| 1. |
- Sjöström, B, et al.
(författare)
-
A method for the preparation of submicron particles of sparingly water-soluble drugs by precipitation in oil-in-water emulsions. II. Influence of the emulsifier, the solvent, and the drug substance
- 1993
-
Ingår i: Journal of Pharmaceutical Sciences. - 0022-3549 .- 1520-6017. ; 82, s. 584-589
-
Tidskriftsartikel (refereegranskat)abstract
- Small particles of two steroids; cholesteryl acetate and b-sitosterol, have been prepared by the following technique: The steroid was dissolved in an organic solvent, which was emulsified in water in the presence of sur--factant, thus giving a water continuous emulsion. As the organic solvent was evaporated the steroid precipitated. One particle was found to form in each emulsion droplet. Particle sizes down to 25 nm were obtained by this method. Particles were prepared from emulsions containing different organic solvents and surfactants and the effect on the size and the colloi--dal stability of the particles were examined. It was found that the final particle suspension is relatively stable provided the initial emulsion is stable. Furthermore, there is a close correlation between the initial emul--sion droplet size and the final particle size. The particle size, therefore, can be varied in the same manner as the size of emulsion droplets, e.g. by changing the emulsification process parameters, the amount and choice of surfactant and the oil/water ratio. Finally, the particle size depends on the choice of solvent and only slightly on the concentration of drug in the oil phase of the emulsion.
|
|
| 2. |
- Claesson, PM, et al.
(författare)
-
Interactions between hydrophilic mica surfaces in triolein: Triolein surface orientation, solvation forces, and capillary condensation
- 1997
-
Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 13, s. 1682-1688
-
Tidskriftsartikel (refereegranskat)abstract
- Results obtained from surface force measurements using hydrophilic mica surfaces in triolein are presented. The forces were determined for different water activities in the triglyceride sample. With anhydrous triolein two oscillations in the force curve are observed. They appear at a separation of 60-50 Å and 30-20 Å. An interfacial ordering of triolein, allowing two molecular layers between the surfaces at the position of the outer oscillation and one molecular layer at the inner one is proposed. This structure at the interface is different from the triglyceride conformation suggested for the bulk system. A dramatic effect of water content on the structural forces is observed. The number and amplitude of the oscillations are dependent on the water content. The oscillations completely disappear when the triolein sample is satured with water, and the force becomes purely attractive. These data are interpreted in terms of preferential adsorption of water molecules onto the hydrophilic mica surface and in terms of a changing water adsorption with surface separation. The adhesion force between the surfaces is strongly increased when the water content is close to its saturation value. The strong adhesion is attributes to the presence of a water capillary around the contact position.
|
|
| 3. |
- Dedinaite, A, et al.
(författare)
-
Interactions between hydrophilic surfaces in triglyceride media - information obtained from surface force measurements
- 1997
-
Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 11, s. 7-12
-
Tidskriftsartikel (refereegranskat)abstract
- The application of surface force measurements for modelling the behaviour of food colloid system, in particular dispersions of hydrophilic particles in oil continuous media, is discussed. Interactions between two mica surfaces across a triglyceride, triolein, in anhydrous state and containing different amounts of dissolved water, have been investigated. The water content influences the layering of triolein molecules at the surfaces and whereby their interactions. The relation between surface force data (e.g. the magnitude of the force barrier and the adhesion force) to the properties of colloidal systems is discussed. Further, the importance of capillary condensation for particle interactions in triolein saturated with water is demonstrated.
|
|
| 4. |
- Johansson, LB-Å, et al.
(författare)
-
Phase equilibria and formation of vesicles of dioleoylphosphatidylcholine in glycerol/water mixtures
- 1993
-
Ingår i: Biochimica et Biophysica Acta - Biomembranes. - 0005-2736 .- 1879-2642. ; 1149, s. 285-291
-
Tidskriftsartikel (refereegranskat)abstract
- The lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) forms a lamellar liquid crystalline phase (La) in arbitrary mixtures of glycerol and water. The phase has been characterized by means of X-ray diffraction, 3IP-NMR spectroscopy and differential scanning calorimetry (DSC). In the La state, and for DOPC concentrations greater than 50% (w/w), the thickness of the lipid bilayer decreases, while the area of the polar head group increases with increasing glycerol concentration. The phase transition from gel to La state occurs in the range of 240 to 260 K. Contrary to a previous (McDaniel, R.V., McIntosh, T.J. and Simon, S.A. (1983) Biochim. Biophys. Acta 731, 97) study of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) we find that in the gel state, the thickness of the DOPC lipid bilayer is greater than that in the La state. This suggests that in the gel state, the lipid acyl chains of DOPC are in extended configuration. The lamellar phase reaches its maximum swelling at about 50% (w/w) of DOPC. At lower DOPC concentrations a two-phase system is formed where the lamellar phase exists in equilibrium with excess of solvent. Unilamellar vesicles can be prepared from a diluted suspension of the lamellar phase either by using the sonicator or extruder technique. We show this by means of 3IP-NMR, EPR and fluorescence spectroscopy. The mean radius of the vesicles, prepared by a sonicator, has been determined at different glycerol/water mixtures. It is found to decrease continously from 100 A at 100% water to a minimum of 75 Å at about 50% water in the solvent mixture. By further decreasing the water content in the solution, the radius rapidly increases, and a mean radius of 450 Å is estimated at a water content of 10%. The rotational relaxation times of a fluorescent probe and two EPR spin probes, solubilized in DOPC vesicles, have been measured at different glycerol/water mixtures. It is found that the rotational rates are always much slower in the systems containing glycerol.
|
|
| 5. |
- Sjöström, B, et al.
(författare)
-
Preparation of submicron drug particles in lecithin-stabililized o/w emulsions I. Model studies of the precipitation of cholesteryl acetate
- 1992
-
Ingår i: International Journal of Pharmaceutics. - 0378-5173 .- 1873-3476. ; 84, s. 107-116
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles of a model drug, viz. cholesteryl acetate. were prepared. The cholesteryl acetate was dissolved in cyclohexane containing lecithin. The organic solution was emulsified in an aqueous solution containing a cosurfactant. A stable o/w-emulsion resulted. The solvent was evaporated from the emulsion and cholesteryl acetate precipitated in the emulsion droplets. The size of the particles was almost not affected by the cholesteryl acetate concentration in cyclohexane. Furthermore, the increase in particle size, as a result of an increased oil/water ratio was negligible. With a blend of phosphatidylcholine and sodium salt of glycocholic acid as emulsifiers, particle sizes down to 25 nm were obtained, The ratio between phosphatidylcholine and sodiumglycocholate seems to be critical. In increasing the ratio above 9/1, the suspension becomes more instable as is noticed by an increase in particle size during storage. The optimal conditions coincide with those giving an extensively swelling lamellar liquid crystalline phase containing phosphatidylcholine and sodiumglycocholate.
|
|
| 6. |
- Sjöström, B, et al.
