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This highlight refers to the PhD by Ivanna Lins Colijn (2023, cum laude)

Within the food industry, membrane separation is commonplace due to its relatively low energy consumption. It allows fractionation of various feeds (e.g., milk) into starting materials for food design. We feel that considerable progress can still be made. For this, the specific properties of the components of interest would need to be taken into account, such as their mobility in flow, and their deformability in relation to the actual membrane structure. Furthermore, improvements are possible through cascaded use of membrane processes, and upgrading waste streams, which leads to new opportunities.

Food design is often done based on a trial-and-error basis,using structure properties as an indicator of product quality.Although this has led to many good p roducts in the market, this‘cook and look’ approach could benefit from insights into dynamic processes as they occur during food formation, storage, and digestion. Currently microfluidic devices are being developed to allow these types of observations, and here we show the latest examples in the field of emulsions and foams, including effects that occur during digestion. We expect that these techniques will supply a stepping stone to thorough understanding at various length and timescales that are all instrumental in designing high-quality food products, and ultimately creating foods with health benefits.

Chitin-based nanoparticles are polysaccharide materials that can be produced from a waste stream of the seafood industry: crustacean shells. These nanoparticles have received exponentially growing attention, especially in the field of medicine and agriculture owing to their renewable origin, biodegradability, facile modification, and functionality adjustment. Due to their exceptional mechanical strength and high surface area, chitin-based nanoparticles are ideal candidates for reinforcing biodegradable plastics to ultimately replace traditional plastics. This review discusses the preparation methods for chitin-based nanoparticles and their applications. Special focus is on biodegradable plastics for food packaging making use of the features that can be created by the chitin-based nanoparticles.

Emulsions fortified with polyunsaturated fatty acids are highly relevant from a nutritional perspective; however, such products are prone to lipid oxidation. In the current work, this is mitigated by the use of natural antioxidants occurring in coffee.Coffee fractions with different molecular weights were extracted from roasted coffee beans. These components were positioned either at the interface or in the continuous phase of emulsions where they contributed to emulsion stability via different pathways.Coffee brew as a whole, and its high-molecular-weight fraction (HMWF), was able to form emulsions with good physical stability and excellent oxidative stability. When added post-homogenization to the continuous phase of dairy protein-stabilized emulsions, all coffee fractions were able to slow down lipid oxidation considerably without altering the physical stability of emulsions, though HMWF was more effective in retarding lipid oxidation than whole coffee brew or low-molecular-weight fraction. This is caused by various effects, such as the antioxidant properties of coffee extracts, the partitioning of components in the emulsions, and the nature of the phenolic compounds. Our research shows that coffee extracts can be used effectively as multifunctional stabilizers in dispersed systems leading to emulsion products with high chemical and physical stability.

In this review, we focus on the role of the interface in lipid oxidation in food emulsions. Mostly, results from this field are a reflection of the effects caused by reaction kinetics and mass transfer, which complicates interpretation. In general, the oil–water interface is the location of initiation of oxidation reactions, while components present there, and in the continuous phase, directly or indirectly affect the reaction. Smaller droplets are expected to oxidize faster, but this can be counteracted by components purposely positioned at the interface or added to the bulk phase. Recent simulation progress is expected to be instrumental in distinguishing these effects, and guides stable emulsion design.

There is a growing interest in replacing dairy proteins with their plant-based counterparts in food emulsions. Plant proteins generally contain a substantial insoluble protein fraction, of which the properties may differ from the soluble proteins. Therefore, the use of a commercial pea protein isolate, its insoluble fraction and whey protein isolate to stabilize oil-in-water (O/W) emulsions is explored. In 100 g/kg O/W emulsions, the use of full pea protein isolate led to physically instable emulsions that showed droplet flocculation and coalescence, whereas its insoluble fraction and whey protein formed physically stable emulsions. The insoluble pea protein fraction was also able to physically stabilize high internal phase O/W emulsions (HIPEs) containing 700 g/kg oil, giving ~10 times higher viscosity than whey protein-based HIPEs. Under oxidative conditions, whey protein-stabilized emulsions showed extensive coalescence, and fast formation of lipid oxidation products. Insoluble pea protein-stabilized emulsions, showed fast lipid oxidation, but this did not affect the physical stability. In contrast, full pea proteins-based emulsions were physically instable in oxidative conditions but showed the lowest accumulation of oxidation products. These results suggest that the constituents of commercial pea protein isolate have specific functionalities, which is important knowledge for the design of stable plant protein-based emulsions.

