Hailong Yu

Bioavailability and delivery of nutraceuticals using nanotechnology.

Nanotechnology is an enable technology that has the potential to revolutionize agriculture and food systems. Driven by increasing consumer demand for healthy food products, researchers have been applying tools and knowledge in nanotechnology to address the issues relevant to food and nutrition. This concise review is mainly focused on nanoemulsions and polymer micelles-based delivery systems which have shown enhanced oral bioavailability and biological efficacies (that is, antiinflammation, anti-cancer, and so on) of different phytochemicals. Nanoemulsions are a class of extremely small droplets that appear to be transparent or translucent with a bluish coloration. They are usually in the range 50 to 200 nm but much smaller than the range (from 1 to 100 mum) for conventional emulsions. Nanoemulsion preparation, characterization, and bioavailability have been discussed. Curcumin nanoemulsions show 85% inhibition of TPA-induced mouse ear inflammation as well as the inhibition of cyclin D1 expression, while dibenzoylmethane (DBM) nanoemulsion shows about 3-fold increase in oral bioavailability compared to the conventional DBM emulsion. Biopolymer micelles show significantly improved water solubility/dispersibility and in vitro anti-cancer activity of phytochemicals. More research efforts are still needed for the understanding of the potential impacts of nanoencapsulated phytochemicals on the human body and environment to address the public concerns.

Encapsulation of epigallocatechin-3-gallate (EGCG) using oil-in-water (O/W) submicrometer emulsions stabilized by ι-carrageenan and β-lactoglobulin.

Oil-in-water (O/W) submicrometer emulsions stabilized by ι-carrageenan and β-lactoglobulin were successfully prepared by high-pressure homogenization (HPH), with the goal to develop biocompatible carriers for the active component of green tea, epigallocatechin-3-gallate (EGCG). The effects of pressure and the number of cycles on the physical properties of emulsions, such as droplet sizes, microstructure, and rheological properties were investigated. The increase in both processing pressure and the number of HPH cycles resulted in a decrease in droplet sizes and viscosities. A submicrometer O/W emulsion with a droplet size of about 400 nm was used to encapsulate EGCG. The results showed that, when EGCG concentration was up to 0.5% in the emulsion, EGCG could be successfully encapsulated in the O/W emulsions stabilized by ι-carrageenan and β-lactoglobulin. Within 14 days, emulsion droplet sizes showed negligible changes. However, when EGCG concentration was >0.5%, significant instability of the O/W emulsions due to the binding between EGCG and β-lactoglobulin was observed, as evidenced by the largely increased droplet sizes from light scattering and the appearance of large aggregates in the optical images. Moreover, EGCG encapsulated in an O/W submicrometer emulsion revealed an enhanced in vitro anticancer activity compared to the free EGCG. This study provides a novel encapsulation formulation to increase the biological efficacy of EGCG.

Investigation of the absorption mechanism of solubilized curcumin using Caco-2 cell monolayers.

Curcumin is a bioactive compound with poor oral bioavailability. Low water solubility and rapid metabolism are two known limiting factors, but the absorption mechanism of solubilized curcumin remains unclear. This study investigated the permeation mechanism of solubilized curcumin using an in vitro Caco-2 cell monolayer model. It was shown that curcumin permeated across the monolayers fairly rapidly [P(app)(A-B) = (7.1 ± 0.7) × 10(-6) cm/s] and the permeation mechanism was found as passive diffusion [P(app)(B-A)/P(app)(A-B) = 1.4]. Furthermore, the permeation rates of curcumin complexed with bovine serum albumin and in the bile salts-fatty acids mixed micelles were also determined as P(app)(mixed micelle) > P(app)(DMSO) > P(app)(protein complex). These results suggested that solubilization agents play an important role in the permeation of solubilized curcumin, and stronger binding between the solubilization agents and curcumin may decrease the permeation rate. The results further suggest that lipid-based formulations, which solubilize curcumin in mixed micelles after lipid digestion, are promising vehicles for curcumin oral delivery.

