, diverse advanced technologies have been developed for emulsion preparation. Compared with other techniques, high-intensity ultrasound (HIUS) and high-pressure homogenization (HPH) are two emerging emulsification methods that are cost-effective, green, and environmentally friendly and have gained significant attention. HIUS-induced acoustic cavitation helps in efficiently disrupting the oil droplets, which effectively produces a stable emulsion. HPH-induced shear stress, turbulence, and cavitation lead to droplet disruption, altering protein structure and functional aspects of food. The key distinctions among emulsification devices are covered in this review, as are the mechanisms of the HIUS and HPH emulsification processes. Furthermore, the preparation of emulsions including natural polymers (e.g., proteins-polysaccharides, and their complexes), has also been discussed in this review. Moreover, the review put forward to the future HIUS and HPH emulsification trends and challenges. HIUS and HPH can prepare much emulsifier-stable food emulsions, (e.g., proteins, polysaccharides, and protein-polysaccharide complexes). Appropriate HIUS and HPH treatment can improve emulsions' rheological and emulsifying properties and reduce the emulsions droplets' size. HIUS and HPH are suitable methods for developing protein-polysaccharide forming stable emulsions. Despite the numerous studies conducted on ultrasonic and homogenization-induced emulsifying properties available in recent literature, this review specifically focuses on summarizing the significant progress made in utilizing biopolymer-based protein-polysaccharide complex particles, which can provide valuable insights for designing new, sustainable, clean-label, and improved eco-friendly colloidal systems for food emulsion. PRACTICAL APPLICATION: Utilizing complex particle-stabilized emulsions is a promising approach towards developing safer, healthier, and more sustainable food products that meet legal requirements and industrial standards. Moreover, the is an increasing need of concentrated emulsions stabilized by biopolymer complex particles, which have been increasingly recognized for their potential health benefits in protecting against lifestyle-related diseases by the scientific community, industries, and consumers.

Interaction between whey protein and soy lecithin and its influence on physicochemical properties and in vitro digestibility of emulsion: A consideration for mimicking milk fat globule

In this study, from the perspective of simulating the milk fat globule (MFG) emulsion, the interaction between soybean lecithin (SL) and the main protein in milk, whey protein (WP), and its effect on physical characteristics and lipid digestion were investigated through multiple spectroscopic techniques and in vitro digestion. The mechanism of SL and WP was static quenching, indicating that a complex formed between WP and SL through hydrophobic interaction and hydrogen bonding. The addition of SL changed the secondary structure of WP. When the ratio of SL to WP was 1:3, the obtained SL-WP emulsion that simulated milk fat globule exhibited the smallest particle size distribution and the highest absolute value of zeta potential. In addition, the emulsion exhibited high encapsulation efficiency (91.67 ± 1.24 %) and good stability. Compared with commercially available infant formula (IF), the final free fatty acid release of prepared SL-WP emulsion was close to that of human milk (HM). The addition of lecithin increased the digestibility of fat and the release of free fatty acids, and the digestive characteristic and particle size change also were closer to that of HM from results of kinetics of free fatty acid release and microstructure analysis.

Improved retention ratio and bioaccessibility of lutein loaded in emulsions stabilized by egg yolk granules-lecithin complex

BACKGROUND

Egg yolk granules (EYGs)-soy lecithin (SL) complex is a newly developed delivery system that is effective for improving the storage stability of hydrophobic bioactive compounds. However, the formation mechanism of EYGs and SL complex and its effect on the gastrointestinal fate of lutein-loaded emulsions needs to be investigated further.

RESULTS

Adding SL greatly improved the surface activity of the EYGs, as evidenced by reduced surface tension and an increased adsorption rate to the oil/water interface. Hydrophobic interaction was the dominant force in the formation of EYG-SL complex, with hydrogen and ionic bonds playing complementary roles. Using the EYG-SL complex, stable oil-in-water emulsions were formed and exhibited an enhanced retention ratio and bioaccessibility of lutein after simulated digestion. Correlation analysis demonstrated that the additional anti-oxidant activity as a result of EYGs was responsible for the high retention of lutein, whereas low surface tension facilitated the micellization of bioaccessible lutein.

CONCLUSION

The present study shows that the EYG and SL have a synergistic effect with respect to improving the retention ratio and bioaccessibility of lutein in emulsions stabilized by EYG-SL complex after digestion and this will guide the development of value-added oil-in-water emulsion products using protein-lecithin complex as a promising nutrient delivery vehicle. © 2022 Society of Chemical Industry.

