New insight into enzymatic cross-linking of globular proteins: from nanostructure to functionality
Sariçay, Y. - \ 2014
University. Promotor(en): Martien Cohen Stuart, co-promotor(en): Renko de Vries; Peter Wierenga. - Wageningen : Wageningen University - ISBN 9789462571211 - 217
enzymatische cross-linking - eiwitten - chemische reacties - alfa-lactalbumine - lactalbumine - nanotechnologie - enzymatic cross-linking - proteins - chemical reactions - alpha-lactalbumin - lactalbumin - nanotechnology
In last two decades, enzymatic cross-linking of proteins has a growing interest in food technology for better tailoring protein functionality. However, the relation between physical and functional properties of enzymatically cross-linked proteins has been hardly addressed so far. The aim of this thesis was to elucidate the effect of enzymatic protein cross- linking on the physical and functional properties of protein nanoparticles at multiple lengthscale. In the first part of this thesis, as a model system, the enzymatic cross-linking of globular whey protein apo-α-lactalbumin (α-LA) by horseradish peroxidase (HRP) was discussed in details. In comparison with HRP, in the second part of the thesis, we also addressed to what extent both laccase (LC) (from trametes versicolor) and tyrosinase (TYR) (from agaricus bisporus) differ in catalyzing oxidative cross-linking of α-LA. Both HRP and LC were capable of creating self-similar large α-LA nanoparticles that have an open architecture at similar lengthscales whereas TYR led to the formation of α-LA oligomers only. All HRP-, LC-nanoparticles and TYR-oligomers exhibited a high extent of secondary structure content preserved whereas their almost all tertiary structure was lost upon enzymatic cross-linking. HRP-catalyzed cross-linking of α-LA resulted in more hydrophilic nanoparticles than LC-cross-linked α-LA nanoparticles. Whereas both HRP- and LC-nanoparticles exhibited very high colloidal and thermal stability against protein aggregation at pH 5.8 and 7.0, HRP- nanoparticles were more stable than LC-nanoparticles upon heating and in the presence of dithiothreitol (DTT). This suggests that, unlike HRP- nanoparticles, not only the dityrosine bonds but also disulfide cross-linking stabilizes LC-nanoparticles. Dilute dispersions of HRP-nanoparticles exhibited a high viscosity and a hydrophilic nature. As these dispersions were concentrated, they jammed above their critical overlapping concentration and thus created physical transparent protein hydrogels at relatively low protein concentration (4% w/v). These properties of HRP- nanoparticle dispersions offer high thickening properties that are comparable with polysaccharide in food applications as protein-based thickeners.
Peroxidase-mediated cross-linking of bovine a-lactalbumin
Heijnis, W.H. - \ 2010
University. Promotor(en): Harry Gruppen, co-promotor(en): Willem van Berkel; Peter Wierenga. - S.l. : s.n. - ISBN 9789085858324 - 120
alfa-lactalbumine - peroxidase - schuimen - schuim - enzymatische cross-linking - alpha-lactalbumin - foaming - foams - enzymatic cross-linking
The research presented in this thesis aimed at controlling the horseradish peroxidase-catalyzed cross-linking of bovine α lactalbumin and the implications of this cross-linking for the foam stabilizing properties. Attention is also given to microreactors and their potential to control the enzymatic cross-linking of proteins.
The proportion of cross-linked α lactalbumin dimers, oligomers and polymers could be directed by variations in ionic strength, pH, H2O2, and temperature.
Covalent α lactalbumin dimers were proteolytic digested. FTMS analysis of the peptide mixture resulted in the unambiguous identification of a Tyr18 Tyr50 dityrosine cross-link. Structural modeling of the α lactalbumin dimer indicated that favorite electrostatics direct the selectivity of the cross-linking reaction and, hence, the formation of an intermolecular cross-link. The formation of the Tyr18-Tyr50 cross-link suggests that further cross-linking of α lactalbumin dimers enables the formation of linear polymers.
A microreactor system was set up to obtain control over the reaction conditions to cross-link proteins. The enzymatic cross-linking of α lactalbumin was analyzed as a function of enzyme and substrate(s) feed. The increase in absorption at 318 nm due to dityrosine formation was found to be directly correlated to the decrease in monomeric α lactalbumin and was shown to be a good tool to monitor the cross-linking reaction.
The α lactalbumin oligomers produced were investigated for their foam stabilizing properties. Cross-linked α lactalbumin oligomers did not stabilize foams, whereas α lactalbumin polymers acted as an anti-foam, destabilizing other protein films.
Detailed characterization of adsorption-induced protein unfolding
Engel, M.F.M. - \ 2004
University. Promotor(en): Ton Visser; Sacco de Vries, co-promotor(en): Carlo van Mierlo. - [S.l.] : S.n. - ISBN 9085040019 - 125 p.
runderserumalbumine - alfa-lactalbumine - moleculaire structuur - grensvlak - fysische eigenschappen - adsorptie - spectroscopie - bovine serum albumin - alpha-lactalbumin - molecular conformation - interface - physical properties - adsorption - spectroscopy
|Soluble complexes of gum arabic with alfa-lactalbumin and beta-lactoglobulin above the protein isoelectric point: analysis in terms of charge patches
Vries, R.J. de - \ 2003
In: Food Colloids, Biopolymers and Materials / Dickinson, E., Vliet, T. van, Cambridge : Royal Society of Chemistry (Special Publications 284) - ISBN 0854048715 - p. 329 - 344.
alfa-lactalbumine - bèta-lactoglobuline - arabische gom - iso-elektrisch punt - colloïdale eigenschappen - macromoleculen - alpha-lactalbumin - beta-lactoglobulin - gum arabic - isoelectric point - colloidal properties - macromolecules