Rethinking Membrane Processes for Food:From Particle Behavior to Innovative Membrane Cascades

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.</p

Effects often overlooked in lipid oxidation in oil-in-water emulsions:Agitation conditions and headspace-to-emulsion ratio

The effects of the agitation conditions and headspace-to-emulsion volume ratio on lipid oxidation in emulsions can be considerable, but have not been systematically investigated yet. In the current paper, lipid oxidation was monitored in model oil-in-water (O/W) emulsions at pH 4.0 and 25°C in the presence of 200 μM iron sulfate. The formation of primary (conjugated dienes and hydroperoxides) and secondary (p-anisidine value and TBARS) oxidation products confirmed that using rotating or shaking devices doubled the rate of oxidation product formation compared to a non-agitated system, as a result of enhanced oxygen transfer. Furthermore, we found that a higher headspace-to-emulsion volume ratio at least doubled the rate of lipid oxidation due to a higher amount of oxygen available per mass of oil, which is in agreement with the kinetics of the reaction. This indicates that the variation in literature data on lipid oxidation in emulsions can be attributed to differences in mixing conditions and volume ratios. These factors are crucial and should be reported systematically along with the agitation conditions, and sampling method. This will enable a better comparison of literature information.</p

Chemical Stability of α-Tocopherol in Colloidal Lipid Particles with Various Morphologies

Colloidal lipid particles (CLPs) are promising encapsulation systems for lipophilic bioactives, such as oil-soluble antioxidants that are applied in food and pharmaceutical formulations. Currently, there is no clear consensus regarding the relation between particle structure and the chemical stability of such bioactives. Using α-tocopherol as a model antioxidant, it is shown that emulsifier type (Tween 20 or 40, or sodium caseinate) and lipid composition (tripalmitin, tricaprylin, or combinations thereof) modulated particle morphology and antioxidant stability. The emulsifier affects particle shape, with the polysorbates facilitating tripalmitin crystallization into highly ordered lath-like particles, and sodium caseinate resulting in less ordered spherical particles. The fastest degradation of α-tocopherol is observed in tripalmitin-based CLPs, which may be attributed to its expulsion to the particle surface induced by lipid crystallization. This effect is stronger in CLPs stabilized by Tween 40, which may act as a template for crystallization. This work not only shows how the architecture of CLPs can be controlled through the type of lipid and emulsifier used, but also gives evidence that lipid crystallization does not necessarily protect entrapped lipophilic bioactives, which is an important clue for encapsulation system design. Practical Applications: Interest in enriching food and pharmaceutical products with lipophilic bioactives such as antioxidants through encapsulation in lipid particles is growing rapidly. This research suggests that for efficient encapsulation, the particle architecture plays an important role; to tailor this, the contribution of both the lipid carrier and the emulsifier needs to be considered.</p

Tiny, yet impactful:Detection and oxidative stability of very small oil droplets in surfactant-stabilized emulsions

Hypothesis: The shelf life of multiphase systems, e.g. oil-in-water (O/W) emulsions, is severely limited by physical and/or chemical instabilities, which degrade their texture, macroscopic appearance, sensory and (for edible systems) nutritional quality. One prominent chemical instability is lipid oxidation, which is notoriously complex. The complexity arises from the involvement of many physical structures present at several scales (1–10,000 nm), of which the smallest ones are often overlooked during characterization. Experiments: We used cryogenic transmission electron microscopy (cryo-TEM) to characterize the coexisting colloidal structures at the nanoscale (10–200 nm) in rapeseed oil-based model emulsions stabilized by different concentrations of a nonionic surfactant. We assessed whether the oxidative and physical instabilities of the smallest colloidal structures in such emulsions may be different from those of larger colloidal structures. Findings: By deploying cryo-TEM, we analyzed the size of very small oil droplets and of surfactant micelles, which are typically overlooked by dynamic light scattering when larger structures are concomitantly present. Their size and oil content were shown to be stable over incubation, but lipid oxidation products were overrepresented in these very small droplets. These insights highlight the importance of the fraction of “tiny droplets” for the oxidative stability of O/W emulsions.</p

Microfluidic model systems used to emulate processes occurring during soft particle filtration

Cake layer formation in membrane processes is an inevitable phenomenon. For hard particles, especially cake porosity and thickness determine the membrane flux, but when the particles forming the cake are soft, the variables one has to take into account in the prediction of cake behavior increase considerably. In this work we investigate the behavior of soft polyacrylamide microgels in microfluidic model membranes through optical microscopy for in situ observation both under regular flow and under enhanced gravity conditions. Particles larger than the pore are able to pass through deformation and deswelling. We find that membrane clogging time and cake formation is not dependent on the applied pressure but rather on particle and membrane pore properties. Furthermore, we found that particle deposits subjected to low pressures and low g forces deform in a totally reversible fashion. Particle deposits subjected to higher pressures only deform reversibly if they can re-swell due to capillary forces, otherwise irreversible compression is observed. For membrane processes this implies that when using deformable particles, the pore size is not a good indicator for membrane performance, and cake formation can have much more severe consequences compared to hard particles due to the sometimes-irreversible nature of soft particle compression