(författare)
-
Preparation of submicron drug particles in lecithin-stabilized o/w emulsions. II. Characterization of cholesteryl acetate particles
- 1993
-
Ingår i: International Journal of Pharmaceutics. - 0378-5173 .- 1873-3476. ; 94, s. 89-101
-
Tidskriftsartikel (refereegranskat)abstract
- Submicron particles of a model drug, viz., cholesteryl acetate (CA), have been characterized. The particles were prepared by precipitation of CA in the dispersed phase of an o/w emulsion stabilized by two different emulsifier systems i.e., (a) a mixture of lecithin and sodium glycocholate and (b) a polyoxyethylene sorbitan fatty acid ester. The particle size has been determined by photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM). The average particle size, by number, was determined by PCS to be 21-144 nm depending on the emulsifier system used in the particle preparation. The smallest mean particle size of 21 nm was achieved with a blend of lecithin and sodium glycocholate. According to TEM pictures, the particles have a smooth surface and are spherical, and the majority of the particles seem to be amorphous, exhibiting neither microporosity in the particles nor aggregation between the particles. The transition temperature of cholesteryl acetate in the particles prepared with the blend of lecithin and sodium glycocholate has been determined by differential scanning calorimetry (DSC). The DSC measurements indicate that the melting point at 105°C of the cholesteryl acetate particles prepared with lecithin/sodium glycocholate is lower than that of the pure macroscopic cholesteryl acetate crystals which is 116°C. The irreversible transition of cholesteryl acetate at about 80°C was not observed in the particle form of cholesteryl acetate prepared with the emulsifier blend of phosphatidylcholine and sodium glycocholate. The suspensions have also been investigated by small angle X-ray scattering (SAXS). The cyclohexane residue in the resulting suspensions was below 25 ppm according to analysis by gas chromatography.
|
|
| 7. |
- Sjöström, B, et al.
(författare)
-
The formation of submicron organic particles by precipitation in an emulsion
- 1994
-
Ingår i: Journal of Dispersion Science and Technology. - 0193-2691 .- 1532-2351. ; 15, s. 89-117
-
Tidskriftsartikel (refereegranskat)abstract
- Submicron organic particles are produced by precipitation in an emulsion. The poorly water soluble organic substance is dissolved in a non-polar solvent. This solution is dispersed in an aqueous phase in the presence of emulsifier. When the non-polar solvent is removed by evaporation, the organic substance precipitates and one particle is formed in each emulsion droplet. Experimental work are here reported on the rate and the influence of the evaporation rate on the formation of cholesteryl acetate particles. An introductory theoretical analysis of the conditions experienced by each droplet during the evaporation is given. The experimental results suggest that the evaporation of the solvent is a rapid process mainly determined by the transport of the droplets to the vicinity of the air water interface. However, the results also show that the size of the particles formed by precipitation in the emulsion, is insensitive to the evaporation conditions, for instance if the evaporation is artificially slow. The particle size is mainly governed by the size of the emulsion droplets. The analysis discuss the possibility that during the evaporation of the emulsion, each individual droplet is emptied of its content of the non-polar solvent very rapidly. The hypothesis that each solid particle is formed during a very short period of time without obtaining a concentration equilibrium within the droplet is tested. However, the order-of-magnitude estimations do not support a kinetic explanation for the fact that the particles obtain the size of the emulsion droplets.
|
|
| 8. |
- Wendin, Karin, 1963-, et al.
(författare)
-
Low-fat mayonnaise : Influences of fat content, aroma compounds and thickeners
- 1997
-
Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 11:1, s. 87-99
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of fat content and thickeners, propylene glycol alginate (PGA; 1.40%) and guar gum (1.55%), on sensory and instrumental quality descriptors on reduced fat mayonnaises (15 and 30% fat) with and without added aroma compounds, citral (semi-polar) and pyroligneous acid (polar), were investigated. One mayonnaise, 82% fat, without added thickener or aroma compounds was used as reference. Sensory evaluation (quantitative descriptive analysis; QDA), rheological analysis (yield stress, maximum viscosity, G' and G''), measurements of particle size and headspace CC-MS analyses were carried out. Correlations between the results were developed Perceived and instrumental texture, and perceived smell and flavour, changed differently in magnitude and direction due to fat content and type of thickener.
|
|
| 9. |
- Andersson, I. M., et al.
(författare)
-
Effects of feed composition, protein denaturation and storage of milk serum protein/lactose powders on rehydration properties
- 2020
-
Ingår i: International Dairy Journal. - : Elsevier BV. - 0958-6946. ; 110
-
Tidskriftsartikel (refereegranskat)abstract
- Whey powder rehydration is expected to be closely linked to both denaturation and lactosylation of the proteins. This study investigated the relation between the forced imbibition rate of spray-dried milk serum protein/lactose powders and the particle morphology and how it is related to the insoluble and lactosylated protein fraction, respectively. Despite extensive variation in protein denaturation, aggregation and lactosylation, only comparably small effects on the forced imbibition rate of the powders and the particle morphology could be observed. A possible explanation for this rather limited effect on the rehydration properties and particle morphology might be that the surface composition of the powder particles is rather similar and dominated by native proteins. These insights have relevance for the formulation of whey powders with improved rehydration properties.
|
|
| 10. |
- Andersson, I. M., et al.
(författare)
-
Impact of protein surface coverage and layer thickness on rehydration characteristics of milk serum protein/lactose powder particles
- 2019
-
Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 561, s. 395-404
-
Tidskriftsartikel (refereegranskat)abstract
- Spray-dried powders were produced from milk serum protein concentrate and lactose in varying ratios, and the rehydration characteristics of the powders were evaluated. The dissolution rate was estimated with a flow-cell based technique, and the external and internal distribution of the powder components were evaluated with X-ray photoelectron spectroscopy and confocal Raman microscopy, respectively. The surface of the powder particles is more or less covered by a thin protein layer. A phase segregation between protein and lactose is observed in the interior of the particle resulting in a protein rich layer in the vicinity of the surface. However, the protein layer in the vicinity of the particle surface tends to become thinner as the bulk protein concentration increases in the powders (from 10 to 60% w/w). The time for the spontaneous imbibition to occur show a linear correlation with the protein surface coverage. The dissolution rate of powders containing 0.1% w/w protein is around 60 times faster than for a powder containing 1% w/w protein but the dissolution rate of powders containing 1% and 100% w/w differ only by a factor of 2. Thus, it is suggested that the outer protein layer becomes denser at the interface as the protein content increases in the powders, thereby causing poorer rehydration characteristics of the powders (especially for low protein concentrations 0.1–1% w/w). This insight has relevance for the formulation of whey protein powders with improved rehydration characteristics. © 2018 Elsevier B.V.
|
|
| 11. |
- Andersson, I. M., et al.
