Effect of Low Temperature Preservation on The Physicochemical and Microbiological Qualitieis of Selected Fish Species of Lake Ziway
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Date
2007-06
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Addis Ababa University
Abstract
With the purpose of determining the effect of frozen storage on quality of fish fillet and
evaluating the existing low temperature preservation technique in the case of Fish Production and
Marketing Enterprise, samples from the same lot of commercially harvested and processed tilapia
fish (Oreochromis niloticus) fillets were frozen at -18 ± 2oc. The physicochemical and
microbiological analyses were carried out at regular 15 days interval on tilapia fish fillets stored
for up to 90 days. The fresh fish fillets were found to contain 18.52±0.08% protein, 0.37 ± 0.01%
fat, 79.87 ± 0.01% moisture and 0.98 ± 0.01% ash contents. During the entire period of storage,
the protein, moisture and ash contents were significantly (p < 0.05) decreased to 17.25 ± 0.088%,
78.50 ± 0.71%, and 0.88 ± 0.02% respectively. However, the fat content of the fish fillets
increased significantly (p < 0.05) to 0.56 ± 0.01 after 90 days of frozen storage. The TVB-N and
pH values were also increased significantly (p < 0.05) from 12.04 ± 0.48 mg N/100g and 6.43 ±
0.01 to 21.75 ± 0.35 mg N/100g and 6.61 ± 0.01 respectively. The total bacterial load in fresh
fish fillets was reduced from 2.57x106 to 8.2x105 CFU/g after 90 days of frozen storage. The total
coliforms and faecal coliforms were also decreased from 460 MPN/g and 23 MPN/g to 23
MPN/g and undetectable level, respectively. From these results it was concluded that freezing, if
not properly used, has a negative effect on reduction of nutritional value of fish products. The
storage of tilapia fish fillets under frozen condition showed a significantly (p < 0.05) higher
deterioration of product quality. The nutritional quality, as estimated by the proximate
composition analysis, underwent a gradual loss of nutrients until day 90, in agreement with loss
of freshness of the fish fillets observed for the TVB-N. Furthermore, the results revealed that
gradual biochemical changes reduce the quality of frozen fish fillets as the duration of storage
increases. Under frozen condition, the overall nutritional quality of tilapia fish fillets was found
to depend on duration of frozen storage.
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Microbiological Qualitieis