ABSTRACT
Amyloid-like fibrils from ß-lactoglobulin have potential as efficient thickening and gelling agents for food and biomedical applications, but the link between fibril morphology and bulk viscosity is poorly understood. We examined how lyophilization and rehydration affects the morphology and rheological properties of semiflexible (i.e., straight) and highly flexible (i.e., curly) fibrils, the latter made with 80 mM CaCl(2). Straight fibrils were fractured into short rods by lyophilization and rehydration, whereas curly fibrils sustained little damage. This was reflected in the viscosities of rehydrated fibril dispersions, which were much lower for straight fibrils than for curly fibrils. Lyophilized straight or curly fibrils seeded new fibril growth, but viscosity enhancement due to seeding was negligible. We believe that the increase in fibril concentration caused by seeding was counterbalanced by a decrease in fibril length, reducing the ability of fibrils to form physical entanglement networks.
Subject(s)
Milk Proteins/chemistry , Milk Proteins/ultrastructure , Amyloid/ultrastructure , Calcium Chloride/pharmacology , Freeze Drying , Lactoglobulins/chemistry , Microscopy, Electron, Transmission , Rheology , Viscosity , Water/chemistry , Whey ProteinsABSTRACT
Self-assembly of amyloid-like nanofibrils during heating of bovine whey proteins at 80 °C and pH 2 is accelerated by the presence of NaCl and/or CaCl(2), but the rheological consequences of accelerated self-assembly are largely unknown. This investigation focused on the impact of CaCl(2) on the evolution of rheological properties and fibril morphology of heated whey protein isolate (WPI), both during self-assembly at high temperature and after cooling. Continuous rotational rheometry of heated 2% w/w WPI showed a nonlinear effect of CaCl(2) on the viscosity of fibril dispersions, which we attributed to effects on fibril flexibility and thus the balance between intrafibril and interfibril entanglements. Small-amplitude oscillatory measurements made in situ during heating of 10% w/w WPI at 80 °C suggest that CaCl(2) is not involved in either fibril structure or gel structure, and this was confirmed with dialysis experiments.
Subject(s)
Biomimetic Materials/chemistry , Milk Proteins/chemistry , Nanofibers/chemistry , Nanotechnology/methods , Amyloid/analysis , Amyloid/chemistry , Amyloid/ultrastructure , Animals , Biomimetic Materials/analysis , Calcium Chloride/chemistry , Cattle , Dialysis , Hot Temperature , Hydrogen-Ion Concentration , Microscopy, Electron, Transmission , Milk Proteins/analysis , Nanofibers/analysis , Nanofibers/ultrastructure , Rheology , Sodium Chloride/chemistry , Viscosity , Whey ProteinsABSTRACT
UNLABELLED: Apparent viscosity and frequency sweep (G', G'') data for sodium caseinate dispersions with concentrations of approximately 18% to 40% w/w were obtained at 20 degrees C; colloidal glass behavior was exhibited by dispersions with concentration >or=23% w/w. The high concentrations were obtained by mixing frozen powdered buffer with sodium caseinate in boiling liquid nitrogen, and allowing the mixtures to thaw and hydrate at 4 degrees C. The low-temperature G'-G'' crossover seen in temperature scans between 60 and 5 degrees C was thought to indicate gelation. Temperature scans from 5 to 90 degrees C revealed gradual decrease in G' followed by plateau values. In contrast, G'' decreased gradually and did not reach plateau values. Increase in hydrophobicity of the sodium caseinate or a decrease in the effective volume fraction of its aggregates may have contributed to these phenomena. The gelation and end of softening temperatures of the dispersions increased with the concentration of sodium caseinate. From an Eldridge-Ferry plot, the enthalpy of softening was estimated to be 29.6 kJ mol(-1). PRACTICAL APPLICATION: The results of this study should be useful for creating new products with high concentrations of sodium caseinate.
