Cuixia Sun

Utilization of interfacial engineering to improve physicochemical stability of β-carotene emulsions: Multilayer coatings formed using protein and protein–polyphenol conjugates

The impact of lactoferrin (LF)-chlorogenic acid (CA) and (-)-Epigallocatechin-3-gallate (EGCG) conjugates on the physicochemical properties of β-carotene emulsions was investigated. Formation of lactoferrin-polyphenol conjugates, which was confirmed by SDS-PAGE, caused changes in the structure and nature of lactoferrin. Based on layer-by-layer electrostatic deposition, β-carotene bilayer emulsions were prepared by lactoferrin and lactoferrin-polyphenol conjugates at pH 7.0. The physicochemical properties of primary and secondary emulsions were evaluated and the results suggested that LF-polyphenol conjugates-stabilized primary and secondary emulsions exhibited better emulsifying properties and improved physical stability of β-carotene bilayer emulsions under freeze-thaw, ionic strength and thermal treatments. In addition, the lactoferrin-polyphenol conjugates could effectively enhance chemical stability of β-carotene in oil-in-water emulsions against heat treatment and ultraviolet light exposure, and the least degradation of β-carotene occurred in LF-EGCG conjugate-stabilized primary emulsion. The interfacial engineering technology utilized in this study may lead to the formation of emulsions with improved physicochemical and functional performance.

Structural characterization and functional evaluation of lactoferrin–polyphenol conjugates formed by free-radical graft copolymerization

Covalent modifications of lactoferrin (LF) with epigallocatechin gallate (EGCG), chlorogenic acid (CA) and gallic acid (GA) were performed by adopting a free-radical grafting procedure in aqueous media. The resulting LF–polyphenol conjugates were characterized in terms of structural and functional properties. Results showed that the covalent binding amount into the LF molecule of EGCG, CA and GA was 68, 58 and 17 nmol mg−1, respectively. Covalent insertion of polyphenols into the LF molecule was verified by SDS-PAGE and MALDI-TOF-MS analysis, and in particular the molecular weight was increased from 84 011 Da (LF) to 85 906 Da (LF–CA conjugate). The circular dichroism and Fourier transform infrared spectroscopy analyses revealed that the content of α-helix increased and the contents of the remaining structures decreased, while the differential scanning calorimetry data indicated that the thermal stability of LF–polyphenol conjugates was enhanced after the modification. In addition, the antioxidant activity of LF–polyphenol conjugates was 0.23- to 2.10-fold (ABTS˙+ scavenging assay), and 0.04- to 2.19-fold (reducing power assay) higher than that of the control LF. Moreover, the covalent modification obviously changed the solubility and emulsifying properties of LF. The emulsifying properties of the LF–CA conjugate were better than those of the LF–EGCG and LF–GA conjugates.

Physicochemical properties of β-carotene emulsions stabilized by chlorogenic acid–lactoferrin–glucose/polydextrose conjugates

In this study, the influence of chlorogenic acid (CA)-lactoferrin (LF)-glucose (Glc) conjugate and CA-LF-polydextrose (PD) conjugate on the physicochemical characteristics of β-carotene emulsions was investigated. Novel emulsifiers were formed during Maillard reaction between CA-LF conjugate and Glc/PD. The physicochemical properties of β-carotene emulsions were characterized by droplet size, ζ-potential, rheological behavior, transmission changes during centrifugal sedimentation and β-carotene degradation. Results showed that the covalent attachment of Glc or PD to CA-LF conjugate effectively increased the hydrophilicity of the oil droplets surfaces and strengthened the steric repulsion between the oil droplets. Glucose was better than polydextrose for the conjugation with CA-LF conjugate to stabilize β-carotene emulsions. In comparison with LF and CA-LF-Glc/PD mixtures, CA-LF-Glc/PD ternary conjugates exhibited better emulsifying properties and improved physical stability of β-carotene emulsions during the freeze-thaw treatment. In addition, CA-LF-Glc/PD conjugates significantly enhanced chemical stability of β-carotene in the emulsions against ultraviolet light exposure.

Fabrication mechanism and structural characteristics of the ternary aggregates by lactoferrin, pectin, and (-)-epigallocatechin gallate using multispectroscopic methods.

