Evaluation of the effect of nisin, sodium acetate and temperature on the quality of Ctenopharyngodon idella fillet inoculated with Staphylococcus aureus

Recently, the high nutritional value of fish and other seafood has caused continuously increasing their consumption in human diet. The meat quality can be decreased during storage due to physical, chemical and microbial changes. Thus, the different methods of preservation should be used to improve the quality and increase the shelf-life of the product. The application of bacteriocinins has been increased to extend the shelflife of food products. Nisin is a kind of bacteriocinins that is produced by Lactococcus lactis bacteria and used as food preservatives. It is accepted such as food additive in many food commodities. Bacteriocinins showed synergistic effects when they used with other antibacterial compounds such as natural preservatives and phenolic compounds. Literature review showed that the antibacterial compounds such as sodium acetate play an important role in preventing the growth of bacteria and increasing the shelf life of fish during different storage conditions. Conventional optimization procedures are performed by altering one parameter at a time and keeping all other parameters at fixed levels. However, these procedures are time consuming and require more experimental data sets. Recently, the use of an orthogonal array approach called ‘Taguchi method’ has been successfully examined in the different field of sciences. Therefore the aim of this research was to investigate the effects of nisin, sodium acetate and temperature on the growth of Staphylococcus aureus in Ctenopharyngodon idella fillet using Taguchi experimental design with an array L4 (23). The fresh Ctenopharyngodon idella with weight of 1 kg were purchased from market (Zabol, South east of Iran) and transported in isothermal iceboxes to the fish product processing laboratory at University of Zabol in 2016. The fishes were cleaned and filleted. Fillets after inoculated with Staphylococcus aureus (103 Log CFU/g) and added nisin (750 and 1000 IU/g) and sodium acetate (1 and 2 %) were stored in different temperatures (4 and 8 °C). Chemical parameters (pH, PV, TBA and TVB-N) and Staphylococcus aureus count were measured at 0, 3, 6 and 9 days. Microscopic analysis was used to observe the microstructure changes at end of storage. The experiments were performed in three replicates. The present study showed that the lowest and highest Staphylococcus aureus growth was observed in treatment 2 (sodium acetate 2%, nisin 750 IU/g, temperature 4°C) and control at 4 and 8° C, respectively. It is noticeable that the growth of Staphylococcus aureus decreased in treatment 3 (sodium acetate 2%, nisin 1000 IU/g, temperature 8° C) during storage at 8° C. Also, the results showed that the temperature was most important factor on the growth of Staphylococcus aureus in the beginning of experiment and the other factors showed their effect during storage. Therefore, the highest and lowest effect was related to temperature and nisin at the end of experiment, respectively. In the present study, the additives could be prevented the growth of bacteria with except in treatment 4 (sodium acetate 1%, nisin 750 IU/g, temperature 8° C). The inhibitory effects of nisin and sodium acetate on the growth of Staphylococcus aureus was better shown with increasing storage time. The TVB-N of fillets increased during storage but this increase was lower in treatment 2 than the other treatments. The temperature and nisin had a significant effect (p