Effect Of Low Temperature Preservation On The Physicochemical And Microbiological Qualitieis Of Selected Fish Species Of Lake Ziway

With the purpose of determining the effect of frozen storage on quality of fish fillet andrnevaluating the existing low temperature preservation technique in the case of Fish Production andrnMarketing Enterprise, samples from the same lot of commercially harvested and processed tilapiarnfish (Oreochromis niloticus) fillets were frozen at -18 ± 2oc. The physicochemical andrnmicrobiological analyses were carried out at regular 15 days interval on tilapia fish fillets storedrnfor up to 90 days. The fresh fish fillets were found to contain 18.52±0.08% protein, 0.37 ± 0.01%rnfat, 79.87 ± 0.01% moisture and 0.98 ± 0.01% ash contents. During the entire period of storage,rnthe protein, moisture and ash contents were significantly (p < 0.05) decreased to 17.25 ± 0.088%,rn78.50 ± 0.71%, and 0.88 ± 0.02% respectively. However, the fat content of the fish filletsrnincreased significantly (p < 0.05) to 0.56 ± 0.01 after 90 days of frozen storage. The TVB-N andrnpH values were also increased significantly (p < 0.05) from 12.04 ± 0.48 mg N/100g and 6.43 ±rn0.01 to 21.75 ± 0.35 mg N/100g and 6.61 ± 0.01 respectively. The total bacterial load in freshrnfish fillets was reduced from 2.57x106 to 8.2x105 CFU/g after 90 days of frozen storage. The totalrncoliforms and faecal coliforms were also decreased from 460 MPN/g and 23 MPN/g to 23rnMPN/g and undetectable level, respectively. From these results it was concluded that freezing, ifrnnot properly used, has a negative effect on reduction of nutritional value of fish products. Thernstorage of tilapia fish fillets under frozen condition showed a significantly (p < 0.05) higherrndeterioration of product quality. The nutritional quality, as estimated by the proximaterncomposition analysis, underwent a gradual loss of nutrients until day 90, in agreement with lossrnof freshness of the fish fillets observed for the TVB-N. Furthermore, the results revealed thatrngradual biochemical changes reduce the quality of frozen fish fillets as the duration of storagernincreases. Under frozen condition, the overall nutritional quality of tilapia fish fillets was foundrnto depend on duration of frozen storage.

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