ORIGINAL PAPER Characterization and inhibition of Rosmarinus officinalis L. polyphenoloxidase Serap Dog ˘an • Mehmet Emin Diken • Yasemin Turhan • U ¨ mran Alan • Mehmet Dog ˘an • Mahir Alkan Received: 15 January 2011 / Revised: 3 March 2011 / Accepted: 22 March 2011 / Published online: 17 June 2011 Ó Springer-Verlag 2011 Abstract Polyphenoloxidase (PPO) from Rosmarinus officinalis L. was fractionated by ammonium sulfate ((NH 4 ) 2 SO 4 ) precipitation and dialysis, and then some of its kinetic properties such as optimum pH and temperature, substrate specificity, thermal inactivation, and inhibition were investigated using 4-methylcatechol, catechol, and pyrogallol as substrates. The protein content of Rosmarinus officinalis L. extracts was determined according to Bradford’s method. Kinetic parameters, K m and V max , were calculated from Lineweaver–Burk plots. According to V max /K m ratio, 4-methylcatechol was the most suitable substrate. The optimum temperature and pH values were 20, 30 and 30 °C, and 7, 8 and 8 for 4-methylcatechol, catechol, and pyrogallol substrates, respectively. The thermal inactivation of PPO was investigated at 35, 55, and 75 °C. The enzyme activity decreased with increasing temperature. The effect of different inhibitors on partly purified Rosmarinus officinalis L. PPO was spectrophoto- metrically investigated. For this purpose, ascorbic acid and L-cysteine were used to inhibit the activity of Rosmarinus officinalis L. PPO at different concentrations. From the experimental results, it was found that L-cysteine is a more effective inhibitor than ascorbic acid due to lower K i values. Keywords Rosmarinus officinalis L. Á Polyphenoloxidase Á Substrate specificity Á Optimum pH and temperature Á Inactivation Á Inhibition Introduction Browning in the plants is a major problem in the food industry and is believed to be one of the main causes of quality loss during postharvest handling and processing. The mechanism of browning in plants is well characterized and is mainly enzymatic in origin [1]. Two of the most important enzymes involved in this mechanism are poly- phenoloxidase (PPO) and peroxidase [2]. PPOs are a group of copper-containing enzymes catalyzing the oxidation of polyphenolic compounds in the presence of molecular oxygen which are responsible for enzymatic browning reactions occurring during harvesting, handling, process- ing, and storage of many plant materials. They possess three different activities connected with each other as (1) catechol oxidase or o-diphenol: oxygen oxidoreductase (EC 1.10.3.1); (2) laccase or p-diphenol: oxygen oxidore- ductase (EC 1.10.3.2); and (3) cresolase or monophenol monooxygenase (EC 1.18.14.1) [3–5]. PPO activity varies among the plants [6]. PPO has been extensively investigated in a variety of tissues in many plants such as lettuce [7], aubergine [8], Origanum [9], apricot [10], Thymus species [11–13], and Salvia [14]. Rosemary, (Rosmarinus officinalis L.), a member of the family Labiatae, is an important medicinal and aromatic plant and grows wild in the Mediterranean basin, where they are appreciated for their aromatic, antimicrobial, and antioxidant properties [15, 16]. Aydemir [17] was partly purified by (NH 4 ) 2 SO 4 precipitation and dialysis, and some kinetic properties of Rosmarinus officinalis L. PPO were S. Dog ˘an (&) Á M. E. Diken Á U ¨ . Alan Department of Biology, Faculty of Science and Literature, Balikesir University, 10145 C ¸ ag ˘ ıs ¸-Balikesir, Turkey e-mail: sdogan@balikesir.edu.tr Y. Turhan Á M. Dog ˘an Á M. Alkan Department of Chemistry, Faculty of Science and Literature, Balikesir University, 10145 C ¸ ag ˘ ıs ¸-Balikesir, Turkey 123 Eur Food Res Technol (2011) 233:293–301 DOI 10.1007/s00217-011-1504-y