Glycated modification of the protein from Rana chensinensis eggs by Millard reaction and its stability analysis in curcumin encapsulated emulsion system

Forest frog (Rana chensinensis) eggs contain high-quality protein but have not been well utilized. In this study, the total protein of forest frog eggs was extracted and 4491 protein/peptides were identified by HPLC-MS/MS. The egg protein was glycated using monosaccharides (lactose, fructose, xylose and glucose). The xylose modified egg protein showed excellent emulsifying ability, high viscosity and uniform structure under the laser confocal microscope in a concentration dependent way (1-3%, w/v). We next used xylose glycated egg protein to encapsulate curcumin to determine the stability of its emulsion system. This emulsion system showed low particle size (< 400 nm) and high Zeta-potential (> 30 mV with absolute value) at pH > 6. The system was stable under 4 °C, 25℃ and 37 °C after seven weeks' storage, especially for the emulsions at 3% and 5% concentrations. Therefore, the glycated frog egg protein can be used to encapsulate hydrophobic nutrients.

Lecithin-sodium caseinate self-assembled complexes as emulsifying agents in oil-in-water emulsion: Acidic medium approach

Surfactant-polyelectrolyte complexes (SPECs) based on lecithin and sodium caseinate were produced and the effects of such binding on the physical, chemical and emulsifying properties were evaluated and compared with the two ingredients in isolation. Negative, neutral, and positive charged SPECs were obtained. Zeta potential values and size distributions of the SPECs were dependent on the mass ratio between compounds. Electrostatic association decreased the polydispersity index in comparison with pure compounds solutions. Analysis of interfacial properties showed that solutions containing SPECs promoted a greater reduction of surface tension and interfacial tension with sunflower oil when compared with pure compounds solutions. Emulsions produced with SPECs in 10:1 lecithin:sodium caseinate ratio proved to be more stable than emulsions prepared with pure compounds. Thus, the complexation improved the emulsifying properties of lecithin and sodium caseinate establishing SPECs as potential natural emulsifiers.

•

Ratio between compounds plays a role in the emulsifying properties of complexes.

•

Complexes promoted faster decrease of interfacial tension with sunflower oil.

•

Complexes formed at Lip:NaCas 10:1 ratio improved the stability of emulsions.

Effect mechanism of ultrasound pretreatment on fibrillation Kinetics, physicochemical properties and structure characteristics of soy protein isolate nanofibrils

Self-assembly of soy proteins into nanofibrils is gradually considered as an effective method to improve their technical and functional properties. Ultrasound is a non-thermal, non-toxic and environmentally friendly technology that can modulate the formation of protein nanofibrils through controlled structural modification. In this research, the effect of ultrasound pretreatment on soy protein isolate nanofibrils (SPIN) was evaluated by fibrillation kinetics, physicochemical properties and structure characteristics. The results showed that the optimum ultrasound condition (20% amplitude, 15 min, 5 s on-time and 5 s off-time) could increase the formation rate of SPIN by 38.66%. Ultrasound reduced the average particle size of SPIN from 191.90 ± 5.40 nm to 151.83 ± 3.27 nm. Ultrasound could increase the surface hydrophobicity to 1547.67 in the initial stage of nanofibrils formation, and extend the duration of surface hydrophobicity increased, indicating ultrasound could expose more binding sites, creating more beneficial conditions for nanofibrils formation. Ultrasound could change the secondary and tertiary structure of SPIN. The reduction of α-helix content of ultrasound-pretreated soy protein isolate nanofibrils (USPIN) was 12.1% (versus 5.3% for SPIN) and the increase of β-sheet content was 5.9% (versus 3.5% for SPIN) during fibrillation. Ultrasound could accelerate the formation of SPIN by promoting the unfolding of SPI, exposure of hydrophobic groups and formation of β-sheets. Microscopic images revealed that USPIN generated a curlier and looser shape. And ultrasound reduced the zeta potential, free sulfhydryl groups content and viscosity of SPIN. SDS-PAGE results showed that ultrasound could promote the conversion of SPI into low molecular weight peptides, providing building blocks for the nanofibrils formation. The results indicated that ultrasound pretreatment could be a promising technology to accelerate SPIN formation and promote its application in food industry, but further research is needed for the improvement of the functional properties of SPIN.