In conventional emulsification devices, interface formation and stabilisation occur within milliseconds. Protein network formation at liquid-liquid interfaces starts at time scales similar to those of droplet formation in conventional emulsification devices (i.e., in milliseconds). Classical methods, like drop tensiometry, do not allow measurements at these time scales. Using a tailor-made microchip, we probed droplet deformation to study the interfacial rheological properties of droplets, within time scales ranging from 0.16 to 1 s. We further investigated the coalescence stability of droplets at the same time scales. Whey protein isolate (WPI), pea protein isolate (PPI), or their blends were used as emulsifiers at 0.01–1 g/L. The rheological properties of the protein-interfaces showed that early network formation takes place (<1 s). WPI-stabilised interfaces were mechanically stronger compared to PPI-stabilised interfaces, and WPI-stabilised droplets were much less prone to coalescence than their PPI counterparts. Although the blend-stabilised films showed high interconnectivity, this did not prevent droplet coalescence, probably due to structural heterogeneity. The insights obtained with the tailor-made microfluidic devices help to capture effects at short time scales and are relevant to unravel phenomena occurring in large scale processing.

Hypothesis: Many traditional or emergent emulsion products contain mixtures of proteins, resulting in complex, non-equilibrated interfacial structures. It is expected that protein displacement at oil-water interfaces depends on the sequence in which proteins are introduced during emulsion preparation,and on its initial interfacial composition.Experiments: We produced emulsions with whey, pea or a whey-pea protein blend and added extra protein post-emulsification. The surface load was measured indirectly via the continuous phase, or directly via the creamed phase. The interfacial composition was monitored over a three-day period using SDSPAGEdensitometry. We compared these findings with results obtained using an automated drop tensiometer with bulk-phase exchange to highlight the effect of sequential protein adsorption on interfacial tension and dilatational rheology.Findings: Addition of a second protein increased the surface load; especially pea proteins adsorbed to pre-adsorbed whey proteins, leading to thick interfacial layers. The addition of whey proteins to a pea

Volatile organic compounds (VOC) present at low concentrations may have a tremendous effect on the flavour profile of e.g. fermented beverages such as wine and beer. Controlling the flavour profile requires a detailed understanding of the physiochemical interactions of these components with the food matrices in which they occur. This thesis tries to answer the question of whether it   is possible to separate any of the major volatile flavours in lager beers, especially isoamyl acetate. The proposed technique to do so had to meet a series of criteria. It had to be mild to protect biological ingredients such as proteins from being damaged, be able to handle high throughput (~100 to 500 m3/hr), satisfy food-grade conditions and must be compatible with current flavour stripping processes. To design such a process, more fundamental knowledge was needed,  especially regarding the thermodynamics of solutions and kinetics of separation. These two topics are therefore addressed throughout the thesis.In chapter II we start with a critical review of the current knowledge on flavour-matrix interactions in aqueous systems. We found that the fundamental data needed to design flavour separation processes for beer have neither been investigated experimentally nor through predictive modelling. The main focus in most papers was on the sensory aspects of flavour retention and release and directly linked to food design, and not to flavour design. Along with providing the first results from our work, we discussed and challenged the experimental techniques and data interpretation methods that are currently common practice, and recommended techniques to avoid pitfalls.Based on our observations in chapter 2, we quantified Henry’s Law Constant (HLC) in chapter   III for the three major flavour compounds in beer (ethyl acetate, isoamyl acetate and isoamyl alcohol) in a model system containing ethanol concentrations below 25 %(v/v). We used the   static head

Interest in supplementing food with iron to counteract dietary deficiencies has been on the rise in recent years. A major challenge is the pro‐oxidant activity of soluble iron, which compromises the chemical stability of the enriched food products. This problem could be mitigated by encapsulating iron, to physically keep it separated from oxidizable substrates, such as unsaturated fatty acids. In the present work, the physical and chemical stability of surfactant‐ or protein‐stabilized oil‐in‐water emulsions fortified with iron was investigated.

