Flow behaviour of water-in-oil emulsions stabilized by wax crystals

The large temperature gradients experienced by crude oil emulsions in pipelines found in colder environments can lead to the precipitation, deposition and build-up of wax-like species from the crude oil onto the pipe wall that result in flow assurance problems. The objective of this thesis was to understand the rheological behaviour of model water-in-oil emulsions stabilized by wax crystals. The microstructure, phase transitions and rheology of model emulsions constisting of water, mineral oil, parrafin wax and the emulsifier polyglycerol polyricinoleate (PgPr) were investigated. Changes in emulsion flow begaviour (steady state and dynamic) as a function of composition, termperature and passage through a laboratory-scale flowloop were investigated, with these parameters significantly affecting shear flow, yield stress and viscoelasticity. The gelation temperature of wax-containing ('waxy') oil was slightly lower than that of its equivalent emulsion due to differences in the structure of the gelled emulsion network. Overall, this study successfully showed that there exist significant differences in the microstructure and flow behaviour of model crude oil emulsions when wax and a dispersed aqueous phase are present.

Flow behaviour of water-in-oil emulsions stabilized by wax crystals

The large temperature gradients experienced by crude oil emulsions in pipelines found in colder environments can lead to the precipitation, deposition and build-up of wax-like species from the crude oil onto the pipe wall that result in flow assurance problems. The objective of this thesis was to understand the rheological behaviour of model water-in-oil emulsions stabilized by wax crystals. The microstructure, phase transitions and rheology of model emulsions constisting of water, mineral oil, parrafin wax and the emulsifier polyglycerol polyricinoleate (PgPr) were investigated. Changes in emulsion flow begaviour (steady state and dynamic) as a function of composition, termperature and passage through a laboratory-scale flowloop were investigated, with these parameters significantly affecting shear flow, yield stress and viscoelasticity. The gelation temperature of wax-containing ('waxy') oil was slightly lower than that of its equivalent emulsion due to differences in the structure of the gelled emulsion network. Overall, this study successfully showed that there exist significant differences in the microstructure and flow behaviour of model crude oil emulsions when wax and a dispersed aqueous phase are present.

The Role of Emulsifiers on the Crystallization of Cocoa Butter and Cocoa Butter-sugar Blends

The crystallization of cocoa butter and 1:1 cocoa butter-sugar blends containing 2 wt% emulsifier was investigated. The emulsifiers studied were soy lecithin, polyglycerol polyricinoleate (PGPR), citric acid esters of mono- and diglycerides (CITREM) and ammonium phosphatides (YN). Lecithin, CITREM and YN enhanced nucleation and growth events substantially, however, had minimal effects on the form IV-to-V transition and enthalpy. PGPR showed a modest enhancement of crystallization kinetics but promoted the formation of form V polymorph similar to that of canola and castor oil. In the presence of sugar, emulsifiers were no longer able to influence nucleation and growth. Sugar also hindered the form IV-to-V transition in the presence of both emulsifier and oil. Overall, results showed that emulsifiers may be used to tune the isothermal crystallization of cocoa butter, though this depends on the presence of dispersed sugar.

The Role of Emulsifiers on the Crystallization of Cocoa Butter and Cocoa Butter-sugar Blends

The crystallization of cocoa butter and 1:1 cocoa butter-sugar blends containing 2 wt% emulsifier was investigated. The emulsifiers studied were soy lecithin, polyglycerol polyricinoleate (PGPR), citric acid esters of mono- and diglycerides (CITREM) and ammonium phosphatides (YN). Lecithin, CITREM and YN enhanced nucleation and growth events substantially, however, had minimal effects on the form IV-to-V transition and enthalpy. PGPR showed a modest enhancement of crystallization kinetics but promoted the formation of form V polymorph similar to that of canola and castor oil. In the presence of sugar, emulsifiers were no longer able to influence nucleation and growth. Sugar also hindered the form IV-to-V transition in the presence of both emulsifier and oil. Overall, results showed that emulsifiers may be used to tune the isothermal crystallization of cocoa butter, though this depends on the presence of dispersed sugar.

The Stability, Microstructure, and Microrheological Properties of Monascus Pigment Double Emulsions Stabilized by Polyglycerol Polyricinoleate and Soybean Protein Isolate

Monascus pigment is a natural food pigment and is commonly used for coloring and as antiseptic of cured meat products, confectionery, cakes, and beverages. However, Monascus pigment is sensitive to environmental conditions. The main aim of this study was to investigate the effect of polyglycerol polyricinoleate (PGPR) and soy protein isolate (SPI) on the particle size, zeta potential, physical stability, microstructure, and microrheological properties of Monascus pigment double emulsions. The effects of ionic strength, heating, and freeze thawing treatment on the stabilities of Monascus pigment double emulsions were also characterized. It was found that the optimum PGPR and SPI concentrations for fabricating Monascus pigment double emulsion were 3.6 and 3.0 wt%, respectively. The fabricated Monascus pigment double emulsion was composed of fine particles with narrow and uniform size distributions. Microrheological property results suggested that the elastic characteristic of the Monascus pigment double emulsion was dominated with increasing PGPR and SPI contents. It was mainly due to the increased collision and interaction between the droplets during the movement resulting in force increasing. Monascus pigment double emulsions with <5 mM CaCl2 prevented calcium to destroy the physical stability of emulsions, while Monascus pigment double emulsions with more than 10 mM CaCl2 formed creaming. After freeze thawing treatment, creaming occurred in Monascus pigment double emulsion. However, it was stable against heating treatment due to heating leading to a dense network structure. It could be contributed to the practical applications of Monascus pigment double emulsions in food products.