Coalescence Of Globules Research Articles

The Stability of Milk Fat-Water Emulsions Containing Monoglyceride and Sorbitan Ester. II.

The structures of oil globule membranes of 30% milk fat water emulsions containing monoglyceride (MG), sorbitan fatty acid ester (SE) and caseinate (CA) were studied by measuring electrophoretic mobilities (EM) of their dispersed oil globules at different pH.EMs were influenced by the hydrocarbon chain length of sorbitan ester (HCL). EM vs HCL pattern of the oil globules coated with SE was quite different from that of the oil globules coated with MG+SE. This fact means that the outer layer of oil globule membranes consited of neither MG nor SE exclusively. Thus, a mosaic model of MG-SE at the oil globule membrane, where MG and SE is supposed to form certain molecular association, can be assumed.EM vs HCL pattern of the oil globules coated with SE and MG+SE, had a resemblance to EM vs HCL pattern of those coated with SE+CA and MG+SE+CA respectively, This behavior seems that SE and MG+SE layers at the oil-water interface could be covered coasely by CA layer.The relation between EM and the rate of globule coalescence for the emulsions containing MG+SE+CA showed good linearity, However, EM appers to have little correlation with stability against coalescence, unless those oil globule membranes have a similar strength.

Stability of Milk Fat-Water Emulsions Containing Monoglycerides and Sorbitan Esters. I.

The rheological characteristics for oil-water interfacial films prepared from oil phase consisting of milk fat (MF), monoglycerides (MG), and sorbitan esters (SE) and aqueous phase consisting of caseinate (CA) and water (W), as model protective films, were studied. All the interfacial films exhibited viscoelastic behavior. From the creep compliance-time curves for the oil-water interfacial films a mechanical model can be derived consisting of a unit of Maxwell Model in series with two units of Kelvin-Voigt Model (6 element model). Instantaneous elasticity (E0) and Newtonian viscosity (ηN) of the said films increased as the hydrocarbon chain length of the sorbitan esters (HCL) increased. From comparison of electrophoretic mobility vs HCL curves for O/W emulsions with the rheological characteristics vs HCL curves for the oil-water interfacial films, instantaneous elastic behavior, Newtonian viscous behavior and retarded viscoelastic behavior of the films might be related to HCL under coexistence of (MG+SE+CA), (MG+SE), (SE) respectively at the oil-water interface. Since the rate of oil globule coalescence for the O/W emulsions prepared from oil phase consisting of MF, MG, and SE, and aqueous phase consisting of CA and W decreased linearly as E0 increased, and the rate decreased drastically at the region where ηN was higher than ca. 25 104 surface P, the mechanical strength of those protective films covering oil droplets in O/W emulsions was suggested as being responsible for the stability of the O/W emulsions.

Dosage form characteristics of microsphere-in-oil emulsions. I. Stability and drug release.

The characteristics of microsphere-in-oil (S/O) emulsion relating to the stability and drug release properties were investigated in comparison with those of water-in-oil (W/O) emulsion. The mean globule sizes of the S/O emulsion and W/O emulsion were 1.6 μm and 1.9 μm, respectively. Visual observation of phase separation revealed that the S/O emulsion was more stable than the W/O emulsion, in good agreement with the results of microscopic observation of the globule coalescence. The S/O emulsion remained stable even after storage in a freezer for one month, whereas the W/O emulsion was completely destroyed by freezing. Concerning the rheological properties, both emulsions showed non-Newtonian plastic flow, but the S/O emulsion had a larger viscosity. Examination of the drug release characteristics showed that the S/O emulsion offered stable incorporation of a drug into the innermost aqueous phase even after redispersion into gelatin solution, in accord with the results of microscopic observation. These results suggest the superiority of the S/O emulsion as a drug delivery system. The reason for this is discussed in relation to several criteria having to do with physical properties.

The stability of soybean oil-water emulsions containing mono- and diglycerides

The stability of 5.0 to 20.0% soybean oil/water emulsions containing KA-2017 (a monoglyceride emulsifier) and KA-2018 (a di/triglyceride emulsifier) were studied. There is a critical molar ratio of fatty acid groups in the monoglyceride compared to the fatty acid groups in the diglyceride at which the stability of the oil globule coalescence reaches a maximum. The electrophoretic data also suggests that some remarkable changes on the oil globule surface occur at this molar ratio of 7 3 . The films of KA-2017-KA-2018 at the oil-water interface show viscoelasticity. This critical molar ratio coincides with the molar ratio at which the interfacial films have the highest instantaneous elasticity. From this point of view, KA-2017 and KA-2018 seem to enter some form of association at the oil-water interface, and make up mechanical strong protective films covering oil globules.

