Nutritional Evaluation of Nile Tilapia (Oreochromis niloticus) Processed by Different Drying Methods in Akwa Ibom State, Nigeria

This study evaluated the effect of different drying methods on the proximate composition, mineral and vitamin content, and heavy metal concentrations of Oreochromis niloticus obtained from Esuk Nwaniba, Uruan Local Government Area, Akwa Ibom State, Nigeria. Fish samples were processed using four drying methods: air drying (FAD), oven drying (FOD), firewood drying (FWD), and firewood + polythene drying (FWP). Proximate parameters (moisture, crude protein, crude lipid, crude fiber, crude ash, and nitrogen-free extract) were determined using AOAC procedures; energy values were calculated with the Atwater system; minerals and heavy metals were analyzed by Atomic Absorption Spectrophotometry (AAS); and vitamins were determined using HPLC and spectrophotometry. Results revealed statistically significant differences across drying methods (p < 0.05). Oven drying retained the highest crude protein (58.66%), lipid (19.13%), energy value (454.21 kcal/100 g), minerals (Ca, K, Fe, P), and vitamins (A, D, E, C, B12). In contrast, firewood + polythene drying produced the poorest nutritional quality, with reduced protein and lipid, the lowest micronutrient retention, and elevated ash levels. Toxicological evaluation showed that oven- and air-dried samples had heavy metal concentrations within FAO/WHO permissible limits, whereas FWP samples exceeded Pb limits by over 100% (0.62 mg/kg vs. 0.30 mg/kg permissible) and Cd limits by 20%, posing serious food safety risks. The findings suggest that oven drying is the most nutritionally efficient and safest method, while the use of polythene in fish drying compromises both nutritional value and consumer health. Adoption of controlled drying technologies and strict prohibition of polythene burning are strongly recommended to improve food safety and nutritional security in local communities.