Title
Limited changes in physical and rheological properties of peroxidase-cross-linked apo-α-lactalbumin after heat treatment
Author
Yunus Saricay, Peter A. Wierenga, Renko de Vries
Year
2016
Journal
Food Hydrocolloids
Abstract
The current study aims at elucidating the effect of heating on the physical properties of peroxidase-cross-linked (apo) α-lactalbumin (α-LA) aggregates with hydrodynamic radii (RH) of 25 nm–100 nm. We consider the effects of heating at a single protein level, and at a particle level for both dilute and dense dispersions of the cross-linked α-LA. From far-UV circular dichroism (CD) spectroscopy, we find that changes in the secondary structure of the cross-linked α-LA are limited upon heating but thermoreversible. Cross-linking already leads to a complete disappearance of all tertiary structure, and heating therefore leads to no further changes of tertiary structure as detected by near-UV CD. The surface hydrophobicity of the cross-linked α-LA, as probed using a fluorometric assay (ANSA), remains unchanged upon heating, whereas heating leads to a significant increase of surface hydrophobicity for uncross-linked α-LA. Prolonged heating leads to a moderate decrease of the particle size of α-LA aggregates, while heating does not affect its electrophoretic mobility. As a consequence of the insensitivity of the physical properties of the cross-linked α-LA to heating, we find that dilute dispersions of the cross-linked α-LA are stable against heat-induced aggregation over a wide range of pH values and salt concentrations. Furthermore, for dense dispersions of α-LA aggregates, that form physical hydrogels, we find that heating has a very limited impact on the rheology of the hydrogels. Our results may be of importance in designing heat-insensitive protein ingredients for novel food formulations.
Instrument
J-715
Keywords
Circular dichroism, Secondary structure, Thermal stability, Tertiary structure, Biochemistry, Food science