The Effect of Storage Temperature and Time on Bacteriological Load and Physicochemical Quality of Nile Tilapia (Oreochromis niloticus) Fillet from Lake Tana, Ethiopia

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Addis Ababa University


Fish and fish products are one of the food items that are of excellent nutritional source but it is highly perishable unless well preserved. Oreochromis niloticus (Nile Tilapia) is the most important fish species of Lake Tana fishery. Bacteriological load and physicochemical changes were evaluated during the storage of Nile Tilapia fillets at -18ºC and 5ºC for 30 days. The fish samples were collected from Lake Tana. Enumeration of Aerobic Colony Count, Enterobacteriaceae count and Psychrotrophic count; determination of protein, ash, and moisture contents, pH and TVB-N changes were undertaken. The analyses of all the parameters were carried out at regular 5 days interval on the fish fillets stored for up to 30 days. Data analysis were performed using SPSS version16 and Microsoft excel 2010. There was significant increase in Aerobic Colony Count, Enterobacteriaceae count and Psychrotrophic count on the fillets stored at 5ºC. The frozen condition showed significant effect on inhibiting all of the three groups of microbial counts. The moisture, protein, fat, and ash contents of fresh Nile tilapia fish fillets were 77.98%, 20.26%, 0.523% and 1.322%, respectively. The fillets stored at 5ºC showed significant decreases in protein and ash contents during 30 days of storage. On the other hand, there were no significant changes in moisture and ash contents of fillets kept under frozen condition for about 30 days. However, there was a significant decrease in crude protein content on the later days of storage under frozen condition. Moreover, TVB-N content of the fish fillets increased from 3.92 to 45.04 mgN/ 100g and 5.37 mgN/100g on samples kept at 5ºC and -18ºC, respectively. pH were also increased from 6.23 to 7.60 and 6.81 on the samples stored at 5ºC and -18ºC, respectively. The result shows that Nile Tilapia from Lake Tana had high protein content, low fat content, and high microbial load on fresh fillets, and freezing can keep the qualities of the fish relatively for longer period within safe levels and refrigeration could be able to keep the qualities briefly. Key words: Bacteriological load, Fresh, Oreochromis niloticus, Refrigeration, and TVB-N.



Bacteriological load, Fresh, Oreochromis niloticus, Refrigeration, and TVB-N.