Effects of Unrefined Oils and Butter on the Physicochemical and Nutritional Properties of Fried Doughnuts

Abstract

Aims: This study aimed to investigate the health implications of using unrefined oils and butter in doughnut preparation by analyzing the physicochemical properties, fatty acid profiles, and elemental compositions of extracted frying oils. Study Design: An experimental laboratory-based study was employed to evaluate the impact of preparing fried doughnuts with unrefined oils and butter combinations on oil quality and stability extracted from the doughnuts. Place and Duration of Study: The study was conducted at the Chemistry Laboratory of Akwa Ibom State University (AKSU) and CTX-ION Analytics, Ikeja, Lagos, between March and June 2025. Methodology: Doughnuts were prepared using locally sourced unrefined oil and butter from shops in Uyo, Akwa Ibom State, selected through purposive sampling. Soxhlet extraction using n-hexane was used to recover oils from fried doughnuts. The oils were analyzed for acid value, free fatty acid (FFA), peroxide value, iodine value, and saponification value. Fatty acid methyl esters (FAMEs) were profiled using GC-MSD, and elemental composition (Ca, Fe, K, Mg, Na, P) was determined by ICP-OES. Results: The doughnut oil recorded a very high peroxide value (136.30 meq/kg), signaling severe oxidative degradation, likely from elevated iron content and high frying temperatures. Iodine and saponification values indicated moderate unsaturation and presence of medium-chain fatty acids. GC-MSD showed retention of both saturated (lauric, myristic) and unsaturated (oleic, linoleic) fatty acids. Elemental analysis revealed high iron and potassium levels, especially in doughnut oil, indicating susceptibility to oxidation and potential health risks. Butter contributed beneficial unsaturated fats but also excessive sodium. Conclusion: Frying with unrefined oils and butter significantly compromises oil quality due to oxidative and hydrolytic degradation. The high peroxide value and mineral-induced oxidation highlight potential health hazards. Improved frying practices, use of antioxidants, and optimized fat blends are recommended to enhance nutritional quality and shelf life of fried snacks like doughnuts.