Demonstration of anti-oxidant properties of mustard seed (Brassica juncea) protein isolate in orange juice

Previous research has shown that formulated and natural beverages containing mixtures of anti-oxidants can produce stable levels of hydrogen peroxide (H₂O₂). The aim of this study was to demonstrate the ultimate anti-oxidant effects of proteins for suppressing H₂O₂, using a protein extract from mustard seed (Brassica juncea). The mustard seed protein isolate (MPI) contained ∼51% protein, and 6.4 mg GAe/g TS of total reducible substances, presumably representing secondary metabolites, including polyphenolics. Dose-dependent suppression of H₂O₂ (present at 110 µM and 550 µM), in fresh and thermally-processed orange juice was complete in the presence of 0.1 mg/mL MPI after 24 hr, with slightly higher anti-oxidant efficacy than the fruit juice-derived reference protein, thaumatin. The combination of thiol-rich amino acid (methionine and cysteine)-containing proteins and other anti-oxidant species in the MPI were highly effective for inhibiting autoxidation-mediated production of H₂O₂ in orange juice, and may be useful for other manufactured beverages.