Interfacial and emulsion-stabilizing properties of zein nanoparticles: differences among zein fractions (α-, ß-, and γ-zein).

According to the solubility in the binary solvent of ethanol water, zein can be classified into α-, ß-, γ-, and δ-zein, and the difference in amino acid compositions of these fractions is believed to affect their physicochemical properties and functionalities. This research comparatively analyzed main zein fractions, namely the α-zein fraction, ß-zein fraction, and γ-zein fraction, on the formation, surface adsorption, and emulsifying properties of their anti-solvent-induced particles. Results showed that all zein fractions were able to form spherical particles through an anti-solvent procedure, and formed particles possessed different surface charge and surface hydrophobicity. γ-Zein fraction particles had the biggest size and lowest surface hydrophobicity, the highest interfacial adsorption speed, and formed the strongest viscoelastic interfacial film, as analyzed through the interfacial rheology results, while ß-zein fraction particles exhibited the poorest interfacial activity. These physicochemical differences were reflected in their emulsifying properties, whereby the γ-zein fraction particle-stabilized emulsion had the maximum tolerance to salt (50, 100, and 200 mM NaCl) and pH (4.0, 7.0, and 9.0). The excellent interfacial properties of the γ-zein fraction presented in this research would afford a new strategy for the effective application of zein.

pH-Induced structural transitions in whey protein isolate and ultrasonically solubilized Persian gum mixture.

The present work evidently reports that ultrasonic depolymerization strongly enhanced complex coacervation between Persian gum (PG) and whey protein isolate (WPI). PG was sonicated at 60 °C, operating frequency of 20 kHz and nominal power output of 800 W for various times followed by mixing with WPI. Acid-induced interaction between the two biopolymers was studied by turbidity, light scattering, zeta potential and viscosity measurements over a wide pH range. Sonication of intact PG (IPG) for 10 min considerably reduced the molecular weight from 4.12 × 106 to 0.76 × 106 g/mol. Besides, ultrasonic fragmentation of water insoluble fraction of PG drove protein containing chains into the soluble phase. Sonicated PG (SPG) was shown to be more flexible with higher number of carboxyl groups available for electrostatic interaction with WPI, such that the complete neutralization did not occur even at protein to polysaccharide ratio of 50: 1. Additionally, scattered light intensity and viscosity measurements revealed two maxima in the pH ranges of 4.4-4.85 and 3.27-4.0, being highly intense for the gum sonicated for 10 min and longer. Considering the pH-behavior of WPI components, the former peak was related to interpolymer complex formation between ß-lactoglobulin and long chain fraction of SPG, while the latter was attributed to intrapolymer association of α-lactalbumin with the short chain oligosaccharides arising from ultrasonic degradation of PG.

Novel strategy for enhancing the color intensity of ß-Carotene: Enriching onto the oil-water interface.

A novel strategy to enhance the color intensity of ß-carotene (BC), namely, "interfacial enriching", was developed in this work. As the sole emulsifier in W/O emulsion, BC particles were enriched onto the droplet surface through emulsifying process. By increasing the concentration of BC in oil phase from 1 mg/g to 5 mg/g, the average droplet size of the emulsion decreased from 92.2 ± 5.1 µm to 34.0 ± 5.4 µm. Too low (e.g. ≤ 1 mg/g) or too high (e.g. ≥25 mg/g) concentration of BC in the oil phase yielded an insufficient coverage or flocculation of the droplets. By enriching onto the interface, the color intensity of BC were enhanced apparently at the reflectance wavelength ranging from 500 nm to 700 nm, compared with that of the BC encapsulated within the emulsion droplets. This enhancement was due to the higher availability of incident light for the BC particles on the interface than that of the BC particles buried inside the droplets.

Iron encapsulated microstructured gel beads using an emulsification-gelation technique for an alginate-caseinate matrix.

