ISBN 978-3-8439-5117-3

978-3-8439-5117-3, Reihe Verfahrenstechnik

Maria Gabriela Gräfenhahn
Functionalization of proteins via extrusion processing: Influence of thermal and mechanical treatment on the denaturation and functionality of whey proteins

284 Seiten, Dissertation Karlsruher Institut für Technologie (2021), Softcover, A5

Zusammenfassung / Abstract

In the scope of this thesis, it could be shown that extrusion processing is a suitable process for the functionalization of whey proteins at concentrations > 40%. Using the closed cavity rheometer insights into the reaction mechanisms of whey proteins were gained at a wide range of concentrations. The results indicated that the protein concentration strongly affected the denaturation behavior of whey protein systems. The higher the protein concentration, the less water is available, less free volume between protein molecules, higher viscosities, changed protein-solvent interactions, and a more compact and entangled system. This is expected to hinder the unfolding of the protein structure and hence the availability of reactive sites, leadind to lower reaction rates, higher values of activation energy, and therefore to higher onset temperatures. Shifting the pH values of the systems away from their pI leads to highly charged macromolecules and by this, to increased electrostatic repulsion, resulting in a more extended and this less entangled configuration, which are expected to be less stable to heat and shear treatments since less disentanglement is needed for the unfolding of the globular structure of whey proteins, leading to lower unfolding activation energy, and by this, to lower onset temperatures. The shear rate is expected to influence the entangled nature of the protein system, inducing rearrangements on the protein conformation, thus positively influencing the unfolding, and as a consequence, the reaction rate. The gained information can be used to further develop existing kinetic models, to obtain thermal and mechanical stress profiles using CFD, and finally to control the reactions during extrusion processing to be able to adjust the final properties of protein-based products in a targeted way.