Effects of heat treatment time on physicochemical properties and antioxidant activity of peony seed oil

【Objective】By comparing the effects of microwave and roasting pretreatments on the physicochemical properties and antioxidant activity of peony seed oil(PSO), the aim was to provide scientific guidance for the production and quality control of PSO. 【Method】The oil of peony seeds was isolated after pretreatment by microwave(700 W for 0.5, 1, 1.5, 2 min) and roasting(120 ℃ for 10, 20, 30, 40 min), without any pretreatment was as control, and the effects of the treatment times of the two methods on physicochemical properties(oil extraction rate, moisture and volatile matter, acid value and iodine value) and antioxidant activity were analyzed. 【Result】The total extraction rate of the peony seed oil increased after microwave and roasting treatment. The extraction rate of PSO increased by 9.44% and 12.08% after microwave for 2 min and roasting for 30 min, respectively. Under microwave treatment, with the increase of treatment time, the acid value, moisture and volatile matter contents, polyphenol content and antioxidant activity of PSO decreased, the lowest contents of polyphenol, moisture and volatiles were detected at microwave treatment for 2 min(2.52 μg/mL and 11.59%, respectively), while the iodine value, saponification(TBA) value, and p-aniside value increased greatly, the value of TBA and p-anisidine reached the maximum value of 261.39 and 2.14, respectively under microwave treatment for 2 min. The saponification value showed a trend of rising first and then flatten. Under roasting treatment, the acid value, moisture and volatile matter contents of PSO increased greatly with the increase of treatment time, however, iodine, saponification, TBA, and p-anisidine values decreased. The acid value reached the highest value of 162.28 mg/g at 40 min of roasting, and the iodine value and saponification value reached the peak of 147.96 g/100 g and 173.35 mg/g at 10 min respectively. The polyphenol content and antioxidant activity showed a first increasing and then decreasing trend, the highest polyphenol content(5.25 μg/mL) was observed at roasting for 20 min. 【Conclusion】The physicochemical properties and antioxidant activities of PSO were greatly affected by microwave and roasting, and the effects of the two heat treatment methods have obvious differences. In general, the microwave pretreatment on oil peony seeds at 700 W is suitable for 1.5 to 2 min, and the roasting pretreatment at 120 ℃ is the best for 20 to 30 min.