## 1 Introduction  
Microbial transglutaminase (MTGase), used as a protein modifier enzyme in the food industry, and in mediated bioconjugation for its extraordinary cross-linking ability in industrial applications [1], is obtained commercially from _Streptoverticillium mobraane_ by fermentation. MTGase exhibits optimum activity at pH 5-8 and at 50 \({}^{\circ}\)C. It can also maintain its activity at some temperatures slightly above freezing point [2, 3, 4]. Furthermore, MTGase does not need any cofactor to show activity. The Food and Drugs Administration (FDA) has included this enzyme on the GRAS (Generally Recognized as Safe) list since 1998 [4]. Some studies have been conducted on the use of microbial transglutaminase in meat products such as restructured/formed dry-cured ham [5, 6, 7, 8], restructured cooked ham [9, 10], cooked ham [11], cooked/restructured pork shoulder [12], chicken doner kebab [13], frankfurter [14], dry-cured lamb ham [15] and pastrma [16].  
Pastrma (a traditional Turkish dry-cured meat product), classified as an intermediate moisture food product, is produced from the whole muscle of certain parts of beef or water buffalo carcasses. The two important groups of microorganisms in pastrma production are lactic acid bacteria and Gram (+)-catalase (+) cocci (mainly coagulase negative staphylococci). In pastrma, the pH and water activity values usually range from 5.50 to 6.00 and 0.85 to 0.90, respectively. Pastrma production consists of the following processes: first curing, then drying, after that pressing and finally covering the meat with a pasta called cemen [17; 18]. Pastrma has a distinctive characteristic regarding its production conditions, production time and raw material when considering similarly processed meat products such as Rohschinken, jambo de Savoie, dry-cured ham, lacon, proscitutto di Parma, Lachschinken, country-style ham and dry-cured pork shoulder. Moreover, the smoking process is not applied in the production process of pastrma [18]. In the dry-curing process, which is the first stage of pastrma production, nitrate and/or nitrite are used together with salt. Before this stage, a process called incision is applied in order for the curing components to diffuse well in the meat [17; 18]. In the incision, the blade is held parallel to the muscle fibers and at an angle of 45\({}^{\circ}\), and cuts are made in a series in the meat [18]. This application may cause textural defects in the final product, and this situation affects consumer preference negatively. The effects of using transglutaminase on both these textural defects and the quality characteristics of traditional pastrma types (surt, kusgomu, sekerpare, kurek and bohca) were investigated during cold storage under modified atmosphere conditions. However, in this study, only the effects of a 0.5% level of MTGase were investigated [16]. On the other hand, the effects of different levels (0.05-0.8%) of MTGase in restructured dry-cured hams were investigated [5; 6; 8]. In a study conducted on dry-cured ham, 1% MTGase was also used [7]. The effects of different transflataminase levels on the quality characteristics of pastrma have not yet been investigated. The aim of this study was to determine the effects of different MTGase levels (0%, 0.25%, 0.50% and 1%) on pH, a\({}_{\text{w}}\), instrumental color, thiobarbituric acid reactive substances (TBARS), volatile compound profile, free amino acid composition and some textural parameters (stress-relaxation and cutting tests) of pastrma (surt type) produced under controlled conditions.