Study of the effect of incorporation of Lactococcus lactis on the shelf life of rainbow trout fillet in glacial condition

The present study was conducted to evaluate the effect of Lactococcus lactis and its supernatant inclusion in order to increase the shelf-life of rainbow trout fillets stored in the refrigerator. Forty-five pieces of cultured rainbow trout with a total weight of 30 kg were prepared and were immersed in solutions of L. lactis with a dilution of 106 CFUml-1 and its supernatant with percentages of 30 and 60. In order to monitor the corruption procedure of fillet samples, chemical, microbial and sensory factors were analyzed on days 0, 5, 10 and 15. Control fillet samples had the highest and samples of fillets treated with pure bacteria contained the lowest number of microorganisms (P ≤0.05). The mean log of the number of psychrophilic, psychotrophic, mesophilic bacteria, yeast and mold per each gram of fillet was significantly lower than that of control (P ≤0.05). The effect of lactic acid bacteria and supernatant on the reduction of thiobarbituric acid and total volatile nitrogen at the end of storage time was significant (P ≤0.05) but were not significant on pH changes (P >0.05). The use of pure bacteria increased the points given to sensory factors. Samples treated with pure bacteria and supernatants were in good condition in term of taste at the end of the maintenance period while other treatments were unusable. Considering the results, L. lactis and its supernatant is suggested improving the shelf life of rainbow trout fillets.