Effects of stigmasterol on the thermal stability of soybean oil during heating

Phytosterols have been attached much attention for its thermal stability, but few research concerned the potential antioxidant activity of stigmasterol with two double bonds and the fate stigmasterol may experience through the whole process. The aim of this research was to comprehensively explore the realistic usage of soybean oil and the antioxidant role that stigmasterol may play. In this research, the degradation of stigmasterol added in soybean oil was evaluated with the treatments of 10-day heating at 60 °C, 9-h heating at 180 °C and 9-h frying at 180 °C. Phytosterol oxidation products and the proposed oxidation mechanisms of stigmasterol in soybean oil were investigated by GC–MS. The results showed that stigmasterol acted as a pro-oxidant at 60 °C but as an antioxidant at 180 °C. The decrease of phytosterol was usually accompanied by the increase amounts of oxidation products. After 10-day heating at 60 °C, the degradation of phytosterol was around 2.52–23.07% with 20.81–241.42 μg/g increase of oxidation products and 7-ketostigmasterol dominated. Heating at 180 °C underwent the most decreased phytosterol of 30.00–37.03% with the most rise of oxidation products 4.6–8.9 times higher than 60 °C. Differently, 5,6β-epoxy and 7β-hydroxy are the main products. According to the results of frying at 180 °C, stigmasterol literally presented excellent thermal stability in soybean oil. This indicated that stigmasterol exhibited antioxidant activity, and soybean oil with added stigmasterol could be suitable for home cooking or frying.