Iron-deficiency anemia is an important health problem in global public issues, and development of iron fortifiers in diets is essential for the decrease of iron deficiency. However, there are problems for iron fortification in food because the common bioavailable iron compounds would contribute to iron-promoted lipid oxidation and unpleasant iron odor, presenting an adverse food quality. Ferrous fumarate loaded microstructured gel beads were prepared by an emulsification-gelation method using an alginate-caseinate matrix, and the gel network was formed by crosslinking of Ca2+ or Fe2+. Internal gelated beads showed relatively symmetrical and homogeneous spheres with no adhesion due to the simultaneous release of Fe2+ to initiate gelation in situ. External gelated beads displayed an irregular and adhesive structure, probably because the random contact between Na-ALG and Ca2+ occurred on the droplet surface, and the immediately gelated hardening layer provided a delay for further Ca2+ diffusion. The gel beads exhibited a lag phase in the promotion of lipid oxidation of the emulsion and restrained the iron odor release from ferrous fumarate. Ferrous ion release from microstructured gel beads in the simulated gastric juice was obviously delayed before a more progressive high release in the simulated intestinal juice, beneficial for iron absorption in the duodenum. The iron encapsulated microstructured gel beads might be developed as a promising safe iron fortifier by relieving lipid oxidation and iron odor.

In situ nanomechanical properties of natural oil bodies studied using atomic force microscopy.

Natural oil bodies (OBs) from plant organs represent an important category of functional ingredients and materials in a variety of industrial sectors. Their applications are closely related to the membrane mechanical properties on a single droplet level, which remain difficult to determine. In this research, the mechanical properties of the membranes of OBs from soybean, sesame, and peanut were investigated in-situ by atomic force microscopy (AFM). Different regions of the force-deformation curves obtained during compression were analyzed to extract the stiffness Kb or Young's modulus of the OB membranes using Hooke's law, Reissner theory, and the elastic membrane theory. At higher strains (ε = 0.15-0.20), the elastic membrane theory breaks down. We propose an extension of the theory that includes a contribution to the force from interfacial tension based on the Gibbs energy, allowing effective determination of Young's modulus and interfacial tension of the OB membranes in the water environment simultaneously. The mechanical properties of the OBs of different sizes and species, as well as a comparison with other phospholipid membrane materials, are discussed and related to their membrane compositions and structures. It was found that the natural OBs are soft droplets but do not rupture and can fully recover following compressive strains as large as 0.3. The OBs with higher protein/oil ratio, have smaller size and stronger mechanical properties, and thus are more stable. The low interfacial tension due to the existence of phospholipid-protein membrane also contributes to the stability of the OBs. This is the first report measuring the mechanical properties of OB membranes in-situ directly.

Trivalent iron induced gelation in Artemisia sphaerocephala Krasch. polysaccharide.

Artemisia sphaerocephala Krasch. polysaccharide (ASKP) has attracted growing attention in the field of food and medical engineering due to its biological activity and colloidal property. In this study, the binding between ASKP and ferric ions was found and the binding mechanism was explored. The results showed that ASKP could form a hydrogel with three-dimensional network structure in the presence of ferric ions. Ferric ions could specifically bind with the carboxyl and hydroxyl groups of the high molecular weight fraction of 60P with the binding stoichiometry of [M3+]/[repeating unit] = 2.5. The possible mechanism of the formation of ASKP-Fe3+ complex was proposed as two binding modes of monodentate and bridging binding. ASKP-Fe3+ complex exhibited higher thermal stability than ASKP revealed with DSC thermograms. The study indicated that ASKP would be a novel gelation biopolymer and the ASKP-Fe3+ complex hydrogel could be exploited as a new iron fortifier.

Structural Characterization and Chain Conformation of Water-Soluble ß-Glucan from Wild Cordyceps sinensis.

Water-soluble ß-d-glucan was obtained from wild Cordyceps sinensis by alkali solution and ethanol precipitation. The structure characteristics were determined using high-performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD), methylation combined with gas chromatography-mass spectrometry, and one-/two-dimensional nuclear magnetic resonance spectroscopy. Results showed that ß-d-glucan had a structure of every seven (1→3)-ß-d-Glcp backbone residues with two (1→6)-ß-d-Glcp branches. Additionally, conformation properties in different solvents were investigated by static light scattering, dynamic light scattering, and HPSEC with multiple detectors. It was found that ß-d-glucan in 0.5 M NaOH had a narrow unimodal distribution of hydrodynamic radius displaying a spherical coil conformation, whereas it formed severe aggregation in dimethyl sulfoxide. In 0.1 M NaNO3, ß-d-glucan mainly existed as a rod-like conformation corresponding to a helical structure together with small aggregates (10%). This work added more information to the understanding of C. sinensis polysaccharides.

