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Abstract Two main groups of seventy five Oreochromis niloticus fish each of weighting 330 ± 20g (yield 150 slice) and 40 Bagrus bayad fish each of weighting 900 ± 100g (yield 150 slice). The obtained slices weighting 80 ± 5g and measures (5 x 7 x 1) cm. Every main group divided into 5 subgroups, 1st (control), 2nd treated by acetic acid (2%), 3rd treated by citric acid (0.5%), 4th treated by mix of (acetic acid 2% and citric acid 0.05%) and 5th treated by thyme oil (0.05%) were subjected to sensory, chemically and microbiologically examination every three days of refrigerated storage at 4±1 oC till signs of spoilage became apparent. Sensory evaluation: The sensory evaluation in both Oreochromis niloticus and Bagrus bayad fish fillets aimed to detect appearance, odour, texture and flavour. a) Oreochromis niloticus: the results revealed that control. samples were sensory acceptable about 4-5 days of refrigerated storage at 4±1 oC, while acetic acid, citric acid, mix and thyme oil treated samples were sensory acceptable about 12, 8-9, 12 and 7-8 days, respectively. b) Bagrus bayad: the results recorded that control samples were sensory acceptable only 4 days of refrigerated storage at 4±1o C, whereas acetic acid, citric acid, mix and thyme oil treated samples were sensory acceptable till 7-8, 7, 9 and 6 days, respectively. Chemical examination: (1) pH measurement: a) Oreochromis niloticus: the mean pH values of control and acetic acid, citric acid, mix and thyme oil treated samples, were 7.22, 4.78, 6.37, 4.76 and 6.56 at 9th day respectively. Whereas acetic acid and mix treated samples recoded 6.40 and 6.36 at 15th day, respectively. b) Bagrus bayad: the mean pH values of control and acetic acid, citric acid, mix and thyme oil treated samples, were 7.47, 4.92, 6.02, 4.83 and 6.57 at 9th day, respectively. Whereas acetic acid. |