Eur Food Res Technol (2007) 225:865–871 DOI 10.1007/s00217-006-0493-8 ORIGINAL PAPER Partial characterization of peroxidase from the leaves of thymbra plant (Thymbra spicata L. var. spicata) Serap Do˘ gan · Pınar Turan · Mehmet Do˘ gan · Oktay Arslan · Mahir Alkan Received: 29 May 2006 / Revised: 19 September 2006 / Accepted: 28 September 2006 / Published online: 29 November 2006 C  Springer-Verlag 2006 Abstract Peroxidase (EC 1.11.1.7; donor: hydrogen- peroxide oxidoreductase) catalyses the oxidation of var- ious electron donor substrates (e.g. phenols, aromatic amines). In this study, the peroxidase was extracted from Thymbra spicata L. var. spicata and, then partially puri- fied with (NH 4 ) 2 SO 4 precipitation and dialysis. The sub- strate specificity of peroxidase was investigated using 2,2 ′ - azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) (ABTS), o-dianisidine, o-phenylenediamine, catechol and guaiacol as substrates. Furthermore, the effects of buffer concentration, pH, temperature and thermal inactivation on enzyme activity were also studied. The results obtained have shown that (i) the best substrate is o-dianisidine, followed by ABTS, cat- echol, guaiacol and o-phenylenediamine, respectively; (ii) the best buffer concentration is 40 mM for o-dianisidine and catechol, 10 mM for ABTS and guaiacol, and 100 mM for o-phenylenediamine; (iii) optimum pH is 2.5 for ABTS and o-phenylenediamine, 6.0 for o-dianisidine, and 7.0 for cat- echol and guaiacol; (iv) optimum temperature is 20 ◦ C for catechol, 40 ◦ C for ABTS, guaiacol and o-dianisidine, and 50 ◦ C for o-phenylenediamine; and (v) the enzyme activity in the thermal inactivation experiments was enhanced with in- crease in temperature with o-dianisidine as a substrate while its activity decreased with o-phenylenediamine. S. Do˘ gan () Department of Biology, Faculty of Science and Literature, Balikesir University, 10145 Balikesir, Turkey e-mail: sdogan@balikesir.edu.tr P. Turan · M. Do˘ gan · O. Arslan · M. Alkan Department of Chemistry, Faculty of Science and Literature, Balikesir University, 10145 Balikesir, Turkey Keywords Thymbra spicata L. var. spicata . Peroxidase . Thymbra leaves . pH . Thermal inactivation . Substrate specificity Introduction Thymbra spicata L. var. spicata belonging to the Lamiaceae family grows wild in some eastern Mediterranean countries. The family is represented by 45 genera, 546 species and 730 taxa in Turkey. The rate of endemism in the family is 44.2% [1]. The leafy part of thymbra has been added to meat, fish and food products for many years due to their organolep- tic properties and are often consumed as herbal teas [2]. Lamiaceae species possess a variety of activities, including antiinflammatory, antioxidant, antibacterial, antifungal, and antiviral properties [3]. They have also been highly valued for their use as antimicrobials due to their essential oils [4, 5]. Furthermore, the thymbra in most countries has been used in medicine industries as a raw material because of its valuable properties. All of these properties make thymbra very impor- tant as a medicine of future. An important food product in the east Anatolian part of Turkey is herb cheese. A number of herbs such as Thymus sp., Allium sp., and Ferula sp. are used in making herb cheese [6]. In addition, the most widely used one is Thymbra. The antibacterial activities of spices and essential oils have been known for a long time, and a number of research projects on the antimicrobial effect of oregano, thymbra and savory plants, essential oils and their derivatives have been reported [2, 4, 7–9]. These herbs are added into the vat to get the desired flavour for the cheese. The pickled herb is also sold in markets, so they can be found throughout the year. Furthermore, the dried leaves of these plants have been used as a spice and as a herbal tea [6, 10]. This plant contains an enzyme called peroxidase (POD). This Springer