Finished projects

Zulhaj Rizki

Rational Design of Cascaded Nanofiltration Systems

PhD Defense on November 3, 2020

In industrial practice, process systems usually consist of multiple units and can be much more complex than a single process unit. The process system, therefore, needs to be designed carefully such that all operational units work synergistically to achieve an overall objective. Designing a process system is a complicated work, which until now is mostly done intuitively. The design is usually developed via a trial-and-error­ process based on heuristic knowledge. The resulting design may be sufficient and acceptable, but the design may not the optimum design. A more rational and objective approach is needed to design a process system to end up with an objective design that is truly optimal. This thesis aims to develop such a rational procedure for designing process systems,  represented by inhomogeneous nanofiltration cascades for fractionation of fructooligosaccharides (FOS). The design process is approached by modelling within four levels of a process system: (1) single stage nanofiltration, (2) nanofiltration cascades, (3) optimization and (4) process design.

Anton Schultze-Jena

High viscosity industrial chromatography for mild food fractionation

PhD defense on October 9, 2019

Agro-food streams, present in large volumes, contain compounds attractive for food industry, if they are separated from unwanted components. Recovery of such components offers a large potential for industrial applications. A trend towards enriched fractions, rather than purified products, enables sustainable process design via chromatographic separation. Chromatography has the potential to fractionate these agro-food streams at large industrial scale, while maintaining functionality and operating in a sustainable and economical manner. The separation mechanism can be fine-tuned to target specific molecular characteristics. Because the streams to be processed are so large, large equipment is required, which renders the process economically unfeasible. Process economics can be improved by reducing the size of the chromatographic installation, which is directly dependent on the volume to be processed. The stream to be processed can be reduced by increase of concentration, which leads to higher viscosity. The aim of this thesis is to understand the interplay between feed viscosity, mass transfer resistance, pressure drop and eventually productivity and water use of a chromatographic system.

Victor Aguirre Montesdeoca

Membrane filtration of food streams: Mechanisms and modelling

PhD defense on November 12, 2018

The mechanisms behind membrane processes such as ultrafiltration and nanofiltration are not yet completely understood when multicomponent, concentrated solutions are used as feed, as is usually the case in the food and biotechnology industry. Under concentrated conditions, the interactions between the mixture components become important and the prediction of permeate flux and rejection is not possible using currently available models. This PhD thesis reduces the gap in the understanding of these complex systems, enabling a better process design and optimization. The aim of the studies contained in this thesis is to improve the accuracy of the predictions of pressure driven filtration by implementing new concepts and descriptions that result from considering the fundamental underlying phenomena acting under realistic concentrated conditions.

Mauricio Opazo Navarrete

Pre-treatment and digestion of plant proteins – The quinoa case

PhD defense on August 28, 2018

The growing global population will place increased pressure on the world’s resources to provide more proteins. It is expected that we need to switch at least partly from animals as sources of protein, to plant-based proteins, to ensure sufficient and sustainable production of proteins for everyone. Animal protein is nutritionally of very high quality, since it contains all essential amino acids, whereas vegetable sources generally lack one or more of the essential amino acids. However, this thesis shows that the image that plant proteins have an inferior amino acid profile and poor digestibility is not accurate. For instance, quinoa contains protein with an almost ideal amino acid profile. Especially the essential amino acids profile is considered to be well-balanced for human nutrition. Besides, quinoa contains almost twice as much dietary fibre as most other grains and is high in phosphorus, magnesium and iron. In addition, the quinoa is a good source of calcium, which is useful for vegans and lactose intolerant people. The gluten-free nature of quinoa, being a non-cereal, is considered safe for celiac patients. Next to the amino acid profile including the essential amino acids, the digestibility is another important factor in determining the quality of a protein source. Generally, the potential use of plant proteins and thus also quinoa protein as a food ingredient is limited by their relatively lower digestibility as compared with animal proteins. However, this thesis shows that the reformulate digestibility can be improved by choosing a proper pre-treatment.

Overall, three main conclusions could be drawn from this thesis. (1) Quinoa protein can be well isolated using conventional wet processes, yielding a QPI with good purity, but can also be concentrated using the new dry fractionation process. Both types of quinoa protein are well digestible according to the in vitro gastric assay that was used. (2)The conditions during processing of the raw materials into protein isolate or concentrate strongly influence the gastric digestibility: the thermal load, but also the pH applied during the isolation change the gastric digestion perhaps even stronger than the original differences between different protein sources. (3) The digestion of dissolved protein is relatively fast, while that of gelled protein is significantly slower; the presence of other components such as starch or fibre slows the gastric digestion significantly down. This may be due to the lower amount of gastric fluid that is available for the protein, the lower swelling of the protein, and the subsequent slower of pepsin into the protein matrix.

