ISBN 9783843933384

978-3-8439-3338-4, Reihe Verfahrenstechnik

Lea Koch
Reactive extrusion of whey protein-citrus pectin blends: Investigations on structural changes and functional properties

189 Seiten, Dissertation Karlsruher Institut für Technologie (2017), Softcover, A5

Zusammenfassung / Abstract

The increased consumer awareness of health and nutrition leads to ever-expanding demands for food products based on natural ingredients. For this purpose, biopolymers such as proteins and polysaccharides are often applied as natural additives to adjust desired product properties. Polysaccharides are mainly used as thickeners, stabilizers and gelling agents, while proteins are mainly applied due to their emulsifying, foaming and gelling properties. However, proteins are highly sensitive to changes in their environmental conditions limiting their industrial application. In particular, the emulsifying properties decrease at high concentrations of ions, high temperature treatments and at a pH near the isoelectric point of the protein.

It is well-known that a covalent linkage of proteins with high molecular polysaccharides can lead to improved emulsifying, foaming and stabilizing properties of the protein. The so-called conjugation of proteins and polysaccharides is based on the initial step of the Maillard reaction. Although several conjugation methods (e.g., dry-heating and wet-heating) have been reported, none of these are implemented for an industrial use as they are too expensive, time-consuming or not sufficiently investigated. Reactive extrusion, a thermomechanical process, is an alternative method for conjugation via the Maillard reaction with high potential for an industrial implementation. Among others, this is based on the assumption that due to shear the reactions taking place are accelerated.

During extrusion processing, thermal and mechanical stresses are coupled to each other and the local extrusion conditions can vary widely. Therefore, reactive extrusion faces the great challenge to control the extrusion conditions and consequently to control the reactions taking place. Furthermore, less is known about the impact of elevated temperatures and shear on the reactions taking place in highly concentrated protein-polysaccharide systems.

The objective of this thesis is to gain a mechanistic understanding on the impact of the extrusion conditions (i.e., temperature and shear rate) on the reactions taking place in highly concentrated whey protein-citrus pectin systems and on the functional properties (e.g., emulsifying properties) of the reaction products. With this knowledge, recommendations for a process development with regard to adjust the functional properties of whey protein-citrus pectin blends can be given.