Correlation of phase inversion temperature with kinetics of globule coalescence for emulsions stabilized by a polyoxyethylene alkyl ether.

The phase inversion temperatures, globule coalescence rates, and long-term stability of oil-in-water emulsions stabilized by polyoxyethylene 4 cetyl ether were measured. Addition of sodium chloride to the aqueous phase depressed the phase inversion temperatures of the emulsions and the cloud point of the surfactant. Linear correlations were obtained between phase inversion temperature and cloud point and also between phase inversion temperature and the logarithm of the globule coalescence rate at constant temperature. This latter finding is consistent with a theory of emulsion type based upon the kinetics of coalescence. The programmed viscometric technique of determining inversion revealed the presence of a liquid crystalline phase below 35 degrees, which contributes significantly to emulsion stability.

Ultrastructure and isolation of glyoxysomes (microbodies) in zoospores of the fungusentophlyctis sp.

A correlative approach, involving light and electron microscopic, cytochemical, and biochemical techniques, was used to study the structure and function of microbodies in zoospores ofEntophlyctis sp. The same population of microbodies already existing in the zoosporangium appeared to be segregated into zoospore initials during cytoplasmic cleavage. Microbodies laid at the anterior end of zoospores and were part of an organized assemblage of organelles, the microbody-lipid globule complex. In the microbody-lipid globule complex, endoplasmic reticulum occurred on the surface of the lipid globules toward the zoospore's exterior, and the microbody, subtended by mitochondria, was appressed to the opposite surface of the lipid globule. The organization of the microbody-lipid globule complex changed as the zoospore swam and encysted. As lipid globules coalesced, the microbody-lipid globule complex became disorganized. After lipid globule coalescence was completed, the microbody-lipid globule complex regained its order, and several microbodies were clustered adjacent to a single lipid globule. The microbodies persisted even in the encysted zoospore, but they were found on all sides of the lipid globule. Microbodies isolated from zoospores contained catalase as well as malate synthase and isocitrate lyase, two enzymes of the glyoxylate cycle. When zoospores encysted greater activities of these glyoxylate cycle enzymes could be detected. The presence of glyoxylate cycle enzymes and the close association between the microbody and lipid globule suggest that microbodies function as glyoxysomes in zoospores and encysted zoospores. The functional significance of the morphological organization of the microbody-lipid complex is discussed in terms of energy production and the conversion of storage lipid into structural components of the cell.

Factors affecting emulsion stability, and the HLB concept

Tbe optimum stability of O/W emulsions stabilized by 1:1 molar ratios of Spans and Tweens is due to association between the emulsifier molecules adsorbed at the oil—water interface. Emulsion stability is related to both surface elasticity and surface viscosity, as derived from interfacial rheological measurements, with a greater dependence on the first named parameter. Discrepancies between activation energies calculated from the temperature dependence of emulsion stability and of surface elasticity suggest that some additional factor is also involved in globule coalescence, e.g., dehydration of the Tween polyoxyethylene chains. Coalescence may be due to the force pressing adjacent globules together giving rise to a compressive stress which increases with time. When it exceeds a critical value, which will be related to the maximum deformation which the globules can withstand, the interfacial film around the globules begins to break down and coalescence begins.' The various analytical procedures for determining HLB values of emulsifiers do not account for interaction between the emulsifiers and the aqueous and oil phases. It may be possible to derive more meaningful values from phase inversion temperature determinations on the emulsions.

Phase inversion temperature as an accelerated method for evaluating emulsion stability

The influence of HLB on the phase inversion temperature (PIT) of O/W emulsions stabilized by Tween-Span blends follows the same trend as the influence of HLB on emulsion stability, with maximum PIT being shown at HLB ∼ 12. There is a general relationship between PIT and emulsion stability with the PIT increasing as the rate of globule coalescence decreases. This suggests that it may be possible to use PIT determinations as a simple and rapid method for evaluating emulsion stability.

母川回帰シロサケの卵成熟過程

The process of oocyte maturation was observed in the chum-salmons, Oncorhynchus keta, captured at Otsuchi Bay and Otsuchi River, Iwate Prefecture, Japan, during the months of November 1969 and 1970. When the female salmons arrived at Otsuchi Bay, the oocytes conatined in their ovaries were either in the end of the growth period of oogenesis or in the beginning of the maturation period. From the time of arrival in the bay until the fish entered the river, a series of changes proceeded in the oocytes. The coalescence of yolk globules was first observed, followed by the migration and segregation of oil drops, the development of cortical cytoplasm, the formation of the blastodisc, the thickening of the chorion around the micropyle, the disappearence of the germinal vesicle, the meiotic division of the nucleus, and the rupture and shrinkage of the follicular envelopes. From the observation on oocyte structure, the maturation period of the oocytes can be devided into four stages, A, B, C and R. Because fish possessing fully ripe eggs in the body cavity were captured in the bay, it is ascertained that the oocytes can complete their maturation process within the bay prior to ascending the river.

