M.A.I. Schutyser

Thermal inactivation kinetics of β-galactosidase during bread baking

In this study, β-galactosidase was utilized as a model enzyme to investigate the mechanism of enzyme inactivation during bread baking. Thermal inactivation of β-galactosidase was investigated in a wheat flour/water system at varying temperature-moisture content combinations, and in bread during baking at 175 or 205°C. In the wheat flour/water system, the thermostability of β-galactosidase increased with decreased moisture content, and a kinetic model was accurately fitted to the corresponding inactivation data (R2=0.99). Interestingly, the residual enzyme activity in the bread crust (about 30%) was hundredfold higher than that in the crumb (about 0.3%) after baking, despite the higher temperature in the crust throughout baking. This result suggested that the reduced moisture content in the crust increased the thermostability of the enzyme. Subsequently, the kinetic model reasonably predicted the enzyme inactivation in the crumb using the same parameters derived from the wheat flour/water system. However, the model predicted a lower residual enzyme activity in the crust compared with the experimental result, which indicated that the structure of the crust may influence the enzyme inactivation mechanism during baking. The results reported can provide a quantitative understanding of the thermal inactivation kinetics of enzyme during baking, which is essential to better retain enzymatic activity in bakery products supplemented with heat-sensitive enzymes.

Effect of pre-treatment on in vitro gastric digestion of quinoa protein (Chenopodium quinoa Willd.) obtained by wet and dry fractionation

Abstract Quinoa protein was isolated from quinoa seeds using wet fractionation that resulted in a protein isolate (QPI) with a high protein purity of 87.1% (w/dw) and a protein yield of around 54%, and a dry fractionation method delivered a quinoa protein concentrate (QPC) with a purity of 27.8% (w/dw) and yield of around 47%. The dry fractionation process only involves milling and sieving and keeps the protein in its natural, native state. The aim was to study the in vitro gastric digestibility of both protein. Attention was paid to thermal pre-treatment of QPI and QPC. QPC showed significantly higher (pu2009<u2009.05) digestibility than QPI samples. The results were interpreted with a simple double exponential model. The fraction of easily digested protein in QPC is higher than for QPI. The better digestibility of the QPC was explained by the prevention of the formation of large aggregates during pre-heating of the protein. Graphical Abstract

Reducing the critical particle diameter in (highly) asymmetric sieve-based lateral displacement devices

Deterministic lateral displacementxa0technology was originally developed in the realm of microfluidics, but has potential for larger scale separation as well. In our previous studies, we proposed a sieve-based lateral displacement device inspired on the principle of deterministic lateral displacement. The advantages of this new device is that it gives a lower pressure drop, lower risk of particle accumulation, higher throughput and is simpler to manufacture. However, until now this device has only been investigated for its separation of large particles of around 785u2009µm diameter. To separate smaller particles, we investigate several design parameters for their influence on the critical particle diameter. In a dimensionless evaluation, device designs with different geometry and dimensions were compared. It was found that sieve-based lateral displacement devices are able to displace particles due to the crucial role of the flow profile, despite of their unusual andxa0asymmetric design. These results demonstrate the possibility to actively steer the velocity profile in order to reduce the critical diameter in deterministic lateral displacement devices, which makes this separation principle more accessible for large-scale, high throughput applications.

Visualizing the hydrodynamics in sieve-based lateral displacement systems

Deterministic lateral displacement (DLD) systems structure suspension flow in so called flow lanes. The width of these flow lanes is crucial for separation of particles and determines whether particles with certain size are displaced or not. In previous research, separation was observed in simplified DLD systems that did not meet the established DLD geometric design criteria, by adjusting the outflow conditions. We here investigated why these simplified DLD systems are able to displace particles, by experimentally investigating the hydrodynamics in the device. Flow lanes were visualized and the local flow velocities were measured using µPIV and compared with 2D fluid dynamics simulations. The size of the flow lanes strongly correlates with the local flow velocity (Vy and Vx), which depends on the hydrodynamics. Therefore, the geometric design criteria of DLD devices is in fact just one method to control the local hydrodynamics, which may also be influenced by other means. These findings give a new perspective on the separation principle, which makes the technique more flexible and easier to translate to industrial scale.

Morphology development during single droplet drying of mixed component formulations and milk

We report on the influence of selected components and their mixtures on the development of the morphology during drying of single droplets and extend the results to the morphology of whole milk powder particles. Sessile single droplet drying and acoustic levitation methods were employed to study single droplet drying. The influence of carbohydrates (lactose and maltodextrin DE12) and proteins (micellar casein or whey protein) on morphology development is very different, since upon concentration protein systems will jam and undergo a colloidal glass transition, whereas carbohydrate systems will gradually increase in viscosity as a consequence of the concentration. Whey protein gives relatively rigid shells due to jamming of the hard sphere proteins, while casein micelles behave as soft spheres that can deform after jamming, which gives flexibility to the shell during drying. The influence of the carbohydrates on the final morphology was found much larger than the influence of the proteins. Caseins influenced morphology only in mixtures with lactose at higher concentrations due to its high voluminosity. Similar observations were done for whole milk, where fat appeared to have no influence. With maltodextrin the influence of the casein was again observed in the shape and smoothness of wrinkles. Both sessile and levitated droplet drying methods provide a similar and consistent view on morphology development.