Effect of arabinogalactan protein complex content on emulsification performance of gum arabic.

The emulsification properties of the standard (STD), matured (EM2 and EM10) and fractionated gum arabic samples via phase separation induced molecular fractionation were investigated to find out how the content of arabinogalactan protein (AGP) complex affects the resulting emulsion properties. Phase separation and the accompanying molecular fractionation were induced by mixing with different hydrocolloids including hyaluronan (HA), carboxymethyl cellulose (CMC), and maltodextrin (MD). Increase of AGP content from 11 to 28% resulted in the formation of emulsions with relatively smaller droplet sizes and better stability. Further increase in the AGP content to 41% resulted in the formation of emulsions with larger droplets. In spite of the larger droplets sizes, these emulsions were extremely stable. In addition, the emulsions prepared with GA higher AGP content better stability in the presence of ethanol. The results indicate that AGP content plays a vital role in emulsion stability and droplet size.

Comparative study on foaming and emulsifying properties of different beta-lactoglobulin aggregates.

Different conditions in food processing lead to different aggregates of protein. ß-Lactoglobulin nanoparticles (BLGNPs) and fibrils (BLGFs) were prepared by adjusting pH and temperature, and thereby their foaming and emulsifying properties were compared to native globular ß-lactoglobulin (NGBLG) at pH 7.0 and pH 4.0. A foam analyser, a microparticle size analyser, an interfacial rheometer and an atomic force microscope (AFM) were used to characterise foaming/emulsifying functionalities and interfacial microstructures/mechanical properties. The foam and emulsion stabilities were assessed by measuring the decay of foam height and the variation of emulsion droplet size, and both were found to be in the order of BLGFs > NGBLG > BLGNPs. Foams were more stable at pH 4.0 while emulsions were more stable at pH 7.0. Surface dilatational modulus (E) of NGBLG and its aggregates at pH 4.0 was greater than that at pH 7.0, with BLGFs showing the highest value of E and thus the highest resistance to membrane damage. The emulsion prepared with NGBLG and its aggregates had more negative charges at pH 7.0 than at pH 4.0. The foaming stability seemed to be more controlled by interfacial elasticity while the emulsion stability was more determined by surface charges. AFM analysis demonstrated different microstructures at the air-water interface between pH 4.0 and 7.0 and among the different protein aggregates, which could well explain their foaming and emulsifying properties.

All-Natural Food-Grade Hydrophilic-Hydrophobic Core-Shell Microparticles: Facile Fabrication Based on Gel-Network-Restricted Antisolvent Method.

Hydrophilic-hydrophobic core-shell microparticles are highly appealing for a variety of industrial applications (foods, pharmaceutics, cosmetics, biomedicines, etc.) owing to their unique properties of moisture resistance and controlled release. However, the fabrication of such structured microparticles proves to be nontrivial due to the difficulty in assembling two materials of distinctly different hydrophilicities and hydrophobicities. This paper reports a facile method to fabricate hydrophilic-hydrophobic core-shell microparticles using all-natural food-grade polysaccharides and proteins, based on a novel principle of gel-network-restricted antisolvent precipitation. Immersion of microgel beads prepared from hydrophilic polysaccharides (i.e., alginates, κ-carrageenan, agarose) into a hydrophobic protein solution (i.e., zein in 70% aqueous ethanol) enables slow and controllable antisolvent precipitation of a protein layer around the microbead surface, leading to the formation of a hydrophilic-hydrophobic core-shell structure. The method applies to various gelling systems and can easily tailor the particle size and shell thickness. The resulting freeze-dried microparticles demonstrate restricted swelling in water, improved moisture resistance, and sustained release of encapsulants, with great potential in applications such as protection of unstable and/or hygroscopic compounds and delivery and controlled release of drugs, bioactives, flavors, etc. The method is rather universal and can be extended to prepare more versatile core-shell structures using a large variety of hydrophilic and hydrophobic materials.

