Characterization of polyphenoloxidase of prawns (Penaeus japonicus). Alternatives to inhibition: additives and high-pressure treatment

Polyphenoloxidase (PPO) presented different specific activities at different locations in the imperial tiger prawn (Penaeus japonicus), with the highest values in the carapace. The procedure achieved a degree of purification, close to 70 times, increasing relative activity by means of ammonium sulphate (0–40%) saturation. Isoelectric focusing showed two bands around pI 5.0. The optimum temperature for PPO reaction with DOPA was between 40 and 60°C, however thermal stability was greatest at temperatures below 35°C. The enzyme was most active at pH 5 and 8, but most stable at basic pH. Pressurization of the enzymatic extract was assayed within a range of 0.1–400 MPa, for 10 min at <10°C. Pressure-induced inactivation was evident, particularly at 300–400 MPa. Total inhibition of the extract was achieved only with ascorbic acid and citric acid at pH 3.0. 80 μg/ml sulphite, 150 μg/ml of kojic acid, 1 g/l of 4-hexylresorcinol or 0.1 g/l of sodium benzoate was required for 80% inhibition.