FASE V: PLANTEAMIENTO ARQUITECTONICO: PROGRAMA ARQUITECTONICO-CUADRO DE AREAS

The overall aim of the PhD work was to enhance the understanding of protein−protein interactions at oil/water interface, in the continuous phase and between the two phases and droplet−droplet interactions on the heat stability, creaming stability and rheological properties of protein-stabilized oil-in-water emulsions in the presence of small- molecular-weight molecules, biopolymers and carbohydrates and at different processing conditions. The specific aims of this thesis were as follow:

x To build and validate model emulsion systems which are suitably complex as the real application and to characterize the physicochemical properties in respect to the inter-particle interactions occurring in the dispersed and continuous phases under heating condition.

x To understand the mechanism(s) that modulates the emulsion stability and rheological properties in a model weakly attractive colloid system containing non- adsorbed protein.

x To investigate the influence of aggregation size of caseins on the droplet size formation, creaming stability, heat stability, microstructure and rheological properties of the model emulsion system.

x To investigate the influence of carbohydrate on the droplet size formation, heat stability, microstructure and rheological properties of the model emulsion system. x To evaluate the heating regime and the choice of protein ingredients on the

emulsion stability and rheological properties of the model emulsion system. x To develop strategies to control/manipulate the emulsion stability and rheological

properties of a sterilized high protein (> 6 g/100 g protein) oil-in-water emulsion stimulant.

To meet those purposes, oil-in-water emulsions prepared with 10−30% w/w oil and 1−10% w/w protein were investigated. Emulsions with high oil content (30% w/w) have been well studied and considered good systems for investigating the adsorption behaviors and rheological properties. The selection of low oil content (10% w/w) was to simulate the oil concentration in real formulations. Milk proteins in their commercial form such as

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MPC, NaCas and WPI, acting as either emulsifier or form the protein-rich continuous phase, were included in all studies as they are used commonly in protein-based emulsion formulations. In addition, the non-food grade emulsifier, Tween 20 was included as a non-protein emulsifier control for non-interacting oil droplets.

The main body of PhD work is organized into 10 chapters and tests the following hypotheses:

x Following the general introduction in Chapter 1. Chapter 2 provides general background on the aspects of protein-stabilized oil-in-water emulsions and literature review with some insight from the published materials of our group (to be submitted, 2014).

x The type of milk protein used as emulsifier or used to form the protein-rich continuous phase affects the heat stability, creaming stability, microstructure and rheological properties of simple oil-in-water emulsions due to different particle size, aggregation state of protein, interfacial configuration, amino acid compositions and mineral content. Chapter 4 describes the potential inter- and intra- protein−protein interactions, droplet−droplet interactions and categorizes

them into four stability models using food-grade ingredients [published as (Liang, Patel, Matia-Merino, Ye, & Golding, 2013b)].

x Protein-rich oil-in-water emulsions tending to phase separate into two discrete phases (cream phase and serum phase) due to depletion effect have been observed in a number of model emulsions obtained in Chapter 4. An increase in non- adsorbed protein concentration promotes stronger depletion interaction potential that may change emulsion destabilization to restabilization due to the formation of space-filling droplet network. Chapter 5 describes and illustrates the impact of depletion attractive force and continuous phase viscosity on the phase separation behaviors of oil-in-water emulsions formed with sodium caseinate (NaCas). Xanthan gum and maltodextrin were used for comparison for the increased continuous phase viscosity effect governed from the addition of increased NaCas [published as (Liang, Graeme, Patel, Matia-Merino, Ye & Golding, 2014)].

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x High temperature heating (i.e. at 120 °C) causes degradation or polymerization of sodium caseinate; subsequently it results in decrease or increase in the particle size and the amount of intact sodium caseinate which influence the depletion interaction potential and therefore the phase separation behavior of caseinate- stabilized oil-in-water emulsions. Chapter 6 extends the knowledge obtained from Chapter 5 and describes the influence of heat treatment on the depletion interaction potential and its impact on the subsequent formation of the space- filling droplet network (to be submitted, 2014).

x Heat-induced inter-particle interactions may derivate significantly if the continuous phase containing high carbohydrate content. Chapter 7 investigates the addition of mono-, di- and polysaccharides (up to 30% w/w) on the heat stability and rheology of oil-in-water emulsions formed with milk protein concentrate (MPC) which have been demonstrated as a promising emulsion system that has good heat stability and low creaming rate in Chapter 4 [published as (Liang, Matia-Merino, Patel, Ye, Graeme & Golding, 2014)].

x Pre-homogenization conditions and different interfacial structure will affect the heat stability, creaming stability and rheological properties by influencing the surface load, denaturation of milk proteins, partitioning of proteins between the oil/water interface and the continuous phase and the protein conformation at oil/water interface. Chapters 8 and 9 describe the effect of interfacial compositions and aggregation state of proteins on the physicochemical properties of protein-stabilized oil-in-water emulsions [Chapter 8 published as (Liang, Patel, Matia-Merino, Ye, & Golding, 2013a)].

x Chapter 10 provides an overall conclusion and recommendations for future research. Industrial significance is described as to how the findings obtained in this thesis may be applied in commercial food/dairy applications.

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