Optimization of supercritical-CO2 extraction of Iris lactea seed oil: Component analysis and antioxidant activity of the oil

Iris lactea Pall. var. chinensis (Fisch.) Koidz. is a widely distributed species and the seeds of this species have been used as medicine. However, the chemical composition and biological activities of the I. lactea seed oil (ILSO) have not been studied. In this present work, extraction time, temperature, and pressure were considered as variables and response surface methodology based on the Box-Behnken design was utilized to identify the optimal conditions for supercritical fluid extraction of the ILSO. Furthermore, the main components (including fatty acids, unsaponifiables, and volatile components) in ILSO extracted with the above optimal conditions were identified by gas chromatography-mass spectrometry. It was found that major fatty acids present in ILSO were linoleic acid (41.31 %), oleic acid (34.74 %), and docosahexaenoic acid (3.18 %). The total content of sterols reached as high as the level of 87.44 % in unsaponifiable matter and sterols with a content over 5% included β-sitosterol (27.14 %) stigmasterol (18.38 %), delta5-avenasterol (15.36 %), campesterol (13.21 %), and betulinicaldehyde (5.80 %). The physicochemical properties of ILSO were analyzed according to Chinese national standards. Total polyphenol content (TPC) and total tocopherol content of ILSO were also determined. These predominant compounds were known by their high biological activities and confirm the potential sources of bioactive compounds existing in ILSO. Based on these identified ingredients, the antioxidant activity of the ILSO was evaluated by two different methods. The antioxidant capacity of ILSO determined by FRAP method was equivalent to 0.4759 m mol/L FeSO₄·7H₂O and 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity in vitro with IC₅₀ value of 3.27 mg/mL. These results provide a rich chemical database for the development of a new oil resource, as well as the possibility of using a byproduct in the production of pharmaceuticals and a rich resource of ornamental plants.