Formation mechanism of Pickering emulsion gels stabilized by proanthocyanidin particles: Experimental and molecular dynamics studies

Semi-rational engineering of an α-L-fucosidase for regioselective synthesis of fucosyl-N-acetylglucosamine disaccharides

α-L-Fucosidases are attractive biocatalysts for the production of bioactive fucosylated oligosaccharides, however, poor regioselectivity and activity for transglycosylation have significantly limited their applications. We have recently derived an α-L-Fucosidase, BF3242, from Bacteroides fragilis NCTC9343, which could efficiently synthesize a mixture of Fuc-α-1,3/1,6-GlcNAc, but its 1,3/1,6-regioselectivity was observably affected by reaction temperature. Here, we integrated loop-targeted random mutagenesis and site-directed mutagenesis to engineer the regioselectivity and transglycosylation activity of BF3242. Loop-targeted random mutagenesis revealed that L266 in the loop-4 (H242-S267) within the model of BF3242 was a key residue for the regioselectivity for transglycosylation, and the saturation mutagenesis at residue L266 uncovered a mutant L266H with a significantly increased 1,3-regioselectivity of 97 % from 69 % of WT BF3242. Subsequently, five designed single-site mutations at the putative aglycone subsites were performed, resulting in a double-site mutant L266H/M285C that increased the overall yield of Fuc-α-1,3/1,6-GlcNAc to 76 % from 68 % of WT BF3242. The saturation mutagenesis at residue M285 finally generated a double-site mutant L266H/M285T with the maximal overall yield of Fuc-α-1,3/1,6-GlcNAc of 85 % and 1,3-regioselectivity of 98 %. The R T/H of L266H/M285T was approximately 2.7-fold higher than that of the WT BF3242. Molecular dynamics simulations revealed that the structural flexibility of the loop-4 was substantially reduced in mutant L266H, and the hydrogen bond formation and binding affinity between mutant L266H/M285T and Fuc-α-1,3-GlcNAc was significantly enhanced. The semi-rationally engineered enzyme L266H/M285T would be a promising biocatalyst for highly 1,3-regioselective synthesis of fucosyl-N-acetylglucosamine disaccharide.

Tough, antibacterial, and antioxidant chitosan-based composite films enhanced with proanthocyanidin and carvacrol essential oil for fruit preservation

Post-harvest fruits are susceptible to microbial infections and spoilage, and the development of multifunctional green preservation films to extend the shelf-life of fruits is desirable. In this study, multifunctional antibacterial and antioxidant fruit preservation films were developed by incorporating natural plant actives of proanthocyanidins and carvacrol essential oils into chitosan-dialdehyde cellulose composite films. The composite film had good mechanical properties, with a tensile strength of 78.8 MPa, a free radical scavenging rate of over 90 %, and enhanced barrier properties against UV light and water vapor. The diameters of the inhibition zones of the composite film for S. aureus and E. coli were 23.65 mm and 22.37 mm, respectively. In addition, the composite film was biocompatible and the survival rate of cells treated with the composite film solution was more than 90 %. Using strawberries as model fruit, we showed that the composite film could effectively inhibit the growth of colonies on the surface of the fruit and reduce the weight loss rate. These results demonstrated that the composite film has great potential for fruit preservation.

Design of Polydopamine@iron Oxide-Coated Ammonium Perchlorate Core-Shell Composites for Enhancing the Combustion Performance of HTPB-Based Propellants

An ammonium perchlorate (AP) composite system with double-coating encapsulation based on the interfacial polymerization behavior of dopamine (DA) in Pickering emulsions was designed to enhance the combustion performance of HTPB-based propellants. The composite system proved highly effective in mitigating the agglomeration issues associated with iron oxide nanoparticles (Fe2O3 NPs) as catalysts, with the AP exhibiting superior performance compared to the composite comprising pure Fe2O3 NPs. The results of the thermal decomposition experiments showed that the HTD temperature of AP@PDA@Fe2O3 was reduced to 318.8 °C, accompanied by a 183.8% increase in heat release and an approximately 30.0% decrease in the activation energy. The combustion rate of AP@PDA@Fe2O3/HTPB was enhanced by approximately 3.0 times higher than that of AP/HTPB. Furthermore, experimental results on safety and surface hydrophobicity showed that the impact sensitivity of the composite AP increased by 28.6%, while the water contact angle was markedly elevated. The reason for the performance enhancement was the synergistic catalytic effect of PDA/Fe2O3 on AP and the dense double-coated structure. This study provided a new idea for the multilevel surface modification of other energy-containing materials.