Emulsion stabilization by non-ionic surfactants: experiment and theory.

The stability of a dispersion is frequently denoted by a rate constant which is a quantitative measure of the time required for the initial concentration of particles to be reduced to some critical value. The flocculation of hydrophobic sols has been treated in a kinetic study by Smoluchowski (1916, 1917) and a second-order reaction process was found to hold. The kinetics of coalescence of emulsion globules has been studied by van den Tempe1 (1953), who reported that coalescence is a first-order reaction process which occurs only between adjacent drops in an aggregate and which is independent of the number of droplets in the aggregate. An emulsion cannot be thermodynamically stable, but it can display a high degree of permanence in the kinetic sense. Therefore, the factors determining the kinetics of degradation of emulsion systems are of great importance. The first elaborate study of the kinetics of emulsion breakdown was made by King & Mukherjee (1939) on emulsions of olive oil and kerosene in aqueous solutions of soaps. They surmised that emulsion instability was due to the preponderance of a large interfacial area of the disperse phase and decided that a reasonable representation of the process of coalescence would be a measure of the decrease with time in the specific interfacial area S of emulsified oil.

Rheological changes in emulsions on aging: IV. O/W Emulsions at Intermediate and Low Rates of Shear

Rheological changes in O/W emulsions stabilized by Aerosol O.T. or sodium oleate have been studied during aging by low shear viscosity and creep compliance tests at a constant low shear stress. Globule coalescence does not produce a continuous fall from the outset in the apparent relative viscosity at any particular rate of shear, and in the swelling factor of the flocculates calculated from these data, nor in the rheological parameters calculated from creep compliance-time data, viz., instantaneous elastic modulus, elastic moduli, and viscosities associated with retarded elasticity, and the Newtonian viscosity, as was observed previously in studies on concentrated W/O emulsions. Instead three distinct phases of change are observed. Initially all parameters increase for several days until maximum values are reached. These may be maintained for a few days, after which all parameters decrease sharply with aging time to values which subsequently change slowly with time. Throughout these changes the density of globule packing appears to be greater than the theoretical value for ordered close packing of rigid spheres. This is attributed to the deformable character of the globule surfaces, which results in their flattening at an increasing number of points as the flocculates grow and the number of contacts between each globule and its neighbors increases. Following optimum packing of globules in the flocculates the rate-determining step is globule coalescence. It relieves the pressure on the globules, thus reducing the degree of distortion. In addition, the fall in the number of globules per unit volume weakens the flocculates by rupture of linkages and reduces the volume of continuous phase which is immobilized within them.

Rheological changes in emulsions on aging: III. At very low rates of shear

Creep compliance-time studies on water-in-Nujol emulsions (30%, 50%, 65% wt/wt disperse phase) stabilized by 1.5% (wt/wt) sorbitan monooleate at a shear stress of 4.9 dynes/cm. 2 indicate that their rheological parameters change drastically during the first hours of aging. The experimental data suggest that the elastic moduli almost disappear, and that the viscosity moduli decrease by as much as one order of magnitude or more. These changes are believed to be associated primarily with the rapid coagulation of globules with diameters not exceeding 0.5 μ. Following rapid flocculation globules associate as dense cores which are linked together by projection of less densely packed globules. With increasing volume concentration of water the cores become larger and the projections shorter. Coalescence of globules during aging produces a more open flocculate structure. The attraction forces between globules in close contact are modified substantially by the adsorbed layers of emulsifying agent so that the attraction potential changes slowly with decreasing distance of globular separation. Nevertheless, flocculated globules are bound together by significant attraction forces, so it is concluded that either the repulsion potential in W/O emulsions is smaller than previously thought, or the adsorbed layer of emulsifying agent reduces the attraction potential by less than calculation suggests.