(författare)
-
Impact of surface properties on morphology of spray-dried milk serum protein/lactose systems
- 2018
-
Ingår i: International Dairy Journal. - : Elsevier BV. - 0958-6946 .- 1879-0143. ; 85, s. 86-95
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigated milk serum protein concentrate/lactose systems with varying ratios and how the morphology of the spray-dried particles of these systems could be described by the surface properties of the feed as well as the protein surface coverage of the particles. An extrapolation of the surface pressure of the feed to 0.3 s, the approximate time for molecular diffusion in an atomised droplet in the spray-dryer, showed a relationship with the particle morphology. At low protein concentrations (<1%), the particles were almost totally smooth. At higher protein concentrations (≥1%), the particles became dented and ridged, and these tended to become deeper and thicker as the protein concentration increased. It is suggested that the surface pressure of the feed at low protein concentrations is the most prominent surface property, whereas the modulus of elasticity seems to be the most prominent surface property for particle surface deformation at higher protein concentrations.
|
|
| 12. |
- Andersson, I. M., et al.
(författare)
-
Particle morphology and rehydration properties of spray-dried microgels and fractal aggregates with varying fractions of native milk serum proteins
- 2021
-
Ingår i: International Dairy Journal. - : Elsevier Ltd. - 0958-6946 .- 1879-0143. ; 112
-
Tidskriftsartikel (refereegranskat)abstract
- To keep their functional properties, it is crucial that protein aggregates maintain their structure after spray drying and that the powders can be fully rehydrated. In this study, microgels and fractal aggregates were prepared by heating a mixture of milk serum protein concentrate and lactose (40/60; %, w/w) at 85 °C for 15 min by varying the pH. Various fractions of native proteins were added to the systems prior to spray drying. This study showed that microgels and fractal aggregates kept their structure after spray drying and reconstitution. The particle morphology could be correlated to the stiffness of the interface of the feed droplet. The forced imbibition rate showed a negative correlation with increasing amount of aggregated proteins in the powders that seems to be a result of denatured/aggregated proteins present at the surface. These findings are of importance for the formulation of spray-dried powders with improved rehydration characteristics. © 2020 The Author(s)
|
|
| 13. |
|
|
| 14. |
- Bergenståhl, B, et al.
(författare)
-
Adsorption structures in food emulsions
- 1992
-
Ingår i: Emulsions. - : Kluwer Academic Publishers. ; , s. 51-60
-
Bokkapitel (refereegranskat)abstract
- Food emulsions in particular, but also most other technical emulsions, are complex mixtures. When surface active components adsorb from a solution of several different surface active molecules, the formed adsorbed layer can roughly be classified in three different structures, i) A monolayer containing one predominant molecule, ii) The formation of one adsorbed monolayer containing a mixture of molecules, iii)Adsorption in layers. A model of an ice cream emulsion is an example in which a layered surface structure is formed. Four different methods were applied to investigate the surface: measurements of the interfacial tension, flocculation rate measurements, electrophoretic mobility measurements and TIRF (Total Internal Reflection Fluorescence). The conclusion we made from this investigation was that the adsorption from solutions with several surface active components might lead to the formation of complex layered structures.
|
|
| 15. |
|
|
| 16. |
- Bergenståhl, B, et al.
(författare)
-
Alkyd emulsions
- 1996
-
Ingår i: Polymeric Materials Encyclopedia. - : CRC Press. ; , s. 154-160
-
Bokkapitel (refereegranskat)abstract
- Introduction: The use of waterborne alkyds as binders in coatings is not new, their history going some 30 years back in time. Mostly, this has been in the form of water soluble alkyds, with high acid numbers that provide the water solubility of the resins after neutralization with amines. Such alkyds are mostly used in industrial coatings. Emulsified water insoluble alkyds have so far found most use in the field of decorative and protective coatings, although their use is still limited. A major factor limiting the use of alkyd emulsions is their low rate of oxidative drying, together with some remaining problems concerning colloidal stability of the emulsions. Several factors are believed to contribute to the reduced drying properties of alkyd emulsions as for example interaction between the drier and other paint components and solubility properties of the drier. A water borne paint is a complex system that besides the alkyd droplets in water also contains pigments, dispersants (to stabilize the pigments), surfactants (stabilizing the alkyd droplets), thickeners and several other additives, see Figure 1. The impaired film properties may at least partly be caused by the surfactant which will remain in the paint film and act as a plasticizer. For the segment decorative and protective coatings in Western Europe the market volumes are as follows (solid binder): Solventbased, low solids: 400 ktonne/annum Waterbased, polymer dispersion: 375 ktonne/annllrn Solventbased, high solids: 20 ktonne/annum Alkyd emulsion based: 15 ktonne/annum In most cases the alkyd emulsion is used as co-binder, especially in (hiding) stains and primers for exterior use. In these segments alkyds in white spirit are however still the binder of choice. In the case of alkyd resins for the decorative field, the environmentally friendly possibilities are either as high solids systems or as waterborne emulsions. With the present state of technology, it is very unlikely that alkyd emulsions can match the performance of the present solvent based siliconized alkyds and other extreme outdoor durable systems. Because of their more conventional permeability behaviour and the higher applied layer thickness, high solids seem more suitable for this purpose. Going to the lower end of the market, high solids systems can be applied in almost every segment, the only limitation being their price. For the lowest segments (primers and stains) their application will be limited.It is in these segments that acrylic dispersions have acquired a good reputation both their performance and price have been accepted. In the middle section, ranging from normal outdoor durable alkyds to the better performance stains, alkyd emulsions can be positioned. Their versatility and excellent environmental score (no volatile organic components are necessary) make them exceptionally suitable for this. In many outdoor applications alkyd emulsions will be compared with acrylate dispersions. Typical advantages of acrylate dispersions are their low particle size, quick drying, and good outdoor durability. The last two of these advantages can also be regarded as a disadvantage, since the drying often is considered to be too quick when only small amounts (under 5 %) of coalescing agent are used. The nomenclature then changes from "quick drying" to "short open times". The advantage of good outdoor durability is a.o. based on a good hydrolysis resistance, meaning that although it may take long, once a coating based on acrylic dispersion has deteriorated, the remainders cannot be removed by the usual alkaline paint stripper or heat gun (the dispersions are thermoplastic). Instead flakes of coating will come loose and remain in the environment. The main disadvantage of acrylate dispersions however, the seriousness of which is once again depending upon the application area, is that there always has to be some compromise between film formation (low MFI ) and good blocking properties (high Tg). Since in alkyd emulsions not all chemistry is "finished" when the film is applied, these emulsions can be expected to outperform the thermoplastic dispersions when it comes to properties that are related with film formation from a low Tg material, such as penetration (one of the factors controlling adhesion) and gloss, combined with good dirt pick-up resistance. Whereas the contents of a particle in a polymer dispersion is a true polymer (MW = 100.000 to 1.000.000), in an alkyd emulsion particle we find an oligomer, with a molecular weight ranging from 2000 to 8000. To make a real polymer out of it, the help of cobalt and atmospheric oxygen is required , just as is the case with a conventional alkyd. The fact that molecular buildup still has to take place also means that "derailments" of the crosslinking process will also take place. This means that a film cast from an alkyd emulsion will still exhibit the usual alkyd yellowing and slightly pungent smell. These are caused by decadienal-like structures and hexaldehyde, respectively, resulting from decomposition of the initial hydroperoxide and subsequent beta scission. Always compare an alkyd emulsion with an alkyd and not with a polvmer dispersion in this respect. The aspects where alkyd emulsions differ mostly form solvent-borne alkyd systems are: a) that they are formulated together with water, inducing a risk of hydrolysis upon storage, b) the disperse state of the alkyd, necessitating a high degree of colloidal stability and c) the peculiarities shown in the drying properties of alkyd emulsions. These aspects will be dealt with in the following paragraphs.
