The quality alterations of rainbow trout mince treated with transglutaminase Pinar Yerlikaya a, * , Hanife Aydan Yatmaz b , Nalan Gokoglu a , Ilknur Ucak c a Akdeniz University, Fisheries Faculty, Antalya, Turkey b Akdeniz University Food Safety and Agricultural Research Center, Antalya, Turkey c Omer Halisdemir University, Faculty of Agricultural Sciences and Technologies, Nigde, Turkey article info Article history: Received 24 October 2016 Received in revised form 12 June 2017 Accepted 14 June 2017 Available online 14 June 2017 Keywords: Transglutaminase Rainbow trout Shelf life Cold storage abstract The use of protein restructuring enzyme transglutaminase (TGase) for extending the shelf-life of rainbow trout mince was determined during refrigerated storage. TGase added into the fish mince in the pro- portions of 0.0%, 0.2%, 0.5% and 1.0% and the quality alterations were evaluated in terms of chemical, microbiological and sensory parameters. The scores of TVB-N and TMA-N, fish spoilage indicators, of the fish mince treated with TGase had lower levels than control samples. It was recorded that the progress in total free amino acids was suppressed with the addition of TGase. The increase in enzyme concentration met successful results in hindering the growth of total psychrophilic bacteria and coliform bacteria. The best results were obtained with the addition of TGase in the concentration of 1.0%. Overall, utilization of TGase can be a useful tool for seafood processing technology to achieve products with extended shelf life. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction The degradation of proteins and lipids, microbiological spoilage, textural alterations, undesired color, flavor and odour changes takes place rapidly in marine derived organisms. Therefore, the researches dealing with quality protection and extending shelf life of seafood continues intensively. It is known that connective tissue of the fish is weaker than land animals. Less fiber bonds, holding together the muscle, lead to soften the texture of fish and allow a favorable ambient for microorganisms (Gokoglu & Yerlikaya, 2015, p. 233). Various enzymes are used to improve some functional characteristics of proteins such as straightening the structure, improving gel-forming ability, water holding capacity and thermal stability. The enzyme transglutaminase (TGase) promotes the polymeri- zation of proteins and catalyzes an acyl transfer between the g- carboxamide group of glutamine and a primary amine such as the 3-amine group of lysine leading to the formation of isopeptide bonds (Grossman, Wefers, Bunzel, Weiss, & Zeeb, 2017). Chambi and Grosso (2006) reported that TGase not only used in the cross-linking of one single type of protein but also applied to the glutamines and lysine of two different types of protein, resulting in the formation of heteropolymers. By coupling two proteins with different structures, new functionalities created, but it is very difficult to ensure that two different proteins are actually coupled and not only large polymers of the separate protein are formed. Covalent cross-links between different proteins cause complex polymeric protein structures leading to changes in physical, chemical and nutritional characteristics of proteins. Usage of the enzyme leads to improvements in the solubility, thermal stability, syneresis, emulsfying properties, gel forming ability and increase water-binding capacity of food proteins (Gaspar & de Goes-Favoni, 2015). TGase was reported to enhance protein stability and increase protein resistance to chemical and proteolytic degradation (Cui,Yuan, Wang, Sun, Fan & Wang, 2017). Also, TGase forms a coating with better oxygen barrier. Recently, TGase is utilized in order to gain restructured meats, reduced-salt and reduced-fat products (Lee, Jang, Kang, & Chin, 2017; Martelo-Vidal, Fernen- dez-No, Guerra-Rodriguez, & Vazquez, 2016). With these proper- ties, TGase is predicted to have the potential to protect the initial quality and extend the shelf life of seafood. In this study, the effect of TGase on the chemical, physical, microbiological and sensory quality of fish mince was determined during refrigerated storage. * Corresponding author. Akdeniz University, Fisheries Faculty, Fish Processing Technology Department, Antalya, Turkey. E-mail address: pyerlikaya@akdeniz.edu.tr (P. Yerlikaya). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt http://dx.doi.org/10.1016/j.lwt.2017.06.034 0023-6438/© 2017 Elsevier Ltd. All rights reserved. LWT- Food Science and Technology 84 (2017) 815e820