Conformational changes influence clogging behavior of micrometer-sized microgels in idealized multiple constrictions

Clogging of porous media by soft particles has become a subject of extensive research in the last years and the understanding of the clogging mechanisms is of great importance for process optimization. The rise in the utilization of microfluidic devices brought the possibility to simulate membrane filtration and perform in situ observations of the pore clogging mechanisms with the aid of high speed cameras. In this work, we use microfluidic devices composed by an array of parallel channels to observe the clogging behavior of micrometer sized microgels. It is important to note that the microgels are larger than the pores/constrictions. We quantify the clog propensity in relation to the clogging position and particle size and find that the majority of the microgels clog at the first constriction independently of particle size and constriction entrance angle. We also quantify the variations in shape and volume (2D projection) of the microgels in relation to particle size and constriction entrance angle. We find that the degree of deformation increases with particle size and is dependent of constriction entrance angle, whereas, changes in volume do not depend on entrance angle

A Multi-Platform Flow Device for Microbial (Co-) Cultivation and Microscopic Analysis

Novel microbial cultivation platforms are of increasing interest to researchers in academia and industry. The development of materials with specialized chemical and geometric properties has opened up new possibilities in the study of previously unculturable microorganisms and has facilitated the design of elegant, high-throughput experimental set-ups. Within the context of the international Genetically Engineered Machine (iGEM) competition, we set out to design, manufacture, and implement a flow device that can accommodate multiple growth platforms, that is, a silicon nitride based microsieve and a porous aluminium oxide based microdish. It provides control over (co-)culturing conditions similar to a chemostat, while allowing organisms to be observed microscopically. The device was designed to be affordable, reusable, and above all, versatile. To test its functionality and general utility, we performed multiple experiments with Escherichia coli cells harboring synthetic gene circuits and were able to quantitatively study emerging expression dynamics in real-time via fluorescence microscopy. Furthermore, we demonstrated that the device provides a unique environment for the cultivation of nematodes, suggesting that the device could also prove useful in microscopy studies of multicellular microorganisms

Linking Findings in Microfluidics to Membrane Emulsification Process Design: The Importance of Wettability and Component Interactions with Interfaces

In microfluidics and other microstructured devices, wettability changes, as a result of component interactions with the solid wall, can have dramatic effects. In emulsion separation and emulsification applications, the desired behavior can even be completely lost. Wettability changes also occur in one phase systems, but the effect is much more far-reaching when using two-phase systems. For microfluidic emulsification devices, this can be elegantly demonstrated and quantified for EDGE (Edge-base Droplet GEneration) devices that have a specific behavior that allows us to distinguish between surfactant and liquid interactions with the solid surface. Based on these findings, design rules can be defined for emulsification with any micro-structured emulsification device, such as direct and premix membrane emulsification. In general, it can be concluded that mostly surface interactions increase the contact angle toward 90°, either through the surfactant, or the oil that is used. This leads to poor process stability, and very limited pressure ranges at which small droplets can be made in microfluidic systems, and cross-flow membrane emulsification. In a limited number of cases, surface interactions can also lead to lower contact angles, thereby increasing the operational stability. This paper concludes with a guideline that can be used to come to the appropriate combination of membrane construction material (or any micro-structured device), surfactants and liquids, in combination with process conditions

Thermoplastic bio-nanocomposites : From measurement of fundamental properties to practical application

Although the discovery of plastic has revolutionized materials used in many industries and by consumers, their non-biodegradable nature has led to one of the greatest problems of our times: plastic waste in the environment. Bioplastics which are biobased and biodegradable, have been suggested as alternatives for their fossil based counterparts, but their properties often do not meet the requirements that standard plastics would, and are in clear need of improvement. One way to do so is by the addition of nanoparticles which, when homogeneously dispersed, have been reported to result in great improvements. However, in practice, homogenous distribution of nanoparticles is not that trivial due to their tendency to aggregate, also after addition to the polymer matrix. Although theoretical frameworks to prevent this process are available, we feel that the options explored in practice are often rather trial and error in nature. For that reason, we review the theories available, aiming to facilitate the design of the nanocomposites for a sustainable future. We first discuss thermodynamic frameworks which revolve around nanoparticle aggregation. To minimize nanoparticle aggregation, the nanoparticle and polymer can be selected in such a way that they have similar polar and dispersive surface energies. The second part is dedicated to nanocomposite processing, where kinetic effects act on the nanocomposite material therewith influencing its final morphology, although it is good to point out that other factors such as reaggregation also affect the final nanocomposite morphology. The third section is dedicated to how nanoparticles affect the polymer matrix to which they are added. We describe how interactions at an atomic scale, result in the formation of an interphasial region which ultimately leads to changed bulk material properties. From these three sections, we conclude that three parameters are often overlooked when designing nanocomposites, namely the surface energies of the nanoparticles and polymers, the aggregation bond energy or strength, and the interphase region. Therefore, in the fourth section we provide an overview of techniques to identify these three parameters. We finish with a summery and outlook for the design of bio nanocomposites, where we bring all insights from the previous four sections together.</p