Co-encapsulation of (-)-epigallocatechin-3-gallate and piceatannol/oxyresveratrol in β-lactoglobulin: effect of ligand-protein binding on the antioxidant activity, stability, solubility and cytotoxicity

The co-encapsulation of multiple bioactive components in a carrier may produce synergistic effects and improve health benefits. In this study, the interactions of β-lactoglobulin (β-LG) with epigallocatechin-3-gallate (EGCG) and/or piceatannol (PIC)/oxyresveratrol (OXY) were investigated by multispectroscopic techniques, isothermal titration calorimetry, and molecular docking. The static quenching mechanism of β-LG by EGCG, PIC and OXY was confirmed by fluorescence spectroscopy and UV-vis absorption difference spectroscopy. The binding sites of these three polyphenols in β-LG were identified by site marking fluorescence experiments and molecular docking. The thermodynamic parameters of the β-LG + EGCG/PIC/OXY binary complex and β-LG + EGCG + PIC/OXY ternary complex were obtained from fluorescence data and used to analyze the main driving force for complex formation. The exothermic binding process was further confirmed by isothermal titration calorimetry. The α-helical content, particle size and morphology of free and ligand-bound β-LG were determined by circular dichroism spectroscopy, dynamic light scattering and transmission electron microscopy, respectively. The effect of EGCG, PIC and OXY on the conformation of β-LG was studied by Fourier transform infrared spectroscopy. In addition, the maximum synergistic antioxidant activity between EGCG and PIC/OXY was obtained by response surface analysis. The effects of β-LG in the binary and ternary systems on the antioxidant activity, stability, solubility and cytotoxicity of the polyphenols were also studied. Finally, the different cytotoxicities of the complexes and nanoparticles of the binary and ternary systems were compared. The results of this study are expected to provide a theoretical basis for the development of β-LG-based carriers co-encapsulating a variety of bioactive components.

Characterization of interactions between whey protein isolate and hyaluronic acid in aqueous solution: Effects of pH and mixing ratio

Interactions between whey protein isolate (WPI) and hyaluronic acid (HA) were characterized as functions of pH (6.0-1.0) and protein to polysaccharide ratio (R, 1:4-10:1). Intramolecular soluble complexes formed at pH_c of 5.6-5.8, followed by intermolecular insoluble complexes formed at pH_Φ1 of 4.4-4.6. Complexes at ratios below 4:1 reached maximum optical value at pH 2.4 while samples above 4:1 peaked at pH 3-3.4 then precipitated. WPI/HA coacervates completely dissociated into soluble complex at pH 1.6-1.8 (pH_Φ2). WPI/HA mixtures showed shear thinning behavior and elastic property. Whey protein underwent significant α-helix structure change when interacting with HA in range of pH_Φ1>pH > pH_Φ2 and at low R values (1:4 and 1:2). Scanning electronic microscope (SEM) pictures showed pH and mixing ratio dependent microstructural changes corresponding with phase transition. Data may provide helpful information for further application of WPI/HA complexes in medical, food and cosmetic fields.

Polymerized Whey Protein Concentrate-Based Glutathione Delivery System: Physicochemical Characterization, Bioavailability and Sub-Chronic Toxicity Evaluation

Glutathione (GSH) is a powerful antioxidant, but its application is limited due to poor storage stability and low bioavailability. A novel nutrient encapsulation and delivery system, consisting of polymerized whey protein concentrate and GSH, was prepared and in vivo bioavailability, antioxidant capacity and toxicity were evaluated. Polymerized whey protein concentrate encapsulated GSH (PWPC-GSH) showed a diameter of roughly 1115 ± 7.07 nm (D50) and zeta potential of 30.37 ± 0.75 mV. Differential scanning calorimetry (DSC) confirmed that GSH was successfully dispersed in PWPC particles. In vivo pharmacokinetics study suggested that PWPC-GSH displayed 2.5-times and 2.6-fold enhancement in maximum concentration (Cmax) and area under the concentration-time curve (AUC) as compared to free GSH. Additionally, compared with plasma of mice gavage with free GSH, significantly increased antioxidant capacity of plasma in mice with PWPC-GSH was observed (p < 0.05). Sub-chronic toxicity evaluation indicated that no adverse toxicological reactions related to oral administration of PWPC-GSH were observed on male and female rats with a diet containing PWPC-GSH up to 4% (w/w). Data indicated that PWPC may be an effective carrier for GSH to improve bioavailability and antioxidant capacity.

