Solubilization of α-tocopherol and curcumin by polyoxyethylene alkyl ether surfactants: Effect of alkyl chain structure.

The effects of the structural characteristics of the alkyl chains of polyoxyethylene alkyl ether-type surfactants (Brij) on the solubilization of α-tocopherol and curcumin by surfactant micelles were investigated: Brij L23 (lauryl; C12:0); S20 (stearyl; C18:0); and Brij O20 (oleyl; C18:1). When α-tocopherol or curcumin were solubilized in Brij micelle solutions below their maximum solubilization concentrations (Cmax), the Brij L23 micelles exhibited the largest increase in dimensions due to the presence of the guest molecules. Above Cmax, excess α-tocopherol existed as microemulsion droplets whereas excess curcumin existed as insoluble crystals. Our results suggest that the guest molecules were preferentially located within the palisade layers of micelles, which can be attributed to the fact that they contained bother polar and non-polar moieties. These results may be important for the formulation of colloidal delivery systems to encapsulate and deliver oil-soluble vitamins and nutraceuticals.

Phylogeography of the Korean endemic Coreoleuciscus (Cypriniformes: Gobionidae): the genetic evidence of colonization through Eurasian continent to the Korean Peninsula during Late Plio-Pleistocene.

BACKGROUND: Freshwater endemism is thought to have been formed through the vicariance of connected water systems or the process by which ancestral populations colonized specific areas. The Korean Peninsula is well recognized for its high level of freshwater endemism with about 40% of freshwater fish species being endemic. OBJECTIVE: In this study, we attempted to reconstruct the process of speciation and phylogenetic dispersal of Coreoleuciscus species, which is endemic in the Korean Peninsula. METHODS: We used fossil-calibrated divergence time estimation and ancestral distributional reconstruction to infer phylogeographic reconstruction of Coreoleuciscus based on mitochondrial cytochrome c oxidate subunit I (COI) sequences (1551 bp). RESULTS: Our phylogeographic analysis based on a total of 626 individuals revealed that the two Coreoleuciscus species have originated from the independent colonization of different lineages in the ancestral populations, probably during the Late Plio-Pleistocene. The full-scale expansion of Coreoleuciscus populations appears to have taken place after major river structures were completed on the Korean Peninsula. We also provided evidence that the common ancestors of Coreoleuciscus was distributed in Eastern Eurasian continent and subsequently dispersed into the tip of East Asia. High genetic diversity was mainly concentrated in large drainage populations, while small populations showed an monomorphism, which could give important implications for planning the conservation and management of Coreoleuciscus. CONCLUSIONS: The phylogenetic background of the rheophilic Coreoleuciscus species can be explained by the colonizer hypothesis that the endemic freshwater fish originated from the common ancestor in continental region.

The full-length mitochondrial genome of Tachysurus fulvidraco (Siluriformes: Bagridae) from Geum river in Korea.

The full-length mitochondrial genome of the yellow catfish, Tachysurus fulvidraco was analyzed by the primer walking method. Its assembled mitochondrial genome was found to be 16,527 bp, consisting of 37 genes (13 protein-coding genes, 22 tRNA gens, and 2 rRNA gens). The gene content and order of T. fulvidraco were congruent with those of typical vertebrate fishes. In the phylogenetic tree, it showed the closet relationship to the another conspecific specimen from China and Pseudobagrus koreanus and well separated from the other species in the family Bagridae.

Influence of structural properties of emulsifiers on citral degradation in model emulsions.

The storage stability of compounds encapsulated in emulsions is strongly influenced by the properties of the droplet interfacial membrane. To evaluate the effect of emulsion droplet interface thickness on the degradation of citral, emulsions were prepared using polyoxyethylene alkyl ether-type emulsifiers with hydrophilic and hydrophobic groups of various sizes. Acid cyclization of citral at pH 3 promoted faster degradation than that at pH 7. Ferrous irons accelerated citral degradation in the emulsions at pH 3 but not at pH 7, because they decomposed the products of the acid-catalyzed cyclization of citral through redox reactions rather than direct degradation. Water-soluble radicals dramatically increased the rate of citral degradation, irrespective of pH. Notably, at low pH, the rate of citral degradation by ferrous irons was higher than that by radicals. These findings suggest that the thickness and density of emulsion droplet surfaces are not important factors for inhibiting citral degradation in emulsions.

Lipid hydroperoxide decomposition in model emulsions stabilized with emulsifiers having various sizes of hydrophilic heads.

