Emulsion stability measurements

The emulsifying properties of proteins have been a subject of concern for those dealing with functional properties of proteins. The studies so far have been restricted to two main approaches emulsifying capacity and emulsion stability measurements. The former measures the maximum oil addition until inversion or phase separation of the emulsion occurs, whereas the latter measures the ability of the emulsion to remain unchanged. 

Emulsion Stability Measurements and Drop Size Determination... 

The preceding treatment relates primarily to flocculation rates, while the irreversible aging of emulsions involves the coalescence of droplets, the prelude to which is the thinning of the liquid film separating the droplets. Similar theories were developed by Spielman [54] and by Honig and co-workers [55], which added hydrodynamic considerations to basic DLVO theory. A successful experimental test of these equations was made by Bernstein and co-workers [56] (see also Ref. 57). Coalescence leads eventually to separation of bulk oil phase, and a practical measure of emulsion stability is the rate of increase of the volume of this phase, V, as a function of time. A useful equation is... 

Water content and viscosity measurements in certain systems show a correlation to emulsion stability [597]. The viscosity provides a more reliable measure of emulsion stability, but measurements of the water content are more convenient. Mixing time, agent amount, settling time, and mixing energy impact the effectiveness of an emulsifier. 

Rheological measurements were carried out to investigate the rheological properties of emulsions stabilized by different fat-water interfaces and the influence of fat droplets on the formation of the protein networks during a process of gelation. 

Emulsion stability of SEDDS is usually good because the droplets are small and have narrow size distributions. However, stability can be measured by determining the flocculation rates, degree of separation, or changes in the diameter of droplets formed on dilution over time during storage under various conditions. 

Emulsion Stability is the property of the emulsifier (the interphase molecules) to stabilize an emulsion following its formation and, sometimes, following certain stress conditions. In this test, only three steps are observed emusification, stress, and measurement. The stress may be only an applied force (gravity or centrifugal forces) or heat or a combination of both. 

Emulsion Stability. The stability of the emulsions was determined by measuring optical density of the solutions following centrifugation. A 0.2% solution of each spray dried powder was prepared in water and the optical density read at 400 nm in a Coleman spectrophotometer. A 0.16% solution of carrier (gum arabic) was used as a blank. This is based on a carrier to flavor ratio of 4 1. The initial optical density of each solution was read and then the solutions were centrifuged in an lEC International Centrifuge at 500 x g for 5, 10, 15, 30, 45 and 60 min. The optical density was read after each time period. 

Emulsion stability using a storage stability test Measure droplet size distribution and concentration at the top and bottom of a hermetically sealed container during storage Results usually expressed as plots of mean droplet size and concentration (volume fraction) as a function or storage time... 

Emulsion stability using a creami ng test Emulsion is placed in a graduated cylinder and held in an environmental chamber. Height of visible boundary between serum and cream layers during phase separation is measured. Height of visible boundary between serum and cream increases us the emulsion breaks down over lime. Results often presented as a plot. 

Latreille, B. and Paquin, P. 1990. Evaluation of emulsion stability by centrifugation with conductivity measurements. J. Food Sci. 55 1666-1672. 

Detailed description of theory, measurements, and applications in emulsion science covering all aspects of emulsion stability. 

Stern model in interface studies, 626 Stokes law, in emulsion creaming, 601 Storage, of emulsions, stability test, 591-594, 597-598, 604-606 Straight-phase HPLC, lipoxygenase activity measurement, 411-412 Strain response, see Stress/strain responses... 

Ultrasonic methods infrared scanning for emulsion stability determination, 597-598 spectrometry, emulsion droplet size determination, 581 velocimetry, to measure fat, 572 Ultraviolet (UV). see also Spectrophotometry protein analysis, CD, 219-243 protein concentrations by... 

Figure 6 Oil droplet size distribution of on olive oil emulsion, stabilized with hydroxy-propyl mcthylceUkiloae, after different emulsification procedures blender (triangles), ultrasonic probe (squares), and ultrasonic homogenize (stars). Theoretical distributions were calculated from Coulter Counter measurements using a software program, assuming spherical particles.