Synthesis and characterization of novel antimicrobial emulsifiers from ε-polylysine.

epsilon-Polylysine (EPL) has been used in the food industry as an antimicrobial additive and also a dietary agent. To generate amphiphilic molecules from EPL, hydrophobically modified epsilon-polylysine graft copolymers, which were denoted as OSA-g-EPLs, were synthesized by reacting EPL with octenyl succinic anhydride (OSA). The success of synthesis was confirmed by (1)H NMR and FT-IR spectroscopy. It was found that OSA-g-EPLs had glass transition temperatures lower than EPL. Furthermore, they were able to form polymer micelles in water and to lower the surface tension of water, confirming their amphiphilic properties. The antimicrobial activities of OSA-g-EPLs were also examined, and the minimum inhibitory concentrations of OSA-g-EPLs against Escherichia coli O157:H7 remained the same as that of EPL. Therefore, OSA-g-EPLs have the potential of becoming bifunctional molecules, which can be used either as surfactants or emulsifiers in the encapsulation of nutraceuticals or drugs or as antimicrobial agents.

Reducing the brittleness of zein films through chemical modification.

Zein protein is a major coproduct of biofuel from corn. To reduce the brittleness of zein films, a new type of zein-based biomaterial, was synthesized by chemical modification of zein with lauryl chloride through an acylation reaction. The final products were confirmed by (1)H NMR, FT-IR analysis, and SDS-PAGE. Thermal analysis detected no microphase separation in the synthesized polymer matrix. As the content of lauryl moiety increased, the glass transition temperatures of modified zein decreased by as large as 25.8 °C due to the plasticization effect of the lauryl moiety. In addition, mechanical and surface properties of cast films from acylated zein were also investigated. The elongation at break of modified zein sheet was increased by about 7-fold at the high modification level with some loss of mechanical strength. The surfaces of modified zein films were as uniform as unmodified zein film but more hydrophobic, further suggesting that no microphase separation happened during the film formation process. This work indicated the potential of these new biomaterials in the development of biodegradable food packaging materials and delivery systems.

Structure of modified ε-polylysine micelles and their application in improving cellular antioxidant activity of curcuminoids

The micelle structure of octenyl succinic anhydride modified ε-polylysine (M-EPL), an anti-microbial surfactant prepared from natural peptide ε-polylysine in aqueous solution has been studied using synchrotron small-angle X-ray scattering (SAXS). Our results revealed that M-EPLs formed spherical micelles with individual size of 24-26 Å in aqueous solution which could further aggregate to form a larger dimension with averaged radius of 268-308 Å. Furthermore, M-EPL micelle was able to encapsulate curcuminoids, a group of poorly-soluble bioactive compounds from turmeric with poor oral bioavailability, and improve their water solubility. Three loading methods, including solvent evaporation, dialysis, and high-speed homogenization were compared. The results indicated that the dialysis method generated the highest loading capacity and curcuminoids water solubility. The micelle encapsulation was confirmed as there were no free curcuminoid crystals detected in the differential scanning calorimetry analysis. It was also demonstrated that M-EPL encapsulation stabilized curcuminoids against hydrolysis at pH 7.4 and the encapsulated curcuminoids showed elevated cellular antioxidant activity compared with free curcuminoids. This work suggested that M-EPL could be used as new biopolymer micelles for delivering poorly soluble drugs/phytochemicals and improving their bioactivities.

Investigation of the cytotoxicity of food-grade nanoemulsions in Caco-2 cell monolayers and HepG2 cells.

Nanoemulsions represent one of the emerging formulations for nutraceutical delivery. However, the possible toxicity associated with the small droplet size (diameter <200 nm) is still unknown. In this study, three nanoemulsions emulsified by modified starch, Tween 20 and whey protein isolate, respectively, were prepared and their cytotoxicity was examined by comparing with the corresponding micron-sized emulsions. Caco-2 cell monolayers were used to mimic the small intestine epithelium. Integrity of the cell membrane and tight junctions was tested by measuring the lactate dehydrogenase leakage and transepithelial electrical resistance, respectively. All three nanoemulsions did not reveal significant difference from their micron-sized counterparts, suggesting no apparent toxicity of the nanoemulsions on the small intestine. Meanwhile, the possible hepatic toxicity was investigated using MTT assay on HepG2 cells. It was found that nanoemulsions made with modified starch and whey protein isolate, but not Tween 20, affected the cell viability/proliferation more than did the micron-sized emulsions. Further in vivo investigation is required to examine the possible hepatic toxicity of nanoemulsions.

