- Onuchuku, P. U. G PhD and Okidhika C. U. PhD
- DOI: 10.5281/zenodo.20056605
- SSR Journal of Multidisciplinary (SSRJM)
The thermal stability of edible oils is a critical food safety concern, particularly for frequently reused cooking oils in developing nations. This study evaluated the oxidative stability and antioxidant capacity of eight commercially refined vegetable oil brands, comprising palm olein, soybean, sunflower, and groundnut oils, purchased from major markets in Port Harcourt, Rivers State, Nigeria, following repeated thermal stress (frying at 180 ± 5°C for 0, 2, 4, 6, and 8 hours). Physicochemical quality indices including peroxide value (PV), free fatty acid content (FFA), p-anisidine value (p-AV), total oxidation value (TOTOX), acid value (AV), saponification value (SV), and iodine value (IV) were determined using standard AOCS and AOAC methods. Antioxidant capacity was assessed via the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay and ferric reducing antioxidant power (FRAP) assay. Tocopherol (vitamin E) content was quantified by HPLC-fluorescence detection. Results revealed that progressive thermal treatment significantly elevated PV, FFA, p-AV, and TOTOX values across all oil types, with groundnut oil exhibiting the highest initial antioxidant capacity (DPPH IC₅₀ = 12.4 mg/mL) and palm olein demonstrating the greatest oxidative stability owing to its higher saturated fatty acid content and residual carotenoid contribution. Soybean and sunflower oils showed the most rapid deterioration, with TOTOX values exceeding regulatory thresholds (CODEX Alimentarius) after six hours of thermal stress. Tocopherol content declined by 58–82% across all samples following eight hours of heating. Several brands did not conform to CODEX and SON (Standards Organisation of Nigeria) quality benchmarks even in their unheated state. These findings underscore the urgent need for consumer education, regulatory enforcement, and improved quality standards for refined vegetable oils in Nigeria.
