Combination Effect of Gamma Irradiation, Thyme Essential Oil and Vacuum Packaging on Shelf Life of Shrimp during Refrigerator Storage

In this research, the effect of gamma irradiation, thyme essential oil (EO) and vacuum packaging treatments on fresh shrimp for a period of 15 days at 4°C during storage was investigated. For this purpose, two concentrations of EO (0.4 and 0.8% v/w) and two doses of radiation (2.5 and 3.5 KGy) were used. Treated shrimps and control sample were subjected to chemical (pH, total volatile basic nitrogen, free fatty acids, peroxide index, thiobarbituric acid reactive substances and color indexes), microbiological (bacteria total count, psychrophilic bacteria and  Escherichia coli) and sensory evaluation and analyses performed on certain days (0, 5, 10 and 15th) of storage. The obtained results showed that pH, FFA, peroxide, TBARS and TVB-N values of all treatments increased in the duration of storage, significantly (p<0.05). Microbial load in all treatments also increased over time. Bacterial growth delayed growing in samples by using of combination of thyme oil, gamma radiation and vacuum packaging. At first, adding thyme EO leds to decrease L* index, but at high concentration of EO (0.8%), color change was decreased significantly (p<0.05). The results of sensory evaluation showed that different treatments had significant effect on sensory parameters of shrimp (p<0.05). Finally, the shrimps treated with combination of vacuum packaging, 0.8% (v/w) EO and 2.5 KGy can be introduced as the best treatment.