Structure and Self-Assembly Properties of a New Chitosan-Based Amphiphile

A new chitosan-based amphiphile, octanoyl-chitosan-polyethylene glycol monomethyl ether (acylChitoMPEG), has been prepared using both hydrophobic octanoyl and hydrophilic polyethylene glycol monomethyl ether (MPEG) substitutions. The success of synthesis was confirmed by Fourier transform infrared (FT-IR) and (1)H NMR spectroscopy. The synthesized acylChitoMPEG exhibited good solubility in either aqueous solution or common organic solvents such as ethanol, acetone, and CHCl(3). The self-aggregation behavior of acylChitoMPEG in solutions was studied by a combination of pyrene fluorescence technique, dynamic light scattering, atomic force microscopy, and small-angle X-ray scattering (SAXS). The critical aggregation concentration (CAC) and hydrodynamic diameter were found to be 0.066 mg/mL and 24.4 nm, respectively. SAXS results suggested a coiled structure of the triple helical acylChitoMPEG backbone with the hydrophobic moieties hiding in the center of the backbone, and the hydrophilic MPEG chains surrounding the acylChitoMPEG backbone in a random Gaussian chain conformation. Cytotoxicity results showed that acylChitoMPEG exhibited negligible cytotoxicity even at concentrations as high as 1.0 mg/mL. All results implied that acylChitoMPEG has the potential to be used for biological or medical applications.

Improved mechanical property and water resistance of zein films by plasticization with tributyl citrate.

Pure zein film is intrinsically rigid and brittle and lacks necessary mechanical properties for industrial processing. In addition, pure zein film is sensitive to high relative humidity, which limits its application in food packaging. To improve these properties, tributyl citrate (TBC) was incorporated into zein film to the mass ratios from 10% to 50%. A significant decrease in Youngs modulus was observed, from 409.86 MPa in pure zein films to 136.29 MPa in zein films with 50% TBC. Among all films, those containing 10% TBC are most flexible and toughest. Both DSC and microscopy methods suggested that the TBC may be loaded up to 20% to avoid microsized phase separation. Through modeling with experimental data, incorporating 50% TBC reduced the water absorption capacity to 12.94% compared to 31.78% by pure zein film. More importantly, the integrity of zein/TBC film was maintained at high relative humidity and even after immersion in water. However, more than 20% TBC in zein films led to microsized phase separation, which was harmful to mechanical properties.

Improving Ice Nucleation Activity of Zein Film through Layer-by-Layer Deposition of Extracellular Ice Nucleators

Zein protein has been of scientific interest in the development of biodegradable functional food packaging. This study aimed at developing a novel zein-based biopolymer film with ice nucleation activity through layer-by-layer deposition of biogenic ice nucleators, that is, extracellular ice nucleators (ECINs) isolated from Erwinia herbicola , onto zein film surface. The adsorption behaviors and mechanisms were investigated using quartz crystal microbalance with dissipation monitoring (QCM-D). On unmodified zein surface, the highest ECINs adsorption occurred at pH 5.0; on UV/ozone treated zein surface followed by deposition of poly(diallyldimethylammonium chloride) (PDADMAC) layer, the optimum condition for ECINs adsorption occurred at pH 7.0 and I 0.05 M, where the amount of ECINs adsorbed was also higher than that on unmodified zein surface. QCM-D analyses further revealed a two-step adsorption process on unmodified zein surfaces, compared to a one-step adsorption process on PDADMAC-modified zein surface. Also, significantly, in order to quantify the ice nucleation activity of ECINs-coated zein films, an empirical method was developed to correlate the number of ice nucleators with the ice nucleation temperature measured by differential scanning calorimetry. Calculated using this empirical method, the highest ice nucleation activity of ECINs on ECINs-modified zein film reached 64.1 units/mm(2), which was able to elevate the ice nucleation temperature of distilled water from -15.5 °C to -7.3 °C.