Physico-sensory and microbial evaluation of ice stored Nile tilapia fillets ( Oreochromis niloticus L.) from Lake Hawassa

Fillets from the Nile tilapia ( Oreochromis niloticus L. ) were obtained from Lake Hawassa, and were exposed to ice storage in five different packages designated as package I (muscle to ice ratio of 1:1 (w/w)), package II (muscle to ice ratio of 1:2), package III (a combination of muscle, ice and water of 1:0.2:0.5 (w/w/w)), package IV (muscle to water ratio of 1:1) and package V (stored in a refrigerator at 4 0 C). Clean fresh fillets contained 5.06 log (c.f.u/g). Fillets stored in ice crystals in the ratio of 1:2 (package II) got spoiled after 24 hours, when the total bacterial count reached 5.31 log (c.f.u/g), while at the ratio of 1:1 (package I), the count reached 5.65 log (c.f.u/g). The fillets from these two packages were organoleptically acceptable for consumption up to the 24th hour of storage and those stored in water at the 1:1 ratio (package IV) were acceptable up to the 15th hour. At rejection, fish exhibited a strong fishy, sulfidy, putrid and ammoniacal odor. The respective counts of total lactics and psychrophiles initially were 1.70 and 4.27 log (c.f.u/g). However, after 24 hours of storage, they reached 2.89 and 5.32 log (c.f.u/g) in package II and 3.68 and 5.46 log (c.f.u/g) in package I, respectively. Our study revealed that the shelf-life of tilapia stored in ice was improved by about 12 hours. Keywords/phrases: Fillets, Ice storage, Lake Hawassa, Oreochromis niloticus . Ethiop. J. Biol. Sci ., 9(2): 183-193, 2010