Background: In recent years, there has been an increasing interest in using food additives from natural sources to improve taste and also extend shelf life of semi-preserved food. The aim of this paper was to examine chemical and microbiological changes promoted by a traditional marinating process in rainbow trout fillets during frozen storage.

Methods: Fish fillets were immersed in traditional marinades and stored at -18 ^°C for 56 days. Some chemical and microbial characteristics like total volatile basic nitrogen (TVN), thiobarbituric acid (TBA), water holding capacity (WHC), pH, mesophilic, and psychrophilic bacterial count were performed with 7 days interval. The results were analyzed by repeated measure ANOVA test using SPSS 16.0 software.

Results: Data showed that although the value of TVN, TBA and, WHC in marinated samples were higher than control ones, but the differences were not significant (p>0.05). The numbers of bacteria in marinated samples were lower than control groups and for psychrophilic bacteria was significant (p<0.05).

Conclusion: The most obvious finding to emerge from this study is that rainbow trout flesh could be marinated and stored at -18 ^˚C for at least 56 days with no major unfavorable changes.