Qi Luo

In vitro gastric digestion of protein-based structured food – an engineering approach

PhD defense on June 25, 2018

To better design food, scientists need to better understand the underlying mechanisms of digestion. The aim of the thesis is to study the physicochemical processes in the gastric digestion of protein-based food matrices, to gain quantitative insight and mechanistic understanding of the gastric digestion of protein food. We first showed the importance of food structure, diffusion processes and enzyme kinetics in the gastric digestion, which defined the further exploration of this thesis. We determined the diffusivity of pepsin in water and in whey protein isolate (WPI) gels by fluorescence correlation spectroscopy (FCS). To further characterize the hindrance of the microstructure in the diffusive mobility of the enzyme, we used enhanced green fluorescent protein (EGFP) as the probe to study the diffusivity of proteins in varied protein gel matrices by FCS. We used isothermal titration calorimetry to study the enzymatic kinetics of pepsin with bovine serum albumin as the substrate. We found that pepsin has a higher activity at pH 2, while its affinity to the substrate is lower. At the same pH, pepsin has lower activity and affinity at higher ionic strengths. To quantitatively understand the gastric pH dynamics, we investigated the buffer capacity of proteins and the acid diffusion in protein gels, both theoretically and experimentally. By integrating the physicochemical processes involved in gastric digestion, we can better understand the disintegration and digestion kinetics of protein-based food matrices.

Karolina Bednarska

Kinetic modelling of enzymatic starch hydrolysis

PhD defense on June 9, 2015

This thesis describes the enzymatic hydrolysis and kinetic modelling of liquefaction and saccharification of wheat starch. We describe a model predicting the outcome of wheat starch liquefaction by α-amylase from Bacillus licheniformis at 50°C. We demonstrate the ability of the model to predict starch hydrolysis products larger than the oligosaccharides considered in the existing models. The model in its extended version follows all the products of wheat starch hydrolysis separately, and despite the quantitative differences, the qualitative predictions are satisfactory. We also show that the difference between the experimental and computed data might stem from the inaccuracy of the subsite map.

The model is used to find a better description of the hydrolysis data at two temperatures (50°C and 80°C), by varying the energy values of the subsite map and evaluating the inhibition. We hypothesize that a subsite map that is based on the cleavage patterns of linear, short molecules does not account for the complexity of hydrolysis of amylopectin. The branched structure of amylopectin molecules influences the composition of the hydrolysis products by restricting the access to some of the bonds. The presence of branches creates steric obstacles for the enzyme. The used α-amylase has difficulties hydrolysing and accommodating α-(1,6)-glycosidic bonds, which imposes on the hydrolysis of the α-(1,4)-glycosidic bonds located in its proximity. On this basis, we analyse the subsite maps in detail and suggest which of the subsites are crucial when making predictions about the product composition of starch hydrolysates. On top of that we propose new subsite maps that allow a quantitative description of the experimental data.

Marta Rodriguez Illera

Structured adsorbents for isolation of functional food ingredients

PhD defense on October 24, 2014

Separation and purification of functional ingredients from raw or waste streams are often done via processes that include a chromatographic step using a packed bed of resin particles that have affinity for the ingredients to be separated. A column packed with these particles presents numerous bottlenecks when dealing with untreated or large streams: a trade-off between mass transfer and hydraulic permeability, a high pressure drop and susceptibility to plugging and fouling. The large equipment (column diameters) and volume of resin needed for a moderate pressure drop and a high capacity, poses problems of elevated costs and complex operation. Other technologies such as radial flow chromatography and polymeric resins membranes may represent an improvement in other applications (e.g. pharma or fine chemicals), but at this point their capacity and costs do not seem to be feasible for the separation of small molecules from larger food streams. The aim of the research discussed in this thesis was to find the principles that determine the suitability of different structured adsorbents, such as monoliths, for the selective adsorption and recovery of high-added value food ingredients of relatively low molecular weight, such as oligosaccharides and bioactive peptides. To ensure a cost-effective process and high capacity for small molecules, we demonstrated the feasibility of using activated carbon, and compared its adsorptive and hydraulic performance in two different structures: porous particles and channeled monoliths (”honeycomb” structures). Furthermore, we assessed the feasibility and window of operation of monoliths in terms of adsorbent and column volume required, compared to packed beds. 

Anja Warmerdam

Synthesis of galacto-oligosaccharides with β-galactosidases

PhD defense on June 18, 2013

Galacto-oligosaccharides (GOS) are carbohydrates that consist of a varying amount of galactose molecules attached to a lactose molecule. They are health beneficial and have prebiotic effects. GOS stimulate the growth of beneficial bacteria in the large intestine and are thought to inhibit the development of colon cancer. For this reasons, GOS are used as an additive to food. They are also added in infant nutrition, since theses sugars resemble the structure of oligosaccharides that are present in human breast milk. They are manufactured through enzymatic synthesis by using glycosidases for transglycosylation of lactose. It is desired to further improve the process, e.g. to obtain a higher product yield and to make better use of the enzyme. To reach these goals we need to enhance the knowledge on the kinetics of the reaction. Process conditions like, temperature, substrate concentration etc. have been studied. We have used Isothermal Titration Calorimetry for kinetic measurements.