Formation, structural characteristics, foaming and emulsifying properties of rice glutelin fibrils

The rice glutelin fibrils (RGFs) were formed under heating at acidic condition, and the optimal condition was achieved at pH 2, 150 mM (ionic strength), 4% (protein concentration), 90 °C and 300 rpm (stirring speed) through the thioflavin T intensity. The atomic force microscopy images showed that the average contour length of RGFs increased from < 100 to 365 nm under the optimal fibrillation. The average particle size of rice glutelin (RG) decreased from 650 to 221 nm after initial heating time. Combining the degraded subunits, it suggested that RG was hydrolyzed to peptides, then these released peptides assembled into the ordered fibrils via intermolecular interactions, accompanying by the structural rearrangement. Additionally, the foaming and emulsifying properties were improved during fibrillation, which could be related to the interfacial properties and structure of RGFs. This work will deepen the understanding of the formation of RGFs and explore their potential application.

The Interplay between Whey Protein Fibrils with Carbon Nanotubes or Carbon Nano-Onions

Whey protein isolate (WPI) fibrils were prepared using an acid hydrolysis induction process. Carbon nanotubes (CNTs) and carbon nano-onions (CNOs) were made via the catalytic chemical vapor deposition (CVD) of methane. WPI fibril-CNTs and WPI fibril-CNOs were prepared via hydrothermal synthesis at 80 °C. The composites were characterized by SEM, TEM, FTIR, XRD, Raman, and TG analyses. The interplay between WPI fibrils and CNTs and CNOs were studied. The WPI fibrils with CNTs and CNOs formed uniform gels and films. CNTs and CNOs were highly dispersed in the gels. Hydrogels of WPI fibrils with CNTs (or CNOs) could be new materials with applications in medicine or other fields. The CNTs and CNOs shortened the WPI fibrils, which might have important research value for curing fibrosis diseases such as Parkinson's and Alzheimer's diseases. The FTIR revealed that CNTs and CNOs both had interactions with WPI fibrils. The XRD analysis suggested that most of the CNTs were wrapped in WPI fibrils, while CNOs were partially wrapped. This helped to increase the biocompatibility and reduce the cytotoxicity of CNTs and CNOs. HR-TEM and Raman spectroscopy studies showed that the graphitization level of CNTs was higher than for CNOs. After hybridization with WPI fibrils, more defects were created in CNTs, but some original defects were dismissed in CNOs. The TG results indicated that a new phase of WPI fibril-CNTs or CNOs was formed.

Process development for a novel milk protein concentrate with whey proteins as fibrils

Milk protein concentrate (MPC) is a preferred ingredient to provide nutritional and functional benefits in various dairy and food products. Altering the protein configuration and protein-protein interactions in MPC can provide a novel functionality and may open doors for new applications. The fibrilization process converts the globular structure of whey proteins to fibrils and consequently increases viscosity and water holding capacity compared with the native protein structure. The objective of the current work was to selectively convert the whey proteins in MPC as fibrils. For this purpose, simulated control model MPC was prepared by combining solutions of micellar casein concentrate (MCC) and milk whey protein isolate (mWPI) to give casein and whey protein in an 80:20 ratio. The mWPI solution was converted to fibrils by heating at low pH, neutralized, and combined with MCC solution similar to control model MPC and termed "fibrillated model MPC." Thioflavin T fluorescence value, transmission electron microscopy, and gel electrophoresis confirmed the fibril formation and their survival after neutralization and mixing with MCC. Further, the fibrillated mWPI showed significantly higher viscosity and consistency coefficient than nonfibrillated mWPI. Similarly, fibrillated model MPC showed significantly higher viscosity and consistency coefficient compared with control model MPC. Hence, the fibrillated model MPC can be used as ingredient to increase viscosity. Heat coagulation time was found to be significantly higher for control model MPC compared with fibrillated model MPC.

Colloidal-like aggregation of a functional amyloid protein

Functional amyloid proteins are self-secreted by microbial cells that aggregate into extracellular networks and provide microbial colonies with mechanical stability and resistance to antibiotic treatment. In order to understand the formation mechanism of functional amyloid networks, their aggregation has been studied in vitro under different physical conditions, such as temperature, salt concentration, and pH. Typical aggregates' morphologies include fibers or plaques, the latter resembling amyloid aggregates in neurodegenerated brains. Here, we studied the pH-reduction-induced aggregation of TasA, an extracellular functional amyloid appearing as fibers in biofilms of the soil bacterium, Bacillus subtilis. We used turbidity and zeta potential measurements, electron microscopy, atomic force microscopy, and static light scattering measurements, to characterize the aggregates of TasA and to compare them with colloidal aggregates. We further studied the aggregation of TasA in the presence of negatively charged nanoparticles and showed that nanoparticles co-aggregated with TasA, and that the co-aggregation was hindered sterically. Based on these studies, we concluded that, similarly to colloidal aggregation, TasA aggregation occurs due to surface potential modulations and that the aggregation is followed by a rearrangement process. Shedding light on the aggregation mechanism of TasA, our results can be used for the design of TasA aggregation inhibitors and promoters.

