Abstract

Horseradish peroxidase (HRP, EC 1.11.1.7) was used in this study to catalyze oxidative cross-linking of casein in the presence of hydrogen peroxide and cross-linker ferulic acid. Cross-linking of casein was demonstrated by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and ultraviolet absorbance analysis. Oxidative cross-linked casein mediated by hydrogen peroxide and ferulic acid was prepared at casein concentration of 5% (w/ w), HRP addition of 3 mkat·g^-1 proteins, ferulic acid addition of 6 mmol·l^-1, 3% (w/w) H₂O₂ addition of 1 ml, reaction temperature 37°C and reaction time 3 h. Analysis results showed that the emulsifying activity index and emulsifying stability index of cross-linked caseinprepared were enhanced compared to that of untreated casein totally. Microstructure of chemical acid-induced gel of cross-linked casein was observed under scanning electron microscopy and appeared to be more compact and uniform than that of casein. Hydrogen peroxide and ferulic acid-mediated oxidative cross-linking of casein catalyzed by horseradish peroxidase might have a beneficial to the emulsifying property or gelation of casein.

Key words: Casein, horseradish peroxidase, cross-linking, emulsifying property, ferulic acid, acidified gel, microstructure.

Abbreviation

HRP, Horseradish peroxidase; SDS-PAGE, sodium dodecyl sulfate - polyacrylamide gel electrophoresis; SPI, soybean protein isolate; EAI, emulsifying activity index; ESI, emulsion stability index; SEM, scanning electron microscopy.