Combined Effect of Vacuum Packaging and Sodium Acetate Dip Treatment on Shelf Life Extension of Rainbow Trout (Oncorhynchus mykiss) during Refrigerated Storage

The present study evaluated the effect of packaging (air, vacuum) with or without addition of sodium acetate (2% W/V) on shelf-life extension of rainbow trout (Oncorhynchus mykiss) under refrigeration, for a period of 18 days. Four different treatments were tested: CAP: control air pack; SAAP: sodium acetate treated aerobic packaging; VP: vacuum packaging in the absence of sodium acetate; and SAVP, sodium acetate under VP. Trimethylamine nitrogen (TMA-N), free fatty acids (FFA) and peroxide values (PV) of SAVP samples were lower compared to the other treatments during the entire refrigerated storage period. In the present study, the thiobarbituric acid (TBA) level showed fluctuations during storage indicating that TBA values may not reveal the actual rate of lipid oxidation. Total viable counts for fresh rainbow trout stored aerobically exceeded 7 log CFU g(-1) after 10-11 days, while treatments SAAP and VP reached the same value on days 12 and 16, respectively. In contrast, SAVP samples did not reach this value throughout the 18-day. Psychrotrophic counts of SAVP samples were significantly (P< 0.05) lower compared to the control samples during storage period. As regards sensory evaluation, shelf-life of trout was longest for SAVP (15-16 days), followed by VP (12-13 days), SAAP (9-10 days), and CAP samples (6-7 days). The results indicated that the combined effect of vacuum packaging and sodium acetate on fish samples preserved their good quality characteristics and extended the shelf-life of the treated samples during refrigerated storage, as supported by the results of microbiological, chemical, and sensory evaluation analyses.