The Effect of Continuous Thermal Treatment on the Chemical Properties of Vegetable Oils and Animal Ghee

The aim of this study was to evaluate changes in selected chemical quality indices of five fat and oil samples available in the Iraqi market (sunflower oil, corn oil, olive oil, vegetable ghee, and animal ghee) during continuous thermal treatment at 180 °C for eight hours under open-air laboratory conditions. The treatment was not intended to reproduce commercial frying, because no food or added moisture was present and repeated frying cycles were not performed. Changes were monitored by measuring peroxide value (PV), acid value (AV), and saponification value (SV) every two hours. The results showed different patterns of change among the tested oils and fats. Sunflower and corn oils showed the highest peroxide values at 6 h (29.38 ± 2.87 and 20.84 ± 2.30 meq O₂/kg, respectively), followed by lower PV values at 8 h, a pattern consistent with the thermal instability of primary oxidation products. Animal ghee maintained comparatively low PV values but showed the highest acid value at 8 h (2.81 ± 0.13 mg KOH/g). Sunflower and corn oils also showed the largest decreases in SV over the treatment period. Because fatty-acid profiles, secondary oxidation products, antioxidants, and polymerized triacylglycerols were not directly measured, mechanistic interpretations of these trends are presented as possible explanations rather than demonstrated causes. Under the tested laboratory conditions, vegetable ghee and olive oil showed comparatively smaller changes in the measured quality indices. However, PV, AV, and SV alone are insufficient to establish product safety or to define a maximum safe heating time. Further studies including secondary oxidation markers, total polar compounds, fatty-acid profiling, and direct polymerization measurements are required before safety recommendations can be made.