|
|
| 17. |
- Bergenståhl, B
(författare)
-
Emulsions
- 1995
-
Ingår i: Physico-Chemical Aspects of Food Processing. - Glasgow, UK : Blackie Academic and Professional. ; , s. 49-64
-
Bokkapitel (refereegranskat)
|
|
| 18. |
|
|
| 19. |
|
|
| 20. |
|
|
| 21. |
|
|
| 22. |
- Bergenståhl, B, et al.
(författare)
-
Surface forces in emulsions
- 1990. - 2
-
Ingår i: Food Emulsions. - : Marcel Dekker. ; , s. 41-96
-
Bokkapitel (refereegranskat)
|
|
| 23. |
- Bergenståhl, B, et al.
(författare)
-
Surface forces in emulsions
- 1997. - 3
-
Ingår i: Food Emulsions. - : Marcel Dekker. ; , s. 57-109
-
Bokkapitel (refereegranskat)abstract
- Emulsions are thermodynamically unstable systems. Therefore, the technical aim of creating "stable emulsions" has to be limited to a control of the instabillity processes (e.g., coalescence, flocculation, creaming, and Ostwald ripening). For this purpose the technologist, in principle, has two tools available: the use of mechanical devices to disperce the system, and the addition of stabilizing additives (natural or artificial) to keep it dispersed. This chapter discusses how the emulsifying additives give rise to stabilizing forces; how these forces affect the kinetics of the instability processes; how they determine the phase behavior of emulsifers; and their relation to the HLB value. The interparticle interactions are determined mainly is coated by lipids and/or proteins. In this chapter we try to point out how a knowledge of interparticle forces, phase behavior, and adsorption may provide an understanding and rationalization of many of the properties of food emulsions.
|
|
| 24. |
|
|
| 25. |
|
|
| 26. |
|
|
| 27. |
- Fäldt, P, et al.
(författare)
-
Fat encapsulation in spray-dried food powders
- 1995
-
Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 72, s. 171-176
-
Tidskriftsartikel (refereegranskat)abstract
- The surface composition of spray-dried sodium caseinate/lactose emulsions with different oil-phases were estimated by ESCA and the particle structure was studied by SEM before and after storage under humid conditions. After spray-drying, powders in which the oil phases consisted of fats with intermediate melting points like hardened coconut oil and butter fat had the highest surface coverage of fat, approx. 34 %. Powder with soy-bean oil as the oil phase had a surface coverage of fat of approx. 15 %. The high melting hardened rape-seed oil was almost completely encapsulated after spray-drying. After storage in a humid atmosphere, fat was released onto all the powder surfaces (surface fat after storage, between 50-65 %) except for those with hardened rape-seed oil in which the fat remained encapsulated. These observations are consistent with the powder structure observed by SEM. The surface composition estimated by ESCA for spray-dried sodium caseinate/lactose-containing emulsions with different amounts of soy-bean oil and a constant lactose/sodium caseinate ratio show an almost completely encapsulated oil-phase after drying. Storage of these powders in a humid atmosphere leads to a release of fat onto the powder surface even if the soy-bean oil content is low ( 1 % of the dry weight). Powders made from soy-bean oil emulsions with sodium caseinate alone exhibit a much lower degree of encapsulation than in the system where lactose is present.
|
|
| 28. |
- Fäldt, P, et al.
(författare)
-
Spray-dried whey protein/lactose/soy-bean oil emulsions 2. Redispersability, wettability and particle structure
- 1996
-
Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 10, s. 431-439
-
Tidskriftsartikel (refereegranskat)abstract
- In the present paper redispersion and wettability experiments of spray-dried whey protein stabilized emulsions are presented. Emulsion droplet size after redispersion gives information about eventual coalescence between emulsion droplets in the powder matrix during drying or storage, resulting in an increase in emulsion droplet size after redispersion. Results from redispersion experiments are combined with previously presented knowledge about powder surface composition and particle structure to elucidate internal processes in the powder matrix and external processes on the powder surface during drying and storage of whey protein powder. The results show that with addition of lactose to whey protein stabilized emulsions, emulsion droplet structure remains intact in the powder matrix during drying since the emulsion droplet size in the redispersed spray dried emulsion is unchanged. In the absence of lactose there is a growth in emulsion droplet size after redispersion of the spray-dried whey protein stabilized emulsion showing that a coalescense of emulsion droplets occurs during the drying or redispersion process. Storage of the whey protein stabilized powders in humid atmosphere (relative humidity 75 %, 4 days) induces changes in some powders. When the powder contains a critical amount of lactose there is a remarkable increase in emulsion droplet size after redispersion of humid stored powders as compared to the emulsion before drying and compared to the redispersed dry-stored powder. In addition, there is a release of encapsulated fat after humid storage of lactose containing powders detected by ESCA. For powders which do not contain any lactose there is no increase in emulsion droplet size after storage in humid atmosphere as compared to the redispersed dry stored emulsion. Addition of only a small amount lactose prevents coalescence of emulsion droplets and the subsequent increase in droplet size during drying. If the lactose content is kept rather low there is neither an effect on the droplet size after storage under humid conditions nor a release of fat onto powder surfaces detected. Furthermore, wettability of the spray-dried whey-protein stabilized emulsions by water is presented. It is concluded that it is beneficial to wettability in water to have as high coverage of lactose on the powder surface as possible. In addition, a review of particle structure for powders with various composition is presented.
|
|
| 29. |
- Fäldt, P, et al.