Interest has recently been rising in the development of food-compatible Pickering emulsions, i.e., particle-stabilized emulsions, and various biobased particles have been demonstrated as useful for such a purpose. Most of the related work has focused on the physical stability of the emulsions, but whether such particles can be advantageous in terms of chemical stability, and in particular, with regard to lipid oxidation, is largely unexplored. Recently, we found that colloidal lipid particles (CLPs) are efficient Pickering stabilizers, and the objective of the present study was to investigate the oxidative stability of emulsions stabilized with those particles. Three types of sunflower oil-in-water (O/W) emulsions were considered: Pickering emulsions stabilized with colloidal lipid particles (CLPs) made of high melting point (HMP) fat (tripalmitin or palm stearin), adsorbed onto the liquid oil droplets; and, as references, two conventional sodium caseinate-stabilized emulsions, of which one contained only liquid oil, and the other liquid oil mixed with HMP fat as the core of the emulsion droplets. In the presence of iron, the latter oxidized faster than conventional liquid oil and Pickering emulsions, resulting in 2- to 3-fold higher amounts of primary and secondary lipid oxidation products. This may be due to intra-droplet HMP fat pushing oxidizable lipids towards the oil-water interface, which would promote lipid oxidation. This shows that the localization of solid fat in O/W emulsions affects lipid oxidation. We also found that CLP-stabilized Pickering emulsions had similar oxidation rates as conventional sodium caseinate-stabilized emulsions containing only liquid oil. This suggests that the potential of such Pickering particles to prevent lipid oxidation is limited. This could be because diffusion of small pro-oxidant molecules is not hindered by Pickering particles, as they cannot form an interfacial barrier that is structurally homogeneous at such a small sca

The operational lifetime of filtration membranes is reduced by the clogging of pores and subsequent build-up of a fouling or cake layer. Designing membrane operations in which clogging is delayed or even mitigated completely, requires in-depth insight into its origins. Due to the complexity of the clogging process, simplified model membranes fabricated in microfluidic chips have emerged as a powerful tool to study how clogs emerge and deteriorate membrane efficiency. However, to date, these have focussed solely on dead-end filtration, while cross-flow filtration is of greater practical relevance at the industrial scale. As such, the microscopic mechanisms of clogging in crossflow geometries have remained relatively ill-explored. Here we use a microfluidic filtration model to probe the kinetics and mechanisms of clogging in crossflow. Our study exposes two findings: (i) the primary clogging rate of individual pores depends only on the trans-membrane flux, whose strong effects are explained quantitatively by extending existing models with a term for flux-controlled flow-enhanced barrier crossing, (ii) cross-membrane flow affects the pore-pore communication, leading to a transition from correlated to uncorrelated clogging of the membrane, which we explain qualitatively by deriving a dimensionless number which captures two essential regimes of clogging at the microscale.

In the quest to find approaches to prepare food grade Pickering emulsions, we studied the formation and stability to coalescence of colloidal lipid particle (CLP)-stabilized emulsions within a cross-flow microfluidic device. We show that the particles can either stabilize or destabilize the emulsions depending on the particle adsorption rate versus droplet formation rate, and on the resulting surface coverage when the droplet is formed. At low surface coverage, when droplet formation is significantly faster than adsorption, CLPs have a destabilizing effect as incomplete surface coverage leads to droplet-droplet bridging. At high surface coverage, the dense particle layer results in an effective barrier against droplet coalescence, resulting in physically stable emulsions. The observed non-monotonic dependency of emulsion droplet stability on surface coverage of CLP-stabilized emulsions is in stark contrast to what is observed for conventional surfactant-stabilized emulsions, and thus should be taken into account for the rational design of Pickering emulsions.

