Journal of Applied Chemical Science International

Introduction: Although vegetable oil is a poor conductor of heat, it is effective for frying because convention current distributes high heat energy uniformly around the food, while conduction transfers heat into the food surface, leading to rapid cooking, moisture loss alongside volatile organic compounds, and formation of crispy texture.

Aim: This study investigates the Gas Chromatography-Mass Spectrometry (GC-MS, Shimadzu QP2010 Ultra) profiling of volatile emissions from the 6^th cycle of repeated akara frying and the 6^th cycle of repeated pork meat frying with emphasis on identifying thermally induced lipid peroxidative products.

Methodology: The steams from akara and pork meat were trapped in water and methanol respectively, while fresh vegetable oil served as control. Fresh vegetable oil, black-eyed beans, and pork meat were procured from Ogbete main market in Enugu, South East Nigeria. The food samples were fried separately at 170 ± 2°C using a closed improvised stainless-steel frying system fitted with a steam-condensation unit. The condensed vapors were trapped in water and methanol and further analyzed using GC-MS. Identification of compounds were based on retention time, mass spectral matching with NIST 2014 library, and similarity index ≥ 80%.

Result: GC-MS results revealed distinct compositional differences among fresh oil, fumes from akara and pork frying. Fresh oil showed long-chain fatty acid esters; hexadecanoic acid hexadecyl ester (36.30%) and 9-hexadecenoic acid eicosyl ester (33.35%) indicating no oxidation. In contrast, fumes from akara frying were dominated by n-hexadecanoic acid (41.29%), 9-octadecenamide (5.96%), and di-n-octyl phthalate (5.34%), suggesting progressive lipid peroxidation and polymerization. Steam emission from pork frying was predominated by pentacosane (17.22%), hentricontane (15.1%), z-9-pentadecenol (8.04%), and hexadecanamide (7.08%), reflecting intense thermal degradation of lipid matrices. The emergence of oxygenated and amide derivatives highlights ongoing oxidative and Maillard-type reactions at elevated temperatures.

Conclusion: The findings confirm that repeated frying substantially alters the volatile composition of vegetable oil, leading to the formation of long-chain hydrocarbons, esters, and amides potentially linked to air pollution and adverse health effects. It is therefore recommended that re-use of cooking oils should be avoided and adequate ventilation ensured in domestic and commercial frying environments.