Fabrication of Composite Structures of Lysozyme Fibril-Zein using Antisolvent Precipitation: Effects of Blending and pH Adjustment Sequences

Antisolvent precipitation is a widely used method to fabricate prolamin-based composites. In the present study, composite structures of lysozyme amyloid fibrils with zein proteins were fabricated using the antisolvent precipitation method by applying different blending and pH adjustment sequences. Globular prolamins were bound to the amyloid fibrils to combine their respective advantages. The dynamic light scattering showed that the composites with a characteristic stabilized behavior (43.60 ± 1.75 mV ∼ 35.20 ± 0.65 mV) were formed at pH 4.0-5.0, in which noncovalent interactions between fibril and particles occurred. Two different structures: fruit tree-like structure and beaded-like structure, were presented in AFM and TEM images due to the different pH adjustment sequences, while blending sequences had negligible effect on the morphology of the composites. A fruit tree-like entity was detected for lysozyme fibril-zein composites, where its "branches" bear zein globular particles. A beaded-like structure was observed for lysozyme fibril-zein composites, where lysozyme fibril was the thread and zein aggregates were the beads. The potential mechanism of this phenomenon can be explained as the fruit tree-like structure being primarily formed through electrostatic interactions while the beaded-like structure is mainly caused by hydrophobic interactions. The composites of fruit tree-like structures hold a more promising stability than those with beaded-like structures. The results of this research would give constructive information for the fabrication of amyloid fibril-prolamin protein composites, which may exhibit the combined advantages of each components and have potential applications in encapsulation and protection of bioactive substances and stabilizing emulsions.

Preparation and Characterization of Soy Isoflavones Nanoparticles Using Polymerized Goat Milk Whey Protein as Wall Material

Soy isoflavones (SIF) are a group of polyphenolic compounds with health benefits. However, application of SIF in functional foods is limited due to its poor aqueous solubility. SIF nanoparticles with different concentrations were prepared using polymerized goat milk whey protein (PGWP) as wall material. The goat milk whey protein was prepared from raw milk by membrane processing technology. The encapsulation efficiencies of all the nanoparticles were found to be greater than 70%. The nanoparticles showed larger particle size and lower zeta potential compared with the PGWP. Fourier Transform Infrared Spectroscopy indicated that the secondary structure of goat milk whey protein was changed after interacting with SIF, with transformation of α-helix and β-sheet to disordered structures. Fluorescence data indicated that interactions between SIF and PGWP decreased the fluorescence intensity. All nanoparticles had spherical microstructure revealed by Transmission Electron Microscope. Data indicated that PGWP may be a good carrier material for the delivery of SIF to improve its applications in functional foods.

Investigating the biomolecular interactions between model proteins and glycine betaine surfactant with reference to the stabilization of emulsions and antimicrobial properties

Binding effect and interaction of 2-pentadecanoyloxymethyl)trimethylammonium bromide (DMGM-14) with bovine serum albumin (BSA) and hen egg white lysozyme (HEWL) were systematically investigated by the fluorescence spectroscopy, circular dichroism (CD) spectroscopy, isothermal titration calorimetry (ITC), surface tension analysis, and molecular docking studies. The emulsion properties and particle size distribution of surfactant/protein complexes containing sunflower oil were studied using static light scattering and confocal laser scanning microscopy (CLSM). The fluorescence spectroscopy and ITC analysis confirmed the complexes formation of DMGM-14 with BSA and HEWL which was also verified by surface tension measurements. CD results explained the conformational changes in BSA and HEWL upon DMGM-14 complexation. Molecular docking study provides insight into the binding of DMGM-14 into the specific sites of BSA and HEWL. Besides, the studies drew a detailed picture on the emulsification properties of DMGM-14 with BSA and HEWL. In addition, the in vitro experiment revealed a broad antibacterial spectrum of DMGM-14 and DMGM-14/HEWL complex including activity against Gram-positive and Gram-negative bacteria. In conclusion, the present study revealed that the interaction between DMGM-14 with BSA and HEWL is important for the pharmaceutical, biological, and food products.