Impact of heat treatment on molecular composition of sunflower, cottonseed, and flaxseed oils

This study investigates compositional changes in sunflower, cottonseed, and flaxseed oils during heat treatment using Fourier Transform Infrared Spectroscopy (FTIR), proton Nuclear Magnetic Resonance spectroscopy ( 1 H NMR), and Gas Chromatography-Mass Spectrometry (GC–MS). Prolonged heating at 180–250 °C increased trans -fatty acids from <2% to ~4–6% in sunflower and cottonseed oils and up to ~20% in flaxseed oil. Saturated fatty acids increased by ~10% in all oils. Sunflower and cottonseed oils showed a reduction in polyunsaturated fatty acids, while flaxseed oil exhibited a strong decrease in monounsaturated fatty acids, from ~15% to <5%. Heating also caused the formation of oxidation products, free and epoxy fatty acids and aldehydes, together with depletion of tocopherols and phytosterols in all oils. Overall, oil type was the main factor determining initial composition and thermal stability. Further research is needed to establish nutritionally safer frying practices and elucidate compositional changes when oils interact with food ingredients during cooking. • Multiplatform GC–MS/FTIR/ 1 H NMR maps heat-induced changes in three oils. • Heating raises TFA, lowers PUFA/MUFA, and depletes native antioxidants. • Flaxseed oil showed the fastest compositional breakdown under heat exposure.