In vitro digestibility and rheological properties of caseinates treated by an oxidative system containing horseradish peroxidase, glucose oxidase and glucose

Sodium caseinate was modified by an oxidative system comprising horseradish peroxidase (HRP), glucose oxidase (GO) and glucose in either a one-step or a two-step protocol. In the former, a sodium caseinate suspension was treated simultaneously with HRP, GO and glucose, whereas in the latter the suspension was treated first with GO and glucose, then subsequently with HRP. Fluorescence spectroscopy or sodium dodecylsulphate-polyacrylamide gel electrophoresis analysis confirmed dityrosine or polypeptide formation in the treated caseinates, respectively. The treated caseinates had higher surface hydrophobicity and lower in vitro digestibility than the original caseinate, as well as a higher apparent viscosity, elastic modulus and viscous modulus. Caseinate treated with the one-step method contained more cross-linked polypeptides and higher surface hydrophobicity, apparent viscosity, elastic and viscous modulus higher and lower in vitro digestibility than caseinate treated with the two-step method. The oxidative system showed its potential to modify functional properties of food proteins.