Changes in physicochemical and sensory characteristics of smoke-dried fish species stored at ambient temperature

Abstract

This study assessed the comparative changes in the physical and chemical  components of five different species of smoked freshwater fish: Bony tongue, Heterotis niloticus, African carp, Labeo coubie, Snake fish, Parachanna obscura, Nile Tilapia, Oreochromis niloticus and African mud catfish, Clarias gariepinus during storage. The fish were smoke-dried to average moisture content of 10.41 ± 0.02% and stored. Fish were packaged in black polythene bags and kept in  perforated plastic containers. The fish were left in the plastic baskets for 56 days at ambient temperature (25-32oC). Samples of fish were assessed weekly for physical attributes such as colour, fragmentation, odour, taste and texture. Proximate  composition was assessed using changes in moisture content, crude protein, lipid and ash content. Biochemical indexes carried out were: Total Volatile Nitrogen (TVN), pH, Peroxide Value (PV) and Free Fatty Acid (FFA) levels. There was a general decline in physical attributes i.e. colour, fragments or cracks, odour, taste and texture of fish during storage. Fluffy woolly mat of moulds were noticed on the Clarias gariepinus from the 5th week of storage. There was a significant (P <0.05) colour change in most species as from the 6th week. During this study, the moisture content increased weekly in the five smoked fish species from the initial average of 10.41±0.02%. This could be attributed to the difference in the moisture of the smoked fish relative to the surroundings. Oreochromis niloticus and Heterotis  niloticus had the best taste value. Apart from Parachanna obscura, the other fatty species, C. gariepinus and L. coubie became less firm as the weeks progressed. There were significant changes (P <0.05) in most of the physical and chemical  characteristics except odour from the 6th week (42 days) of storage. There were also significant differences (P <0.05) between the initial and final values of the  proximate and chemical constituents of the different species of fish. The study showed that keeping quality of smoked fish under ambient conditions decreases with increase in length of storage.

Keywords: Freshwater fish, hot smoking, storage