| 1. |
- Helstad, Kristina
(författare)
-
Casein imaging using atomic force microscopy
- 2003
-
Ingår i: International Symposium on Future Technologies for Food Production and Future Food Scientists, Proceedings. - 0280-9737. ; :162, s. 88-88
-
Konferensbidrag (refereegranskat)
|
|
| 2. |
- Helstad, Kristina, et al.
(författare)
-
Liquid droplet-like behaviour of whole casein aggregates adsorbed on graphite studied by nanoindentation with AFM
- 2007
-
Ingår i: Food Hydrocolloids. - : Elsevier BV. - 0268-005X. ; 21:5-6, s. 726-738
-
Tidskriftsartikel (refereegranskat)abstract
- AFM measurements in the force volume mode were performed over the total penetration depth for different positions on casein aggregates adsorbed to a graphite surface in a liquid cell. The stiffness of the force curves was correlated to indentation depths, layer depth and lateral position within the aggregates with the aim of arriving at a credible explanation for the shapes of the force curves. The commonly used Hertz-based models did not fit the experimental data. The ratio between the height and diameter of the adsorbed casein aggregates was found to be linear, suggesting surface energy dominated liquid droplet behaviour. To investigate the possibility, numerical simulations were performed using the Surface Evolver, an interactive finite element program for the study of surfaces shaped by surface tension and other energies. Simulated force curves were in good agreement with experimental findings, both with respect to slope as a function of indentation as well as describing the variation with indentation position on the aggregate due to interfacial and geometric effects. By comparing the simulated force curves to the measurement data it was found that there would have been an interfacial energy equivalent to 10 mJ/m2.
|
|
| 3. |
- Helstad, Kristina, et al.
(författare)
-
Nanorheological properties of casein
- 2005
-
Ingår i: Food Colloids: Interactions, Microstructure and Processing. - : The Royal Society of Chemistry. - 0260-6291. - 9780854046386 ; :298, s. 218-229
-
Konferensbidrag (refereegranskat)
|
|
| 4. |
- Helstad, Kristina
(författare)
-
Nanorheological Studies of Caseins
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To be able to improve the quality of dairy products and dairy processes, knowledge of casein molecules, casein micelles and casein aggregates is important. The rheological properties of casein products, casein gels and adsorbed layers of casein, have been widely investigated. However, the micellar properties of casein could, until recently, only be studied by ensemble methods such as dynamic light scattering and microscopic techniques, using dried or frozen samples. Nano-techniques, such as atomic force microscopy (AFM) have now made it possible to make complementary nanorheological measurements in a liquid environment. In this thesis, the observed nanorheological properties of single casein micelles, adsorbed thin casein layers and rennet-induced casein-retentate gels, are presented and discussed. The ultimate objective of these studies was to investigate the relationship between the local and the macroscopic rheological properties of cheese. The renneted casein gels were produced from casein retentate from ultrafiltration (UF), as another objective of the work was to increase our knowledge on cheese production from concentrated milk. Natural rennet-induced cheese is essentially a particulate calcium phosphate-para-casein matrix, composed of interconnected and overlapping strands of partially fused para-casein aggregates, which are in turn made up of para-casein micelles. To increase our knowledge on the nanorheological behaviour of the building blocks of the casein matrix, the first step was to investigate single adsorbed casein micelles. In the AFM measurements, the nanorheological properties of adsorbed casein micelles could not be explained by any model describing an elastic material (Paper I). Preliminary results led to investigations of the possibility that surface tension phenomena could explain the rheological behaviour. Results from computer modelling confirmed that essential features of such model corresponded to the relation between force and indentation from AFM measurements. A surface tension of 10 mNm-1 was calculated for a casein micelle attached to a hydrophobic graphite surfaces in a Ca-imidazole buffer environment (Paper III).
|
|
| 5. |
|
|
