Temperature-driven alterations in trans octadecanoic acid isomers of high-TFA soybean oil during heating

Abstract

Trans-fatty acid (TFA) formation and degradation during heating in real-life situations remain a major public-health concern, particularly in countries where soybean oil contains elevated baseline TFA levels. This study examined temperature-driven alterations in C18 cis/trans isomers in soybean oil rich in TFA (3.35%) during continuous heating at 180±5°C for 8 h. Fatty-acid profiles were quantified hourly using GC-FID with cis/trans standard calibration. Continuous heating steadily changed polyunsaturated fatty acids (PUFA) to more saturated (SFA) and monounsaturated (MUFA) fractions, driven by PUFA degradation (p < 0.001). Total TFA did not exhibit a significant linear increase (p = 0.152), yet isomer-specific trends revealed distinct pathways: trans-oleic acid (TOA) increased steadily (R² = 0.988; p < 0.001), indicating cis to trans isomerization; trans-linoleic acid (TLA) rose modestly due to increases in trans, trans and cis, trans isomers; while trans-linolenic acid (TLnA) declined sharply (p < 0.01), consistent with preferential oxidation of highly unsaturated trans isomers. Multivariate analyses supported these dynamics. Hierarchical clustering separated fatty acids into: (i) SFA–MUFA–TOA (increasing, thermally stable), (ii) PUFA–TLnA (highly degradable), and (iii) TLA–TTFA (non-linear behavior). Principal Component Analysis (PC1 = 82.1%, PC2 = 15.1%) showed a clear time-dependent trajectory driven by PUFA loss and accumulation of SFA/MUFA and selected trans isomers.

Bangladesh J. Sci. Ind. Res. 61(1), 9-18, 2026