Study of the Effect of Nisin and Rosemary Extract on Sensory and Microbial Spoilage Indicators of Rainbow Trout (Onchorynchus mykis) in Cold Storage Conditions

In order to investigate the effect of nicine and rosemary extract (Rosmarinus officinalis) on sensory and microbial spoilage indicators of rainbow trout in cold storage conditions, four treatments were used including: control treatment (uncoated fillets), fillet coated with 0.1% nisin, fillets coated with 0.5%  nisin and 1% rosemary extract and fillet coated with 0.1% nisin and 2% rosemary extract. Quality control tests were carried out in 4 day interals during the 12 day period including microbial tests, counting the total number of bacteria, counting the psychrotrophic bacteria and counting the lactic acid bacteria, and sensory assessments such as color, odor and texture. The results indicated that increasing the storage time caused the significant increase in the total number of the bacteria, the number of the psychrotrophic bacteria and the lactic acid bacteria, and color, odor and texture indices in the control treatments (p <0.05). The effect of coating by 0.5% nisin plus 1 and 2% of rosemary extract on the total number of bacteria, the number of the psychrotrophic bacteria and the lactic acid bacteria and color, odor and texture indices during the storage period was significant (p<0.05). The treatments coated with 0.1% nisin, had no significant effect on the control of the samples’ spoilage compared to the above samples. The results indicated that the use of higher doses of Rosemary extract is effective in increasing the shelf life of rainbow trout in cold storage conditions.