(författare)
-
Spray-dried whey protein/lactose/soybean oil emulsions. 1. Surface composition and particle structure
- 1996
-
Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 10, s. 421-429
-
Tidskriftsartikel (refereegranskat)abstract
- Emulsions made of whey protein, lactose and soy bean oil were spray-dried and the chemical surface composition of the dried powders estimated by electron spectroscopy for chemical analysis (ESCA). In particular, the ability of whey protein to encapsulate fat is enlightened. Additionally, the structure of the spray-dried powder particles was studied by scanning electron microscopy. The powders were examined after storage in both dry and humid atmosphere (relative humidity 75 %, 4 days). It was found that the ability of whey protein to encapsulate soy-bean oil is rather low as compared to sodium caseinate with a large part of the powder surface covered by fat after spray-drying. After storage in humid atmosphere there is a release of encapsulated oil onto the powder surface in most cases, and a fat coverage increase. The release of fat onto the powder surfaces causes the particle structure to change dramatically for powders containing a critical amount of lactose. Such powders agglomerate and lose structure completely. In comparison, powders containing no lactose under humid conditions also causes a release of fat onto the powder, however in this case particle structure remains intact. Powders containing only a small amount of lactose, up to about 25 % of emulsion dry weight, do not exhibit a release of fat onto the powder surfaces after storage under humid conditions and the structure of these powder particles do not change. Presence of lactose in whey protein stabilized emulsions, however, do not increase fat encapsulation by whey protein, as reported earlier for sodium caseinate stabilized emulsions that were spray-dried. During spray-drying of whey protein/lactose solutions there is a strong overrepresentation of surface-active whey protein on the powder surface. Whey protein coverage increases even further when the powders are stored under humid conditions, also making them lose structure.
|
|
| 30. |
- Fäldt, P, et al.
(författare)
-
Stabilization by chitosan of soybean oil emulsions coated with phosphilipid and glycocholic acid
- 1993
-
Ingår i: Colloids and Surfaces. - 0166-6622 .- 1873-4340. ; 71, s. 187-195
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction between chitosan, a cationic polyelectrolyte having a pKa of about 6.2, and emulsified lipids been measured as a function of pH by electrophoretic mobility. The strongest adsorption of chitosan has been observed on emulsion droplet surfaces stabilized with sodium glycocholic acid (bile salt) mixed with phosphatidyl choline pH of about 5. The forces acting between layers Or chitosan adsorbed on negatively charged solid surfaces (mica) measured as a function Or pH. From these measurements it is clear that, al low pH, the adsorption of cationic chitosan on to the negatively charged mineral surface results in a charge reversal. When the pH is increased (without changing the adsorbed amount), the charge passes through zero, and, at higher pH values, a negative charge develops. The range of the steric force was used to describe the structure of the adsorbed chitosan layer at different pH values. The flocculation behaviour of an emulsion stabilized by phospholipid and bile salt emulsifiers and adsorbed chitosan been rationalized by considering the forces acting between negatively charged solid surfaces coated with a chitosan layer.
|
|
| 31. |
- Fäldt, P, et al.
(författare)
-
The surface composition of spray-dried protein-lactose powders
- 1994
-
Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 90, s. 183-190
-
Tidskriftsartikel (refereegranskat)abstract
- The surface composition of spray-dried mixtures of lactose/protein and lactose/glycine were estimated by means of ESCA. The results show that even with a low concentration of protein (0.01% wt) in the solution to be dried, protein starts to appear on the surface of the powder. At a protein/lactose ratio of 1/99 the protein starts to dominate the powder surface. At a protein/lactose ratio of 20/80, ~70 % of the surface is covered by protein. The results are similar for the proteins sodium caseinate and bovine albumin. The spray-drying of mixtures of lactose/glycine gives a different result. In this case, the surface composition of the powder reflects the composition of the mixture to be dried The surface tensions of the solutions show that the proteins have a higher surface activity than lactose, since even a small amount of protein added to a lactose solution lowers the surface tension considerably. Glycine affects the surface tension to only a minor extent. These results show that the composition of the air-water interface of the drying droplets is reflected in the surface composition of the dried powder. In addition, scanning electron microscopic pictures show that the changes in the powder structure when protein is added to the solution are associated with the presence of protein on the surface. When the surface coverage of protein increases, dents start to appear on the particles. The powders made from lactose/glycine solutions are highly agglomerated regardless of the glycine concentration.
|
|
| 32. |
- Granelli, K, et al.
(författare)
-
Influence of surface structure on cholesterol oxidation in model food powders
- 1996
-
Ingår i: Journal of the Science of Food and Agriculture. - 0022-5142 .- 1097-0010. ; 71, s. 75-82
-
Tidskriftsartikel (refereegranskat)abstract
- Three milk-resembling powders having different oil-phases were prepared and stored for six months at room temperature. Samples were taken monthly for estimation of the surface composition by "electron spectroscopy for chemical analysisz (ESCA) and analyses of the level of cholesterol oxides by gas chromatography. The highest fat coverage was obtained with technical tristearin as oil-phase. This preparation had, directly after spray-drying and during the first period of storage, around 75 % of the powder surface covered by fat. During the later storage period this coverage decreased. This powder also had the largest increase in cholesterol oxides during storage, ending in 159 µg / g cholesterol. The powder contsining highmelting pure tristearin had a low surface coverage of fat, originally about 25 % and decreased during the storage period. Little increase in cholesterol oxides was observed ending, in 52 µg / g cholesterol. The third powder containing liquid triolein as oil-phase, had a surface coverage of about 50 % throughout the storage period. The cholesterol oxidation rate was in between the two tristearin powders, ending in 75 µg / g cholesterol. The lipid present at the powder surface will undoubtedly be exposed to oxygen in air. However, lipids present inside the powder particles may also be reached by oxygen through cracks and pores in the particles. The results for the investigated powders indicate that the surface composition is of major importance for the oxidation of cholesterol. No correlation between cholesterol oxidation and solvent extractable fat (free fat) was found for the investigated powders.
|
|
| 33. |
- Haghshenas, N, et al.
(författare)
-
The exchange rate between dissolved tripalmitin and tripalmitin crystals
- 2001
-
Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 21, s. 239-243
-
Tidskriftsartikel (refereegranskat)abstract
- The focus of this paper is on understanding the exchange between dissolved fats and fat crystals in dispersions by quantifying the rate of the exchange between the fats in solution and in crystals. In the studies reported here, tripalmitin (PPP) was used as model fat. The dispersions contained PPP crystals and dissolved radio-labelled PPP (14C-PPP, used as the probe) in a medium chain triglyceride oil (MCT). The exchange process between the dissolved 14C-PPP and unlabelled PPP crystals was followed using a radio-detector. The effect of the crystal concentration on the exchange rate was studied. The results suggested that the rate of the exchange is dependent upon both the dissolution of the surface of the crystals and also diffusion and crystallisation of the dissolved compounds.
|
|
| 34. |
- Hansen, PHF, et al.
