Microbiological assessment of stored Tilapia guineensis

Abstract

Microbiological analysis of Tilapia guineensis was assessed at two ice stored temperatures, -18 and 4°C, for 4 weeks. Bacteria and fungi counts decreased from 7.9 × 103 to 5.4 × 101 cfu/g for bacteria and 6.2 × 103 to 3.2 × 102 cfu/g for fungi in the samples stored at -18°C, while for the samples stored at 4°C, an increase was shown in counts from 7.9 × 103 to 7.6 × 107 cfu/g for bacteria and 6.2 × 103 to 6.8 × 104 cfu/g for fungi. Pseudomonas, Staphylococcus, Bacillus,Proteus, Micrococcus and Aeromonas sp. were the bacteria species isolated before cold storage, while only Pseudomonas, Staphylococcus, Bacillus andProteus sp. were isolated from samples stored at -18°C. The same organisms isolated before cold storage were also isolated for samples stored at 4°C. Fungal species isolated before cold storage include: Cladiosporium, Aspergillus andFusarium sp. All these fungi species were also isolated from samples stored at -18°C. Cladiosporium, Pichia, Aspergillus and Fusarium sp. were isolated from samples stored at 4°C. The level of bacteria and fungal growth in fish stored at 4°C temperature exceeded the acceptable microbiological limits (102/g for moulds and 103/g for bacteria). However, the pH of fish was found to increase in the two stored temperatures. It was within the alkaline range in the -18°C stored samples, but within the acidic range in the 4°C stored samples. There were significant differences (P<0.05) in the microbiological composition of the ice stored Tilapia guineensis within the same temperature and between the two temperatures. The quality of the 4°C stored sample deteriorated faster than that of the -18°C. Thus, storage temperature and duration have effects on the quality of stored fish. Key words: Tilapia guineensis, fish, sample, bacteria.