Thermal Oxidation of Phytosterols in Purified Vegetable Oils With Typical Fatty Acid Compositions

Abstract

Vegetable oils are the main source of phytosterols (PS) for human beings. However, vegetable oil usually requires high-temperature treatment during the cooking process of Chinese food, which in turn causes the PS to be oxidized to form phytosterol oxidation products (POPs) that are harmful to the human body. The influence of the unsaturation degree of vegetable oils on PS oxidation was evaluated under heating at 180°C for up to 180 min. The higher the degree of unsaturation in vegetable oil, the slower the degradation of PS occurred and the fewer POPs were formed. The degree of unsaturation of vegetable oils affected not only the degradation rate of PS but also the formation pathways of POPs. In the fully saturated hydrogenated palm oil (HPO), the generation of 7-hydroxy-PS and its subsequent conversion to 7-keto-PS were different from those in the other oil matrices. Additionally, the content of 5,6-epoxy generated in HPO was significantly greater than those in the other three oil matrices, which could be further transformed to triol-PS, resulting in a higher content of triol-PS in the HPO system. However, when the heating time exceeded 90 min, triol-PS could be quickly degraded by dehydration.

Practical Applications: The present findings demonstrated that the degree of unsaturation in vegetable oils governed the thermal oxidation behaviour of phytosterols (PS) and the formation of phytosterol oxidation products (POPs). Oils with higher levels of unsaturated fatty acids, such as perilla seed oil, exhibited delayed PS degradation and suppressed POPs generation under heating conditions. These findings suggest that selecting unsaturated fatty acid-rich oils for most Chinese cooking methods (excluding extended deep-frying) could effectively mitigate POPs generation, thereby reducing associated health risks.