(författare)
-
Orthokinetic aggregation in two dimensions of monodisperse and bidisperse colloidal systems
- 1999
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 220, s. 269-280
-
Tidskriftsartikel (refereegranskat)abstract
- Orthokinetic aggregation of colloids trapped at the air-liquid interface was studied by direct imaging in a couette cell. This method allowed us to follow the temporal evolution of both the cluster-mass distribution and the cluster structure at a shear rate where Brownian aggregation is suppressed. The interactions between the monodisperse latex particles floating at the air-water interface were controlled either by varying the electrolyte concentration or by creating a bidisperse system through addition of small particles. The results show that the clusters in all the systems are characterized by a high fractal dimension; indicating that the clusters are rearranged and densified by the shear. Kinetic analysis suggests that aggregation of the monodisperse systems mainly proceeds through homogeneous aggregation, i.e. large clusters sticking to other large clusters. The weakly aggregated monodisperse system displayed a transition from heterogeneous to homogenous aggregation of clusters with time which could be related to an incubation time. The bidisperse system, finally, with a size ratio around 10, favored a more heterogeneous aggregation between small and large clusters throughout the aggregation process; a slightly lower fractal dimension was observed compared to the strongly aggregated monodisperse system.
|
|
| 35. |
- Johansson, D, et al.
(författare)
-
Lecithins in oil-continuous emulsions. Fat crystal wetting and interfacial tension
- 1995
-
Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 72, s. 205-211
-
Tidskriftsartikel (refereegranskat)abstract
- Lecithin is a powerful emulsifier widely used in foods, feeds and pharmaceuticals, which functions mainly due to its adsorption properties. Lecithin adsorbs to fat crystals at the triglyceride oil/water interface, and makes their surface more polar (observed as an increase in the contact angle measured through the oil at the interface: fat crystal/oil/water). This adsorption process is quick (less than five minutes) for relatively polar lecithins like soybean phosphatidylcholine (PC), and results in highly polar surfaces (contact angle ≈180°). Less polar lecithins give a slow adsorption (some hours) and less polar crystals (contact angle < 90°). The adsorption of different lecithins to the oil/water interface, observed as a decrease in interfacial tension, follows the adsorption pattern to the fat crystals (the more polar the lecithin the quicker the adsorption). There is a relationship between the high polarity of fat crystals and the poor functionality of lecithin in margarine (margarines spatters during frying). There is also a relationship between a high polarity of fat crystals and a high ratio of polar to nonpolar phospholipids (SPI+PA+LPC/SPE) in lecithin. The correlations migth be via aggregation properties of lecithin in the oil, which should influence both the adsorption kinetics and the structure of adsorbed layers. A monoglyceride (monoolein) shifts the adsorption kinetics of lecithin (soybean PC) to fat crystals and the structures of adsorbed layer. The reason is probably a formation of mixed aggregates between monoolein and soybean PC.
|
|
| 36. |
- Johansson, D, et al.
(författare)
-
Sintering of fat crystal networks in oil during post-crystallization processes
- 1995
-
Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 72, s. 911-920
-
Tidskriftsartikel (refereegranskat)abstract
- Several foods contain semisolid fats consisting of solid crystals dispersed in a liquid oil. In oil continuous margarine, butter and chocolate, fat crystals determine properties such as consistency, stability against oiling-out and emulsion stability. Trends towards foods with less fat and/or less saturated fat create a need for understanding and controlling the properties of fat crystal dispersions. Fat crystals form a network in oil due to mutual adhesion. A source of strong adhesion is formation of solid bridges (sintering), and has been studied in this work through sedimentation and rheological experiments. Results indicate that sintering may be created by crystallization of a fat phase with a melting point between that of the oil and the crystal. Generally speaking, ß´ crystals were sintered by ß´ fat bridges favoured by rapid cooling, and ß crystals by ß fat bridges favoured by slow cooling. The necessity of the same polymorphic form of the crystal and bridge indicated that solid bridges rather than bridges formed by small crystal nuclei were formed. A maximum in sintering ability for an optimal sintering fat concentration occurred due to competition between bridge formation and other crystallization processes. Some emulsifiers influenced the sintering process. For example, monooolein made it more pronounced, while technical lecithin had the opposite effect.
|
|
| 37. |
- Johansson, D, et al.
(författare)
-
Surface interactions in oil continuous food dispersions
- 1993
-
Ingår i: Food Colloids and Polymers: Stability and Mechanical Properties.Proceedings of a conference in Lunteren, The Netherlands, 8-10 April 1992. ; , s. 323-331
-
Konferensbidrag (refereegranskat)abstract
- We have previously shown that in an oil continuous system, emulsifiers adsorb to fat or to, the more polar, sugar crystals and thereby influence their properties. The adsorption has been measured with about 10 different common food emulsifiers and has been directly measured by the serum displacement method.A simple way to evaluate the consequence of the adsorption is sedimentation experiments where an increased sediment volume indicates an increased adhesion. Sedimentation experiments have shown that the adsorbed layers both can increase or decrease the adhesive forces between sugar and fat crystals. We also observed large differences between sugar and fat crystals. In experiments with trace amounts of water present we have found the adsorption and the interaction very sensitive to the water content in the system. The adsorption isotherms are compared with contact angle measurements in the three phase contact water/crystal/oil. A strong correlation is found in both the receding and the advancing contact angles.An increased adhesion causes an increased viscosity and rigidity and a reduced adhesion results in a much more liquid oil dispersion. A satisfying correlation between the sedimentation experiments and rheological experiments was found. Through a comparison with a network model the character of the force is compared with different interaction models (water bridges and van der Waals forces).The influence of the adsorbed emulsifiers on the sintering of fat crystals is also studied in a set of preliminary experiments.
|
|
| 38. |
- Johansson, D, et al.
(författare)
-
The influence of food emulsifiers on fat and sugar dispersions in oils. I. Adsorption, sedimentation
- 1992
-
Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 69, s. 705-717
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption isotherms of several emulsifiers to fat and sugar crystals dispersed in oils have been determined. Further, the influence of the emulsifiers on the interactions between the crystals has been estimated in sedimention experiments, where an increased sediment volume due to adsorption corresponds to an increased adhesion between the crystals and vice versa. Most of the emulsifiers examined adsorb weakly to fat crystals and form tight monolayers, resulting in increased adhesion between the crystals at high concentrations. On the other hand, loosely packed layers are formed at low concentrations, and a decreased adhesion is observed. Unsaturated monoglycerides and phospholipids cause a decrease in adhesion for all concentrations examined. The emulsifiers adsorb more strongly to sugar crystals than to fat crystals and form tightly packed monolayers with hydrocarbon chains directed to the oil. The crystals are then stabilized sterically - the adhesion between them is weaker and the sediments are more compact. At low concentrations the opposite behaviour often occurs. Monoglycerides interact in a specific way with sugar and cause an increased adhesion between the crystals for all concentrations examined. Phospholipids reduce the adhesion between sugar crystals, resulting in much denser sediments. Saturated monoglycerides in amounts over the solubility limit, tend to precipitate as a network between fat or sugar crystals, which causes bulky sediments and results in better stability against oiling out.
|
|
| 39. |
- Johansson, D, et al.