Protein isolation using affinity chromatography

PhD defense on December 7, 2012

Many product or even waste streams in the food industry contain components that may have potential for e.g. functional foods. These streams are typically large in volume and the components of interest are only present at low concentrations. A robust and highly selective separation process should be developed for efficient isolation of the components. Affinity chromatography is such a selective method. Ligands immobilized to a stationary phase (e.g., a resin or membrane) are used to bind the component of interest. Affinity chromatography is, however, a costly process, due to the batch-wise operation, the large amount of solvents required and the high costs of the ligands and stationary phases. Therefore, its current use is mainly limited to lab-scale purifications and pharmaceutical applications.

The aim of this research was to investigate the potential of affinity chromatography for the isolation of minor protein in the food industry. The discovery of the VHH ligand, based on the binding domain of a llama antibody, has led to a new class of highly selective ligands, which can be produced on a large scale. We studied the chromatography process to measure productivity, but also to develop a rational protocol for decisions on suitable stationary phases and process configurations. The research presented in this thesis provides insights in the opportunities and challenges for large-scale affinity chromatography.

Ruben Kolfschoten

Reaction and separation opportunities with microfluidic devices

PhD defense on February 25, 2011

Microfluidic devices make precisely controlled processing of substances possible on a microliter level. The advantage is that, due to the small sizes, the driving forces for mass and heat transfer are high. The surface to volume ratios are also high, which can benefit many surface oriented processes. In addition, because of their small volumes, microfluidic devices reduce reagent consumption and risk of failure compared to larger counterparts. Furthermore, the parallelization of such devices can increase productivity while maintaining their characteristics. Overall, these advantageous properties give many opportunities for reaction and separation processes. Although researchers have intensively studied microfluidics for analytical and sensory applications, microfluidics for preparative processes is still in its infancy. This thesis research involved exploring these processes for biocatalysis and bioseparations with microfluidic devices. The purpose of this thesis was to yield a better understanding of microfluidics for the preparative processes and larger scale production. We therefore addressed subjects including microfluidic parallelization, membrane separation, biocatalysis, and design. The presented research is useful for further developing innovative process intensification by means of microfluidic devices

Jan Swarts

Effective use of enzyme microreactors : thermal, kinetic and ethical guidelines

PhD defense on June 10, 2009

Microreactor technology is reported to have many benefits over regular chemical methods. Due to the small dimensions over which temperature and concentration gradients can exist, mass and heat transfer can be very quick. This could minimize the time needed for heating and mixing, due to a reduction in diffusion limitation. Furthermore, a very low fluid to chip volume ratio could facilitate a very stable fluid temperature.

The goal of this thesis research was to investigate the effect of the use of microreactors on enzyme kinetics and the thermal behaviour of fluids inside the chip. First, the effect of the design and use of a microsystem on the fluid temperature inside the microfluidic chip was investigated experimentally and with computer models. A stable and predictable temperature is of great importance for running (enzymatic) processes in a microchip. Next, we used model enzyme reactions to investigate whether the enzyme kinetics were different on micro and bench scale, and when diffusion would play a role. Furthermore, some social and ethical aspects of microreactor technology applications were studied.

Tim Baks

Process development for gelatinisation and enzymatic hydrolysis of starch at high concentrations

PhD defense on October 12, 2007 (cum laude)

Enzymatic hydrolysis of starch is encountered in day-to-day life for instance in the dishwasher during removal of stains with detergents or in our mouth during chewing of starch-based foods in the presence of saliva. The reaction is also important for the (food) industry, for example for the production of beer or bio-ethanol. In industry, it is usually preceded by gelatinisation to make the starch molecules available for the enzymes. Both gelatinisation and hydrolysis are usually carried out at a starch concentrations of 30 weight-%. Increasing the starch concentration during these processes can lead to a higher productivity, lower energy consumption, lower use of water and a higher enzyme stability. However, the drawback is that the gelatinisation temperature and the viscosity increase at these conditions. By using the proper process equipment, it is possible to overcome these drawbacks and to perform the gelatinisation and hydrolysis at high starch concentrations leading to the advantages mentioned above. The purpose of this study was therefore to develop a process for gelatinisation and enzymatic hydrolysis of wheat starch at high starch concentrations (more than 40 weight-%). Besides the development of such a process, analysis methods were developed to measure the main process parameters at these conditions.

Marieke Bruins

Oligosaccharide production with thermophilic enzymes

PhD defense on June 23, 2003

Floor Boon

Enzymatic synthesis of oligosaccharides : kinetics, process parameters, and reactor design

PhD defense on March 10, 2000