Title
Importance of physical vs. chemical interactions in surface shear rheology
Author
Wierenga, P.A.
Kosters, H.
Egmond, M.R.
Voragen, A.G.J.
de Jongh, H.H.J.
TNO Kwaliteit van Leven
Publication year
2006
Abstract
The stability of adsorbed protein layers against deformation has in literature been attributed to the formation of a continuous gel-like network. This hypothesis is mostly based on measurements of the increase of the surface shear elasticity with time. For several proteins this increase has been attributed to the formation of intermolecular disulfide bridges between adsorbed proteins. However, according to an alternative model the shear elasticity results from the low mobility of the densely packed proteins. To contribute to this discussion, the actual role of disulfide bridges in interfacial layers is studied. Ovalbumin was thiolated with S-acetylmercaptosuccinic anhydride (S-AMSA), followed by removal of the acetylblock on the sulphur atom, resulting in respectively blocked (SX) and deblocked (SH) ovalbumin variants. This allows comparison of proteins with identical amino acid sequence and similar globular packing and charge distribution, but different chemical reactivity. The presence and reactivity of the introduced, deblocked sulfhydryl groups were confirmed using the sulfhydryl-disulfide exchange index (SEI). Despite the reactivity of the introduced sulfhydryl groups measured in solution, no increase in the surface shear elasticity could be detected with increasing reactivity. This indicates that physical rather than chemical interactions determine the surface shear behaviour. Further experiments were performed in bulk solution to study the conditions needed to induce covalent aggregate formation. From these studies it was found that mere concentration of proteins (to 200 mg/mL, equivalent to a surface concentration of around 2 mg/m2) is not sufficient to induce significant aggregation to form a continuous network. In view of these results, it was concluded that the adsorbed layer should not be considered a gelled network of aggregated material (in analogy with three-dimensional gels formed from heating protein solutions). Rather, it would appear that the adsorbed proteins form a highly packed system of proteins with net-repulsive interactions. © 2005 Elsevier B.V. All rights reserved.
Subject
Nutrition
Food technology
Air-water interface
Chemical modification
Ovalbumin
Surface rheology
Thiolation
Elasticity
Gels
Proteins
Shear stress
Surface chemistry
Air-water interface]
Ovalbumin
Surface rheology
Thiolation
Rheology
disulfide
ovalbumin
adsorption
animal
article
chemistry
chicken
elasticity
flow kinetics
protein conformation
surface property
Adsorption
Animals
Chickens
Disulfides
Elasticity
Ovalbumin
Protein Conformation
Rheology
Surface Properties
To reference this document use:
http://resolver.tudelft.nl/uuid:5a53d30d-41dd-451a-8630-d6b5f1c21be4
DOI
https://doi.org/10.1016/j.cis.2005.11.001
TNO identifier
239137
ISSN
0001-8686
Source
Advances in Colloid and Interface Science, 119 (2-3), 131-139
Document type
article