The ternary aggregates were fabricated by lactoferrin (LF), pectin (high methylated pectin (HMP)/low methylated pectin (LMP)), and (-)-epigallocatechin gallate (EGCG) through three different fabrication methods at pH 5.0. The turbidity, particle size, and ζ-potential of ternary aggregates were influenced by the types of pectin, the concentration of EGCG, and fabrication methods. The fluorescence intensity of LF decreased with an increase in EGCG concentration for all ternary aggregates. Far-UV circular dichroism results indicated that EGCG could alter the secondary structure of LF with an increase in the proportion of β-sheet structure at the cost of unordered coil structure. According to near-UV circular dichroism results, EGCG could also modulate the tertiary structure of LF at the presence of pectin. In addition, EGCG could increase the viscoelasticity of the ternary aggregates with HMP, leading to better stability of the ternary aggregates. An opposite result was observed for the ternary aggregates with LMP. These findings should provide an insight into the fabrication mechanism and applications of ternary aggregates formed by protein, polysaccharide, and polyphenol in the food, pharmaceutical, and cosmetic industries.

Preparation, characterization and stability of curcumin-loaded zein-shellac composite colloidal particles

Curcumin-loaded zein-shellac composite particles were prepared by the antisolvent co-precipitation method. The encapsulation efficiency of curcumin was significantly improved from 82.7% in zein particles to 93.2% in zein-shellac complex particles. The result of differential scanning calorimetry suggested that curcumin in the polymeric matrix was in an amorphous state. Fourier transform infrared spectroscopy analysis revealed that curcumin had non-covalently interacted with zein and shellac, mainly through hydrogen bonding and hydrophobic interaction. Aggregates in irregular shapes, with large sizes, were found by atomic force microscopy, and conglutination, integration or fusion of different entities into network structures occurred at a high level of shellac. At the mass ratio of zein to shellac of 1:1, curcumin in the complex particles exhibited improved photochemical and thermal stability. Curcumin-loaded zein-shellac complex particles allowed the controlled release of curcumin in both PBS medium and simulated gastrointestinal fluids.

Structural characterization, formation mechanism and stability of curcumin in zein-lecithin composite nanoparticles fabricated by antisolvent co-precipitation

Curcumin (Cur) exhibits a range of bioactive properties, but its application is restrained due to its poor water solubility and sensitivity to environmental stresses. In this study, zein-lecithin composite nanoparticles were fabricated by antisolvent co-precipitation technique for delivery of Cur. The result showed that the encapsulation efficiency of Cur was significantly enhanced from 42.03% in zein nanoparticles to 99.83% in zein-lecithin composite nanoparticles. The Cur entrapped in the nanoparticles was in an amorphous state confirmed by differential scanning calorimetry and X-ray diffraction. Fourier transform infrared analysis revealed that hydrogen bonding, electrostatic interaction and hydrophobic attraction were the main interactions among zein, lecithin, and Cur. Compared with single zein and lecithin nanoparticles, zein-lecithin composite nanoparticles significantly improved the stability of Cur against thermal treatment, UV irradiation and high ionic strength. Therefore, zein-lecithin composite nanoparticles could be a potential delivery system for water-insoluble bioactive compounds with enhanced encapsulation efficiency and chemical stability.

The Interaction between Zein and Lecithin in Ethanol-Water Solution and Characterization of Zein–Lecithin Composite Colloidal Nanoparticles

Lecithin, a naturally small molecular surfactant, which is widely used in the food industry, can delay aging, enhance memory, prevent and treat diabetes. The interaction between zein and soy lecithin with different mass ratios (20:1, 10:1, 5:1, 3:1, 2:1, 1:1 and 1:2) in ethanol-water solution and characterisation of zein and lecithin composite colloidal nanoparticles prepared by antisolvent co-precipitation method were investigated. The mean size of zein-lecithin composite colloidal nanoparticles was firstly increased with the rise of lecithin concentration and then siginificantly decreased. The nanoparticles at the zein to lecithin mass ratio of 5:1 had the largest particle size (263 nm), indicating that zein and lecithin formed composite colloidal nanoparticles, which might aggregate due to the enhanced interaction at a higher proportion of lecithin. Continuing to increase lecithin concentration, the zein-lecithin nanoparticles possibly formed a reverse micelle-like or a vesicle-like structure with zein in the core, which prevented the formation of nanoparticle aggregates and decreased the size of composite nanoparticles. The presence of lecithin significantly reduced the ζ-potential of zein-lecithin composite colloidal nanoparticles. The interaction between zein and lecithin enhanced the intensity of the fluorescence emission of zein in ethanol-water solution. The secondary structure of zein was also changed by the addition of lecithin. Differential scanning calorimetry thermograms revealed that the thermal stability of zein-lecithin nanoparticles was enhanced with the rise of lecithin level. The composite nanoparticles were relatively stable to elevated ionic strengths. Possible interaction mechanism between zein and lecithin was proposed. These findings would help further understand the theory of the interaction between the alcohol soluble protein and the natural small molecular surfactant. The composite colloidal nanoparticles formed in this study can broaden the application of zein and be suitable for incorporating water-insoluble bioactive components in functional food and beverage products.