Shear induced diffusion (SID) based flow segregation is a technique that can be used for concentration and fractionation purposes, and it has the potential to become an economical and sustainable alternative for e.g., membrane separation. When compared to conventional microfiltration, problems related to fouling and cleaning are expected to be minimal. To make the best use of the opportunities that this technique holds, detailed insights in flow and particle behavior are needed. Modelling this process allows for us to chart particle segregation in flow, as well as the effect of suspension removal through a pore and the restoration of the flow profile after the pore. As a starting point, we take the computation fluid dynamics (CFD) model that is presented in a previous study. A difference in channel height to particle diameter ratio influences the entrance length of the SID profile as well as its fully developed profile. When extracting liquid through one pore, particles are systematically transmitted at a lower concentration (59–78%) than is present in the bulk. The recovery lengths of the SID profile after the pore were short, and thus pores can be placed at realistic distances, which forms a good foundation for further design of this novel separation technology that will ultimately be applied for fractionation of particles taking relatively small differences in diffusive behavior as a starting point.

Delivery of lipid fractions in the lower small intestine can induce feelings of satiety, but is only possible when lipids escape the highly efficient lipolysis and adsorption in the upper gastrointestinal (GI) tract. Our objective was to gain insight in the stability of multilayered interfaces in simulated GI conditions, and their suitability for intestinal delivery of undigested lipids. Oil-in-water emulsions (d32 ∼ 5–30 μm; one- to five-layered interfaces) were produced by sequentially adsorbing biopolymers with opposite charges at pH 3.0: whey protein isolate (WPI) (cationic), pectin (anionic), chitosan (cationic). Corresponding multilayered structures were characterized using reflectometry. Influence of layer composition and thickness on its protectiveness against lipolysis of emulsions was studied in simulated GI conditions. Multilayered WPI/pectin emulsions had an improved physical stability compared to WPI-stabilized emulsions, during both storage and in vitro gastric incubation, whereas chitosan-containing emulsions were physically unstable. Reflectometry and CLSM results showed that a greater number of layers increased the adsorbed amount, forming a mesoscopically heterogeneous structure. Under simulated intestinal conditions, however, outer layers instantaneously destabilized. Accordingly, similar initial lipolysis rates were recorded for all emulsions. Yet, compared to only WPI the final extent of lipolysis was lowered by addition of a second and a third layer under mild in vitro conditions. This moderate protective effect disappeared when harsher digestive conditions were applied. From this work, it became clear why multilayered interfaces (initially built under acidic pH) can improve gastric stability of emulsions, but are prone to disintegration under intestinal conditions. This knowledge is important for designing food systems that control release of lipolytic products in targeted locations of the GI tract; the emulsions reported her

The increasing prevalence of overweight and obesity requires new, effective prevention and treatment strategies. One approach to reduce energy intake is by developing novel foods with increased satiating properties, which may be accomplished by slowing down lipolysis to deliver substrates to the ileum, thereby enhancing natural gut-brain signalling pathways of satiety that are normally induced by meal intake. To develop slow release food additives, their processing in the gastrointestinal tract has to be understood; therefore, we start from a general description of the digestive system and relate that to in vitro modelling, satiety and lipolytic mechanisms. The effects of physicochemical lipid composition, encapsulation matrix and interfacial structure on lipolysis are emphasized. We give an overview of techniques and materials used, and discuss partitioning, which may be a key factor for encapsulation performance. Targeted release capsules that delay lipolysis form a real challenge because of the high efficiency of the digestive system; hardly any proof was found that intact orally ingested lipids can be released in the ileum and thereby induce satiety. We expect that this challenge could be tackled with structured o/w-emulsion-based systems that have some protection against lipase, e.g., by hindering bile salt adsorption and/or delaying lipase diffusion.

'Foods and food ingredients are produced at very large scale on a daily basis; however, insight in the underlying mechanisms that take place at micrometre scale is lacking. This is because of the small scale and the high speed at which things occur. Food microtechnology combines investigation in small channels for example in microfluidic devices with high speed imaging and modelling, and uses this to push the food process technology of the future in fast forward mode.'