| 1. |
- Eskilsson, K, et al.
(författare)
-
Self-aggregation of triblock copolymers at the solid silica-water interface
- 1999
-
Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 15, s. 5150-5157
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the adsorption and surface aggregation behavior of triblock copoly(ethylene oxide-tetrahydrofuran-ethylene oxide) copolymers, EOn/2THFmEOn/2, at the silica-water interface. In this work, we have used both time-resolved fluorescence spectroscopy and atomic force microscopy to study the morphology of the adsorbed layers. We confirm previous suggestions that the copolymers self-assemble at the silica surface to form discrete micelle-like structures. The surface aggregation, however, starts at a much lower copolymer concentration than the corresponding micellization process in solution. The time-resolved fluorescence measurements reveal that the copolymer aggregates are smaller at the surface than those in bulk solution. The AFM measurements that were performed clearly confirm the existence of discrete micelle-like copolymer aggregates at the silica surface. An interesting result seen in the AFM surface topography images is that, for the high molecular weight copolymer, we observe no surface aggregates at some parts of surface. We believe this is related to the polydispersity of the copolymer. Single high molecular weight copolymers may effectively compete for surface area with surface aggregates formed by a copolymer fraction of lower molecular weight.
|
|
| 2. |
- Hansson, A., et al.
(författare)
-
Effect of changes in pH on the release of flavour compounds from a soft drink-related model system
- 2001
-
Ingår i: Food Chemistry. - 0308-8146 .- 1873-7072. ; 74:4, s. 429-435
-
Tidskriftsartikel (refereegranskat)abstract
- Citric acid and phosphoric acid were added in variable amounts to a soft drink model system to show their effect on the release of six flavour compounds. High concentrations of the acids decreased the release of esters, probably because of the presence of large amounts of the dissociated form of the acids. However, the same amounts of added citric acid had no effect on flavour release when pH was regulated with sodium hydroxide. Changes in pH values achieved by adding hydrochloric acid also had no effect on flavour release. These results indicate that pH values used in soft drinks do not affect the release of flavour molecules. It is more likely the citric acid and the phosphoric acid, particularly their dissociated forms, which decrease the release of the esters. The other flavour compounds were not affected. Copyright © 2001 Elsevier Science Ltd.
|
|
| 3. |
- Hansson, A., et al.
(författare)
-
Multivariate analysis of the influence of pectin, white syrup, and citric acid on aroma concentration in the headspace above pectin gels
- 2002
-
Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 50:13, s. 3803-3809
-
Tidskriftsartikel (refereegranskat)abstract
- Pectin gels consist of polysaccharide networks surrounded by water. The gel networks can prevent release of aroma molecules from the gel to the gas phase above. In this study static headspace measurements were performed to correlate aroma concentration in the gas phase above pectin gels to different amounts of the gel ingredients. As a consequence, aroma concentration in the headspace in relation to gel texture, as characterized by rheology measurements, was also studied. Aroma concentration in the headspace above strong gels was low, due to entrapment of aroma molecules within the gel structure. Viscous solutions generally gave a high aroma concentration in the headspace, but owing to a complex matrix, this was lowered when large amounts of the gel ingredients were added. However, a high correlation between interaction terms and square terms of design variables and rheology parameters with aroma compounds indicated nonlinear and complex relationships.
|
|
| 4. |
- Silvander, M, et al.
(författare)
-
Liposomal surface potential and bilayer packing as affected by PEG-lipid inclusion
- 2000
-
Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 16, s. 3696-3702
-
Tidskriftsartikel (refereegranskat)abstract
- The surface potentials and the packing properties of phospholipid liposomes containing anionic lipids with covalently attached poly(ethylene glycol) polymers (PEG(2000)-PE) were investigated. The negative surface potential induced by the PEG-lipid in EPC/cholesterol and SPC/cholesterol liposomes was determined by means of titration of the fluorescent probe 4-heptadecyl-7-hydroxycoumarin (HC). The shift in the apparent pK of the probe corresponds to an induced potential of -13 mV for 5 mol % PEG-lipid in the phospholipid/cholesterol (ionic strength = 150 mM). For EPC liposomes without cholesterol, 5 mol % PEG-lipid did not cause any detectable shift in the pK of the probe. This indicates that the EPC liposome surface in fact carries a net negative charge. The above results were supported by determinations of the potential. The packing order of the outer and inner parts of the phospholipid/cholesterol bilayer membranes was investigated by fluorescence depolarization anisotropy of the probes HC and 1,6-diphenyl-1,3,5-hexatriene (DPH). The PEG-lipid inclusion caused an increase in the anisotropy of HC, located at the water/hydrocarbon interface. In addition, a small increase in anisotropy was observed for DPH upon PEG-lipid inclusion. Since DPH is situated in the hydrocarbon region, these data together with the HC data indicate that the PEG-lipids impose restrictions on the molecular motion in the outer as well as the inner parts of the hydrocarbon region.
|
|
