Interfacial properties of saponins from Quillaja saponaria Molina and their functionality in dispersed systems

The aim of the present thesis was to connect interfacial properties of saponins at aqueous interfaces with their behavior in dispersed systems. Thereby the influence of changes in pH and ionic strength and interactions with β-lactoglobulin were discussed using spectroscopic equipment and knowledge on molecular structure. Saponins are phytochemicals that can be found in numerous plant species in low concentrations. Due to their amphiphilic structure, saponins are surface active and may be used in dispersed systems like emulsions and foams. Molecular structure of saponins is highly variable as different aglyone types exist to which a varying quantity and type of sugar residues may be linked. Although it is known that saponins with a triterpenoid aglycone form viscoelastic films, knowledge on corresponding foam properties is scarce. In the present thesis six saponins, which differed in molecular structure, were analyzed with respect to interfacial and foam properties. It was shown that high complex dilational and shear moduli were a requirement for stable foams but not a guarantee for high stability. However, it was also shown that the type of aglycone and length of the sugar chains had the highest impact on foam stability. A saponin extract from Quillaja saponaria Molina (QS) is already approved for application in food products in the EU and US. But until now only little is known about interactions between QS and food-relevant ingredients like proteins. There has been evidences that QS and β-lactoglobulin (β-LG) form complexes, which affected interfacial properties. In the present thesis fluorescence experiments showed complex formation in the bulk and interfacial rheology indicated strong interactions at the air/water-interface. The interactions between QS and β-LG tremendously increased foam stability. In contrast mixtures of QS and β-LG negatively affected emulsion stability by inducing aggregation of oil droplets. Food systems may not only contain proteins but may also be a mixture of multiple dispersed phases. It was shown that oil droplet size of the emulsion and pH are key factors in controlling stability of foamed emulsions. Stability may further be enhanced by sequentially adding QS to a β-LG-emulsion. Summarizing the results, experimental data showed that molecular structure of saponins distinctly affects foam stability. In addition, it was shown that mixing QS with β-LG may lead to synergistic or antagonistic effects in dispersed systems. However, it is necessary to perform experiments, which further deepen our understanding on the relationship of molecular structure and interfacial properties as well as behavior in dispersed systems. Furthermore, future research should focus on the underlying intermolecular interactions between proteins and QS to explain interfacial properties of mixtures of both.

Author dc:creator

• Böttcher, Sandra

Advisor dc:contributor.advisor

• Drusch, Stephan

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Identifier URI

http://dx.doi.org/10.14279/depositonce-6160

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/6734