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• W59456685 abstract "Structure of fat-containing dairy products such as ice cream and whipped cream is governed by crystallisation of fat globules (diameter above 1 µm) embedded in the overall matrix of the food products. Downsizing of oil droplets to the nanometre-size range (below 0.4 µm for food applications) may enhance the physical stability of the milk fat nanoemulsions, and alter the crystallisation and structural characteristics of emulsified milk fat. The latter was due to the physical barrier of the limited volume and sharp curvature of nano-sized particles. Thus, utilisation of dairy-based nano-sized fat particles may tune the structure or develop novel texture of the dairy products. This thesis aimed to investigate the physical stability and crystallisation behaviour of emulsified milk fats in the nanometric-size scale. A comprehensive study was conducted on characterisation of physical stability, crystallisation behaviour, crystal structures and polymorphs of the emulsified Triacylglycerols (anhydrous milk fat, stearin and olein fractions) in the dairy nanoemulsions (0.18 – 0.20 µm) against the conventional emulsions (1.00 – 1.20 µm), using various physico-chemical techniques including Differential Scanning Calorimetry, Small- and Wide-angle X-ray Scattering, Cryogenic Transmission Electron Microscopy and particle sizing. To demonstrate the impact of nano-sized fat particles on functionality of the dairy emulsions, foaming properties of the dairy emulsions having micron- to nanometric-size ranges were also investigated. It was observed that high energy approach (microfluidization at 103-123 MPa for 3-6 passes) was feasible to produce the dairy nanoemulsions. Preparation of the nanoemulsions was optimised using Response Surface Methodology to achieve the minimum mean droplet sizes, which were in range of 0.18 – 0.20 µm. Under different environmental conditions such as pH, ionic strength, heat treatment, and freeze-thaw cycles, similar responses were found between the micron- and the nano-sized droplets. The type of emulsifiers (WPC: whey protein concentrate, NaCN: sodium caseinate) had a significant impact on the physical stability of the emulsions. In a comparison of the micron-sized droplets, an extensive droplet aggregation was shown by WPC-stabilised nanoemulsions, while NaCN-Stearin nanoemulsions were less prone to fat destabilisation. Crystallisation properties of the dairy emulsions were dependent on droplet size (0.13 – 3.10 µm), types of emulsifiers (WPC, NaCN, and Tween80), and cooling rates (1, 5, and 10 oC min-1). All three factors and fat composition influenced the crystallisation temperatures, crystallisation enthalpies and solid fat content of the emulsified milk fats. Generally, a decrease in droplet size led to a corresponding decrease in the crystallisation parameters possibly due to a supercooling effect. The dairy nanoemulsions appeared to have different crystal structures and morphologies as compared to their micron-sized counterparts. The emulsified milk fats in the dairy emulsions crystallised into compound crystals which showed co-existence of three to four types of fat polymorphs (α, β’1, β’2, β1, and/or β2), coupled with either triple (3L) and/or double (2L) chain length structures. The 2L structure occurred for both droplet sizes of the emulsified stearin fraction, but the nano-sized droplets showed a higher 2L structure. The droplet size had a more pronounced impact on the fat crystals of the emulsified olein fraction. The micron-sized olein particles had both 2L and 3L structures, whereas the nano-sized olein particles had only a 2L structure. The internal structure of the emulsified milk fats in the nano-sized particles consisted of stacking of individual lamellar layers of about 3.8 - 4.2 nm in thickness, which corresponded with the SAXS recording (4.1 - 4.2 nm). Upon crystallisation, the spherical shape of oil droplets in liquid state tended to be deformed into various anisometric geometries, due to the elongation and protrusion of fat crystals resulting from a highly sharp curvature of the nano-sized droplets. The nano-sized olein fat particles exhibited a more polyhedral shape than that of the stearin. The foaming study was undertaken based on the assumption that in absence of fat coalescence nano-sized hydrophobic fat particles having a large surface area can be independently adsorbed onto the air-water interface, thereby potentially enhancing foaming properties of whippable dairy emulsions. The results showed that smaller particle size led to a higher apparent viscosity and a lower solid fat content. Hence, an adverse impact of the particle size was found on the foaming properties of the emulsions, with this impact being reflected in a lower percentage overrun and faster foam destabilisation. However, for WPC-Stearin emulsion systems with higher solid fat content (52-80%), there was no statistically significant difference between micron-sized and nano-sized emulsions in the foaming properties. The findings of this current study provided a better understanding of the influence of the nanometric confinement of oil droplets in conjunction with other variables such as fat composition, type of emulsifiers, and cooling rate, on their crystallisation properties in the emulsified state. For the first time, the macroscopic morphologies of milk fat in nanoemulsions were revealed. The knowledge gained from this study can potentially be employed in utilising nano-sized fat particles in food applications." @default.
• W59456685 created "2016-06-24" @default.
• W59456685 creator A5066659102 @default.
• W59456685 date "2014-09-29" @default.
• W59456685 modified "2023-09-24" @default.
• W59456685 title "Physical Properties of Milk Fat in Nanoemulsions" @default.
• W59456685 doi "https://doi.org/10.14264/uql.2014.179" @default.
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