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Oil-in-water (O/W) emulsions, where oil droplets are dispersed in an aqueous phase, often experience various physical and chemical destabilization phenomena, which compromise the quality and shelf life of the final products. To achieve acceptable shelf life, emulsifiers (e.g., surfactants and animal proteins) and synthetic antioxidants (e.g., ethylenediaminetetraacetic acid and butylated hydroxyanisole) are currently used. However, over the past decade, sustainable and natural food ingredients have become preferred options. This has been a strong incentive for the present work, which has aimed at identifying the potential of biobased Maillard reaction products (MRPs) to both physically and chemically stabilize emulsions.In this thesis, we investigate the potential of MRPs, either prepared in model systems or inherently present in foods, to act as dual-function ingredients (i.e., physical stabilizers and antioxidants) in food emulsions.The first part of the thesis was designed to study the MRPs prepared in model systems: In Chapter 3, we characterized the chemical and structural features of various Maillard reaction fractions prepared from soy protein isolate (SPI) and carbohydrates (dextran or glucose). We found that the Maillard reaction progressed further with glucose than dextran, with SPI-dextran conjugates showing higher activity than SPI-glucose conjugates, and water-soluble fractions showing higher activity than insoluble fractions. Therefore, a comprehensive understanding of the physicochemical properties in each fraction could be obtained. In Chapter 4, we further assessed the ability of initial stage MRPs (SPI-dextran conjugates) to prevent lipid oxidation, when added to the continuous phase of pre-formed stock emulsions. We found that the addition of protein-based compounds increased the oxidative stability of emulsions without significantly affecting the physical stability of emulsions. Therefore, it is possible to engineer oxidatively stable emulsions b

Many food products contain oil-in-water (O/W) emulsions, i.e., droplets of oil in a water phase. Due to the thermodynamic incompatibility between the two liquids, the droplets need to be covered by emulsifiers to ensure physical stability. The most widely used food emulsifiers are dairy proteins which are present in e.g., beverages, infant formula or dressings. However, their production has a large impact on the environment, therefore, plant proteins are currently considered as promising alternatives. Yet, the full replacement of dairy proteins by plant proteins brings along a number of technological challenges (e.g., functionality, product taste, pre-treatments). It can therefore be advantageous to rather consider partial replacement, but the properties of dairy-plant protein blends with regard to food systems’ stabilisation had been largely unexplored. In the present work, we aimed to achieve a rational compromise between technical functionality of such blends, and product quality. We investigated formation and stability of protein blend-stabilised emulsions and focussed on the relevant interfacial phenomena. To do so, we used a multiscale approach based on characterisations at different length- and time scales. In the first chapters (Chapter 2-4), we focussed on the long term interfacial phenomena when using protein blends to formulate emulsions. We assessed the related properties of blends of pea protein isolate (PPI) with either whey protein isolate (WPI) or with sodium caseinate (SC) in Chapter 2. We showed a synergistic behaviour in terms of physical stability of the emulsions, when the blends were used. The blend-stabilised emulsions had higher surface loads compared to the individual protein-stabilised emulsions, which showed that more proteins were needed to stabilise the interface. Furthermore, compositional rearrangements at the interface were observed over days. More specifically, after emulsion formation, whey proteins were able to partly displace

A major trend in the food industry is the protein transition from animal- to plant-derived proteins. Prior to the utilisation of these ingredients, plant proteins must be extracted from the plant or crop. The most common extraction processes are extensive processes with many processing steps, requiring copious amounts of water and energy, and generating substantial amounts of waste streams. Also, this processing might alter plant protein functionality, leading to protein aggregation and lower solubility. A solution is a milder and more sustainable process, but less processing leads to protein extracts with lower protein purity due to the presence of more non-proteinaceous components, such as lipids and phenols. The aim of this thesis was to investigate the contribution of these non-proteinaceous components to the interfacial and foaming properties of mildly derived plant protein extracts. The system of interest is rapeseed, as it is high in both phenols and lipids.We performed these studies by producing a mildly derived plant protein extract and systematically mixing purified proteins with phenols or lipids. The mildly derived rapeseed protein extract was able to form stiff and viscoelastic solid-like interfacial layers, as shown by Lissajous plots in non-linear surface rheology. However, the stiffness of the interfacial films reduced at higher bulk concentrations, indicating an impact of the non-proteinaceous components. The presence of non-proteinaceous components was also shown by performing atomic force microscopy (AFM) on Langmuir-Blodgett films. The main rapeseed phenol sinapic acid was able to interact non-covalently and covalently with proteins. Covalent interaction even led to the formation of large aggregates. The protein-phenol interaction reduced the ability of the proteins to form stiff interfacial layers, leading to less stable foams.An advantage of mild purification is the extraction of intact oleosomes, which are normally disrupted in the defatting s