Oil/water interface behavior of hesperidin methylchalcone and its application in nano-emulsions

The behavior of hesperidin methylchalcone (HMC) at the oil/water interface was examined through experimental and molecular simulation methods, and a nano-emulsions based on HMC was subsequently fabricated. The findings indicated that HMC spontaneously aggregated at the oil-water interface, leading to a reduction in interfacial tension and an increase in interfacial thickness. Furthermore, its glycoside and benzene ring showed tendencies to interact with water and medium-chain triglyceride, respectively. The HMC addition amount (w), homogenization times (n) and homogenization pressure (p) significantly influenced the formation of the nano-emulsions. The nano-emulsion with an oil-droplet size of 277.26 ± 13.62 nm was obtained at w = 1.0 %, p = 200 bar, and n = 6. When compared to the Tween 20 nano-emulsion, the HMC nano-emulsion demonstrated superior storage stability, antioxidant activity, and lutein bioaccessibility. It could achieve the slow release of HMC. These findings not only broaden the application range of HMC but also contribute to the advancement of functional nano-emulsions.

Characterization and Pickering emulsifying ability of Adinandra nitida leaf polysaccharides

Herein, Adinandra nitida leaf polysaccharides (ANPs) were isolated, identified, and used as a particle emulsifier to stabilize Pickering emulsions. ANP was identified as a polysaccharide with a weight-average molecular weight of 383.10 ± 8.57 kDa that was mainly composed of galacturonic acid (43.94 ± 3.63 mol%), arabinose (17.44 ± 1.06 mol%), glucose (8.53 ± 0.65 mol%), and rhamnose (4.88 ± 0.32 mol%). The main glycosidic linkages included t-Ara(f)-(1→, →4)-Gal(p)-(1→, and →4)-Gal(p)-UA-(1→, with molar percentage ratios of 8.97 %, 19.68 %, and 47.05 %, respectively. ANP possessed a reducing power and ABTS radical scavenging ability. ANP could also reduce the interfacial tension between medium-chain triglycerides (MCT) and water in a concentration-dependent manner, demonstrating its emulsifying role. When the addition amount (c) ≥ 3 %, ANP could stabilize the O/W-type MCT-based Pickering emulsion gel with an oil-phase volume fraction of 70 %, and c was proportional to mechanical parameters such as gel strength, macroscopic viscosity index, and elastic index.

Pickering emulsion gel of polyunsaturated fatty acid-rich oils stabilized by zein-tannic acid green nanoparticles for storage and oxidation stability enhancement

HYPOTHESIS

Poor storage stability and oxidative deterioration are the common drawbacks of edible oils rich in polyunsaturated fatty acids (PUFAs). We hypothesized that the natural zein/tannic acid self-assembly nanoparticles (ZT NPs) could be employed as stabilizers to anchor at the oil-water interface, thus constructing Pickering emulsion gel (PKEG) system for three types of PUFA-rich oils, soybean oil (SO), fish oil (FO) and cod liver oil (CLO), to improve the storage and oxidation stability.

EXPERIMENTS

ZT NPs were prepared by the anti-solvent coprecipitation method, and the three-phase contact angle, FT-IR, and XRD were mainly characterized. To observe the shell-core structure and oil-water interface details of SO/FO/CLO PKEGs by confocal laser scanning microscope and cryo-scanning electron microscope. Accelerated oxidation of FO was performed to assess the protective effect of PKEG on lipids.

FINDINGS

The SO, FO, and CLO PKEGs stabilized by 2 % ZT NPs, with oil fraction (φ = 0.5-0.6), were obtained. PKEGs show high viscoelasticity, clear shell-core structure spatial network structure, and ideal storage stability. Under accelerated oxidation, the degree of oxidative rancidity of FO PKEG was obviously lower than that of free FO. Overall, this work opens up new possibilities for using natural PKEG to prevent oxidative deterioration and prolong the shelf-life of PUFA-rich oils.

Improved Emulsifying Performance of Agarose Microgels by Cross-Interfacial Diffusion of Polyphenols

Noninterface-active polysaccharides can acquire better emulsifying properties through microgelation, yet optimizing their emulsifying performance remains a significant challenge. This study introduces a novel approach to enhance the emulsifying performance of polysaccharide microgels by leveraging the cross-interfacial diffusion of polyphenols, which promotes the interfacial adsorption of microgels. Tannic acid (TA) was predispersed in oil phases and subsequently emulsified with agarose microgel (AM) suspensions, and the impacts of TA diffusion on the emulsifying performance of AMs was investigated. In addition, the transmittance profiles of oil-water biphasic systems were found to innovatively indicate the cross-interfacial diffusion of TA and the interfacial adsorption of AMs. The current results suggest that an appropriate level of TA incorporation can benefit the emulsifying performance of AMs, correlating with decreased droplet sizes and improved physical stability of the emulsion. However, excessive TA might trigger the clustering of AMs before they reach the interfacial layer, adversely affecting the emulsion stability. In conclusion, the cross-interfacial diffusion of polyphenols offers a promising strategy to overcome the stability challenges encountered in polysaccharide microgel-stabilized emulsions.

