Effect of temperature on spoilage of fresh and frozen fish sold in markets in Ibadan
The study determined the progression of spoilage in response to temperature and also ascertained the wholesomeness of fish offered for sale at different times of the day from selected markets in Ibadan. Fresh and frozen fish were bought from Sango and Bodija markets in Ibadan,
the temperature was recorded and the samples were transported in a Coleman cooler to the laboratory for further analysis. Upon arrival, the temperature was again recorded and samples were exposed to different environmental temperatures; assessment for spoilage was conducted
on the fish samples at 3 hourly intervals thereafter. Assessment was based on physical appearance of fish and enzyme analysis through measurement of changes in trimethylamine (TMA) concentration in fish muscles using picrate method. Chemical analysis showed progressive rise in TMA during storage. TMA values revealed no statistically significant (p=0.99) difference at p<0.05 in the spoilage rate of frozen and fresh fish while the difference in the optical densities was statistically significant (p=0.01).The TMA value recorded in live-fish at the start of the experiment (2.2 mg TMA/100g of fresh-fish muscle) was considerably lower than that of frozen fish (4.08 mg TMA/100g of frozen-fish muscle); the reverse was the case after 9 hours of storage with TMA values rising to 10.91 mg TMA/100g in fresh-fish muscle and 7.54 mg TMA/100g in frozen-fish muscle. Safe presentation and marketing practices and establishment of fish inspection services is hereby recommended.
Keywords: Fish spoilage, Clarias gariepinus, Trimethylamine (TMA), Nigeria