Cross-linking of whey proteins by enzymatic oxidation

The applicability of enzymatic oxidation for polymerization of whey proteins [in whey protein isolate (WTPI)] has been investigated, using three different oxidoreductases with different specificities (microbial peroxidase, fungal laccase, and bovine plasma monoamine oxidase) to induce oxidation. All three enzymes mere able to induce formation of oligomers and polymers of whey proteins under various conditions, but their modes of action seemed to diverge, as they affected the two main whey proteins beta-lactoglobulin and alpha-lactalbumin differently: for example, peroxidase (in the presence of hydrogen peroxide) mainly acted on beta-lactoglobulin, laccase (in the presence of chlorogenic acid) mainly worked on a-lactalbumin, and monoamine oxidase acted somewhat on both proteins. None of the oxidoreductases induced full polymerization of WPI, as opposed to cross-linking with microbial transglutaminase with a reductant present, which polymerizes the whey proteins fully. None of the oxidoreductases could induce gelling of WPI solutions with 10-20% protein.