Construction and characterization of sesame meal-stabilized Pickering high internal phase emulsions and their application in cake production

Pickering high internal phase emulsions (HIPEs) show promise for solid fat replacement and nutrient delivery, but the availability of safe and easily accessible food-borne particulate emulsifiers is a bottleneck limiting their practical application. In this study, the feasibility of using sesame meal as an emulsifier for the construction of sunflower oil-based Pickering HIPEs was evaluated. These HIPEs were then characterized in terms of their microstructural and mechanical properties, and utilized as a substitute for butter in cake production. Results showed that sesame meal is rich in protein, and has a particle size (median diameter, 46.40 ± 0.83 μm), and wettability that makes it suitable for use as an emulsifier. It stabilized O/W type Pickering HIPEs formulated with sunflower oil with a volume fraction of up to 80 %. The mechanical properties of these Pickering HIPEs were positively correlated with the concentration of sesame meal. Sunflower oil-based HIPEs prepared from sesame meal can partially replace butter for cake preparation when φ = 80 % and c = 9.0 %, and enhance the internal pore structure of cake when butter substitution (Wb) ≤ 30 %. This provides a new way to use sesame meal and new type of food-grade Pickering HIPEs.

Physicochemical properties and in vitro digestive behavior of astaxanthin loaded Pickering emulsion gel regulated by konjac glucomannan and κ-carrageenan

This study aimed to elaborate the combination effect of polysaccharides on physicochemical properties and in vitro digestive behavior of astaxanthin (AST)-loaded Pickering emulsion gel. AST-loaded Pickering emulsion gel was prepared by heating Pickering emulsion with konjac glucomannan (KGM) and κ-carrageenan (CRG). The microstructure revealed that adding the two polysaccharides resulted in Pickering emulsion forming a network structure. It exhibited a denser and more uniform network structure, enhancing its mechanical properties four times and increasing its water-holding capacity by 20 %. In vitro digestion experiments demonstrated that the release of free fatty acids from the Pickering emulsion gel (4.25 %) was notably lower than that from conventional Pickering emulsion (17.19 %), whereas AST bioaccessibility was remarkably low at 0.003 %. It provided a feasible strategy to regulate the bioaccessibility in Pickering emulsion, which has theoretical significance to guide the current eutrophic diet people.

A novel Pickering emulsion gels stabilized by cellulose nanofiber/dihydromyricetin composite particles: Microstructure, rheological behavior and oxidative stability

Particle concentrations (w) and oil content (Φ) are crucial factors influencing the gel stability of Pickering emulsions. To understand the stabilization mechanism comprehensively, we prepared emulsion gels stabilized by CNF/DMY composite particles at various w (0.5-1.5 wt%) and Φ (0.2-0.6, v/v). The microstructure revealed the adsorption of these particles at the oil-water interface, with excess particles forming a three-dimensional network structure in the continuous phase. Rheological studies showed that the network structure of Pickering emulsions was significantly influenced by w and Φ, resulting in improved emulsion gel strength that hindered the movement of oil droplets and oxygen in the continuous phase, thereby enhancing emulsion stability. Three scenarios for the critical strain (γco) were observed: at Φ = 0.2, γco decreased with increasing w, while at Φ = 0.4, γco increased with increasing w. At Φ = 0.6, γco remained relatively constant regardless of w. In conclusion, adjusting particle concentration and oil content enabled the control of microstructure, rheological properties, and antioxidant capacity of emulsion gels. These findings could be a valuable resource for formulating and ensuring the quality of emulsion gel-based products in the food industry.

Molecular dynamics simulations of the interfacial behaviors and photo-oxidation of phytosterol under different emulsion oil content

Phytosterol, recognized for its health benefits, is predominantly extracted from plants and exhibits significantly reduced stability under varying light conditions. Their photooxidation is significantly influenced by emulsion interfaces. This study examined the mechanism of interface structure on phytosterol photooxidation with unparalleled molecular precision, utilizing molecular dynamics simulations and experimental procedures. Hydrogen bonding between the hydroxyl group at the C3 position of phytosterols and water molecules, coupled with van der Waals forces between the hydrophobic regions and the oil phase, induced phytosterol molecules to disperse toward the interface. The elevated polarity of the oil phase, specifically in tributyrin, facilitated the permeation of water molecules into the oil phase. This was achieved by diminishing the emulsion's interfacial tension, thereby fostering the development of more interface or micelles, and accelerating the photooxidation process of phytosterols. These simulations unraveled that the preponderance of phytosterol distribution is localized and oxidized at the oil-water interface.