Modulation of calcium-induced gelation of pectin by oligoguluronate as compared to alginate.

Previous studies have demonstrated that oligoguluronate (guluronate block extracted from alginate, GB) was an efficient modulator of the gelation and gelling properties of macromolecular alginate in the presence of calcium. Here we report totally different modulatory effects of the oligomer when used to modify the gelation of low methoxyl pectin (LMP). GB was found to promote the gelation of LMP in the range of R ([Ca]/[guluronate + galacturonate]) < 0.25 and could make non-gelling systems gellable. This is significantly different from the case of alginate where no gelation could be induced at all. In the range of 0.25 < R < 0.60, the addition of GB was found to inhibit the gelation of LMP, whereas it had a negligible effect on the gelation of alginate as long as a fixed R was considered. In the range of R > 0.60, GB was found to promote the gelation of LMP again, which is similar to the case of alginate. The results were in consistence with microstructural observations by AFM. The different modulatory effects of GB were thought to arise from the different gelation mechanisms of LMP and alginate, that is, a progressive dotting growth of LMP dimers vs. a critical zippering growth of alginate dimers during Ca-induced crosslinking. The mechanism of GB modulating the gelation of LMP was proposed and compared to that for alginate.

Ultrasonic degradation of Persian gum and gum tragacanth: Effect on chain conformation and molecular properties.

The present study introduces the ultrasonic modification of two Iranian native gum exudates, Persian gum (PG) and gum tragacanth (GT) for the first time. They were sonicated at a constant frequency of 20 kHz and temperature of 60 °C for various times (0, 2, 5, 10, 20, 30 and 40 min) and the changes in their molecular properties were investigated using oven drying, gel permeation chromatography-multiangle laser-light scattering (GPC-MALLS), rheometery and FTIR analysis. Results indicated that the soluble dry mass of both hydrocolloids was extensively enhanced (from less than 10% at time zero to more than 90% at the end of treatment time) by sonication. Moreover, the molecular weight and viscosity of gums dispersions were decreased with the increase of the treatment time. Fracture in polysaccharide chains was confirmed by analysis of the molecular weight parameters. Calculation of chain breaks and polydispersity index (PDI) revealed that scissions occurred at the backbone as well as the side branches. PG, owing to its higher molecular weight, displayed more extensive and faster degradation than GT. However, the chain rupture of GT was twice more than that of PG at the end of sonication time. The specific volume for gyration (SVg) and molecular density (ρ) showed that intact PG contains compactly packed molecules with greater number of cross-linked bonds compared to GT. Furthermore, the conformational changes into semi-flexible chains and worm-like coils were determined for both gums after 40 min sonication. Variation of the molecular density along with the results of FTIR analysis demonstrated that ultrasonication broke C-O-C bonds in both PG and GT leading to more flexible chains.

Preparation and stability of nano-scaled gel beads of λ-carrageenan bound with ferric ions.

Iron-deficiency anemia (IDA) is a major global public health problem, and the iron fortifiers in diet are clearly needed in the prevention and improvement of IDA for humans. A novel nano-scaled gel beads of λ-carrageenan (λ-car) specifically binding with ferric ions was developed to be a promising iron fortifier with no adverse organoleptic changes on food. Turbidity measurement, thermogravimetric analysis and Fourier transform infrared spectroscopy confirmed the successful chelating. The gel beads of λ-car-Fe3+ complex showed good dispersibility and solvent stability. The in vitro cell viability of HepG2 cells treated with λ-car-Fe3+ was over 75% at 5 mg/mL of ferric ions, indicating a significant cytotoxicity reduction of ferric ions. The stability of λ-car-Fe3+ complex powder was obviously increased against browning during 60 d storage with zein coating, which was attributed to the prevention of moisture permeation. Zein coated gel beads also performed a slow release of ferric ions in simulated gastrointestinal juices, resulting from the compact and hydrophobic zein surface delaying the dissociation of λ-car-Fe3+ in acidic environment. This λ-car-Fe3+ complex would have a great potential as a safe iron fortifier and facilitate iron supplementary with the advantage to relieve the side effects of iron ions.

