Effects of Mozafati, Piaroum, Zahedi date extracts and their combination on the chemical, microbial and sensory properties of farmed rainbow trout (Oncorhynchus mykiss) fillets during refrigeration (4˚C)

Rainbow trout fillet is susceptible to microbial and oxidative spoilage. Therefore, it is essential to use preservatives to extend its shelf life. Date extract has significant antibacterial and antioxidant properties. This research was conducted to study the effect of aqueous date extracts on chemical, microbial and sensory properties of farmed rainbow trout during refrigeration. Total phenolic and flavonoid content were determined through Folin-Ciocalteu and colorimetric method. The first step of study was performed for determination the antimicrobial activity of date extracts against the inherent flora of fish fillet, lactic acid bacteria, Pseudomonas and Enterobacteriaceae by disc diffusion method. In parallel with antimicrobial tests, sensory evaluation was also performed for choosing the best concentration of extracts in order to applying on fish fillets. In the second step of study, fish fillet samples were immersed in date extracts (3% w/v for 5 minute), packaged in zip–bags and stored at 4 oC over a period of 17 days. The extract-free fillet was used as control. The samples were analyzed for microbiological (mesophilic, lactic acid bacteria, Pseudomonas and Enterobacteriaceae counts) and chemical (PV, TBARS and TVB-N) parameters. The 5-point hedonic method was carried out for sensory evaluation by 30 trained panelists. Analyses were conducted at 2 h after preparation and 1, 3, 5, 7, 9, 11, 13, 15 and 17 days of storage.  Phenolic and flavonoids contents showed no significant differences between date extracts (p>0.05). Total bacterial counts, Enterobacteriaceae, Pseudomonas, TBARS, PV and TVB-N showed no significant difference in test samples (p>0.05). These parameters were within an acceptable range up to 15 days for test samples while the control samples had a shelf life of 5 days. Samples preserved by Piaroum extract had the longest shelf life while samples preserved by the combination of extracts had the shortest. According to the results, the Piaroum, Zahedi, Mozafati date extracts and their combination could be used as natural preservatives for trout fillet shelf-life extension.