Effects of Pre-Cooking Processes on the Proximate Composition and Polycyclic Aromatic Hydrocarbons Content of Traditional Smoked Clarias Gariepinus (African Catfish)

Abstract

Clarias gariepinus (African Catfish) is a fresh water fish commonly consumed by Nigerians in terms of animal protein. Smoking is the preservative technique commonly adopted in order to extend its shelf life due to its perishable nature. Smoking when carried out with traditional method using hardwood fire involves direct contact of the material being smoked with the smoke which allows for deposition of the polycyclic aromatic hydrocarbons (PAHs) onto the food products. This is responsible for a high contamination levels with carcinogenic polycyclic aromatic hydrocarbons (PAHs). Several processes such as milling, leaching, salting and washing according to various researchers have resulted in the decrease of the natural toxicity of some food products by eliminating specific undesirable components such as PAHs. In this study fresh, smoked and processed fish samples were analyzed for proximate composition using AOAC method and polycyclic aromatic hydrocarbon contamination. Thirteen (13) PAH types were identified using an extraction method into hexane, further clean-up is carried out on a silica SPE- cartridge. The concentrated extract was analyzed by GC-FID using a Thermo Fisher Scientific, Waltham, MA USA. The nutritional value parameters of processed samples determined were not significantly different (P< 0.05) from the smoked sample except protein and fat due to leaching. Values obtained for protein and fat due to different treatment methods ranged between 55.3% to 63.2% and 15.1% to 25.3% respectively. Individual processed sample values obtained for protein and fat were as follows: 63.2% for smoked sample, 62.2% for sample steeped in cold water only, 61.4% for sample steeped in cold water plus salt, 58.4% for sample steeped in hot water only, 57.7% for sample steeped in hot water plus salt, 59.3% for the muscle while the skin recorded 55.3%. Fat content for the smoked and processed samples were as follows: 24.6%, 24.5%, 24.2%, 23.9%, 23.9%, 15.1% and 17.6% for smoked sample, sample steeped in cold water only, sample steeped in cold water plus salt, sample steeped in hot water only, sample steeped in hot water plus salt, muscle and skin respectively. From the study, various processing methods adopted in this research study pose no health hazard to the consumer. Total polycyclic aromatic hydrocarbons concentrations varied from 1.61μg/kg to 2.83μg/kg, smoked fish steeped in hot water without salt had the least total PAHs concentration while the skin recorded the highest concentration. The levels in the samples were in decreasing total mean concentration order in μg/kg: 2.83 (skin only), 2.52 (smoked fish sample), 2.42 (fresh), 2.33 (smoked fish steeped in cold water only), 2.14 (smoked fish steeped in hot water plus salt), 2.05 (sample steeped in cold water plus salt), 1.90 (muscle), and 1.61 (sample steeped in hot water only). The levels of Benzo[a]pyren found in the smoked dried and processed fish samples varied between 0.29μg/kg to 0.54μg/kg which was however lower than the European regulatory maximum level for smoked meat and fishes (5μg/kg). Values of Benzo[a]pyren recorded due to different treatment samples ranged from (0.52μg/kg, 0.52μg/kg, 0.52μg/kg, 0.43μg/kg, 0.35μg/kg to 0.29μg/kg) for the smoked sample, samples steeped in cold water only, cold water plus salt, hot water plus salt, muscle only and hot water without salt respectively. Processing with hot water without salt proved to be most effective method at reducing PAHs levels in smoked Clarias gariepinus (African catfish)