Thermal loss of phytosteryl/stanyl fatty acid esters during heating: Intramolecular structural susceptibility and intermolecular matrix regulation.

Phytosteryl/stanyl fatty acid esters are widely used as cholesterol-lowering ingredients in functional foods, but the relative contributions of molecular structure and lipid environment to their thermal loss remain unclear. This study aimed to clarify these effects using sitosteryl/stanyl palmitate, oleate, and linoleate as model compounds. Sitosteryl/stanyl ester loss increased with temperature, heating time, and acyl-chain unsaturation, while sitostanyl esters were more stable than sitosteryl esters. Moiety-level and kinetic analyses showed that the dominant degradation site shifted from the steryl skeleton in palmitate esters to the acyl chain in linoleate esters, whereas high temperature promoted synchronized whole-molecule degradation. Oil matrices markedly reduced ester loss, with stronger protection from more unsaturated matrices, suggesting a possible competitive oxidation effect. α-Tocopherol inhibited ester degradation, whereas squalene and β-carotene showed pro-oxidant behavior at 180 °C. These results suggest that thermal stability was governed by intramolecular structural susceptibility and intermolecular regulation by the lipid environment.