Shuqin Xia

Liposome as a Delivery System for Carotenoids: Comparative Antioxidant Activity of Carotenoids As Measured by Ferric Reducing Antioxidant Power, DPPH Assay and Lipid Peroxidation

This study was conducted to understand how carotenoids exerted antioxidant activity after encapsulation in a liposome delivery system, for food application. Three assays were selected to achieve a wide range of technical principles, including 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging, ferric reducing antioxidant powder (FRAP), and lipid peroxidation inhibition capacity (LPIC) during liposome preparation, auto-oxidation, or when induced by ferric iron/ascorbate. The antioxidant activity of carotenoids was measured either after they were mixed with preformed liposomes or after their incorporation into the liposomal system. Whatever the antioxidant model was, carotenoids displayed different antioxidant activities in suspension and in liposomes. The encapsulation could enhance the DPPH scavenging and FRAP activities of carotenoids. The strongest antioxidant activity was observed with lutein, followed by β-carotene, lycopene, and canthaxanthin. Furthermore, lipid peroxidation assay revealed a mutually protective relationship: the incorporation of either lutein or β-carotene not only exerts strong LPIC, but also protects them against pro-oxidation elements; however, the LPIC of lycopene and canthaxanthin on liposomes was weak or a pro-oxidation effect even appeared, concomitantly leading to the considerable depletion of these encapsulated carotenoids. The antioxidant activity of carotenoids after liposome encapsulation was not only related to their chemical reactivity, but also to their incorporation efficiencies into liposomal membrane and modulating effects on the membrane properties.

Liposomes as vehicles for lutein: preparation, stability, liposomal membrane dynamics, and structure.

Lutein was loaded into liposomes, and their stability against environmental stress was investigated. Subsequently, these findings were correlated with the interactions between lutein and lipid bilayer. Results showed that the liposomes with loaded lutein at concentrations of 1 and 2% remained stable during preparation, heating, storage, and surfactant dissolution. However, with further increase in the loading concentration to 5 and 10%, the stabilization role of lutein on membrane was not pronounced or even opposite. Membrane fluidity demonstrated that at 1 and 2%, lutein displayed less fluidizing properties both in the headgroup region and in the hydrophobic core of the liposome, whereas this effect was not significant at 5 and 10%. Raman spectra demonstrated that lutein incorporation greatly affected the lateral packing order between acyl chains and longitudinal packing order of lipid acyl chains. These results may guide the potential application of liposomes as carriers for lutein in nutraceuticals and functional foods.

Liposomes as delivery systems for carotenoids: comparative studies of loading ability, storage stability and in vitro release

This study compared the loading ability of various carotenoids into liposomal membrane, lipid peroxidation inhibition capacity, storage stability and in vitro release behavior in simulated gastrointestinal (GI) media. It was found that carotenoids exhibited various incorporating abilities into liposomes ranging from the strongest to the weakest: lutein > β-carotene > lycopene > canthaxanthin. A similar trend was also observed in their antioxidant activities against lipid peroxidation during preparation. Storage measurements demonstrated that a liposomal membrane can strongly retain β-carotene and lutein, whereas this effect was not pronounced for lycopene and canthaxanthin. In vitro release experiments showed that lutein and β-carotene were hardly released in a simulated gastric fluid, while displaying a slow and sustained release in a simulated intestinal fluid. By contrast, lycopene and canthaxanthin underwent fast and considerable release in GI media. Dynamic light scattering indicated that carotenoid incorporation strongly affected the particle stability and dispersion during preparation and GI incubation. The differences in molecular release may be attributed to the different modulating effects of carotenoids. Our results may guide the potential application of liposomes as carriers for the controlled delivery of carotenoids in nutraceutical and functional foods.

Modulation of the carotenoid bioaccessibility through liposomal encapsulation.

