Properties of novel biosurfactants: linking the molecular, meso- and macrolength scales

Dimitrijev, Mirjana (2011). Properties of novel biosurfactants: linking the molecular, meso- and macrolength scales PhD Thesis, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland.

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Author Dimitrijev, Mirjana
Thesis Title Properties of novel biosurfactants: linking the molecular, meso- and macrolength scales
School, Centre or Institute Australian Institute for Bioengineering and Nanotechnology
Institution The University of Queensland
Publication date 2011-11
Thesis type PhD Thesis
Supervisor Anton Middelberg
Lizhong He
Total pages 147
Total colour pages 13
Total black and white pages 134
Language eng
Subjects 030406 Proteins and Peptides
100302 Bioprocessing, Bioproduction and Bioproducts
030603 Colloid and Surface Chemistry
Formatted abstract
Surfactants are molecules which stabilise the interface between two immiscible phases such as air and water, therefore enabling the formation of kinetically-stable foams. Their use encompases applications as broad as household detergents, frothing agents for minerals extraction, and food stabilisers, resulting in a global industry that was valued at > US$20 billion in 2010. Most surfactants in production today are of the chemical type, and are derived from petrochemical sources. In light of increasing environmental concerns, there is a drive and opportunity for the development of greener, renewable and biodegradable surfactants. Peptide-based biosurfactants are both renewable and biodegradable and therefore offer a promising alternative, however are too expensive when produced at relevant scales, and are a new technology which is not yet well understood. This thesis aimed to address this second issue by using designed peptide and protein sequences as tools to study the link between properties at the molecular, meso (interfacial), and macro (foam) scales. In order to improve understanding of the role of molecular properties on interfacial rheology, a commonly-studied meso-scale property, a method was developed to improve the characterisation of interfacial extensional stress-strain curves. The method was based on an approach widely applied to viscoelastic 3D polymers, highlighting the analogy between such systems and interfacially-adsorbed protein/peptide films. A concatameric biosurfactant protein (a repeating sequence of four identical peptides) was introduced, and shown to have good expression, purification, and functional properties. The bulk four-helix bundle design of this biosurfactant protein shows potential as an approach for overcoming cost-barriers currently limiting biosurfactant application. Interfacial adsorption and rheology (meso-scale properties) of the biosurfactant protein were compared to that of its peptide monomer, in order to isolate the effects of molecule size and bulk structuring (molecular-scale properties). Acid hydrolysis of the biosurfactant protein produced peptide variants similar to its repeating monomer unit, however with a significant extent of glutamine deamidation. Due to alteration of surface charge structure (meso-scale), the effect of deamidation on foaming behaviour was much more significant than that of molecule size, as observed by comparing the protein to its monomer and hydrolysis products. Bulk aggregation, induced by the addition of ZnSO4, had the effect of stabilising foams in some cases but destabilising foams in others; this appeared to be related to biosurfactant net charge. By using strategically-designed protein and peptide biosurfactant sequences, this thesis contributes new insights into the relationship between molecular, meso, and foam scale properties of such biosurfactants, a link which is currently unestablished but necessary for progression of biosurfactant technology.
Keyword Biosurfactant
Interfacial rheology

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Created: Mon, 06 Aug 2012, 14:36:39 EST by Mirjana Dimitrijev on behalf of Scholarly Communication and Digitisation Service