To obtain a PPO-enriched fraction and to remove high molecular
weight proteins from the sample, ammonium sulphate precipitation
was used and different concentrations of ammonium
sulphate were tested to achieve optimum extraction of PPO from
the grape juice (data not shown). The resulting enzyme extract obtained
was 11.43 ± 0.42 U min1 mg protein1 and approximately
37-fold with 83% recovery of the grape PPO activity