The low bioaccessibility of carotenoids is currently a challenge to their incorporation in pharmaceutics, nutraceuticals and functional foods. The aim of this study was to evaluate the modulating effects of liposome encapsulation on the bioaccessibility, and its relationship with carotenoid structure and incorporated concentration. The physical stability of liposomes, lipid digestibility, carotenoids release and bioaccessibility were investigated during incubation in a simulated gastrointestinal tract. Analysis on the liposome size and morphology showed that after digestion, the majority of particles maintained spherical shape with only an increase of size in liposomes loading β-carotene or lutein. However, a large proportion of heterogeneous particles were visible in the micelle phase of liposomes loading lycopene or canthaxanthin. It was also found that the release of lutein and β-carotene from liposomes was inhibited in a simulated gastric fluid, while was slow and sustained in a simulated intestinal fluid. By contrast, lycopene and canthaxanthin exhibited fast and considerable release in the gastrointestinal media. Both carotenoid bioaccessibility and micellization content decreased with the increase of incorporated concentration. Anyway, the bioaccessibility of carotenoids after encapsulated in liposomes was in the following order: lutein>β-carotene>lycopene>canthaxanthin. Bivariate correlation analysis revealed that carotenoid bioaccessibility depended strongly on the incorporating ability of carotenoids into a lipid bilayer, loading content, and nature of the system.

Preparation and pH Stability of Ferrous Glycinate Liposomes

Ferrous glycinate liposomes were prepared by reverse phase evaporation method. The effects of cholesterol, Tween 80, ferrous glycinate concentration, hydrating medium, pH of hydrating medium, and sonication strength on the encapsulation efficiency of liposomes were investigated. Encapsulation efficiency was significantly influenced by the different technique parameters. Ferrous glycinate liposomes might be obtained with high encapsulation efficiency of 84.80% under the conditions of optimized technique parameters. The zeta potential and average particle size of liposomes in the hydrating medium of pH 7.0 were 9.6 mV and 559.2 nm, respectively. The release property of ferrous glycinate liposomes in vitro was investigated in simulated gastrointestinal juice. A small amount of ferrous glycinate was released from liposomes in the first 4 h in simulated gastrointestinal juice. The mean diameters of liposomes increased from 559.2 to 692.9, 677.8, and 599.3 nm after incubation in simulated gastrointestinal juice of pH 1.3, 7.5, and 7.5 in the presence of bile salts, respectively. Results showed that the stability of ferrous glycinate in strong acid environment was greatly improved by encapsulation in liposomes, which protected ferrous glycinate from disrupting the extracapsular environment by lipid bilayer. The bioavailability of ferrous glycinate, as the iron source for biological activity including hemoglobin formation, may be increased. The ferrous glycinate liposomes may be a kind of promising iron fortifier.

Transglutaminase cross-linking effect on sensory characteristics and antioxidant activities of Maillard reaction products from soybean protein hydrolysates.

To improve the yield of Maillard peptides, a microbial transglutaminase (MTGase) was used to increase the content of 1000-5000Da peptides in soybean protein hydrolysates by using a cross-linking reaction. The sensory characteristics and antioxidant activities of corresponding Maillard Reaction Products (MSPC) was then evaluated. After cross-linking treatment the content of 1000-5000Da peptides in protein hydrolysates and the yield of Maillard peptides increased by 21.19% and 8.71%, respectively, which contributed to the improved mouthfulness of MSPC. The bitter amino acids were significantly decreased and the umami acids were markedly increased in MSPC. Volatile compounds identified by GC-MS analysis showed that the content of the important meaty flavour compounds (such as 2-methyl-3-furanthiol, bis(2-methyl-3-furyl)disulfide) of MSPC were dramatically higher than that of MRPs from uncross-linking peptides. Combined with sensory evaluation, it was confirmed that MTGase cross-linking improved the flavour Characteristics and did not affect the antioxidant activity of MSPC.

Contribution of beef base to aroma characteristics of beeflike process flavour assessed by descriptive sensory analysis and gas chromatography olfactometry and partial least squares regression

Descriptive sensory analysis and gas chromatography-mass spectrometry (GC-MS) analysis were conducted to investigate changes in aroma characteristics of beeflike process flavours (BPFs) prepared from enzymatically hydrolyzed beef (beef base) of different DH (degree of hydrolysis) with other ingredients. Five attributes (beefy, meaty, simulate, mouthful and roasted) were selected to assess BPFs. The results of descriptive sensory analysis confirmed that BPF2 from beef base of moderate DH 29.13% was strongest in beefy, meaty and simulate characteristics; BPF4 and BPF5 from beef base of higher DH (40.43% and 44.22%, respectively) were superior in mouthful and roasted attributes respectively; while BPF0 without beef base gave weaker odour for all attributes. Twenty six compounds from GC-MS were selected as specific compounds to represent beef odour based on their odour-active properties assessed by a detection frequency method of GC-O and correlation of their contents with sensory attributes intensity. Correlation analysis of molecular weight (MW) of peptides, odour-active compounds and sensory attributes through partial least squares regression (PLSR) further explained that beef base with DH of 29.13% was a desirable precursor for imparting aroma characteristics of beeflike process flavour.

