Effects of herbal essential oils used to extend the shelf life of freshwater-reared Asian sea bass fish (Lates calcarifer)

Abstract

Sensory and microbiological characteristics of Asian sea bass (Lates calcarifer) fish raised in a freshwater pond were evaluated during cold storage for 33 days. Whole fish (averaging 400 g each) were stored in a cold storage room at 0 to 2°C. Essential oils of herbs - thyme (Thymus vulgaris) and oregano (Origanum vulgare) - added at 0.05% (vol/vol) were used as preservatives. On the basis of the sensory test results as well as the bacteriological tests, the addition of oregano and thyme essential oils can considerably slow the process of spoilage. The fish treated with these oils were still fit for human consumption after 33 days of storage. The results obtained through sensory tests are corroborated to a great extent by the chemical (hypoxanthine) tests and to a lesser extent by the physical (Cosmos units) tests. The initial total bacteriological counts were 1.7 × 103 CFU/cm2 on the fish surface and <102 CFU/g in the fish flesh, and in the control treatment (without preservatives), these counts rose continuously, reaching around 107 CFU/cm2 on the fish surface and 103 CFU/g in the flesh after 33 days of storage at 0 to 2°C. The use of herbal essential oils as preservatives, on the other hand, resulted in a maximal count of 105 CFU/cm2 on the fish surface, while the bacterial count in the flesh remained <102 CFU/g by the end of the 33-day storage period at 0 to 2°C.