Reversible adsorption of proteins at the oil/water interface I. Preferential adsorption of proteins at charged oil/water interfaces

The behaviour of positively and negatively charged oil-in-water emulsions, stabilized with hexadecyl trimethyl ammonium bromide and sodium hexadecyl sulphate respectively in the presence of protein solutions has been studied. Under certain conditions proteins will adsorb to a charged oil/water interface. When finely dispersed oil-in-water emulsion was used to provide this oil/water interface, adsorption of protein resulted in flocculation of the oil droplets. Flocculation of emulsion on the addition of protein is pH conditioned and occurred on the acid side of the isoelectric point of the protein with negatively charged and on the alkaline side with positively charged oil globules. No flocculation occurred on the alkaline side of the isoelectric point with a negative emulsion or the acid side with a positive emulsion. The amount of protein required to cause maximum clarification of the subnatant fluid corresponded with that needed to give a firmly gelled protein monolayer at the interface, namely, 2∙5 mg. of protein/sq. m. of interfacial area. With that amount of protein the flocculated oil globules remained discrete and no coalescence or liberation of free oil occurred. If only 1 mg. of protein/sq. m. of interfacial area was added, flocculation was followed by rapid coalescence of oil globules and liberation of free oil. If smaller amounts still were used, no visible change in the dispersion of the oil droplets could be seen macroscopically. With greater amounts than 2∙5 mg. /sq. m. of interfacial area, up to ten times the monolayer concentration was adsorbed to the interface. Sodium chloride affected the flocculation range, and instead of the clear-cut change-over between the positive and negative interfaces at the isoelectric point of the protein, overlapping occurred. 5% sodium chloride shifted the flocculation point about 1 unit of pH . The addition of sodium chloride also altered the point of maximum clarification. Thus with haemoglobin the maximum clarification point was shifted from 2∙5 to 1∙7 mg. /sq. m. of interfacial area by the addition of 1% sodium chloride. The adsorption of protein on to charged oil/water interfaces was reversible. This was best demonstrated with haemoglobin. Thus, haemoglobin was adsorbed at pH 5∙0 to a negative emulsion—the red floccules were washed and transferred to a buffer at pH 10. The haemoglobin was released and the emulsion was redispersed. The effect of adsorption and desorption on the structure of the protein molecule has been studied with haemoglobin. By solubility and colour tests it was shown that the haemoglobin molecule was changed to parahaematin by adsorption and subsequent desorption from a charged oil /water interface. Molecular weight and shape determinations were carried out on the desorbed protein. Two proteins have been separated by this adsorption mechanism. This was demonstrated on a mixture of album in and haemoglobin. Some applications of the flocculation technique are indicated and the significance of the phenomena described are discussed.

Reversible adsorption of proteins at the oil/water interface I. Preferential adsorption of proteins at charged oil/water interfaces

The behaviour of positively and negatively charged oil-in-water emulsions, stabilized with hexadecyl trimethyl ammonium bromide and sodium hexadecyl sulphate respectively in the presence of protein solutions has been studied. Under certain conditions proteins will adsorb to a charged oil/water interface. When finely dispersed oil-in-water emulsion was used to provide this oil/water interface, adsorption of protein resulted in flocculation of the oil droplets. Flocculation of emulsion on the addition of protein is pH conditioned and occurred on the acid side of the isoelectric point of the protein with negatively charged and on the alkaline side with positively charged oil globules. No flocculation occurred on the alkaline side of the isoelectric point with a negative emulsion or the acid side with a positive emulsion. The amount of protein required to cause maximum clarification of the subnatant fluid corresponded with that needed to give a firmly gelled protein monolayer at the interface, namely, 2·5 mg. of protein/sq.m, of interfacial area. With that amount of protein the flocculated oil globules remained discrete and no coalescence or liberation of free oil occurred. If only 1 mg. of protein/sq.m, of interfacial area was added, flocculation was followed by rapid coalescence of oil globules and liberation of free oil. If smaller amounts still were used, no visible change in the dispersion of the oil droplets could be seen macroscopically. With greater amounts than 2·5 mg./sq.m, of interfacial area, up to ten times the monolayer concentration was adsorbed to the interface. Sodium chloride affected the flocculation range, and instead of the clear-cut change-over between the positive and negative interfaces at the isoelectric point of the protein, overlapping occurred. 5 % sodium chloride shifted the flocculation point about 1 unit of pH. The addition of sodium chloride also altered the point of maximum clarification. Thus with haemoglobin the maximum clarification point was shifted from 2·5 to 1·7 mg./sq.m. of interfacial area by the addition of 1 % sodium chloride. The adsorption of protein on to charged oil/water interfaces was reversible. This was best demonstrated with haemoglobin. Thus, haemoglobin was adsorbed at pH 5·0 to a negative emulsion— the red floccules were washed and transferred to a buffer at pH 10. The haemoglobin was released and the emulsion was redispersed. The effect of adsorption and desorption on the structure of the protein molecule has been studied with haemoglobin. By solubility and colour tests it was shown that the haemoglobin molecule was changed to parahaematin by adsorption and subsequent desorption from a charged oil/water interface. Molecular weight and shape determinations were carried out on the desorbed protein. Two proteins have been separated by this adsorption mechanism. This was demonstrated on a mixture of albumin and haemoglobin. Some applications of the flocculation technique are indicated and the significance of the phenomena described are discussed.