Fabrication of Epigallocatechin-3-gallate Nanocarrier Based on Glycosylated Casein: Stability and Interaction Mechanism

Polyphenols normally have strong binding affinity with proteins, which may lead to protein precipitation. Glycosylation of protein via Maillard reaction in mild condition may inhibit the precipitation. This study prepared nanocomplexes of epigallocatechin-3-gallate (EGCG) and protein, and their stability against environmental stress was investigated. Subsequently, these findings were correlated with the interactions between EGCG and casein. Results showed that glycosylated casein displayed strong encapsulating and retaining capacity to EGCG, and no obvious aggregation or fusion appeared in the concentration range of 0.25-5.00 mg/mL during storage. The in vitro release demonstrated that casein, especially glycosylated casein, could effectively protect EGCG from degradation in alkaline pH and displayed a slow and sustained release in intestinal fluid, which may be attributed to the inhibiting effects of casein binding on the motion freedom of EGCG. Fluorescence quenching spectra demonstrated that the steric hindrance induced by dextran could inhibit the interaction between casein and EGCG. These findings demonstrated that glycosylated casein could be used as a promising and effective nanocarrier for EGCG.

Modulating effect of lipid bilayer–carotenoid interactions on the property of liposome encapsulation

Liposomes have become an attractive alternative to encapsulate carotenoids to improve their solubility, stability and bioavailability. The interaction mechanism of carotenoid with lipid bilayer is one of the major concerns in improving the delivery efficiency of liposomes. In this study, the microstructure and carotenoid encapsulation efficiency of liposomes composed of native phospholipid (egg yolk phosphatidylcholine, EYPC) and nonionic surfactant Tween 80 were investigated by atomic force microscopy, dynamic light scattering, and Raman spectroscopy, respectively. Subsequently, the effects of carotenoid incorporation on the physical properties of liposomal membrane were performed by Raman spectroscopy, fluorescence polarization, and electron paramagnetic resonance. Results showed that the incorporation of carotenoids affected the liposomes morphology, size and size distribution to various extents. Analysis on the Raman characteristic peaks of carotenoids revealed that lutein exhibited the strongest incorporating ability into liposomes, followed by β-carotene, lycopene, and canthaxanthin. Furthermore, it was demonstrated that carotenoids modulated the dynamics, structure and hydrophobicity of liposomal membrane, highly depending on their molecular structures and incorporated concentration. These modulations were closely correlated with the stabilization of liposomes, including mediating particle aggregation and fusion. These findings should guide the rationale designing for liposomal encapsulation technology to efficiently deliver carotenoids in pharmaceutics, nutraceuticals and functional foods.

Dual Effects of Chitosan Decoration on the Liposomal Membrane Physicochemical Properties As Affected by Chitosan Concentration and Molecular Conformation

This study was devoted to a further understanding of the dependence of liposomal membrane properties on chitosan conformation and proved the dual effects of chitosan. The concentration dependence of chitosan conformation in aqueous solution was illustrated by surface tension and fluorescence probe techniques. Fluorescence and Raman spectra were subsequently employed to investigate the dynamic and structural changes of the liposomal membrane resulting from chitosan decoration. Results showed that the unfolded and crimped chains of chitosan flatly adsorbed onto the membrane surface via electrostatic attraction and favored liposome stability. Furthermore, the adsorption of crimped chains seemed stronger due to the embedding of their hydrophobic moieties. However, the presence of chitosan coils induced the increase in membrane fluidity, the intrachain disorder in lipid molecules, and the gauche conformation change of choline group. Dynamic light scattering and lipid oxidation measurements demonstrated that this perturbation was correlated with the permeation of coils into the lipid bilayer.