ABSTRACT
We studied the stability of monodispersed polystyrene latex dispersions with protein fibrils at different concentrations at pH 2 using microscopy and diffusing wave spectroscopy. At low fibril concentrations, fibrils induced bridging flocculation due to the opposite charges between fibrils and the latex particles. At higher fibril concentration the dispersions were stabilized due to steric and/or electrostatic repulsion. Upon further increasing fibril concentration, we find that the dispersion is destabilized again by depletion interaction. At even higher fibril concentration, the dispersions are stabilized again. These dispersions have a higher stability compared to the dispersions without fibrils. Interestingly, these dispersions contain single particles and small clusters of particles that do not grow beyond a certain size. Although the stabilization mechanism is not clear yet, the results from microscopy and diffusing wave spectroscopy point in the direction of a kinetic barrier that depends on fibril concentration.
Subject(s)
Protein Aggregates , Whey Proteins/chemistry , Colloids , Diffusion , Latex , Microscopy , TemperatureABSTRACT
We report that the stability of an aqueous food grade fibril system upon pH change is affected by the presence of peptides that are formed during the process of fibril formation. We discuss several other relationships between food relevant properties and nano-scale characteristics, and compare these relationships for aqueous fibril systems to those of oil based fibril systems. In such fibril systems, dynamics, self-organisation, and sensitivity to external conditions, play an important role. These aspects are common to complex systems in general and define the future challenge in relating functional properties of food to molecular scale properties of their ingredients.
Subject(s)
Lactoglobulins/chemistry , Peptides/chemistry , Animals , Cattle , Electrophoresis, Polyacrylamide Gel , Food , Hydrogen-Ion Concentration , Lactoglobulins/ultrastructure , Microscopy, Electron, Transmission , Oils/chemistry , Protein Conformation , Protein Stability , Water/chemistryABSTRACT
Assembly of proteins or peptides into fibrils is an important subject of study in various research fields. In the field of food research, the protein fibrils are interesting candidates as functional ingredients. It is essential to understand the formation and properties of the fibrils for successful application of the fibrils in food products. This paper describes the impact of recent research on the general view of the process of fibril formation from ß-lg and the properties of the fibrils that are formed, leading to better control of applications for the fibrils. There is a need for a better understanding of the behavior of fibrils in more complex food systems.
Subject(s)
Food Analysis , Lactoglobulins/chemistry , Peptides/chemistry , Hot Temperature , Hydrogen-Ion Concentration , Protein ConformationABSTRACT
Recently it was found that protein hydrolysis is an important step in the formation of ß-lactoglobulin fibrils at pH 2 and elevated temperatures. The objective of the present study was to further investigate the influence of hydrolysis on the kinetics of fibril formation. Both the hydrolysis of ß-lactoglobulin and the growth of the fibrils were followed as a function of time and temperature, using SDS polyacrylamide gel electrophoresis and a Thioflavin T fluorescence assay. As an essential extension to existing models, the quantification of the effect of the hydrolysis on the fibrillar growth was established by a simple polymerization model including a hydrolysis step.
Subject(s)
Lactoglobulins/chemistry , Lactoglobulins/metabolism , Protein Multimerization , Benzothiazoles , Hydrogen-Ion Concentration , Hydrolysis , Kinetics , Models, Chemical , Peptide Fragments/chemistry , Peptide Fragments/metabolism , Protein Structure, Quaternary , Temperature , Thiazoles/metabolismABSTRACT
The length distribution of whey protein fibrils is important for application purposes. However, it is hard to influence the length distribution of whey protein fibrils during production. One way of influencing the length distribution of the mature fibrils is exposing them to an external field, like a flow field. In this research whey protein fibrils were exposed to elongational flow to fracture the fibrils. A simple experimental setup was used to establish a range of elongational strain rates. The length distribution of the fractured fibrils was determined using transmission electron microscopy and was shown to be controllable at relatively low strain rates.
Subject(s)
Milk Proteins/chemistry , Whey ProteinsABSTRACT
The molecule 4,5-dianilinophthalimide was recently found to be an efficient compound in disaggregating amyloid fibrils involved in the Alzheimer's disease. In this study we have investigated whether the compound 4,5-dianilinophthalimide was able to disaggregate fibrils derived from beta-lactoglobulin. In addition to a Thioflavin T fluorescence assay, flow-induced birefringence was used as an independent technique to measure the total length concentration of the fibrils. An additional advantage of the latter technique is that not only the total length concentration, but also the length distribution of the fibrils can be measured. The results from flow-induced birefringence showed that the total amount of fibrils and also the length distribution of the fibrils was not influenced by the addition of 4,5-dianilinophthalimide, even though this was suggested by the results of the Thioflavin T assay. The results of flow-induced birefringence were confirmed by rheological measurements and transmission electron microscopy. Our findings show that the use of a Thioflavin T assay in order to probe the possible disaggregating effect of certain compounds can give misleading results.