(författare)
-
The influence of food emulsifiers on fat and sugar dispersions in oils. II. Rheology, colloidal forces
- 1992
-
Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 69, s. 718-727
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of food emulsifiers on the viscoelastic properties (storage modulus and yield value) of fat and sugar dispersions in vegetable oils has been investigated. It was found that almost all of the emulsifiers tested influence the rheology of the dispersions. The magnitude and the direction of the rheological changes depend on both the type and amount of emulsifier. In most cases relatively small changes occur, especially for fat crystals. Generally speaking, the largest changes are caused by lecithins and saturated monoglycerides. The magnitudes of colloidal forces and the equilibrium distances between the particles have been estimated from the rheological network model of van den Tempel and from the correlation of the yield value to the interaction energy by Gillespie et. al.. The results indicate that van der Waals forces alone can not be responsible for the interparticle interaction in fat or sugar dispersions. The formation of water bridges is discussed as a probable source of interaction in both cases. Further, the validity of the network model for the fat and sugar dispersions in oils is questionable.
|
|
| 40. |
- Johansson, D, et al.
(författare)
-
The influence of food emulsifiers on fat and sugar dispersions in oils. III. Water content, purity of oils
- 1992
-
Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 69, s. 728-733
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of water on the interactions between fat and sugar crystals dispersed in triglyceride (vegetable oils) was qualitatively estimated from sedimentation and rheological experiments. The experiments were performed both with and without food emulsifiers (monoglycerides and lecithins) present in the oil. The effects of minor natural oil components (non triglycerides) on the interactions and on the emulsifier adsorption to the crystals were examined by comparing a commercial refined oil and a chromatographically purified oil. The results show that water generally increases the adhesion between fat and sugar crystals in oils and also increases the surface activity of the oil soluble food emulsifiers. Minor oil components give a small increase in the adhesion between fat and sugar crystals in oils, but do not influence the adsorption of food emulsifiers in any systematic way.
|
|
| 41. |
- Landström, K, et al.
(författare)
-
A fluorescence method for quantitative measurements of specific protein at powder surfaces
- 1999
-
Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 12, s. 429-440
-
Tidskriftsartikel (refereegranskat)abstract
- A new method using fluorescence labeled proteins was developed to determine the quantitative amount of specific protein at the powder surface. The method is based on steady-state fluorescence measurements of pyrene labeled proteins with oxygen gas phase quenching at the powder surface. The surface load of protein was measured for spray-dried dextran powders containing bovine serum albumin (BSA). The results show a patchwise surface load of about 1.3 mg/m2 at a concentration of 0.33 % (dry weight) BSA in the powder. The patchwise surface load stays constant with increased BSA concentration in the powder.
|
|
| 42. |
|
|
| 43. |
- Löfborg, N, et al.
(författare)
-
Molecular exchange in thermal equilibrium between dissolved and crystalline tripalmitin by NMR
- 2003
-
Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 80, s. 1187-1192
-
Tidskriftsartikel (refereegranskat)abstract
- An NMR technique to measure the exchange kinetics at thermal equilibrium in dispersions of moderately soluble crystalline material is presented. By monitoring the exchange of molecules between pools in solid and dissolved form one can characterize the surface specific exchange rate. Illustrative experiments were performed in a model system with b-type crystals of tripalmitin as the solid phase and tripalmitin, a fraction of it deuterated, dissolved in a medium chain triglyceride oil as the liquid phase. The concentration of deuterated tripalmitin in the solvent was followed by 2H NMR after the crystals, that initially lack deuterated tripalmitin, were immersed in the liquid. The variation of the 2H concentration in the solvent provided the surface specific exchange rate. No systematic errors, due to the slight difference in properties of the deuterated tripalmitin (2H-PPP) compared to hydrogenated tripalmitin (1H-PPP), were observed. The methodology worked well between crystal concentrations of 2 and 4-wt%.
|
|
| 44. |
- Malmsten, M, et al.
(författare)
-
Adsorption of apolipoprotein B at phospholipid model surfaces
- 1995
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 172, s. 485-493
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of apolipoprotein B (Apo B) at a series of surfaces was investigated with in situ ellipsometry. For silica and methylated silica, the adsorbed amount (G), the adsorbed layer thickness (del) and the mean adsorbed layer refractive index (nf) were obtained by a procedure involving studies of the bare substrate at two different ambient refractive indices, as well as four-zone averaging. The adsorbed amount of Apo B is much higher at silica than at methylated silica. Despite this, the adsorbed layer thickness is the same at the two surfaces, and the adsorbed layer formation proceeds similarly. In both cases, the adsorbed layer formation occurs through the adsorption of Apo B molecules in an essentially random orientation, the difference between silica and methylated silica being the number of molecules adsorbed per unit area. Furthermore, the adsorption of Apo B at phospholipid surfaces was investigated. It was found that the adsorption at phosphatidylcholine (PC) was quite limited, whereas that at phosphatidic acid (PA) was substantial. Studies with mixed PA/PC layers showed that the Apo B adsorption depends on the mixed phospholipid layer composition in an essentially linear fashion. Finally, mixed phospholipid layers of PC and ganglioside GM1, as well as phosphatidylinositol (PI) layers, showed a dramatic preferential adsorption of Apo B over, e. g. human serum albumin (HSA), IgG, fibronectin and fibrinogen.
|
|
| 45. |
- Malmsten, M, et al.
(författare)
-
Sphingomyelin from milk – characterization of liquid crystalline, liposome and emulsion properties
- 1994
-
Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 71, s. 1021-1026
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of sphingomyelin obtained from bovine milk were investigated. In particular, the properties of liposomes and emulsions prepared from the sphingomyelin, as well as the liquid crystalline behaviour, were investigated and compared to those of related phosphatidylcholine systems. Like sphingomyelins from other sources, sphingomyelin from milk contains a large fraction of long and saturated acyl groups, which results in a high (35-82°C, depending on the lipid concentration) gel-to-liquid crystal transition temperature (Tc). At high sphingomyelin concentrations, a lamellar phase forms above Tc, while below Tc, a swelling gel phase is obtained. The gel phase swells to about 20 wt% water, whereas above Tc, the swelling continues to about 40 wt% water. The limiting areas per molecule are 51 and 68 Å2 below and above Tc, respectively. Sphingomyelin from milk forms liposomes readily in the presence of cholesterol. The liposomes formed have a diameter of about 100 nm, and are stable even at 0.1 M NaCl or HCl. Materials entrapped in the liposomes are released rather slowly (typically 40 % over 5 h). A comparison shows that the sphingomyelin liposomes behave similarly to those formed by phosphatidylcholine systems. Furthermore, sphingomyelin from milk forms stable o/w emulsions with soy bean oil. The size of the emulsion droplets obtained was about 200 nm. Both the size of the emulsion droplets and its dependence on electrolyte addition correlate closely with those of emulsions formed by the corresponding phosphatidylcholine system. Therefore, it is possible to use sphingomyelin as an alternative for saturated phosphatidylcholines, which may be advantageous for oral and dermal pharmaceutical applications, as well as in cosmetics.
|
|
| 46. |
- Millqvist-Fureby, Anna, et al.