Certain comb-type silicone surfactants have been shown to stabilize emulsions in the presence of salts, alcohol and organic solvents that normally cause failure of emulsions stabilized using conventional hydrocarbon surfactants and a study by Wang et al. [66,67] investigated the cause of this stability. Interaction forces due to silicone surfactants at an interface were measured using AFM. Steric repulsion provided by the SPE molecules persisted up to an 80% or higher ethanol level, much higher than for conventional hydrocarbon surfactants. Nonionic hydrocarbon surfactants lose their surface activity and ability to form micelles in... 

D. E. Tambe and M. M. Sharma, Hydrodynamics of thin liquid-films bounded by viscoelastic interfaces, J. Colloid Interface Sci. 147, 137-151 (1991) Factors controlling the stability of colloid-stabilized emulsions. 1. An experimental investigation, J. Colloid Interface Sci. 157, 244-253 (1993) Factors controlling the stability of colloid-stabilized emulsions. 2. A model for the rheological properties of colloid-laden interfaces, J. Colloid Interface Sci. 162, 1-10 (1994) Factors controlling the stability of colloid-stabilized emulsions. 3. Measurement of the rheological properties of colloid-laden interfaces, J. Colloid Interface Sci. 171, 456-462 (1995). 

For the moderately hydrophilic hydroxyethyl methacrylate, cyclohexane and hexadecane were chosen as the continuous phase. As initiators, PEGA200 which is soluble in the monomer phase, but not in cyclohexane, turned out to be applicable. AIBN which is mainly soluble in the cyclohexane phase could also be successfully used. KPS cannot be employed as initiator due to solubility problems. Small amounts of water act as lipophobe, and it could be shown by turbidity measurements that the addition of water increases the emulsion stability. 

It has to be clear that, once diluted and injected (or administered in ocular and other routes), the emulsion stability and fate are determined by three measurable parameters. The first is the partition coefficient of each emulsion component (including added drugs and agents) between the emulsion assembly and the medium. To some extent this partition coefficient is related to oil-water and/or octanol-water partition coefficients. For example, it was well demonstrated that per component of which logP is lower than 8, the stability upon intravenous (IV) injection is questionable [42,138], The other two parameters are kQff, a kinetic parameter which describes the desorption rate of an emulsion component from the assembly, and kc, the rate of clearance of the emulsion from the site of administration. This approach is useful to decide if and what application a drug delivery system will have a chance to perform well [89],... 

The emulsifying capacity of the yeast proteins was progressively improved with the extent of succinylation (Table IX) as measured by the turbidimetric technique (89). The modified yeast proteins had excellent emulsifying activities compared to several other common proteins. McElwain et al. (88) observed that succinylation of yeast protein increased emulsion viscosity but decreased emulsion stability. 

Dispersion behaviour in systems with liquid/liquid or liquid/gas interfaces (i.e. droplet or bubbles) has traditionally been described in terms of rheological properties, wetting properties, including contact angle and interfacial tensions, or phase behaviour and stability measurements. Direct force measurements provide a means to fundamentally probe the interactions between deformable interfaces that significantly impact the dispersion (or emulsion) behaviour. 

Two Liquid/Liquid interfaces. Measuring the interactions between two liquid droplets with AFM is a natural extension of the one droplet problem and more relevant to emulsion stability. The first and only such measurement is between alkane droplets in... 

Reimers and Schork [94, 95] report the use of PMMA to stabihze MM A miniemulsions enough to effect predominant droplet nucleation. Emulsions stabilized against diffusional degradation by incorporating a polymeric costabilizer were produced and polymerized. The presence of large numbers of small droplets shifted the nucleation mechanism from micellar or homogeneous nucleation, to droplet nucleation. Droplet diameters were in the miniemulsion range and reasonably narrowly distributed. On-hne conductance measurements were used to confirm predominant droplet nucleation. The observed reaction rates were dependent on the amount of polymeric costabilizer present. The latexes prepared with polymeric costabilizer had lower polydispersities (1.006) than either latexes prepared from macroemulsions (1.049) or from alkane-stabilized miniemulsions (1.037). 

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