Many food products contain lipid droplets dispersed in an aqueous phase (e.g., milk, mayonnaise), thus are oil-in-water (O/W) emulsions. Food emulsions may be subjected to destabilization, both from a physical and a chemical perspective. Physical destabilization is generally prevented by the use of conventional emulsifiers such as surfactants and proteins. Chemical destabilization, in particular lipid oxidation, is a major concern in food products, especially when healthy polyunsaturated fatty acids are present, and this degradation is usually mitigated by the use of synthetic antioxidants, often in large amounts.The use of alternative ingredients for the formulation of food emulsions has been emerging, for example solid particles (so-called Pickering particles, that are very popular nowadays) that irreversibly adsorb to the interface and therewith provide high physical stability; or natural antioxidants such as tocopherols and rosemary extracts, which are attractive in the current clean-label trend to prevent lipid oxidation. The efficiency of these natural antioxidants is unfortunately often not optimal, which can be explained by their tendency to locate into the oil or water phase, whereas lipid oxidation is initiated at the oil-water interface, and thus is the place where antioxidants should be located to optimally exert their protective effect.The objective of this project was to develop food emulsions with a new and controlled architecture directed at yielding both excellent physical and oxidative stability. In these emulsions the oil droplets were covered by food-grade Pickering particles that exert a double role: they act as physical stabilizers, and as a reservoir for antioxidant molecules located close to the oil-water interface, therewith preventing the first lipid oxidation events, which is expected to drastically enhance antioxidant activity.The first part of this thesis focused on the preparation and characterization of a new food-grade lipid-based Pic

Plant protein-based foods have gained a huge interest in the past years due to environmental and health reasons. A special category of food products has been developed to mimic animal-based products using plant proteins, known as meat analogues. The technological challenge is to make a structure similar to the natural fibrous structure in meat, while still delivering food with high nutritional value. High temperature-based processes have been used to reach desirable fibrous structures, but such process conditions induce physicochemical protein modifications that can reduce functionality and protein quality. Meat provides high quality proteins and is a source of a highly bioavailable iron form. The latter motives the incorporation of this micronutrient into meat analogues. The incorporation of the most bioavailable form of iron, water-soluble iron may, however, be hampered by its prooxidant activity, which can result in lipid and protein oxidation in the final product, altering the nutritional and sensory aspects. Therefore, the encapsulation of iron is often proposed to prevent oxidation reactions in fortified food. This thesis aimed to assess and control the protein quality in plant protein-based meat analogues, as a function of the presence of soluble iron as free or encapsulated form, and of the conditions applied for the structuring process. First, two methods of encapsulation were described. The effect of iron addition was compared to the effect of processing, regarding the occurrence of protein oxidation. Then the extent of protein oxidation over each processing step from the raw plant material, to the final product, was quantified. Lipid and protein oxidation were observed in iron encapsulates, but the subsequent application of iron in meat analogues had only a marginal effect on protein oxidation compared to that of the process conditions. Furthermore, the associated physicochemical changes due to protein oxidation and processing were not detrimental to gast

My PhD project aimed at developing an edible product for non-invasive weight management, and targeted a natural feedback mechanism to induce satiety: the ileal brake. In order to trigger the ileal brake mechanism, lipids and their non-absorbed metabolites need to be sensed in the ileum. We aimed at inducing this mechanism through targeted release of lipids after oral intake, for which we developed multi-layered emulsions and emulsion-alginate beads. We showed that emulsion-alginate beads control in vitro lipolysis as a function of bead size and alginate concentration, and confirmed these findings under dynamic in vitro gastrointestinal conditions (DIDGI). Moreover, ingestion of yoghurt with emulsion-alginate beads significantly reduced food intake by 6% in overweight volunteers compared to a control group, suggesting that activation of the ileal brake was achieved. These findings have important implications for the development of weight management strategies, and understanding satiety in general.

Emulsions are dispersions of one liquid in another that are commonly used in various products, and methods such as high-pressure homogenisers and colloid mills are used to form emulsions. The size and size distribution of emulsion droplets are important for the final product properties and thus need to be controlled. Rapid coalescence of droplets during emulsification increases droplet size and widens the size distribution, and therefore needs to be prevented. To increase stability of emulsions, emulsifiers are added to adsorb at the oil-water interface before droplets collide. The time allowed for emulsifier adsorption is typically in the range of sub-milliseconds to seconds and to optimise emulsification processes, emulsifier adsorption and coalescence stability need to be measured in this time-scale, for which the microfluidic methods described in this thesis were developed. Chapter 2 provides an overview of existing literature on cross-flow microfluidic emulsification. The effects of various parameters such as microfluidic design, shear forces, and interfacial tension forces on droplet formation and the resulting droplet size are discussed, as well as the use of microfluidics to produce food-grade emulsions. Based on this evaluation, the methods to elucidate interfacial tension and coalescence stability are chosen, and these are presented in the next chapters. To measure emulsifier adsorption in the sub-millisecond time-scale, a tensiometric method was developed using a cross-flow microfluidic Y-junction, which is described in Chapter 3. This method is based on the relation between droplet size and interfacial tension at the moment of droplet formation, which is referred to as the acting interfacial tension. The acting interfacial tension of a system with hexadecane as the dispersed phase and sodium dodecylsulfate (SDS, a model surfactant) solutions as the continuous phase was successfully measured for droplet formation times ranging from 0.4 to 9.4 milliseconds