Effect of sulfuric acid hydrolysis on the structure and Pickering emulsifying capacity of acorn starch

The acid-hydrolyzed acorn starch samples (HAS-1, HAS-2, HAS-3, and HAS-4) were prepared from natural acorn starch (NAS) at sulfuric acid concentrations of 1, 2, 3, and 4 mol/L for 2 d. The particle characteristics and structures of HAS were investigated, and Pickering high internal phase emulsions (HIPEs) based on HAS were constructed and characterized. The results showed that with an increase in sulfuric acid concentration, the size, yield, amylose content, molecular weight, and amylopectin chain length of HAS gradually decreased. HAS retained an A-type crystal structure, and its relative crystallinity and short-range order degree gradually increased with increasing sulfuric acid concentration. Acid hydrolysis treatment improved the wettability of NAS, and its effect was positively correlated with the sulfuric acid concentration. HAS-3 and HAS-4 could stabilize the Pickering HIPEs with an oil phase volume fraction of 80% at c ≥ 1.5%. The mechanical properties of the HIPEs were positively correlated with c.

Fabrication, characterization and application of Pickering emulsion gels stabilized by defatted grape seed powder

The feasibility of defatted grape seed powder (DGSP) stabilizing Pickering emulsion gels as butter substitute was investigated. The Pickering emulsion gel was constructed using DGSP through high-speed homogenization, and the effects of particle concentration (c) and oil-phase (Medium chain triglyceride) volume fraction (φ) on its structure and properties were investigated. Its application as a butter substitute was also evaluated. The results showed that DGSP had various particle shapes, a wide particle size distribution (3-130 μm), and a three-phase contact angle of 128.9 ± 2.3°. The O/W Pickering emulsion gels with φ ≥ 60% could be obtained at c ≥ 2%. The droplet diameter was negatively correlated with c and positively correlated with φ, while the gel strength was positively related to c and φ. The resulting emulsion gel demonstrated solid-like viscoelastic behavior and pseudoplasticity, and had the potential to serve as a butter substitute. The results can promote the application of grape seeds in food.

The Effect of Acid Hydrolysis on the Pickering Emulsifying Capacity of Tartary Buckwheat Flour

The effect of sulfuric acid hydrolysis on the Pickering emulsifying capacity of Tartary buckwheat flour (TBF) rich in starch was evaluated for the first time. The results indicate that the sulfuric acid concentration and hydrolysis time had a significant impact on the Pickering emulsifying capacity of acid-hydrolyzed Tartary buckwheat flour (HTBF). A low sulfuric acid concentration (1-2 mol/L) could reduce the particle size of HTBF, but it also decreased the Pickering emulsifying ability. At a sulfuric acid concentration of 3 mol/L, appropriate treatment time (2 and 3 days) led to particle aggregation but significantly improved wettability, thereby resulting in a rapid enhancement in emulsifying capacity. Under these conditions, the obtained HTBF (HTBF-D2-C3 and HTBF-D3-C3) could stabilize medium-chain triglyceride (MCT)-based Pickering high-internal-phase emulsions (HIPEs) with an oil-phase volume fraction of 80% at the addition amounts (c) of ≥1.0% and ≥1.5%, respectively. Its performance was significantly superior to that of TBF (c ≥ 2.0%). Furthermore, at the same addition amount, the droplet size of HIPEs constructed by HTBF-D3-C3 was smaller than that of HTBF-D2-C3, and its gel strength and microrheological performance were also superior to those of HTBF-D2-C3, which was attributed to the higher wettability of HTBF-D3-C3. The findings of this study can facilitate the in-depth application of Tartary buckwheat and provide references for the development of novel Pickering emulsifiers.

