Structural characteristics, emulsifying and foaming properties of laccase-crosslinked bovine α-lactalbumin mediated by caffeic acid

Abstract

In this study, laccase (LA) was chosen as a commonly employed enzyme to research the impacts of enzyme-catalyzed crosslinking (polymerization) on the structural, emulsifying and foaming properties of bovine α-lactalbumin (α-LA) in the presence of caffeic acid (CA). High pressure size exclusion chromatography (HPSEC) and sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated the formation of α-LA aggregates (dimers, trimers, and polymers) by LA-induced crosslinking with CA, consistent with the particle size distribution results. LA-induced treatment exhibited pronounced influences on the conformation, secondary and tertiary structure of α-LA, as confirmed by circular dichroism (CD), and fluorescence spectroscopy. For α-LA-LA-CA, α-helix content was progressively decreased from 33.3% (0 h) to 24.7% (24 h). LA-catalyzed crosslinking resulted in the exposure of interior hydrophobic groups, and the increase of zeta-potential values of α-LA. Apparent viscosity of α-LA was considerably enhanced by LA-induced crosslinking with CA. The emulsifying activity and stability of α-LA can be considerably improved with LA-catalyzed crosslinking with CA except at 24 h incubation time. Compared with controls, LA-catalyzed polymerizations of α-LA molecules with CA led to the increase of foaming activity and stability regardless of incubation time. After 24 h incubation, the foaming stability (FS) of α-LA was 81.0%, whereas the value was 88.0% for α-LA-LA-CA. This research indicates that LA-induced modification possesses great potential in ameliorating the emulsifying and foaming capacities of α-LA. • Laccase led to the significant polymerization of α-lactalbumin with caffeic acid. • Laccase-catalyzed crosslinking led to the changes of the structure of α-lactalbumin. • Laccase-catalyzed crosslinking increased the emulsifying properties of α-lactalbumin. • Laccase-catalyzed crosslinking increased the foaming activity of α-lactalbumin. • Laccase-crosslinked α-lactalbumin aggregates showed potential as functional ingredients.