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 degreesC, however thermal stability was greatest at temperatures below 35 degreesC. 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 or 0.1-400 MPa, for 10 min at < 10 degreesC. 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 mug/ml sulphite, 150 mug/ml of kojic acid, 1 g/l of 4-hexylresorcinol or 0.1 g/l of sodium benzoate was required for 80% inhibition. (C) 2001 Elsevier Science Ltd. All rights reserved.