The vulnerability of oils in emulsions to oxidation depends on the structural and physicochemical properties of oil droplet interface. To evaluate the implications of the interfacial characteristics of emulsion droplets on lipid oxidation, particularly lipid hydroperoxide decomposition, emulsions were prepared using emulsifiers with various lengths of polar groups because the length of hydrophilic heads of emulsifiers could be an important factor in determining the thickness of the droplet surface. The decomposition rate constants of cumene hydroperoxide in emulsions showed that the cumene hydroperoxide in emulsions having a thick emulsion droplet interface was decomposed faster than in emulsions having a loosen one. Our findings also showed that the denseness of the droplet interface affected cumene hydroperoxide decomposition in emulsions. Conclusively, this study suggested that the interfacial thickness and denseness of the emulsion droplets influence oxidative stability of emulsions.

Ostwald Ripening Rate of Orange Oil Emulsions: Effects of Molecular Structure of Emulsifiers and Their Oil Composition.

Ostwald ripening, one of the frequently observed instability of flavor oil emulsions, can be easily prevented by adding triacylglycerols to the oil phase. The effect of interfacial characteristics of the emulsion droplets (particularly thickness) on the effectiveness of triacylglycerol inhibition of Ostwald ripening was evaluated in this study. The prepared emulsions were stabilized with emulsifiers with different-size hydrophilic groups, which correlate to droplet interfacial thickness. Emulsions with an oil phase of pure orange oil were unstable due to Ostwald ripening. Modifying the oil phase by adding corn oil or medium-chain triacylglycerol (MCT) effectively inhibited droplet growth. Thicker and less dense droplet surfaces in the emulsions required more triacylglycerol, regardless of its type, to resist Ostwald ripening. When the oil phase contained the same amounts of triacylglycerols, MCT was more effective at inhibiting Ostwald ripening than corn oil. Compared with corn oil, MCT more effectively inhibited Ostwald ripening of the emulsions containing micelles. PRACTICAL APPLICATIONS: When food and beverage industries produce food products containing flavor or essential oils vulnerable to Ostwald ripening as emulsion forms, the findings in this work could provide useful information on the interfacial engineering of emulsions and on how to modify the oil compositions of emulsions using triacylglycerols to improve the stability of these emulsions against Ostwald ripening.

Impact of antioxidant on the stability of ß-carotene in model beverage emulsions: Role of emulsion interfacial membrane.

The effect of the thickness and density of droplet interfacial membrane on the chemical stability of ß-carotene in emulsions was investigated, and its impact on the effectiveness of oil-soluble antioxidants to retard ß-carotene degradation was examined. ß-Carotene was incorporated into the emulsions stabilized by PEGylated emulsifiers having various-sized hydrophilic groups. In the presence of oxidative stresses (pH, iron ions, and radicals in this study), it was observed that the interfacial thickness was relevant to the stability of ß-carotene encapsulated into emulsion droplets. Particularly, iron-mediated carotene degradation was effectively retarded in the emulsions having a thin interfacial membrane than ones with a thick interfacial membrane. The interfacial denseness also affected ß-carotene stability but its ability to retard ß-carotene degradation was influenced by the interfacial thickness. Although ß-carotene degradation rate decreased upon the addition of oil-soluble antioxidants, its antioxidant activity depended on what prooxidant promoted the degradation of ß-carotene in the emulsions.

Influence of emulsion interfacial membrane characteristics on Ostwald ripening in a model emulsion.

Ostwald ripening is a major destabilization mechanism for emulsions containing flavor oils with relatively high water solubilities. Emulsions with different oil phase compositions were prepared that were stabilized by polyoxyethylene alkyl ether-type emulsifiers with differently sized hydrophilic and hydrophobic groups. Emulsions prepared using only orange oil were highly unstable to Ostwlad ripening during storage. When emulsifier concentration was increased, Ostawald ripening in emulsions containing emulsifiers with small hydrophilic groups was inhibited, while size increment of droplets in emulsions containing emulsifiers with large hydrophilic groups was not. Droplet enlargement was effectively inhibited by incorporating corn oil into the oil phase prior to homogenization. However, the concentration of corn oil required to inhibit Ostwald ripening varied depending on the structural characteristics and concentrations of the emulsifiers present. These results could have important implications for the selection of emulsifiers to improve the physical stability of orange oil emulsions for use in the food and beverage industries.