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

•Low levels of hydrogen peroxide are variably produced in fruit juices.•As for orange juice, H2O2 production was inversely correlated with protein content.•Mustard seed protein isolate (MPI) was tested as an antioxidant (AOX) protein.•Production of H2O2 in fresh orange juice was completely inhibited by MPI after 24 hr.•Anti-oxidant efficacy of MPI was higher than the reference protein, thaumatin.•MPI may be a useful AOX and stabiliser of autoxidation in beverages.