Molecular simulation for food protein-ligand interactions: A comprehensive review on principles, current applications, and emerging trends

In recent years, investigations on molecular interaction mechanisms between food proteins and ligands have attracted much interest. The interaction mechanisms can supply much useful information for many fields in the food industry, including nutrient delivery, food processing, auxiliary detection, and others. Molecular simulation has offered extraordinary insights into the interaction mechanisms. It can reflect binding conformation, interaction forces, binding affinity, key residues, and other information that physicochemical experiments cannot reveal in a fast and detailed manner. The simulation results have proven to be consistent with the results of physicochemical experiments. Molecular simulation holds great potential for future applications in the field of food protein-ligand interactions. This review elaborates on the principles of molecular docking and molecular dynamics simulation. Besides, their applications in food protein-ligand interactions are summarized. Furthermore, challenges, perspectives, and trends in molecular simulation of food protein-ligand interactions are proposed. Based on the results of molecular simulation, the mechanisms of interfacial behavior, enzyme-substrate binding, and structural changes during food processing can be reflected, and strategies for hazardous substance detection and food flavor adjustment can be generated. Moreover, molecular simulation can accelerate food development and reduce animal experiments. However, there are still several challenges to applying molecular simulation to food protein-ligand interaction research. The future trends will be a combination of international cooperation and data sharing, quantum mechanics/molecular mechanics, advanced computational techniques, and machine learning, which contribute to promoting food protein-ligand interaction simulation. Overall, the use of molecular simulation to study food protein-ligand interactions has a promising prospect.

Evaluating the role of glycyrrhizic acid on the dynamic stabilization mechanism of the emulsion prepared by α-Lactalbumin: Experimental and silico approaches

The role of glycyrrhizic acid (GA) on the dynamic stabilization mechanism of the α-Lactalbumin (α-La) emulsion was evaluated in this study. Smaller particle size and higher zeta potential value were observed in the α-La/GA emulsion as compared to the α-La emulsion. Ultra-high-resolution microscopy revealed that the interfacial film formed around oil droplets by α-La/GA complex was thicker compared to that of either α-La or GA. The appearance of a new peak at 1679 cm-1 in FTIR of the α-La/GA emulsion attributed to the stretching vibration of CO, providing evidence of the formation of a stable emulsion system. The results from dynamic molecular simulation showed GA induced the formation of an interfacial adsorption layer at the oil-water interface, reducing the migration ability of GA. The findings indicate that the presence of GA in the α-La emulsion effectively enhances its stability, highlighting its potential as a valuable emulsifying agent for various industrial applications.

Cryoprotective effect of soybean oil on surimi gels and the mechanism based on molecular dynamics simulation

The effect of soybean oil (SO) on freeze-thaw (F-T)-treated surimi was investigated and its related mechanism was revealed by molecular dynamics (MD) simulations. The results displayed that SO has a disrupting effect on the structure of fresh samples. However, in the F-T-treated samples, surimi gels supplemented with SO had a more uniform microstructure. Simultaneously, when SO was added from 0% to 7% in the F-T-treated samples, the gel strength increased from46.66 to 51.86 N · mm $$ 46.66\ \mathrm{to}\ 51.86\;\mathrm{N}\cdotp \mathrm{mm} $$ (p < .05), the physically bound water was increased from 92.90% to 94.15% (p < .05), and storage modulus was increased from 5939 to 6523 Pa. Triglycerides of SO generated hydrophobic interactions with myosin mainly in carbon chains. Computational results from MD simulations illustrated that the structure of myosin combined with triglycerides was more stable than that of myosin alone during temperature fluctuations (-20 to 4°C). During ice crystal growth, triglycerides absorbed on the myosin surface inhibited the growth of surrounding ice crystals and mitigated the ice crystal growth rate (from 7.54 to 5.99 cm/s). The addition of SO during the F-T treatments allowed myosin to be less negatively affected by ice crystal formation and temperature fluctuations and ultimately contributed to the formation of a more uniform network gel structure.

Characterization of polysaccharide from Lonicera japonica Thunb leaves and its application in nano-emulsion

The polysaccharides in honeysuckle leaves (PHL) were separated and characterized for the first time. The nano-emulsion stabilized by PHL and whey protein isolate (WPI) were also fabricated based on the ultrasonic method. The results indicated that PHL was mainly composed of glucose (47.40 mol%), galactose (19.21 mol%) and arabinose (20.21 mol%) with the weight-average molecular weight of 137.97 ± 4.31 kDa. The emulsifier concentration, WPI-to-PHL ratio, ultrasound power and ultrasound time had significant influence on the droplet size of PHL-WPI nano-emulsion. The optimal preparation conditions were determined as following: emulsifier concentration, 1.7%; WPI/PHL ratio, 3:1; ultrasonic power, 700 W; ultrasonic time, 7 min. Under the above conditions, the median diameter of the obtained nano-emulsion was 317.70 ± 5.26 nm, close to the predicted value of 320.20 nm. The protective effect of PHL-WPI emulsion on β-carotene against UV irradiation was superior to that of WPI emulsion. Our results can provide reference for the development of honeysuckle leaves.