Heavy metal contaminants and processing effects on the composition, storage stability and fatty acid profiles of five common commercially available fish species in Oron Local Government, Nigeria

Abstract

Five commercially available common fish species: catfish ( Chsysichthyes nigrodigitatus), tilapia ( Oreochromis nilotichus), ilisha (Ilisha africana), bonga ( Ethmalosa fimbriata) and mudskipper ( Periophthalmus koelreuteri) in Oron Local Government Area were evaluated for their content of heavy metals and the effects of salting on nutrient contents, oxidative stability and fatty acid profiles of smoke-dried fish cakes. Concentrations of heavy metals in edible muscle, liver and gill tissues were determined while the oxidative rancidities in unsalted and salted smoke-dried fish cakes, packed in low-density polyethylene (LDPE) bags and stored at 30 ± 1 °C were assessed using peroxide value (POV), thiobarbituric acid (TBA) value, free fatty acid (FFA) contents and sensory evaluation techniques. Generally the analytical data for Cu, Zn and Pb in the muscle, gills and liver of test samples were significantly low. Similarly, insignificant concentrations (<0.001 mg/100 g) of Hg, As, Cr and Cd were obtained in the fish tissues. The protein and lipid contents of the fish cakes ranged from 60.8–63.9% to 7.3–9.1%, respectively. Salting caused minimal reductions in the nutrient contents of the dried fish cakes. The POV, TBA, FFA and taste panel scores were highest during the first week of storage and declined thereafter. Salted smoke-dried samples had higher POV, TBA and FFA values than unsalted samples. Panel preference ratings for flavour/aroma and desirability characteristics of the fish cakes were in the order: C. nigrodigitatus > O. nilotichus > E. fimbriata > I. africana > P. keolreuteri. Palmitic acid (C16:0) was the predominant saturated fatty acid in the test samples. The eicosapentaenoic acid (EPA) contents of unsalted smoke-dried C. nigrodigitatus was 4.9%, Oreochromis niloticus 6.5%, Ilisha africana 2.6%, E. fimbriata 5.6% and P. koelreuteri 7.64%. The docosahexaenoic acid (DHA) contents of salted smoked dried fish were 1.8% ( C. nigrodigitatus), 4.8% ( O. niloticus), 9.5% ( I. africana), 5.5% ( E. fimbriata) and 12.3% ( P. koelreuteri).