Effects of temperature and solvent condition on phase separation induced molecular fractionation of gum arabic/hyaluronan aqueous mixtures.

Effects of temperature and solvent condition on phase separation-induced molecular fractionation of gum arabic/hyaluronan (GA/HA) mixed solutions were investigated. Two gum arabic samples (EM10 and STD) with different molecular weights and polydispersity indices were used. Phase diagrams, including cloud and binodal curves, were established by visual observation and GPC-RI methods. The molecular parameters of control and fractionated GA, from upper and bottom phases, were measured by GPC-MALLS. Fractionation of GA increased the content of arabinogalactan-protein complex (AGP) from ca. 11% to 18% in STD/HA system and 28% to 55% in EM10/HA system. The phase separation-induced molecular fractionation was further studied as a function of temperature and solvent condition (varying ionic strength and ethanol content). Increasing salt concentration (from 0.5 to 5 mol/L) greatly reduced the extent of phase separation-induced fractionation. This effect may be ascribed to changes in the degree of ionization and shielding of the acid groups. Increasing temperature (from 4 °C to 80 °C) also exerted a significant influence on phase separation-induced fractionation. The best temperature for GA/HA mixture system was 40 °C while higher temperature negatively affected the fractionation due to denaturation and possibly degradation in mixed solutions. Increasing the ethanol content up to 30% showed almost no effect on the phase separation induced fractionation.

The emergence and pitfalls of international tissue banking.

The rapid growth of tissue banking and associated international organisations following the fall of the Berlin wall in 1991 is described. This surge in collaboration led to a world-wide constructive movement to use and to produce human tissues. As the years progressed industrialisation, led by the USA, improved the quality of tissue allografts but led higher costs and consolidation within the developing industry. The growth of litigation more than kept pace with the industrial progress. One landmark case is described, the outcome of which could revolutionise the current practices now applied to eliminate possible viral contamination of implanted tissue grafts.

Stability and digestibility of one- or bi-layered medium-chain triglyceride emulsions with gum Arabic and whey protein isolates by pancreatic lipase in vitro.

Interfacial engineering approaches have been used to design functional foods so as to control lipase-induced digestion of emulsified lipids and release of bioactive lipophilic components in the gastrointestinal tract. In this study, emulsion droplets with the interface stabilized with gum Arabic (GA) and whey protein isolate (WPI) were prepared by mixing or sequential adsorption. WPI/GA intramolecular soluble complexes (ISCs) have superior emulsifying properties in stabilizing oil-in-water emulsions. The impact of the interfaces for WPI/GA ISC-layered (one-layered) and double-layered emulsions formed by sequential deposition of WPI or GA on the lipolysis of emulsions was investigated using an in vitro simulated gastrointestinal model. Transglutaminase and dithiothreitol were introduced to crosslink the interfacial proteins and improve the interfacial stability. The ISC-layered emulsion was less stable to aggregation than the double-layered ones in simulated gastric fluid due to dissociation of ISCs caused by the electrostatic screening of ions and proteolysis of interfacial proteins driven by pepsin. The ISC-layered emulsion conferred a significant slower rate and extent of lipid digestion compared to the double-layered emulsions post gastric proteolysis (P < 0.05). It is presumed for the ISC-layered emulsion that the destabilization to aggregation and coalescence within the simulated gastrointestinal fluids and the steric hindrance of the robust and thick interfacial layer might contribute to delaying free fatty acids release. It suggests that both the initial interfacial properties and the stability of the emulsified lipid droplets within the simulated gastrointestinal fluids play an important role in determining the rate and extent of lipid digestion. It is predicted that direct destabilization of emulsified lipids using interfacial engineering approaches has the potential of modifying lipid digestibility or bioactive release at specific sites within the gastrointestinal tract.

Specific binding of trivalent metal ions to λ-carrageenan.