Glycosylation improves the functional characteristics of chlorogenic acid–lactoferrin conjugate

In the present study, a chlorogenic acid (CA)–lactoferrin (LF) conjugate prepared via alkali treatment was glycoslated with glucose (Glc) or polydextrose (PD) by the Maillard reaction. Formation of the covalent CA–LF–Glc/PD ternary conjugates was confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and fluorescence analyses. The results showed that the grafting ratio between the CA–LF conjugate and Glc/PD was 40.50% for the CA–LF–Glc ternary conjugate and 11.72% for the CA–LF–PD ternary conjugate. Conjugating CA and Glc/PD onto LF changed the conformation of the protein, leading to a reduction in the α-helix content and an increase in the unordered structure. The thermal stability of the CA–LF conjugate was remarkably improved by the Maillard-type conjugation. According to AFM and DLS results, the ternary conjugates showed coarser structures and bigger particle sizes than their mixtures. The reducing power was increased from 206.91 μmol Trolox g−1 of CA–LF conjugate to 255.76 and 273.25 μmol Trolox g−1 sample, respectively, in CA–LF–Glc and CA–LF–PD ternary conjugates, indicating the glycosylation was an effective way to improve the antioxidant activity of the CA–LF conjugate. Moreover, the ternary conjugates were employed to encapsulate β-carotene as a model biologically active macromolecule, and they could enhance the physicochemical stability of β-carotene emulsions. This work presented a simple and general approach to the preparation of polyphenol–protein–polysaccharide conjugates that could be potentially employed as food-grade biomacromolecules in the food and pharmaceutical industries.

Inhibition of the Aggregation of Lactoferrin and (−)-Epigallocatechin Gallate in the Presence of Polyphenols, Oligosaccharides, and Collagen Peptide

The aggregation of lactoferrin and (-)-epigallocatechin gallate (EGCG) was inhibited by polyphenols, oligosaccharides, and collagen peptide in this study. Polyphenols, oligosaccharides, or collagen peptide can effectively prevent the formation of lactoferrin-EGCG aggregates, respectively. The addition sequence of lactoferrin, polyphenols (oligosaccharides or collagen peptide) and EGCG can affect the turbidity and particle size of the ternary complexes in the buffer solution; however, it hardly affected the ζ-potential and fluorescence characteristics. With either positive or negative charge, polyphenols and collagen peptide disrupted the formation of lactoferrin-EGCG aggregate mainly through the mechanism of its competition with EGCG molecules which surrounded the lactoferrin molecule surface with weaker binding affinities, forming polyphenols or a collagen peptide-lactoferrin-EGCG ternary complex; for neutral oligosaccharides, the ternary complex was generated mainly through steric effects, accompanied by a change in the lactoferrin secondary structure induced by gallic acid, chlorogenic acid, and xylo-oligosaccharide. Polyphenols, oligosaccharides, or collagen peptide restraining the formation of lactoferrin-EGCG aggregate could be applied in the design of clear products in the food, pharmaceutical, and cosmetic industries.

Effects of Dynamic High-Pressure Microfluidization Treatment and the Presence of Quercetagetin on the Physical, Structural, Thermal, and Morphological Characteristics of Zein Nanoparticles

The effects of dynamic high-pressure microfluidization (DHPM) and the addition of quercetagetin on the physical, structural, thermal, and morphological characteristics of zein nanoparticles were investigated. The result of Fourier transform infrared spectroscopy revealed that DHPM treatment caused the structural changes of zein, and the primary interactions between zein and quercetagetin were hydrogen bond and hydrophobic effects. Both of the DHPM treatment and the addition of quercetagetin resulted in the decrease of fluorescence intensity, the improved thermal stability, and the reducing of α-helix and the increase of β-sheets as proved by fluorescence spectra, differential scanning calorimetry thermograms, and circular dichroism spectra, respectively. It was found that the combined DHPM treatment and the addition of quercetagetin with mass ratio of zein to quercetagetin of 40:1 exhibited the morphology of nanospheres with more compact structure and uniform particle distribution.