Factors affecting the freeze–thaw stability of emulsions (original) (raw)
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Colloids and Surfaces A-physicochemical and Engineering Aspects, 2002
Emulsified n-hexadecane or confectionery coating fat (CCF) were repeatedly thermally cycled (40 to −10-40°C at 1.5°C min − 1 ) in a differential scanning calorimeter. There is a single exotherm on cooling each emulsion (at 0.5 and 5°C, respectively) corresponding to lipid crystallization by homogeneous nucleation. However, on subsequent cooling cycles, an increasing proportion of the CCF crystallization enthalpy occurs at a higher temperature (15°C) corresponding to crystallization of non-emulsified fat. (The net enthalpy of crystallization is constant). The second peak is taken to be due to destabilized fat and increases with number of cycles and dispersed phase volume fraction. All n-hexadecane emulsions are stable to freeze-thaw. When the CCF emulsions are cooled more rapidly (5°C min − 1 ) there is no destabilization. Micrographs are presented and used to argue the destabilization is due to a collapse of partially coalesced structures on reheating.
arXiv: Soft Condensed Matter, 2019
The freeze-thaw cycling of particle-stabilised emulsions can alter the emulsion structure and stability. This could have significant consequences for using particle stabilisation in industrial applications where increased stability is generally desirable. It is therefore important to characterise the behaviour and stability of these composites under the influence of freeze-thaw cycles. Water-in-oil Pickering emulsions stabilised by poly(methyl methacrylate) particles were subjected to freeze-thaw cycles of the continuous phase under two different conditions - uniform and non-uniform freezing. Confocal microscopy was used to study the emulsion behaviour and structure during these processes. The effect of droplet size and cooling rate on uniformly frozen emulsions was also considered. The final structure of the emulsion after a single freeze-thaw cycle is strongly dependent on the freezing method. Uniformly frozen emulsions show crumpled droplet structures, while non-uniformly frozen ...
Freeze-drying of emulsified systems: A review
International Journal of Pharmaceutics, 2016
Colloidal systems such as emulsions, microemulsions and nanoemulsions are able to transport active molecules, enhance their solubility and stability and minimize their side effects. However, since they are dispersions with an aqueous continuous phase they have some disadvantages such as the risk of microbiological contamination, degradation by hydrolysis, physico-chemical instability and loss of pharmacological activity of the drug. Freeze drying, in which the water is removed from the preparation by sublimation under vacuum, has been suggested as a means to resolve these problems. Lyophilized products are very stable and are easy to transport and store. However, there is very little information in the literature about the application of this technique to emulsified systems. The aim of this review is to evaluate the lyophilization process as a tool for increasing the shelf life of emulsified systems such as emulsions, microemulsions and nanoemulsions. In addition, the mechanism of cryoprotection and the techniques that can be used to characterize the freeze-dried systems are discussed.
Journal of Food Engineering, 2015
The effect of maltodextrin (MDX) concentration on the stability of multilayer linseed oil-in-water emulsions before and after freeze-thawing has been studied. Interfacial double-layer emulsions were obtained by performing electrostatic deposition of sodium alginate (SA) onto whey protein isolate (WPI) coated oil droplets at pH 5 (10 wt% oil, 1 wt% WPI 0.25 wt% SA). MDX was also added to emulsions formulation in different concentrations (0-20 wt%), and the systems were then stored at two freezing temperatures (À18 and À80°C). Stability of emulsions was studied using droplet size, f-potential, as well as microstructure determinations and monitoring backscattering profiles versus time. Non-frozen emulsions showed smaller droplet sizes at higher MDX concentrations thus reducing creaming mechanisms and improving emulsion stability. In the absence of MDX, emulsions were highly unstable after freeze-thawing and destabilized faster at À18°C than at À80°C, which was attributed to the formation of larger ice crystals at slower freezing rates that promoted interfacial membrane disruption leading to extensive droplet coalescence and oiling off. Both systems showed macroscopic phase separation within the first hour of analysis. The addition of MDX greatly improved emulsion stability after freezing, as emulsions showed no phase separation after thawing during one week storage. This behavior was attributed to MDX cryoprotectant effect, that could have considerably reduce the amount of ice formed during freezing, thereby maintaining the integrity of the interfacial WPI-SA bilayer surrounding oil droplets. Our results suggest that 20 wt% MDX emulsions were the most stable systems both to creaming destabilization and to freeze-thawing processes.
Prediction of the Amount of Ice Formation in the Water Dispersed Phase of a W/O Emulsion
2016
This paper deals with investigation of the effect of solute concentration on the amount of ice formation from some materials such as pure water, NaCl and glycerol solutions were dispersed into a W/O emulsion system. The investigations were carried out by inserting sample emulsions into a steady cooling-heating program at constant heating rate, ሶ ܶ = 2.5 K/min from T = (20 to-60)oC, that considered all the water have frozen, then heated back to the initial temperature, T = 20oC to bring about the frozen one to the liquid state using differential scanning calorimetry (DSC-131 evoSetaram, France). The proportion of ice formed, P was then calculated from the recorded thermogram, at which the melting signal is related to the total amount of water frozen. The way the droplets frozen during cooling process is described from the thermodynamics ice/solution phase diagram completed by the curves that give the freezing conditions. The results indicated that the proportion of ice formed calcula...
International Journal of Refrigeration, 2006
This study focuses on an emulsion as a new thermal storage material for ice storage. Two types of emulsions were formed using an oilewater mixture with a small amount of additive. A silicone, light and lump oils were used. The water contents of the emulsions were 70, 80 and 90%. The additive was an amino group modified silicone oil. No depression of freezing point was observed for the emulsions because of their hydrophobic properties. In order to determine the structure of the emulsions, their electrical resistances were measured. Moreover, components of the liquids separating from the emulsions were analyzed. The results indicated that one emulsion was a W/O type emulsion, while the other was an O/W type. Finally, adaptability of the two emulsions to ice storage was discussed, it was concluded that a high performance ice slurry could be formed by the W/O type emulsion. Ó 2006 Elsevier Ltd and IIR.
Food Chemistry, 2020
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International Dairy Journal, 2000
Ice cream at six di!erent levels of emulsi"cation was produced by freezing in a conventional scraped surface freezer and with a serial con"guration of a conventional freezer followed by a low-temperature extruder. The aim was to examine the in#uence of emulsi"ers on the process, since both emulsi"er addition and low-temperature extrusion may have similar e!ects on promotion of colloidal structure in ice cream. Ice cream samples from both processes were analyzed for sti!ness at draw, fat destabilization indices, melting performance, and microstructure. Low-temperature extrusion generally promoted enhanced fat destabilization, however, fat particle size and solvent extractable fat showed di!erent dependencies on emulsi"cation level from the two processing systems. Although solvent extractable fat reached high levels with increasing emulsi"cation, fat particle size data suggested that fat agglomerate size was controlled by mechanical shearing. Signi"cant di!erence between the two systems was seen also in the meltdown test, where melting rates for unemulsi"ed and slightly emulsi"ed mixes led to a very low melting rate and high shape retention in extruded ice cream. Scanning electron microscopy detected generally smaller air bubbles for extruded ice creams. Enhanced fat structuring around the air bubble and into the serum phase was also shown for unemulsi"ed extruded samples.