Carrageenans are a family of sulphated cell wall polysaccharides extracted from seaweeds and are widely used in different industrial sectors. Relative to κ-carrageenan (κ-car) and ι-carrageenan (ι-car), the ionic binding behavior of λ-carrageenan (λ-car) is far less studied. In this work, the interaction and binding behavior between λ-car and metal ions of different valency (Na+, K+, Mg2+, Ca2+, Fe2+, Fe3+, Al3+, Cr3+) have been investigated. In contrast to the non-specific interaction of the monovalent and divalent cations, specific binding has been identified between λ-car and Fe3+/Al3+. The specific binding could lead to either precipitation or gelation of λ-car, depending on the way of introducing Fe3+/Al3+ ions. Fe3+ and Al3+ exhibit the same binding stoichiometry of [M3+]/[repeating unit] = 1.0, with the former having a relatively larger binding constant. Cr3+, though having very similar physical properties with Fe3+/Al3+, is incapable of binding specifically to Cr3+. The phenomena could not be interpreted in terms of counterion condensation, and are rather attributable to a mechanism in which hexa-coordination of Fe3+/Al3+ and entropy-driven cation dehydration play crucial roles in driving the binding of the trivalent metal ions to λ-car.

Phase behavior, rheological characteristics and microstructure of sodium caseinate-Persian gum system.

In this study, the phase behavior of sodium caseinate-Persian gum mixtures was investigated. The effect of thermodynamic incompatibility on phase distribution of sodium caseinate fractions as well as the flow behavior and microstructure of the biopolymer mixtures were also studied. The phase diagram clearly demonstrated the dominant effect of Persian gum on the incompatibility of the two biopolymers. SDS-PAGE electrophoresis indicated no selective fractionation of sodium caseinate subunits between equilibrium phases upon de-mixing. The microstructure of mixtures significantly changed depending on their position within the phase diagram. Fitting viscometric data to Cross and Bingham models revealed that the apparent viscosity, relaxation time and shear thinning behavior of the mixtures is greatly influenced by the volume ratio and concentration of the equilibrium phases. There is a strong dependence of the flow behavior of sodium caseinate-Persian gum mixtures on the composition of the equilibrium phases and the corresponding microstructure of the system.

Novel nano-particulated exopolysaccharide produced by Klebsiella sp. PHRC1.001.

In recent decades, microbial synthesis of polysaccharides with special functional properties has attracted increasing attention. This work reported a novel exopolysaccharide (EPS)-producing strain, Klebsiella sp. PHRC1.001 isolated from activated sludge. Physicochemical, rheological, emulsifying and toxicological properties of the obtained EPS were characterized. The EPS was mainly composed of d-glucose and l-arabinose, and was found to exist in aqueous solution in a nano-particulated form (∼50nm in diameter) with a strong tendency of aggregation. Rheological analysis showed that the EPS aqueous solution was a typical pseudoplastic fluid at higher concentration and could form weak gel upon alkaline treatment followed by neutralization. The EPS exhibited excellent emulsifying properties in stabilizing oil-in-water emulsions presumably by a Pickering mechanism owing to its nanoparticle structure. Acute toxicity test showed that 1.8g EPS per kg of body weight caused no toxic effect on mice. PHRC1.001 EPS has the potential to be a novel industrial polysaccharide.

Comparison of structural features and antioxidant activity of polysaccharides from natural and cultured Cordyceps sinensis.

Four polysaccharides (named as P1, P2, and P3 from three natural Cordyceps sinensis and P4 from cultured C. sinensis) were obtained by hot-water extraction and ethanol precipitation and their structural characteristics as well as antioxidant potentials were compared. Results revealed that the backbone of P1, P2, and P3 comprised α-1,4-glucose, with a branching point mainly at position 6 and terminating at glucose. On the other hand, the structure of P4 was highly complex, mainly comprising glucose, galactose, and mannose, with 1,4-glucose and 1,4-galactose as the main chain. For in vitro antioxidant assays, all the four polysaccharides showed similar scavenging capacity against DPPH and hydroxyl radicals, whereas P1 had a relatively low ferric reducing ability, possibly related to a combination of factors such as the phenolic compounds and amino acids that conjugated in polysaccharides.