Effect of smoking technologies on nutritional values and safety of Mormyrus Caschive and Oreochromis Niloticus (Linnaeus, 1758) in Terekeka, South Sudan

Abstract

The effect of smoking technologies on nutritional values and safety of smoked fish was determined to guide adoption of suitable kiln that maintains good quality and prolongs shelf life of smoked fish in South Sudan. A total of 300 fresh Mormyrus caschive and Oreochromis niloticus were bought, 36 fresh samples were iced and the remaining 264 samples were divided into two batches for pit and chorkor smoking. Samples were analyzed for chemical composition using standard methods of the association of official analytical chemists (2005); polycyclic aromatic hydrocarbons-PAHs using gas chromatography-mass spectrometry and microbial load using standard methods of BAM (2005), ICMSF (1986) and ISO (2003, 2008) and sensory attributes of smoked fish were assessed by “a control test panel of 20 individuals” using 9-point hedonic grading scale. Input-output analysis was done to determine the economics of smoking 100 kg using pit and chorkor kilns. Results revealed that chorkor significantly reduced moisture in M. caschive (10.0±0.83%) and O. niloticus (15.1±0.48%) more than pit kiln 15.3±0.57 % and 17.3±0.42% respectively. Effective removal of water from fish could be attributed to the concentration of smoke heat (at temperature range of 60-80oC) associated with the construction materials and enclosed characteristics of chorkor kiln. Although both smoking methods concentrated crude protein, fats and ash, higher values of nutrients were recorded in chorkor than in pit smoked fish because of effective removal of water from fish. Seven types of PAHs consisting of low molecular weight, 2-ringed-naphthalene, 3-ringed; anthracene, fluorene, acenaphthene & phenanthrene, and medium molecular weight Benzo [a] anthracene and chrysene, 4-ringed were recorded from both smoked fish species. Fluorene and naphthalene dominated the PAHs with pit smoked fish containing significantly higher levels of fluorene (3.83±0.10 µg/kg) and naphthalene (5.86±4.16µg/kg) than chorkor smoked samples. Higher PAHs in pit smoked fish could be attributed to open combustion of firewood resulting into higher temperatures which consequently lead to increase in oils on fish surface with subsequent deposition and penetration of PAHs. Corresponding to water activity, microbial load (TPC) increased at a rate of 1.7 times faster for pit smoked M. caschive and 1.1 times for O. niloticus than chorkor smoked fish. Similarly, mold load increased at a rate of 1.5 times faster for pit smoked M. caschive and 2.2 times for O. niloticus than samples smoked using chorkor kiln. Overall, chorkor smoked fish had better sensory attributes than pit smoked samples after one month storage. Although chorkor construction was expensive, the economic return was higher than for pit technology. This was due to short smoking time (twice in 24 hours) and utilization of small quantity of firewood (4bundles/round) in chorkor compared to once in 24 hours and 8 bundles of firewood for pit. Therefore, chorkor kiln produced better quality smoked fish in terms of nutrients, safety, sensory characteristics and shelf life, and it is an economically viable technology for preserving fish. The study recommends its adoption for artisan fisheries in South Sudan.