(författare)
-
An aqueous polymer two-phase system as carrier in the spray-drying of biological material
- 2000
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 225, s. 54-61
-
Tidskriftsartikel (refereegranskat)abstract
- This investigation describes a novel concept in formulation of carrier systems for spray-drying of biological materials. As carrier materials a system composed of poly (vinyl pyrrolidone) (PVP) and dextran was used. This system yields an aqueous two-phase system in which each phase is enriched in one of the polymers. By varying the composition of the system, the effective structure of a 'stirred' such system can be varied, covering the entire range from dextran continuous to PVP continuous. This facilitates encapsulation of either of these polymers in a spray-drying operation. In an attempt to investigate the spray-drying from such a system, the surface composition of the spray-dried powder obtained from various compositions of the two-phase system was analysed by electron spectroscopy for chemical analysis (ESCA), providing information on the distribution of the polymers in the powder and thus also in the spray droplets. The two-phase system was applied for spray-drying of live bacteria. The survival rate of the bacteria depended on the composition of the two-phase system. The storage stability of the bacteria in these formulations was investigated after storage at room temperature under dry conditions for four weeks, and it was found that the survival rate was 10-45%. The results therefore show that this type of formulation holds promise for future applications for micro-organisms as well as other sensitive biological materials such as proteins.
|
|
| 47. |
- Millqvist-Fureby, Anna, et al.
(författare)
-
Spray-drying of trypsin – Surface characterisation and activity preservation
- 1999
-
Ingår i: International Journal of Pharmaceutics. - 0378-5173 .- 1873-3476. ; 188, s. 243-253
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study trypsin mixed with various carbohydrates, i.e. lactose, sucrose, mannitol, a-cyclodextrin and dextrin, was spray-dried in order to investigate the effects of spray-drying on this enzyme, with particular emphasis on the effects of interactions between trypsin and the surface formed during spray-drying. The protein was strongly over-represented at the surface of the powder particles, the surface coverage ranging from 10 to 65%, depending on the amount of trypsin in the solids (0.2-5%). This indicates that the protein adsorbs at the air/liquid interface of the spray-droplets, and that this surface is largely preserved also after drying. The surface concentration of protein in the spray-dried powders could be controlled by adding a surfactant to the mixture before drying, since the surfactant adsorbs preferentially at the air/liquid interface of the spray droplets, thus expelling protein from the surface. In general, the residual activity of trypsin in these non-optimised formulations was 90% or higher, and in no case less than 82%. It was found that the loss of activity could partly be explained by inactivation of the protein adsorbed at the surface. For mannitol and sucrose, however, the level of inactivation was higher than could be explained by surface inactivation alone, and additional mechanisms must also be considered.
|
|
| 48. |
- Millqvist-Fureby, Anna, et al.
(författare)
-
Surface characterisation of freeze-dried protein/carbohydrate mixtures
- 1999
-
Ingår i: International Journal of Pharmaceutics. - 0378-5173 .- 1873-3476. ; 191, s. 103-114
-
Tidskriftsartikel (refereegranskat)abstract
- In the present investigation freeze-drying of proteins (BSA or trypsin) together with various carbohydrates, i.e. lactose, sucrose, mannitol, a-cyclodextrin and dextrin, has been studied with particular emphasis on the surface composition of the freeze-dried powders. The proteins were found to be over-represented on the powder surface as compared to the bulk concentration of protein. The mechanism behind the surface accumulation is believed to be that proteins adsorb preferentially over carbohydrates to the ice/liquid interface in the frozen sample. The degree of surface accumulation depended on the carbohydrate used, and was increased in annealed samples compared to reference samples. The activity of trypsin was fairly preserved well (58-90%) in the freeze-dried powders, but depended on the carbohydrate excipient, whilst the surface composition had little effect on the activity. The activity preservation was improved when the protein concentration was raised from 1% to 10% in the solids. The surface composition of powders containing mixtures of mannitol and dextrin as excipients depended on the ratio between the two carbohydrates, with the lowest surface coverage of protein obtained in 50/50 mixtures.
|
|
| 49. |
- Millqvist-Fureby, Anna, et al.
(författare)
-
Surface composition of spray-dried milk protein-stabilised emulsions in relation to pre-heat treatment of proteins
- 2001
-
Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 21, s. 47-58
-
Tidskriftsartikel (refereegranskat)abstract
- Several important technical properties of spray-dried food powders depend on particle-liquid interactions (e.g. wettability, dispersability) and particle-particle interactions (e.g. flowability). It can be assumed that the chemical composition of the surface layer of the particles to a large extent determine these properties. The present study has been aimed to investigate the relation between the surface composition of spray-dried milk protein-stabilised emulsions and pre-heat treatment of the proteins. Solutions of WPC were heat-treated at low (60-90°C) and high (140°C) temperature and the degree of denaturation was determined, prior to the preparation of emulsions with rapeseed oil. The surface composition of the dry powders were established by using ESCA (electron spectroscopy of chemical analysis).The emulsions were characterised by droplet size distribution before spray drying and after dissolution of the powders. Also free fat extractions and estimations of wettability (dissolution rates) were performed. The powder surface coverage of protein decreased with increasing degree of protein denaturation before the emulsification, whereas the emulsion droplet size increased both before spray drying and after reconstitution of powders. The free fat extraction as well as the dissolution rate, whereof the latter decreased with increasing surface fat coverage, correlated well with the fat coverage of the powder surface.
|
|
| 50. |
- Mol, L, et al.
(författare)
-
Forces in dimethyldodecylamine oxide- and dimethyldodecylphosphine oxide- water systems measured with an osmotic stress technique
- 1993
-
Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 9, s. 2926-2932
-
Tidskriftsartikel (refereegranskat)abstract
- The structural parameters of the hexagonal and lamellar phase of the dimethyldodecylamine oxide (DDAO)-water and the dimethyl-dodecylphosphine oxide (DDPO)-water systems have been determined using X-ray diffraction. In addition the relative vapour pressure of water in equilibrium with these phases was determined as a function of surfactant concentration and temperature. This allowed the determination of the swelling pressure in the lamellar phase. It was found that the swelling pressure was considerably higher in the DDAO-water system than in DDPO-water. For both surfactants, but most pronounced so for DDPO, the swelling pressure decreased with increasing temperature. The results obtained are discussed in the light of the ongoing debates about i) the relative importance of steric/protrusion forces and hydration forces between surfactant bilayers, and ii) the molecular origin of the temperature dependence of the interactions displayed in several non-ionic - water systems.
|
|
